EP1495306A1

EP1495306A1 - Surface cleaning and particle counting

Info

Publication number: EP1495306A1
Application number: EP02807182A
Authority: EP
Inventors: John Samuel Batchelder
Original assignee: Convey Technology Inc
Current assignee: Convey Technology Inc
Priority date: 2002-04-02
Filing date: 2002-04-02
Publication date: 2005-01-12
Also published as: JP2005521887A; KR100809988B1; AU2002307046A1; JP4383178B2; KR20050002922A; EP1495306A4

Abstract

A method and an apparatus for detecting removable particulates initially on a test surface or surface to be inspected. The removable particles are transferred to a portion of a tacky surface (130)on a carrier by adhering and then removing the portion of the tacky surface (130)from the test surface. The carrier is received by a positioning means (131) and passed through the field of view of a surface inspection means (100)guided by a controller (170). Signals from the surface inspection means are combined with coordinates from the controller (170)to produce particle coordinates, which indicate particulates initally on the test surface. Particle coordinates on the tacky surface (130)measured before the tacky surface (130)is adhered and removed from the test surface can be compared with particle coordinates measured after the tacky surface (130)is adhered and removed from teh test surface. Several test surfaces can be sequentially inspected using the same carrier by storing particle coordinates after each measurements andcomparing the recent measurement with thecumulative previous measurements. The tacky surface (130)and the associated particle coordiantes can be conveyed to other analytical instuments for subsequent analysis.

Description

Surface Cleaning and Particle Counting

Technical Field

This invention relates to controlling particulate contamination on surfaces of products, machine tools, and work areas. More particularly, the invention relates to measuring the removable particulate contamination on surfaces in semiconductor manufacturing, data storage manufacturing, fluid filter inspection, display manufacturing, clean rooms, pharmaceutical manufacturing and handling, precision mechanical manufacturing, optics manufacturing, aerospace manufacturing, and health care industries.

Background Art

Quantified measurements of particulate contamination can comprise a total number of particles detected on the inspected surface, a total number of particles per area of the inspected surface, a size histogram of the total number of particles detected per area of the inspected surface, a cumulative particulate volume or area, or a combination of these measurements. Surface particle contamination measurements are generally performed by light scattering or image analysis.

US Patents 4,898,471 and 5,343,290 describe surface particle contamination measurements optimized for inspecting semiconductor wafers.

US Patent 4,766,324 describes comparing two scans of the same monitor wafer to determine particles added to or removed from the wafer between the two scans.

This invention also relates to removing particulates from surfaces. More particularly, the invention relates to cleaning processes to remove particulate contamination which are used in manufacturing systems to prevent localized defects, to prevent optical or beam scattering, prevent cross contamination of processing materials, to allow close mating of surfaces, to remove magnetic contaminants, and to sanitize surfaces. Surface particle removal is generally performed with the use of solvents, fluid shear, ultrasonics, transfer to a tacky surface, or mechanical agitation. US Patent 4,009,047 describes contacting a sheet to be cleaned with a tacky roller.

US Patent 4,705,388 describes determining when a web-cleaning tack roller requires rejuvenation by measuring the optical reflectivity of the roller.

US Patent 5,373,365 describes measuring the reflectivity of a web-cleaning roller, and from that inferring the contamination level on the roller.

US Patent 5,671,119 describes cleaning an electrostatic chuck in a semiconductor process tool by adhering and removing a dummy tacky wafer to the chuck.

US Patent 5,902,678 describes cleaning a surface by applying an anti-static pressure sensitive film to a surface, irradiating the film with ultraviolet light, and removing the film.

US Patent 6,023,597 describes a method for forming a conformable anti-static roller.

Teknek Electronics Limited of Inchinnan, Scotland, makes printed circuit board cleaning products that first contact the circuit board with a conformal rubber roller, and then contact the rubber roller with an adhesive coated roller.

This invention further relates to combining cleaning a surface and to measuring the removable particulates on that surface. Combining these processes is useful for inspecting surfaces that are otherwise difficult to inspect by currently available techniques because the surfaces are too rough, optically scattering, or large. They are also useful because they combine a cleaning process that adds value to a product with a measurement that improves the control of the process.

US Patent 5,253,538 is embodied in the product QIII® available from Pentagon

Technologies of Freemont, CA. It describes inspecting a planar surface for particulates by shearing gas across the surface using a nozzle assembly, and subsequently inspecting that gas using an airborne particle counter.

US Patent 5,939,647 describes a system similar to a QIII for planar surface inspection in which the sampling head is attached to a handle by a gimbal. US Patent 6,269,703 describes releasing particles from a surface using a fluid applied to shear across the surface. The fluid is then inspected for particulates.

The Surfex product from Particle Measuring Systems of Boulder, CO, inspects surfaces by ultrasonic cleaning in an aqueous bath followed by inspection of the water by a liquid particle counter.

This invention further relates to retaining particulates removed from a surface on a carrier, determining the locations of the particles on the carrier, and passing the carrier and the locations of the particles on the carrier to other analytical instruments like electron microscopes, optical review stations, and x-ray absorption. Retaining the found particles gives tracability to the measurement technique. It allows follow up analysis to be performed on archived carriers to analyze product failure mechanisms and process changes.

US Patent 5,655,029 describes detecting a region of interest on a specimen with one microscope and conveying the specimen and the coordinates to a second microscope for automated review.

It would be desirable to provide a combination of surface particulate removal and particle measurement that would not scuff, abrade, or otherwise interact with the surface to generate more contamination. It would be desirable that the technique would not require the immersion of the surface in a solvent, allowing inspection of large, or vertically oriented, or solvent sensitive surfaces. It would be desirable that the technique would clean and inspect complex, rough, or non-planar surfaces. It would be desirable that the technique would inspect and clean interior surface of manufacturing tools with limited or confined access. It would be desirable that particulates that have been removed and detected from a surface would subsequently be analyzable by alternative analytical instruments.

Disclosure of Invention

This invention is a method and an apparatus that detects removable particulates initially on a test surface or a surface to be inspected. The removable particles are transferred to a portion of a tacky surface on a carrier by adhering and then removing the portion of the tacky surface from the test surface. The carrier is received by a positioning means and passed through the field of view of a surface inspection means guided by a controller. Signals from the surface inspection means are combined with coordinates from the controller to produce particle coordinates, which indicate particulates initially on the test surface. Particle coordinates on the tacky surface measured before the tacky surface is adhered and removed from the test surface can be compared with particle coordinates measured after the tacky surface is adhered and removed from the test surface. Several test surfaces can be sequentially inspected using the same carrier by storing particle coordinates after each measurement and comparing the most recent measurement with the cumulative previous measurements. The carrier and the associated particle coordinates can be conveyed to other analytical instruments for subsequent analysis.

Brief Description of Drawings

Fig.l is a perspective view of the most preferred embodiment of the apparatus.

Fig.2a is a perspective view of a handle means applying a carrier of a tacky surface to a non-planar test surface.

Fig.2b is a perspective view of a handle means attached to a carrier of a tacky surface.

Fig.3 is a histogram showing the removal of polystyrene latex spheres from a monitor silicon wafer using a tacky roller.

Fig.4a is a plan and cross sectional view of a carrier of a tacky surface.

Fig.4b is a plan and cross sectional view of a handle means.

Fig.5 is a data flow diagram showing data transfer paths between calculation means.

Fig.6 is a perspective view of a box for transporting several carriers and a removable data storage element.

Fig.7 shows several types of alignment marks proximate to the tacky surface. Fig.8 shows a perspective view of a carrier of a tacky surface with a pattern of alignment marks and a low tack strip.

Fig.9 shows a perspective view of a carrier of a tacky surface with a protective covering.

Fig.10 show a perspective view of the illumination and focus optics of a preferred embodiment.

Figs.1 la and b show cross sectional views of the illumination and focus optics in Fig.10.

Fig.12 shows a cut-away perspective view of a handle means with rotary motion detection and RF communication.

Fig.13 shows a perspective view of an embodiment utilizing a flying spot scanner.

Fig.14a is a plan view of an embodiment using an intermediate tacky surface for groove inspection.

Fig.14b is a cross section view referencing Fig.14a.

Fig.14c is a cross section view referencing Fig. 14a.

Fig.l4d is a perspective view of an embodiment using an intermediate tacky surface for groove inspection.

Fig.15 is a perspective view of an embodiment using a flexible tacky sheet for in-situ cleaning and inspection.

Fig.16 is a perspective view of an embodiment using a flexible tacky sheet for in-situ cleaning and inspection.

Fig.17 shows pixels in the coordinate system of the tacky surface.

Fig.18 shows voxels associated with two detector arrays as they would be imaged near the tacky surface. Modes For Carrying Out The Invention

Particulate contamination can differ from other features of a surface in that there is an interface between the particulate and the original surface. If the adhesion at that interface is comparable to the cohesion of the surface material, the particle is so firmly adhered that it will not likely be removed later to become particulate contamination in some process or apparatus. If the adhesion is weak enough that the particle is removable, the particle is of more interest for contamination control.

For specificity and brevity we will subsequently describe as 'tacky' a surface that has been engineered to removably adhere to the surface being inspected. A tacky material is the bulk composition forming the tacky surface and its immediately adjoining volume. The degree of adhesion depends on many factors, including surface energies of the tacky surface and the surface to be inspected, adsorbed liquid layers on those surfaces, adsorbed molecular contamination on those surfaces, contact time and pressure between the surfaces, the ambient temperature, the compliance of both surfaces, mechanical interlocking due to roughness of both surfaces, inter-diffusion, and chemical reactions. Generally higher adhesive forces between the tacky surface and a particle will remove a larger fraction of the particle population on a surface. A tacky surface with too strong an adhesive bond to the test surface can cause failure mechanisms. One such failure mechanism is cohesive failure of the tacky material; this can lead to depositing portions of the tacky material on the test surface. Another failure mechanism is forming permanent adhesion of the tacky surface to the test surface. The tacky surface acts as a sampler of removable particulates from the surface under test.

Tacky surfaces for testing surfaces with high surface energy, such as the native oxide found on silicon monitor wafers, need to have relatively low adhesion forces, so that the adhesion between the test surface and the tacky surface does not exceed the cohesive forces within the tacky material. The tacky surface found on clean room removable tape model 1310 from the UltraTape Industries of Oregon, US, shows good particle removal without residue when used on monitor silicon wafers. A higher tack such as that found on model 4658F tape from the 3M Company of Minnesota, US, is appropriate for lower surface energy test surfaces such as polycarbonate. US Patent 5,902,678 describes a pressure sensitive adhesive on a flexible backing that demonstrates good particle removal characteristics. US Patent 5,187,007 describes a pressure sensitive adhesive used in wafer dicing; the characteristics of this film make it useful as a tacky surface in the following embodiments. The tacky films sold by Gel-Pak Corporation predictably adhere and cleanly release from test surfaces. The most preferred embodiment for the tacky material is a hydrophilic polyurethane of the type described in US Patent 3,821,136. Preferred additives to the tacky material include additives to improve ionic and electronic conduction of the tacky material so that it can dissipate static electricity; a useful

19 maximum resistivity for the tacky surface is 10 ohms per square centimeter. A preferred additive to the tacky material is a dye or pigment such as carbon black. A light absorber reduces background and sub-surface light scatter from incident illumination transmitted through the tacky surface. Those skilled in the art will appreciate that there is a spectrum of possible compositions for the tacky material, and that a particular test surface may require a specialized tacky surface.

There are a variety of reasons why small particles are more difficult to detect on most tacky surfaces than they would be on surfaces typically used for particle inspection, such as monitor silicon wafers. Tacky materials are generally somewhat optically translucent; they do not strongly absorb or reflect illumination, so that light can emerge from a tacky surface after scattering from sub-surface features, contaminants, or variations in index of refraction. The surfaces are generally not globally flat or smooth, but have localized height variations that require small fields of view in order to maintain focus. The surfaces are generally not locally smooth, so that grazing illumination or Lloyd's mirror collection is necessary to reduce surface scatter. Even with darkfield illumination, surface imperfections can occur that mimic the light scatter characteristics of particles. The large molecular weights of the bulk constituents are difficult to filter, so that there can be particulates and other contamination below the tacky surface that can flicker in and out of detectability depending on small changes in focus position with respect to the surface and illumination intensity. Index of refraction variations in the bulk material can generate relatively high levels of background light scatter.

Tacky surfaces will typically not appear to be particle free at the time that they are to be adhered to a test surface. Some of these particle signals are due to actual particles, index variations, or surface imperfections, as just described. Some will be transferred from the protective layer applied to the tacky surface isolating the tacky surface from environmental contamination during handling and storage. Some will be from handling the tacky surface in preparation to applying it to the test surface.

Embodiment One

Fig.l shows the most preferred embodiment of the invention, in which the carrier with the tacky surface (130) is mounted on a positioning means (131) in the field of view of a surface inspection means (100). The carrier can be inspected before it has be adhered to and removed from a test surface, after being applied to and removed from a first test surface, or after being applied to and removed from several test surfaces in succession.

The surface inspection means (100) of this embodiment is an automated darkfield optical microscope. Light from a halogen lamp (102) is spatially filtered by baffles (104), is filtered by a cold mirror (105) to reduce its infrared content, and is reflected by a ring mirror (106) towards the darkfield illumination mirror of an infinite conjugate objective (108). The objective (108) is mounted to a frame (140). The illumination is incident on the carrier of the tacky sheet (130) at nearly grazing angles. Scattered light from the tacky surface is imaged by the darkfield objective (108), passing through the clear central aperture of the ring mirror (106), and is divided by a beam splitter (112) into two imaging paths (114 and 122). Light on path (114) passes through a filter (115) that removes light from the focusing laser (126), and then is imaged by a tube lens (114) onto a linear CCD detector array (118). Light on path (122) passes through a tube lens (120) and is reflected by a hot mirror (121) onto a second linear CCD detector array (124). The detectors (118 and 124) are driven by X coordinate timing information from analysis electronics (180) over signals in (181 and 182), and the detectors transmit grazing illumination scatter intensity information to the analysis electronics (180). The first tube lens (114) and detector array (118) is imaged to a plane at the tacky sheet that is within approximately three depths of focus of the tacky surface. If the second tube lens (120) and detector array (124) is utilized, it should be imaged at least one depth of focus farther from the tacky surface and deeper into the bulk material supporting the tacky surface than the first lens and detector array. If the second tube lens and detector array is not utilized the beam splitter (112) should be removed; this single CCD configuration is a preferred embodiment for tacky surfaces with very low bulk contamination and scattering. The carrier of the tacky sheet (130) is attached to a handle means (132); this combination will be subsequently discussed in more detail.

Small particles scatter shorter wavelengths more strongly, so optical sources with more short wavelength energy are preferred. Alternative preferred embodiments for illumination include an arc lamp, light emitting diodes, and a laser. Incoherent illumination typically generates less noise in the detected image than coherent illumination. An objective with a numerical aperture between 0.5 and 0.95 is preferred to restrict the depth over which particles can be detected. Immersion optics is not preferred, since particles can be nearly index matched to the immersion fluid. The second detector array can be omitted if the bulk material supporting the tacky surface is generally free of localized light scattering, and the thickness of the bulk material is at least eight depths of focus. Alternative preferred embodiments for the detectors include CMOS linear arrays, CCD and CMOS two dimensional arrays, TDI arrays, and position sensing photomultipliers.

The handle means (132) is received by the positioning means (131), which passes the carrier of the tacky sheet (130) through the field of view of the surface inspection means (100). The positioning means (131) will now be collectively described. The carrier of the tacky sheet (130) is mounted on the handle means (132), which mates with a spindle (133) attached to a gear reducer (134), servo motor (136), and encoder (138); these rotate the carrier of the tacky surface (130) under the control of a controller (170); this is the θ motion of the carrier with respect to the objective. The gear reducer (134) mounts to an angle bracket (136) that attaches to a pivoting plate (135). The grip of the handle means (132) is held by a spring clip (137) attached to the angle bracket. A flexure hinge (144) connects the pivoting plate (135) to a riser block (143) fixed to an elevator plate (142). The elevator plate (142) is constrained to move in one dimension parallel to the frame (140) by linear bearings (145). Z motion varying the spacing between the objective (108) and the tacky surface is driven by a voice coil magnet (156) mounted on the elevator plate (142), a voice coil (157) mounted on the pivoting plate (135), and a drive circuit in the controller (170). The mechanical position of the pivoting plate (135) is monitored by an LVDT sensor (158) attached to the elevator plate (142) coupled to its corresponding core attached to the pivoting plate (135). A motor (150) on a bracket (152) attached to the elevator plate (142) rotates a leadscrew (154) attached to the pivoting plate (135). The controller (170) drives the motor (150) to control the X position of the elevator plate (142).

Additional preferred embodiments for generating the θ motion also include air bearings, microsteppers, brushless motors, and DC motors. Additional preferred embodiments for the ord and Z motion include flexures, air bearings, linear bearings, squeeze bearings, inchworms, piezoelectric transducers, linear voice coils, and leadscrews. Additional preferred embodiments for monitoring θ , X, Y, and Z_la include capacitive sensors, incremental optical sensors, air gages, eddy current sensors, inductance sensors, and optical displacement sensors.

The controller (170) is a combination of electronic hardware, firmware, and software that coordinate the motion of the various degrees of freedom of positioning means, that receives and processes sensor position information, and that responds to external commands controlling the scanning of a tacky surface. The controller (170) is preferably one or more real time microcontrollers in communication with a general purpose microprocessor. In an alternative embodiment the controller (170) can be a time sliced portion of the processing capability of a general purpose microprocessor. External communication to the controller (170) is through at least one of the following: a keyboard, a display, a touch panel, an infrared link, an RF link, a dedicated serial interface, a dedicated parallel interface, a local area network, and a wide area network.

The analysis electronics is preferably a combination of analog pre-processing, ASICs, FPGAs, CPLDs, FIFOs, RAM, one or more general purpose processors, one or more digital signal processors, magnetic disk, removable storage, and communication capability.

The controller (170) is a combination of electronic hardware, firmware, and software that coordinate the motion of the various degrees of freedom of positioning means, that receives and processes sensor position information, and that responds to external commands controlling the scanning of a tacky surface. The coarse optical focus detector comprises a photodiode (190) positioned to capture a portion of the incident and reflected illumination. The fine optical focus detector comprises a laser (126), a beam splitter (127) and adjustable mount (128), a single axis position sensitive detector (129), and connection to the associated signal conditioning electronics in the controller (170) through a cable (176). The focus systems will be discussed subsequently in more detail.

Less preferred embodiments of the surface inspection means (100) include non-optical measurement techniques such as scanning electron microscopy, atomic force microscopy, an acoustic microscopy. In some applications sensitivity will be enhanced by condensing vapor preferentially on the particles transferred to the tacky surface from a saturated atmosphere.

Figs. 2 and 3 show the carrier of the tacky sheet (130) and the handle means (132) in more detail. In the most preferred embodiment the surface of the tacky sheet is generally cylindrical; this allows inspection of a non-planar test surface (202), as shown in Fig.2a. Fig.2b shows the handle means (132) with the attached carrier of the tacky sheet (130) in an idle position resting on a slab (206). A pin (208) in the handle means (132) provides stability. A collar (210) joins the grip to a bearing that allows the carrier of the tacky sheet (130) to rotate freely with respect to the handle means (132), and will be subsequently described in more detail. In an alternative preferred embodiment a robot or automated device manipulates the handle means to apply the tacky surface to a test surface.

Fig.3 shows data taken by deliberately contaminating a test surface and then using a handle means (132) and tacky sheet (130) to remove the contamination. A monitor silicon wafer with a native oxide is first inspected by a darkfield scatter particle inspection tool of a standard design to produce the control data, the middle of the three rows of histograms in Fig.3. Particle size is inferred from the light scatter intensity from pixels, each corresponding to approximately 0.01 square millimeters on the wafer surface. The gradual increase of control particle density below 0.3 microns is likely to be due to light scatter from sources other than single particles. A water suspension of polystyrene latex spheres with diameters 0.3 microns and 2.0 microns is nebulized onto the wafer to produce the 0.3/2μm PSL histogram data. A roller with a hydrophilic polyurethane tacky surface is then rolled once over the surface of the wafer to produce the 'After rolling' data. Though the high surface energy of the test surface generally makes it adhesive to particles, the roller is able to remove more than 90% of the applied particles of both sizes, as well as removing some of the contamination present on the control surface.

A detail of the carrier of the tacky sheet (130) is shown in the left view and its associated cross section A of Fig.4a. The rigid core of the carrier (406) is a hollow plastic cylinder with a closed end. A conformal layer such as Dupont 4949 black very high bonding acrylic foam tape (404) is applied circumferentially to the rigid core (406) to provide an optically absorbing backing, an adhesion promoter for the tacky material, and surface comformality. A conformal support layer under the tacky surface improves wetting of the tacky surface with the test surface. A conformal layer also allows rolling of complex surface curvatures; it allows a generally tacky surface to intimately contact a test surface that has two radii of curvature. It also allows the interior of a pipe to be inspected by an axial motion of the handle means (132). A solvent solution containing the hydrophilic polyurethane tacky material is dip or roll coated onto the combination of the rigid core (406) and the conformal layer (404); this solution dries to form a film of tacky material (402) with a tacky surface (401).

Details of the handle means (132) are shown in the left view and its associated cross section B of Fig.4b. A bobbin (416) is connected to a collar (210) with a sealed bearing (418) and a C-ring (420). The grip (408) attaches to the collar (210) using screws passing through the pin (208). A spindle (133) from the positioning means (131) mates with a close tolerance hole (422) in the bobbin (416). Elastomeric o-rings (414) provide traction so that the bobbin (416) can be easily manually inserted and removed on the spindle (133) but that the bobbin does not slip on the spindle when the positioning means (131) applies torque to the spindle.

The plastic core (406) slides over the bobbin (416); the opening of the plastic core mates with a lip on the bobbin (424), and a captured o-ring (410) urges eight captured metal balls (410) in the bobbin (416) to apply a centering force outwards on the inner surface of the plastic core (406). The handle means should generate as close to zero contamination as possible; the closed end of the plastic core (306) helps to contain particles that may be generated by the receiving and rolling processes. Since the carrier of the tacky sheet is a relatively inexpensive consumable, the handle means must accurately mate with rigid carrier cores (406) that have a substantial tolerance in inner diameter and ellipticity. Alternative preferred embodiments of the carrier of the carrier of the tacky sheet (130) are subsequently described. The inner approximately cylindrical surface of the plastic core (406) is the most preferred axial feature for the carrier to engage the handle means. Alternative preferred embodiments include a tapered hole, a hexagonal hole, a square hole, a threaded hole, an axle, a tapered pin, a hexagonal rod, a square rod, and a threaded rod. The inner cylindrical surface of the bobbin (416) is the most preferred method for the handle means to engage the positioning means (131). Alternative preferred embodiments for mechanically mating the positioning means with the handle means include a tapered pin and hole, a bayonet mount, a screw and nut, a shaft with a keyway, and a shaft with a detent.

Fig.5 shows the data flow of the most preferred embodiment. The carrier of the tacky sheet (130) is scanned through the field of view of the surface inspection means (100) by the positioning means (131) as directed by a controller (170). The two CCD arrays (118 and 124) produce signals (181 and 182) containing light scatter intensity (I) and position (X) information; these arrive at the analysis electronics (180). Additional information on the current position of the carrier of the tacky sheet ( θ , ord, Z_opt, Zι_ab) is simultaneously transmitted from the controller (170) over a communication means (171) to the analysis electronics (180). The intensity and coordinate information are combined in a first calculation means (508) to generate particle coordinates (I, abs, ord, Z) in the coordinates of the carrier of the tacky surface (130). The details of the first calculation means will be subsequently described. The output of the first calculation means is labeled differently in Fig.5 for the different instances that the carrier of the tacky sheet (130) is inspected. Particle data resulting from a scan prior to adhering and removing the tacky sheet from the test surface is unexposed particle coordinates (510). Particle data from a scan after adhering and removing the tacky sheet from the test surface is first exposed particle coordinates (511). Particle data following adhering and removing the tacky sheet from subsequent test surfaces are (512), (513), and (514), respectively; these subsequent test surfaces could be repeated measurements of the original test surface, but are more likely measurements of alternative test surfaces. In principle an arbitrary number of clean test surfaces can be so inspected with a single carrier attached to a tacky surface; in practice the number of repeated uses is limited primarily by the accumulation of contamination on the tacky surface. In the simplest preferred embodiment, there is no prior scan (510); the particle coordinates (511), generated while scanning a tacky surface that has been applied to and removed from the test surface, are assumed to represent particles transfened from the test surface; this represents an upper limit to the number of particles transfened from the test surface. In the most preferred embodiment the prior scan (510) is stored in a first memory means (520). A second calculation means (530) identifies particles that were transferred from the test surface (570) as those particle coordinates from (511) that have no corresponding particle coordinates from the stored previous scan (550). To re-use the tacky surface, a second memory means (521) stores the scan data (511), a third calculation means (541) combines particle data from the first and second memory means (550) and (551) to form (561), and an instance of the second calculation means (531) identifies particles that were transferred from the second test surface (571) as those particle coordinates from (512) that have no corresponding particle coordinates in (561). Two additional test surfaces can be measured using third memory means (522) and fourth memory means (523), instances of the third calculation means (542) and (543), and instances of the second calculation means (532) and (533), generating the outputs (572) and (573). Further repetitions are calculated in a similar manner. The particle data is stored in a removable storage medium (506) such as a writable CD ROM or DND, so that it can later be transferred to a separate analytical instrument.

In the most preferred embodiment, a carrier movement measurement means in the handle keeps track of the rotations of the carrier as it is rolled over the test surface or surfaces. This carrier movement measurement means will be subsequently described. The data from the carrier movement measurement means is communicated (506) to a fourth calculation means (580) to translate the particles that were transferred from the test surface (570) into a density of removable particles from the test surface (590). The fourth calculation means divides the number of particles detected from the test surface by the area of the tacky surface and by the number of revolutions detected by the carrier movement measurement means. In a similar manner, densities of removable particles (591, 592, and 593) calculated from scans of subsequent test surfaces (571, 572, and 573) and the corresponding instance of the fourth calculation means (581, 582, and 583).

In the most preferred embodiment the first calculation means utilizes a convolution filter to improve the contrast of a pixel compared to its immediate, surroundings. Corrections are applied for fixed pattern noise and gain variations in the detector arrays. Small pixel sizes improve the contrast of particles compared to surface roughness and bulk subsurface scatter, so that high speed detector arrays and pipelined analysis hardware is preferred. The output of the calculation means can be transmitted to an operator by a display, a printout, or an enunciator. The output of the calculation means can be communicated to a WAN or LAN through a variety of interfaces known to those skilled in the art.

Fig.6 shows how carriers of the tacky surface (130) could be packaged for use with the surface inspection means (100) and the handle means (132). Several carriers (130) are stored in individual compartments formed in a molded sheet (606) contained in a box formed by a bottom (608) and a hinged top (604). The carriers are angled to allow the handle means (132) to engage and remove any carrier while in its individual compartment. After a carrier had been used, it can be replace in its compartment, so that the compartment becomes the archival storage location for the carrier. A writable CD (610) resides on a post formed in the molded sheet; the CD serves as the removable storage medium for the carriers in the box.

Fig.7 shows six configurations for alignment marks proximate to the tacky surface. In the most preferred embodiment the alignment marks simulate some of the light scatter characteristics of particles. In this configuration the alignment mark coordinate detection means is the surface inspection means plus additional hardware or software to distinguish and decode the alignment mark based on characteristics of the alignment mark like its orientation, location, signal strength, and neighboring features. Particulates such as metallic or latex spheres (704) can be deposited on top of the tacky surface, or they can be pressed somewhat into the bulk of the tacky material (402). Carbon black can be electrophotographically deposited, or inks can be jetted or silkscreened to form the alignment marks (706). Often the tacky bulk material (402) is doctored, dipped, or spray coated onto a supporting substrate (714); in this case the alignment marks can be pre- deposited on the buried surface of (714) prior to the application of the tacky material. Alignment marks can comprise naturally occurring scattering features on the tacky surface, in the bulk of the tacky material (710), or on the back surface of the tacky material. The surface of the tacky material can be distorted with scribe lines or stylus marks (720). The most preferred embodiment is to cleanly ablate small pockets (722) in the tacky surface using a localized energy source, such as an excimer or carbon dioxide laser. A UN light source can change the cross linking of localized volumes embedded in the surface (724), causing index of refraction variations that can scatter light. In less preferred embodiments, alignment marks can be utilized that require additional detection means, such as magnetization patterns, sprocket holes, and oriented gratings.

For any of the embodiments that require repeated inspection of the tacky surface, the alignment marks can be used to translate coordinates so that the handle means can be reinstalled in a random orientation. Since the shape and pattern of alignment marks is known, the location of the alignment marks can be used as an input to the first calculation means (508) for appropriately translating each data scan. Fig.8 shows a preferred configuration for a carrier of a tacky surface with alignment marks (800). The most preferred embodiment utilizes a sequence of alignment marks (804) in a pattern analogous to a bar code. The locations of some marks in the code indicate the orientation of the surface. Other types of information can also be contained in the code, such as a serial number, an expiration date, and the composition of the tacky material. The marks can be a one or two dimensional array. The marks can have variations in width, height, depth, and spacing.

The carrier of the tacky surface in Fig.8 has an additional feature. A strip of non-tacky material (802) spans the length of the tacky surface, so that there is a small range of rotation angles of the rotary joint for which only the non-tacky surface (802) will be in contact with the test surface. For these orientations of the rotary joint, the carrier of the tacky surface can be easily lifted off of the test surface. This is useful to limit the shear forces on the tacky sheet to eliminate cohesive failure of the tacky material during removal of the tacky surface from the test surface. It is also useful in reducing the forces applied to the handle means and the test surface when removing the carrier of the tacky surface from the test surface. Fig.9 shows a protective film (902) wrapped around the carrier of the tacky surface (130). In the most preferred embodiment the outer surface of this protective film is also tacky; this aids in storing and replacing the film after the carrier has be used. A color-coded tag (804) aids in starting the removal of the protective film. In an alternative preferred embodiment the film is dip or roller coated onto the carrier of the tacky surface to dry as a removable conformal coating.

Figs.10 and 11 describe the focusing systems of the preferred embodiment in more detail. Fig.10 shows a view of the carrier of the tacky surface (130), the illuminator, the objective, and the focus sensors. The functioning of the illumination and imaging optics have been previously described. Sectional views A-A and B-B are indicated in Fig.10; these sectional views are given in Figs.l la and lib, respectively. An incident focus beam (1102) from a laser source (126), such as a 650nm solid state laser, is partially reflected by a beam splitter (127) into the tube lens (120), the central clear aperture of the ring mirror (106), and the exit pupil of the objective (108). The incident focus beam (1102) enters the objective (108) off axis, so that the incident focus beam illuminates the tacky surface (401) at a non-zero angle of incidence. The reflected focus beam (1104) exits the objective (108), passes through the clear aperture of the ring mirror (106), and is imaged by the tube lens (120) through the beam splitter (127) onto a position sensing diode (129). Varying the Z_opt distance between the tacky surface in the field of view and the objective causes a shift in the position where the reflected focus beam (1104) illuminates the position sensing diode (129); this changes the ratio of the two output signals from the position sensing diode, which is interpreted by the controller (170) as the present position of the tacky surface (401) with respect to the plane of focus of the objective. There are several situations for which the reflected focus beam (1104) will not strike the position sensing diode; these include the carrier of the tacky sheet (130) being missing or mounted incorrectly, a large particle in the field of view causing a large apparent shift in Z_opt, and a seam or alignment mark. In these situations the additional optical sensor (190) is helpful for reliable performance of the focus servo loop. Since the surface of the tacky sheet is cylindrical, some of the incident illumination from the halogen lamp (102) emerges between the objective (108) and the carrier of the tacky sheet (130); more light strikes detector (190) as the separation gets bigger. The signal from (190) acts as a coarse focus feedback signal. In an alternative preferred embodiment the focus signal is provided by sensing the intensity of an optical beam in the plane of focus that passes through the optical axis. That beam is deflected and attenuated as the tacky surface moves through focus towards the objective.

Fig.12 shows a preferred embodiment of the handle means that senses rotation of the carrier of the tacky surface (130) as it is rolled across the test surface. Two concentric rings of hollows (1204) are etched into the externally facing surface of the bobbin (416), leaving a regular array of pads (1206) in quadrature. A printed circuit board (1208) with capacitive sensing circuit elements is positioned in the hollowed out handle (1202) in close proximity to the pads (1206), allowing the incremental position and direction of rotation of the bobbin to be sensed. Half of the hollowed out handle (1202) has been omitted for clarity. An RF antenna (1212) detects when the handle has been inserted in the positioning means and broadcasts the recent rotational history of the bobbin. This information is used by a fourth calculation means to interpret the measured particle counts as a particle aerial density on the test surface. Batteries (1210) power the detection circuits, the RF generator, and the memory. The overall geometry of the handle means is generally mirror symmetric so that it is ambidextrous. In less prefened embodiments, rotation sensing is performed with one of the following: a Hall effect sensor, an incremental optical encoder, a motor generator, and a gear train. In less preferred embodiments rotation data is transmitted out of the handle means using one of the following: mating electrical contacts, capacitive contacts, and optical coupling. The rotational data can be received by the controller (170) or by an external processor in communication with the controller.

The force applied by the handle means to press the tacky surface towards the test surface has some affect on particle removal rates. To obtain more uniform results, an alternative preferred embodiment introduces compliance into the handle means to regulate the applied force. In an additional alternative preferred embodiment a force gage measures the applied forces as the tacky surface is being adhered to and removed from the test surface; these measured values are then reported to the controller in the same manner as the roller rotations just described. In alternative preferred embodiments the handle means comprises means to record ancillary information pertinent to the test surface, such as a bar code reader or a voice digitizer.

Embodiment 2

Fig.13 shows an embodiment of the scanner means (100) that utilizes a flying laser spot. A solid state laser (1302) generates a beam (1304) that is swept across a focusing mirror (1310) by a galvo coil (1308) oscillating a mirror (1306). The beam returning from the mirror comes to a focus as it grazes across the tacky surface; the position of the moving mirror determines the position of the laser on the tacky surface. A photomultiplier tube (1312) collects light scattered from surface features of the tacky surface.

Embodiment 3

Figs.14a through 14d show an alternative preferred embodiment configured for inspecting high curvature surfaces such as the grooves supporting wafers in a semiconductor front opening unified pod, or FOUP (1402). Fig.Hd is the perspective view. Figs.14b and c are cross sectional views from the plan view in Fig.14a. A flexible tubular sheet of material with a tacky surface (1410) acts as a transfer surface or transfer roller between the surface of the grooved material (1402) and the carrier of the tacky sheet (130). The flexible tubular sheet (1410) is stretched around two bearing rollers (1412 and 1413) separated by a guide plate (1414) attached to the collar (210). As the handle means is manipulated to roll the lower roller (1413) over the test surface, the tacky surface of the flexible tube progressively adheres to and releases from the test surface, transporting particles from the test surface along the guide plate to the carrier of the tacky surface (130). The carrier of the tacky surface (130) is chosen to generally adhere to particles more tenaciously than the tubular sheet (1410) adheres to particles, so that particles transferred from the test surface to the tubular sheet are then transferred to the carrier of the tacky sheet (130). The drawings in Fig.14 are scaled for the grooves found in FOUPs for 200 millimeter wafers, and for a carrier of a tacky sheet that is 25 millimeters in diameter and in length. Embodiment 4

Fig.15 shows an alternative preferred embodiment adapted for in-situ inspection and cleaning in process tooling. A flexible sheet with a tacky surface (401) is dispensed from one cylindrical core (1520) and taken up by another cylindrical core (1521). Two servo motors (1522) control the tension and progression of the flexible sheet. A conformal roller (404) is supported by a frame (1510) on a motorized pivot (1512). Test surfaces (1502) to be inspected on support (1504) pass underneath the rollers as part of the manufacturing process flow. A sequence of alignment marks (804) and low-tack portions (802) along the tacky sheet can be present to allow a sequence of test surfaces to be rolled by the conformal roller (404) before the two cylindrical cores are removed and mounted in a surface inspection means and the tacky sheet is inspected.

Fig.16 shows the configuration of Fig.15 adapted to use UN release adhesive films, such as those manufactured by Νitto Denko for backside grinding of silicon wafers, or those described in US Patent 5,902,678. In this case there is an application roller (1610) and a removal roller (1612). The region between the two rollers (1610 and 1612) can be illuminated by a UN lamp (1606) with a reflector (1602). When the film is initially applied to the test surface (1502) it is highly adhesive and binds to both the test surface and to particles on the test surface. After UN exposure in the region between the rollers (1604), the film removes easily from the test surface. Less preferred embodiment of adhesion release means than UN irradiation include exposure to liquid solvents, water vapor, and temperature change.

Adhesion modifiers can be usefully applied to all embodiments. Pre-treating a test surface or the tacky surface with a corona discharge such as produced by adhesion enhancement products from Softal 3DT LLC increase the adhesion between the particles and the tacky surface. Applying vapor to the tacky surface as it is adhered to the test surface can improve the release between the tacky surface and the test surface.

Fig.17 shows a preferred calculation means for all of the embodiments. Each rectangle or pixel (1702) represents a possible location of a particle coordinate on the tacky sheet.

The darkened rectangles or pixels (1704) represent particle coordinates associated with a single particle. Several pixels can be affected by a single particle if the particle is large, if the particle is close to the boundary between pixels, if the particle is out of focus, if the strongly illuminated pixel saturates its detector, or if the particle is in a region of overlap between successive scans. Rather than reporting each pixel (1704) as an occurrence of a different particle, it is preferable to merge adjacent or nearly adjacent pixels. This can be done by the first calculation means, or in the most preferred embodiment as part of the output of the second calculation means.

Fig.18 shows the image (1802) of the first detector array (118) at the tacky surface (401), and the image (1804) of the second detector array (124) below the tacky surface (401) in the bulk of the tacky material (402). This is applicable to all preferred embodiments that utilize optical detection with at least two detector arrays. The primary purpose of the second detector array is to identify those light scatter events that become more intense with increasing depth from the tacky surface; these light scatter events are assumed to not be from particles transferred from test surfaces, and are ignored. The separation of the images of the two arrays normal to the tacky surface (401) should be at least a depth of focus for the sensing wavelength, numerical aperture of the objective, and index of refraction of the bulk of the tacky material (402). If there is a buried interface between the bulk of the tacky material (402) and a supporting layer (1814), the image of the second detector array (1804) should be above that interface. Less preferred embodiments for acquiring similar depth information include confocal microscopy, Nipkow wheels, and Linnick interferometry.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, the various features of most prefened embodiment may be used and interchanged with the alternative prefened embodiments, and vice-versa. These and other changes will be apparent to one skilled in the art.

Claims

CLAIMS:

Claim 1. An apparatus that detects removable particulates initially on a first test surface, the removable particles being transferred to a portion of a tacky surface by adhering and then removing the portion of the tacky surface from the first test surface, the first exposed surface being the portion of the tacky surface removed from the first test surface, the unexposed surface being the first exposed surface prior to being adhered^' to and removed the first test surface, and the tacky surface being supported by a carrier, comprising:

a controller;

a surface inspection means that transmits to the controller a particulate signal coordinate for each particulate detected in the sensible field of view of the surface inspection means;

a positioning means which receives the carrier, and which passes the portion of the tacky surface across the sensible field of view of the surface inspection means in response to positioning commands from the controller;

a first calculation means to combine the particulate signal coordinates received by the controller with positioning commands to the positioning means, wherein the first calculation means assigns unexposed particle coordinates to particulate signal coordinates from the unexposed surface, and the first calculation means assigns first exposed particle coordinates to particulate signal coordinates from the first exposed surface;

a first memory means that stores unexposed particle coordinates from the first calculation means; and

a second calculation means to combine first exposed particle coordinates from the first calculation means with unexposed particle coordinates from the first memory means to determine the number of removable particles initially on the first test surface; whereby particles with first exposed particle coordinates that have no corresponding unexposed particle coordinates comprise removable particles initially on the first test surface.

Claim 2. The apparatus of Claim 1 additionally detecting removable particulates initially on a second test surface, wherein the second exposed surface is the first exposed surface after being adhered to and removed from the second test surface, the first calculation means assigning second exposed particle coordinates to particulate signal coordinates from the second exposed surface, further comprising:

a second memory means that stores first exposed particle coordinates from the first calculation means; and

a third calculation means to combine second exposed particle coordinates from the first calculation means with unexposed particle coordinates from the first memory means and with first exposed particle coordinates from the second memory means to determine the number of removable particles initially on the second test surface; whereby particles with second exposed particle coordinates that have neither corresponding unexposed particle coordinates or first exposed particle coordinates comprise removable particles initially on the second test surface.

Claim 3. The apparatus of claim 1, further comprising a removable storage means in which is stored first exposed particle coordinates, whereby the coordinates of particles on the first exposed surface corresponding to removable particles initially on the first test surface can be conveyed or archived.

Claim 4. The apparatus of claim 1, wherein the unexposed surface has an associated alignment mark, further comprising an alignment mark coordinate detecting means.

Claim 5. The apparatus of claim 4, wherein the alignment mark comprises a spatially varying code including at least one of the following features: a deposited feature, a printed feature, a buried natural feature, a scribed feature, an ablated feature, and a reacted feature.

Claim 6. The apparatus of claim 4, wherein the first calculation means translates the particulate signal coordinates received by the controller referencing the alignment mark coordinate.

Claim 7. The apparatus of claim 1, wherein the number of removable particles initially on the first test surface is transmitted by the apparatus using one of the following communication links: serial, parallel, LAN, WAN, RF, optical, and removable media.

Claim 8. The apparatus of claim 1, further comprising a focus servo means that controls the placement of the portion of the tacky surface within the sensible field of view of the surface inspection means.

Claim 9. The apparatus of claim 1, wherein the surface inspection means utilizes grazing optical illumination.

Claim 10. The apparatus of claim 1, wherein the surface inspection means utilizes an optical flying spot scanner.

Claim 11. The apparatus of claim 1, wherein the surface inspection means utilizes an electron beam microscope.

Claim 12. The apparatus of claim 1, further comprising a handle means that removably engages the carrier while optionally the handle means removably engages the positioning means, whereby the handle means allows substantially contamination free manipulation of the carrier when applying the portion of the tacky surface to a test surface, and the handle means provides the mechanical interface for mounting the carrier on the positioning means.

Claim 13. The apparatus of claim 12, further comprising:

a carrier movement measurement means that detects and stores relative movement between the carrier and the handle means that occurs during adhering and then removing the portion of the tacky surface from the first test surface; a data transmission means between the handle means and the first calculation means; and

a fourth calculation means that combines the number of removable particles initially on the first test surface from the second calculation means with the relative movement between the carrier and the handle means to form the aerial density of initially removable particles on the first test surface.

Claim 14. The apparatus of claim 1, the surface inspection means further comprising two sensing elements, the first sensing element primarily sensing the presence of particles proximate to the surface, and the second sensing element primarily sensing the presence of particles below the surface.

Claim 15. An apparatus that detects removable particulates initially on a test surface, the removable particles being transfened to a portion of a tacky surface by adhering and then removing the portion of the tacky surface from the test surface, the exposed surface being the portion of the tacky surface removed from the test surface, the tacky surface being supported by a carrier, comprising:

a controller;

a positioning means which receives the carrier, and which passes the portion of the tacky surface supported by the carrier across the sensible field of view of the surface inspection means in response to positioning commands from the controller; and

a first calculation means to combine the particulate signal coordinates received by the controller with positioning commands to the positioning means to determining the number of particles on the exposed surface; whereby the number of particles detected on the exposed surface is an upper limit to the number of removable particulates initially on the test surface.

Claim 16. The apparatus of Claim 15 additionally detecting removable particulates initially on a second test surface, wherein the second exposed surface is the first exposed surface after being adhered to and removed from the second test surface, the first calculation means assigning second exposed particle coordinates to particulate signal coordinates from the second exposed surface, further comprising:

a first memory means that stores first exposed particle coordinates from the first calculation means; and

a second calculation means to combine second exposed particle coordinates from the first calculation means with unexposed particle coordinates from the first memory means to determine the number of removable particles initially on the second test surface; whereby particles with second exposed particle coordinates that have no corresponding first exposed particle coordinates comprise removable particles initially on the second test surface.

Claim 17. The apparatus of claim 16, wherein the unexposed surface has an associated alignment mark, further comprising an alignment mark detecting means.

Claim 18. The apparatus of claim 17, wherein the alignment mark is comprised of a spatially varying code including at least one of the following: a deposited feature, a printed feature, a buried natural feature, a scribed feature, an ablated feature, and a reacted feature.

Claim 19. An apparatus that detects removable particulates initially on a test surface, the removable particles being transfened to a portion of a tacky surface by adhering and then removing the portion of the tacky surface from the test surface, the exposed surface being the portion of the tacky surface removed from the test surface, comprising: a controller;

a tacky surface inspection means that transmits to the controller a particulate signal coordinate for each particulate detected in the sensible field of view of the convex surface inspection means;

a positioning means which receives the tacky surface, and which passes the portion of the tacky surface across the sensible field of view of the convex surface inspection means in response to positioning commands from the controller; and

a calculation means to combine the particulate signal coordinates received by the controller with positioning commands to the positioning means to determining the number of particles on the exposed surface; whereby the number of particles detected on the exposed surface is an upper limit to the number of removable particulates initially on the test surface.

Claim 20. The apparatus of claim 19, further comprising an adhesion release means, the adhesion release means being applied to the tacky surface after the tacky surface is adhered to the test surface and before the tacky surface is removed from the test surface, the adhesion release means reducing the force required to remove the tacky surface from the test surface.

Claim 21. A method of detecting removable particulates initially on a test surface, the removable particles being transferred to a portion of a tacky surface by adhering and then removing the portion of the tacky surface from the test surface, the exposed surface being the portion of the tacky surface removed from the test surface, the tacky surface being supported by a carrier, comprising:

(a) receiving the carrier on a positioning means responsive to a controller;

(b) passing the exposed surface through the sensible field of view of a surface inspection means in response to positioning commands from the controller; (c) generating a particulate signal coordinate from the surface inspection means in response to each particulate detected on the exposed surface passing through the sensible field of view of the surface inspection means; and

(d) calculating the number of particles on the exposed surface by combining the positioning commands of the controller with particulate signal coordinates; whereby the number of particles detected on the exposed surface is an upper limit to the number of removable particulates initially on the test surface.

Claim 22. A method of detecting removable particulates initially on a first test surface, the removable particles being transferred to a portion of a tacky surface by adhering and then removing the portion of the tacky surface from the first test surface, the first exposed surface being the portion of the tacky surface removed from the first test surface, the tacky surface being supported by a carrier, comprising:

(a) receiving the carrier on a positioning means responsive to a controller prior to adhering and then removing the first exposed surface from the first test surface;

(b) passing the portion of the tacky surface through the sensible field of view of a surface inspection means in response to positioning commands from the controller;

(c) generating a particulate signal coordinate from the surface inspection means in response to each particulate detected on the portion of the tacky surface passing through the sensible field of view of the surface inspection means, wherein the particulate signal coordinates form the unexposed particle coordinates;

(d) storing the unexposed particle coordinates; (e) releasing the carrier from the positioning means, whereby the removable particles initially on a first test surface may be transferred to the portion of the tacky surface by adhering and then removing the portion of the tacky surface from the first test surface;

(f) receiving the carrier on the positioning means after the portion of the tacky surface is adhered to and removed from the first test surface;

(g) passing the portion of the tacky surface through the sensible field of view of the surface inspection means in response to positioning commands from the controller;

(h) generating a particulate signal coordinate from the surface inspection means in response to each particulate detected on the portion of the tacky surface passing through the sensible field of view of the surface inspection means; and

(i) calculating the number of particles initially removed from the first test surface and deposited on the portion of the tacky surface by combining the positioning commands of the controller with particulate signal coordinates and with the stored unexposed particle coordinates, whereby particles with particle coordinates that have no conesponding unexposed particle coordinates comprise removable particles initially on the first test surface.

Claim 23. The method of claim 22, further comprising moving the portion of the tacky surface with respect to the surface inspection means while the positioning means is passing the portion of the tacky surface through the sensible field of view of the surface inspection means so that the portion of the tacky surface remains in the field of focus of the surface inspection means.

Claim 24. The method of claim 22, further comprising detecting alignment mark coordinates associated with the portion of the tacky surface.

Claim 25. The method of claim 24, wherein the step of generating a particulate signal coordinate from the surface inspection means further comprises translating the particulate signal coordinates with respect to the alignment mark coordinates.

Claim 26. The method of claim 22, further comprising transmitting a portion of the particle signal coordinates to an external analysis system.

Claim 27. The method of claim 22, further comprising a tacky transfer surface, wherein initially removable particles from the first test surface are transfened first to the tacky transfer surface and then to the portion of the tacky surface.

Claim 28. The method of claim 27, wherein the tacky transfer surface is a flexible tube supported by rollers small enough to fit into wafer support grooves in a FOUP used in semiconductor processing.

Claim 29. A method of detecting removable particulates initially on a test surface, the removable particles being transfened to a portion of a tacky surface by adhering and then removing the portion of the tacky surface from the test surface, the exposed surface being the portion of the tacky surface removed from the test surface, the tacky surface being supported by a carrier, comprising:

(a) receiving the carrier on a positioning means responsive to a controller;

(b) passing the exposed surface through the sensible field of view of a surface inspection means in response to positioning commands from the controller;

(c) generating a particulate signal coordinate from the surface inspection means in response to each particulate detected on the exposed surface passing through the sensible field of view of the surface inspection means; and