WO2008070635A2

WO2008070635A2 - Method and system for determining a critical dimension of an object

Info

Publication number: WO2008070635A2
Application number: PCT/US2007/086310
Authority: WO
Inventors: Michael J. Mater
Original assignee: Coherix, Inc.
Priority date: 2006-12-01
Filing date: 2007-12-03
Publication date: 2008-06-12
Also published as: WO2008070635A3; WO2008070635A9

Abstract

The present invention includes systems and method of measuring a critical dimension of an object. The system of the present invention includes a multiwavelength interferometric imaging system having an image receiver that is adapted to receive reflected light and calculate a critical dimension of an object in response thereto. The system can also include a gage block defining a known dimension that is disposed at a predetermined distance from the multiwavelength interferometric imaging system. The gage block can define a surface that at least partially reflects incident light, and can be adapted to hold the object in a predetermined position during an imaging operation. During the imaging operation at least a portion of the light incident on the image receiver is reflected from the gage block, thereby allowing the image receiver to calculate a critical dimension of the object in response to the received image.

Description

METHOD AND SYSTEM FOR DETERMINING A CRITICAL DIMENSION OF AN OBJECT

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of US Provisional Application number

60/868,120 filed 01 DEC 2006 and entitled "Method of measuring flatness and a critical dimension simultaneously", which is incorporated in its entirety by this reference.

TECHNICAL FIELD

[0002] The present invention relates generally to the field of interferometry, and more particularly to the field of interferometric methods and systems for use in an industrial setting.

BACKGROUND

[0003] A number of industries around the world use interferometric imaging systems to measure various qualities of a surface, including is regularity, flatness or smoothness. For example, interferometric imaging can be used in the semiconductor industry to measure the surface characteristics of a semiconductor wafer, and precision machine manufacturers can use interferometric imaging to measure the regularity or smoothness of a precision machined part or component. These types of measurements are critical to product performance on the user end as well as quality control and product design on the manufacturer end.

[0004] Unfortunately, most interferometric imaging systems are limited in scope to two dimensions, and those that can handle three dimensional imaging usually are limited to the extent that they cannot provide any information about the i of 22 object below its surface. It can be useful in certain applications to be able to measure and/or verify another dimension or measurement of an object, such as its thickness or a distance between two related parts. For example, a semiconductor manufacturer might be interested in measuring the thickness of a semiconductor wafer in order to ensure proper performance and/or consistency among a batch of wafers. Similarly, an automotive manufacturer might be interested in measuring the distance between a cylinder head mating surface and the crankshaft-receiving hole in a motor block to ensure optimum performance and to avoid any adverse effects of an elongated or shortened cylinder bore. Such measurements are difficult, if not impossible, to obtain using a conventional interferometric imaging system as any two objects in the imaging system's field of view must be known to within half a wavelength of each other in order to resolve position ambiguity. Given the relatively short wavelengths of a typical interferometric imaging system, this requirement has curtailed the development of the use of imaging systems to measure critical features of an object. [0005] As such, there is a need in the art of interferometry for systems and/or methods of measuring a critical dimension of an object that is economical, efficient, precise and scalable for use in different industries and/or on different types of objects.

SUMMARY OF THE PRESENT INVENTION

[0006] Accordingly, the present invention includes systems and methods of measuring a critical dimension of an object. A system of the present invention includes a multiwavelength interferometric imaging system having an image receiver that is adapted to receive reflected light and calculate a critical dimension of an object in response thereto. The system can also include a gage block defining a known dimension that is disposed at a predetermined distance from the multiwavelength interferometric imaging system. The gage block can define a surface that at least partially reflects incident light, and can be adapted to hold the object in a predetermined position during an imaging operation. During the imaging operation at least a portion of the light incident on the image receiver is reflected from the gage block, thereby allowing the image receiver to calculate a critical dimension of the object in response to the received image.

[0007] The present invention further includes a first method of measuring a critical dimension of an object. The first method can include the steps of providing an object disposed in a gage block of known dimensions and providing a multiwavelength interferometric imaging system. The method can further include the step of irradiating, substantially simultaneously, at least a portion of the object and at least a portion of the gage block with the multiwavelength interferometric imaging system such that radiation emitted from the multiwavelength interferometric imaging system is at least partially and substantially simultaneously reflected from the portion of the object and the portion of the gage block. The method can further include the steps of receiving, at an image receiver, an image of the portion of the object and the portion of the gage block in response to the at least partially reflected radiation, and calculating a critical dimension of the object in response to the image of the portion of the object and the portion of the gage block. [0008] The present invention also includes a second method of measuring a critical dimension of an object. The second method can include the steps of irradiating, with a multiwavelength interferometric imaging system, at least a portion of a surface of the object and at least a portion of a surface the gage block such that at least a portion of the radiation is reflected from the surface of the object and the surface of the gage block and determining a relative distance measurement between the surface of the object and the surface of the gage block in response to the reflected radiation. The method can further include the step of calculating the critical dimension of the object as a function of the relative distance measurement and the known dimensions of the gage block.

[0009] Other features, aspects and advantages of the present invention are described in detail below with reference to the figures.

BRIEF DESCRIPTION OF THE FIGURES

[0010] FIGURE i is a schematic diagram of a system for determining a critical dimension of an object in accordance with one embodiment of the present invention. [0011] FIGURE 2 is a cross-sectional diagram of one variation of the system depicted in FIGURE i.

[0012] FIGURE 3 is a cross-sectional diagram of another variation of the system depicted in FIGURE l.

[0013] FIGURE 4A is a plan view of another variation of the system depicted in FIGURE 1.

[0014] FIGURE 4B is a cross-sectional view of the variation of the system shown in FIGURE 4.

[0015] FIGURE 5A is a plan view of a motor block that can be analyzed according to the principles of the present invention. [0016] FIGURE 5B is an end view of the motor block shown in FIGURE 5A. [0017] FIGURE 6 is a perspective view of a gage block usable in the present invention in the analysis of a motor block such as that shown in FIGURES 5A and 5B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The following description of the preferred embodiments of the invention is not intended to limit the invention to these preferred embodiments, but rather to enable any person skilled in the art of interferometry to make and use this invention.

[0019] The present invention includes a system for measuring a critical dimension of an object in accordance with a preferred embodiment. As shown in FIGURE 1, the system 10 of the preferred embodiment includes a multiwavelength interferometric imaging system 12 that includes at least an image receiver 24 that is adapted to receive reflected light and calculate a critical dimension of an object 32 in response thereto. In a first variation of the system 10 of the preferred embodiment, the multiwavelength interferometric imaging system 12 can also include a first light source 14, a second light source 18, a first optical element 20 for combining light reflected by the object 32 and/or a gage block 28 and light from the second light source 18, and a second optical element for focusing the combined light onto the image receiver 24. In the first variation of the system 10 of the preferred embodiment, the multiwavelength interferometric imaging system 12 can be arranged around an optical axis 16 and further include an off-axis parabolic mirror 26 for directing light from the first light source 16 to the object 32 and/or gage block 28 and directing light reflected from the object 32 and/or gage block 28 to the first optical element 20.

[0020] The system 10 of the preferred embodiment further includes a gage block 28 defining known dimensions (d) that is disposed at a predetermined distance from the multiwavelength interferometric imaging system 12. The gage block 28 defines a surface 30 that at least partially reflects incident light, and is adapted to hold the object 32 in a predetermined position during an imaging operation. During the imaging operation at least a portion of the light incident on the image receiver 24 is reflected from the gage block 28, or the surface of the gage block 30, depending on the exact geometry and configuration of the gage block 28 as described in greater detail herein.

[0021] In a second variation of the system 10 of the preferred embodiment, the critical dimension of the object 32 is a thickness of the object 32. As used herein, the term thickness should be understood to include a distance measurement between an illuminated surface of the object 32 and another surface of the object 32, wherein the other surface of the object 32 may be planar, curved, regular, irregular, parallel or oblique to the illuminated surface, or any other suitable surface for which a distance measurement is sought. Knowing the thickness of the object is important to a number of industries, including at least in the semiconductor and/or integrated circuit industries and the precision machined parts, aerospace, automotive or manufacturing supply industries.

[0022] In one alternative of the second variation of the system 10 of the preferred embodiment, the thickness of the object 32 is calculated as a function of the known dimensions of the gage block 28, a distance measurement to the surface of the object 34 and a distance measurement to the gage block 28. In particular, the thickness of the object 32 can be calculated as the known dimensions of the gage block 28 less an absolute value of the difference between a distance measurement of the surface of the object 34 and a distance measurement of the gage block 28, which can include for example a distance measurement to a surface 30 of the gage block 28, depending again on the geometry and configuration of the gage block 28. [0023] In another alternative to the second variation of the system 10 of the preferred embodiment, the known dimensions of the gage block 30 includes a distance between a surface 30 of the gage block subject to irradiation from the multiwavelength interferometric imaging system 12 and a base portion 31 of the gage block 28 upon which the object 32 is disposable. Alternatively, the known dimensions of the gage block can include a thickness of the gage block 38 subject to irradiation from the multiwavelength interferometric imaging system 12, such as for example the gage block shown in FIGURES 3, 4A and 4B. In yet another alternative, the thickness of the object 32 can be calculated according to one or more known dimensions of the gage block 28, including for example those noted above as well as any other geometrical feature and/or orientation of the gage block 28 that is indicative of the relative position of the object 32 disposed thereon and/or therein. [0024] As noted above, the gage block 28 of the system 10 of the preferred embodiment can be configured according to any number of variations and/or alternative geometries and adapted to hold or contain different types of objects depending upon the application. In a third variation of the system 10 of the preferred embodiment, the gage block 28 can be configured as a saddle upon which the object 32 is disposable, such as that shown in FIGURES 1 and 6. Alternatively, in a fourth variation of the system 10 of the preferred embodiment, as shown in FIGURE 2, the gage block 36 includes a spindle upon which the object 32 is disposable. The spindle configuration can be useful in holding an object 32 having a cavity, hollow or hole, for example a disk such as a semiconductor wafer having a centralized hole for receiving a holder.

[0025] In a fifth variation of the system 10 of the preferred embodiment, the gage block can include a cradle within which the object 32 is disposable. For example, as shown in FIGURES 3, 4A and 4B, the object 32 is disposed within the gage block 38 in such a manner that light can be reflected off of more than one surface of the object 32. As shown in FIGURE 3, the object 32 can be immobilized through the use of one or more pins 40 or other mechanical or electromechanical devices for ensuring that the object 32 is substantially stationary with respect to the gage block 38. As shown in FIGURES 4A and 4B, the gage block 38 can further define one or more holes 35 for precisely locating the position of the gage block 38 in the plane in which the surface 34 of the object 32 is disposed. The features of the fifth variation of the system 10 of the preferred embodiment allow for images to be received of more than one surface of the object 32, which in turn permits the image receiver 24 to overlay the distinct images to within pixel accuracy and determine the critical feature of the object 32 to within pixel accuracy.

[0026] In a sixth variation of the system 10 of the preferred embodiment, the gage block can be configured to hold a motor block or any other precision machined part for industrial, commercial or consumer use. As shown in FIGURES 5A and 5B, a motor block 50 defines a cylinder head mating surface 52. In the automotive industry, it is desirable to know the characteristics of the cylinder head mating surface 52, including for example its flatness and/or smoothness. It is also desirable to know the distance between the cylinder head mating surface 52 and the crankshaft-receiving hole 53 (depicted as a partial cylindrical opening for clarity). Light 56 from a multiwavelength interferometric imaging system 12 of the type described herein can be used to determine each of the aforementioned characteristics of the motor block, as well as many other characteristics desirable in the automotive and manufacturing industries.

[0027] As shown in FIGURE 6, a gage block 64 may be used for holding a motor block 50 for analysis in accordance with the sixth variation of the system 10 of the preferred embodiment. The gage block 64 defines one or more surfaces 62 that can be imaged by a multiwavelength interferometric imaging system 12 of the type described herein substantially simultaneously with the imaging of one or more surfaces of a motor block 50. Additionally, the gage block 64 can include one or more fiduciary holes 68 for receiving a pin 67 and substantially securing the motor block 50 in position relative to the gage block 64. In such an instance, the motor block 50 can include one or more fiduciary holes 58 for receiving the pin 67 disposed through the fiduciary hole 68 of the gage block 64. Additionally, the gage block 64 can include a crankshaft hole 66 for receiving a pin 65 as a stand-in for a crankshaft. The pin 65 and the crankshaft hole 66 are alignable with the crankshaft-receiving hole 53 of the motor block 50 Accordingly, as the distance between the crankshaft hole 66 and the surface 62 of the gage block 64 is a known dimension, the image receiving 24 described above can be configured to calculate the distance between the cylinder head mating surface 52 and the crankshaft-receiving hole 53 in accordance with the principles set forth herein. [0028] In a seventh variation of the system 10 of the preferred embodiment, the image receiver 24 can be further adapted to calculate a smoothness of the object in response to the critical dimension of the object. The image receiving 24 can include any type of photodetector or photedetector array, as well as any necessary processors, controllers or computers to perform the calculations described herein. The computational hardware, firmware and/or software of the image receiver 24 can be integrated with the photodetection apparatus, or each element can form a standalone portion of the image receiver 24.

[0029] The image receiver 24 can be adapted to perform various functions and/or steps, which can be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions and/or steps described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0030] The image receiver 24 of the system 10 of the preferred embodiment can also include one or more software modules adapted to read machine executable code. A software module may reside in Random Access Memory (RAM), flash memory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. A storage medium can be coupled to the image receiver 24 such that the image receiver 24 can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the image receiver 24.

[0031] The present invention further includes a first method of determining a critical dimension an object. The method of the preferred embodiment can include the steps of providing an object disposed in a gage block of known dimensions and providing a multiwavelength interferometric imaging system. The gage block and multiwavelength imaging system can be of any suitable type, such as for example those described herein. The method of the preferred embodiment can further include the step of irradiating, substantially simultaneously, at least a portion of the object and at least a portion of the gage block with the multiwavelength interferometric imaging system such that radiation emitted from the multiwavelength interferometric imaging system is at least partially and substantially simultaneously reflected from the portion of the object and the portion of the gage block. The method of the preferred embodiment can further include the steps of receiving, at an image receiver, an image of the portion of the object and the portion of the gage block in response to the at least partially reflected radiation, and calculating a critical dimension of the object in response to the image of the portion of the object and the portion of the gage block.

[0032] In a first variation of the method of the preferred embodiment, the critical dimension of the object is a thickness of the object. As noted above, the term thickness should be understood to include a distance measurement between an illuminated surface of the object and another surface of the object, wherein the other surface of the object may be planar, curved, regular, irregular, parallel or oblique to the illuminated surface, or any other suitable surface for which a distance measurement is sought. Knowing the thickness of the object is important to a number of industries, including at least in the semiconductor and/or integrated circuit industries and the precision machined parts, aerospace, automotive or manufacturing supply industries.

[0033] In one alternative of the first variation of the method of the preferred embodiment, the thickness of the object is calculated as a function of the known dimensions of the gage block, a distance measurement to the surface of the object and a distance measurement to the gage block. For example, the thickness of the object can be calculated as the known dimensions of the gage block less an absolute value of the difference between a distance measurement of the surface of the object and a distance measurement of the gage block.

[0034] In another alternative to the first variation of the method of the preferred embodiment, the known dimensions of the gage block includes a distance between a surface of the gage block that reflects radiation from the multiwavelength interferometric imaging system and a base portion of the gage block upon which the object is disposable. Alternatively, the known dimensions of the gage block can include a thickness of the gage block subject to irradiation from the multiwavelength interferometric imaging system, such as for example the gage block described above with reference to FIGURES 3, 4A and 4B. In yet another alternative, the thickness of the object can be calculated according to one or more known dimensions of the gage block, including for example those noted above as well as any other geometrical feature and/or orientation of the gage block that is indicative of the relative position of the object disposed thereon and/or therein.

[0035] As noted above, the exact geometry and function of the gage block can be selected in part depending upon the object with which it interfaces, as well as any particular application and/or industry in which the method of the preferred embodiment is usable. Example gage blocks are described above with reference to the system of the preferred embodiment, and in particular with reference to FIGURES l, 2, 3, 4A, 4B and 6. As noted above, the gage block can be configured as a spindle, a saddle, a cradle, or any other suitable geometry for holding the object in a predetermined fashion and reflecting at least a portion of the light emitted by the multiwavelength interferometric imaging system into the image receiver for image processing in accordance with the principles described herein.

[0036] The present invention further includes a second method of measuring a critical dimension of an object disposed on a gage block having known dimensions. The method of the preferred embodiment includes the steps of irradiating, with a multiwavelength interferometric imaging system, at least a portion of a surface of the object and at least a portion of a surface the gage block such that at least a portion of the radiation is reflected from the surface of the object and the surface of the gage block and determining a relative distance measurement between the surface of the object and the surface of the gage block in response to the reflected radiation. The method of the preferred embodiment can further include the step of calculating the critical dimension of the object as a function of the relative distance measurement and the known dimensions of the gage block. [0037] In a first variation of the method of the preferred embodiment, the irradiating step further includes substantially simultaneously irradiating the at least a portion of the surface of the object and the at least a portion of the surface of the gage block with the multiwavelength interferometric imaging system. Substantially simultaneous imaging of the object and the gage block can result in a single image, from which data can be more easily extracted in order to perform the computations of the critical dimension of the object. As noted above, the critical dimension of the object can be for example its thickness, which is defined herein as a distance measurement between an illuminated surface of the object and another surface of the object, wherein the other surface of the object may be planar, curved, regular, irregular, parallel or oblique to the illuminated surface, or any other suitable surface for which a distance measurement is sought.

[0038] In a second variation of the method of the preferred embodiment, the known dimensions of the gage block includes a distance between a surface of the gage block subject to irradiation from the multiwavelength interferometric imaging system and a base portion of the gage block upon which the object is disposable. Alternatively, the known dimensions of the gage block can include thickness of the gage block subject to irradiation from the multiwavelength interferometric imaging system such as for example the gage block described above with reference to FIGURES 3, 4A and 4B. In yet another alternative, the thickness of the object can be calculated according to one or more known dimensions of the gage block, including for example the distance between the crankshaft hole and the surface of the gage block described with reference to FIGURES 5A, 5B and 6. [0039] As described above, the exact geometry and function of the gage block can be selected in part depending upon the object with which it interfaces, as well as any particular application and/or industry in which the method of the preferred embodiment is usable. Example gage blocks are described above with reference to the system of the preferred embodiment, and in particular with reference to FIGURES l, 2, 3, 4A, 4B and 6. Alternatively, the gage block can be configured as a spindle, a saddle, a cradle, or any other suitable geometry for holding the object in a predetermined fashion consistent with the systems and methods described herein. [0040] As a person skilled in the art of interferometry will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiment of the invention without departing from the scope of this invention defined in the following claims.

Claims

CLAIMS What is claimed is:

1. A method of determining a critical dimension an object comprising the steps of:

• providing an object disposed in a gage block of known dimensions;

• providing a multiwavelength interferometric imaging system;

• irradiating, substantially simultaneously, at least a portion of the object and at least a portion of the gage block with the multiwavelength interferometric imaging system such that radiation emitted from the multiwavelength interferometric imaging system is at least partially and substantially simultaneously reflected from the portion of the object and the portion of the gage block;

• receiving, at an image receiver, an image of the portion of the object and the portion of the gage block in response to the at least partially reflected radiation; and

• calculating a critical dimension of the object in response to the image of the portion of the object and the portion of the gage block.

2. The method of claim i, wherein the critical dimension of the object is a thickness of the object.

lό of 22

3- The method of claim 2, wherein the thickness of the object is calculated as: the known dimensions of the gage block less an absolute value of the difference between a distance measurement of the surface of the object and a distance measurement of the gage block.

4. The method of claim 3, wherein the known dimensions of the gage block includes a distance between a surface of the gage block subject to irradiation from the multiwavelength interferometric imaging system and a base portion of the gage block upon which the object is disposable.

5. The method of claim 1, wherein the known dimensions of the gage block includes a thickness of the gage block subject to irradiation from the multiwavelength interferometric imaging system.

6. The method of claim 1, wherein the gage block includes a spindle upon which the object is disposable.

7. The method of claim 1, wherein the gage block includes a saddle upon which the object is disposable.

8. A method of measuring a critical dimension of an object disposed on a gage block having known dimensions, the method comprising the steps of: a. irradiating, with a multiwavelength interferometric imaging system, at least a portion of a surface of the object and at least a portion of a surface the gage block such that at least a portion of the radiation is reflected from the surface of the object and the surface of the gage block; b. determining a relative distance measurement between the surface of the object and the surface of the gage block in response to the reflected radiation; and c. calculating the critical dimension of the object as a function of the relative distance measurement and the known dimensions of the gage block.

9. The method of claim 8, wherein step a. further comprises substantially simultaneously irradiating the at least a portion of the surface of the object and the at least a portion of the surface of the gage block with the multiwavelength interferometric imaging system.

10. The method of claim 8, wherein the critical dimension of the object is a thickness of the object.

11. The method of claim 8, wherein the known dimensions of the gage block includes a distance between a surface of the gage block subject to irradiation from the multiwavelength interferometric imaging system and a base portion of the gage block upon which the object is disposable.

12. The method of claim 8, wherein the known dimensions of the gage block includes a thickness of the gage block subject to irradiation from the multiwavelength interferometric imaging system.

13. The method of claim 8, wherein the gage block includes a spindle upon which the object is disposable.

14. The method of claim 8, wherein the gage block includes a saddle upon which the object is disposable.

15. A system for measuring a critical dimension of an object, the system comprising:

• a multiwavelength interferometric imaging system comprising an image receiver adapted to receive reflected light and calculate a critical dimension of an object in response thereto; and

• a gage block defining known dimensions and disposed at a predetermined distance from the multiwavelength interferometric imaging system such that during an imaging operation at least a portion of the light incident on the image receiver is reflected from the gage block, wherein the gage block is adapted to hold an object in a predetermined position during the imaging operation.

16. The system of claim 15, wherein the critical dimension of the object is a thickness of the object.

Yj. The system of claim 16, wherein the thickness of the object is calculated as: the known dimensions of the gage block less an absolute value of the difference between a distance measurement of the surface of the object and a distance measurement of the gage block

18. The system of claim 16, wherein the known dimensions of the gage block includes a distance between a surface of the gage block subject to irradiation from the multiwavelength interferometric imaging system and a base portion of the gage block upon which the object is disposable.

19. The system of claim 16, wherein the known dimensions of the gage block includes a thickness of the gage block subject to irradiation from the multiwavelength interferometric imaging system.

20. The system of claim 15, wherein the gage block includes a spindle upon which the object is disposable.

21. The system of claim 15, wherein the gage block includes a saddle upon which the object is disposable.

22. The system of claim 15, wherein the gage block comprises a cradle within which the object is disposable.

23. The system of claim 15, wherein the gage block is adapted to hold a semiconductor wafer.

24- The system of claim 15, wherein the gage block is adapted to hold a motor block.

25. The system of claim 15, wherein the image receiver is further adapted to calculate a smoothness of the object in response to the critical dimension of the object.