WO2015003759A1

WO2015003759A1 - Shaped filter for spectrometer detector arrays

Info

Publication number: WO2015003759A1
Application number: PCT/EP2013/077870
Authority: WO
Inventors: Kris Naessens; Bert Luyssaert; Ronny Bockstaele
Original assignee: Trinean Nv
Priority date: 2013-07-10
Filing date: 2013-12-20
Publication date: 2015-01-15
Also published as: GB201312403D0; GB2516078A

Abstract

A spectrometer (100) for optically characterizing a species in the ultraviolet and/or visible wavelength range is described. The spectrometer comprises a filter (110) for reducing or blocking a spectral portion of an impinging radiation and a detector (120) adapted for distinctively detecting spectral components of radiation impinging on a sensor surface. The filter (110) is directly mounted on a sensor surface of the detector and is a shaped filter having (110) a shape for partly covering the detector surface and partly leaving the detector surface open, the filter being adapted for blocking a spectral portion of impinging radiation at the covered sensor surface. In this way second or higher order diffraction beams can be blocked from reaching the detector surface. It also relates to a corresponding detector.

Description

Shaped filter for spectrometer detector arrays Field of the invention

The invention relates to the field of spectrometry. More specifically it relates to filters for use in spectrometry for location dependent filtering of higher order diffraction signals before they reach the detection region of a detector.

Background of the invention

Spectrometry is a widely spread characterization technique based on optical absorption and/or transmission of radiation by species of interest. Spectrometers for the ultraviolet (10 - 400 nm) and visible (400 - 800 nm) wavelength region typically comprise a diffractive element, such as a diffraction grating, to split the incoming radiation into its constituent wavelengths, some optical elements like lenses or mirrors to collimate and focus the radiation, and a detector array for detecting the radiation. The detector array typically comprises a plurality of pixels, wherein each pixel detects a wavelength or certain small wavelength band. The detector array typically used may be a photodiode array, CMOS array, CCD array or line camera. They typically are manufactured from a piece of semiconductor material, mostly silicon, mounted into a package, often ceramic, with the electr(on)ical connection between the two parts, i.e. the detector and the connecting pins, performed by wire bonds. To guarantee a stable atmosphere and to protect the electronics from damage by handling, the open top part of the package is mostly sealed with a transparent cover, e.g. a glass cover. In applications where ultraviolet light is to be detected this cover needs to be transparent to this wavelength region and fused silica glass is commonly used.

One of the most common used diffractive elements for spectrometry is a diffraction grating. A diffraction grating typically comprises of a large number of parallel grooves or other diffracting features on a surface. A beam of incident radiation is diffracted at these grooves or lines, resulting in the spreading of the different spectral components of the impinging radiation. For particular scattering directions, only radiation that is scattered from adjacent grooves with its phase shifted by an integer multiple of the wavelength undergoes constructive interference. If a wavelength satisfies this condition, the exact half wavelength will also satisfy the condition, meaning that a diffraction grating will send both the full wavelength and half the wavelength (referred to as 1^st order and 2^nd order diffraction) in the same direction. Similarly also third order diffractions (whereby radiation of a third of the wavelength are diffracted in the same direction), fourth order diffractions (whereby radiation of a quarter of the wavelength is diffracted in the same direction), or other higher order diffractions may occur. In such a case, radiation from this diffraction direction impinging on a detector pixel will result in difficulties to distinguish between absorption at a specific wavelength or at half the wavelength, which can lead to difficulties or impossibilities for identifying the species of interest.

For a number of applications, it is important to be able to do spectral characterisation over a broad spectral range, as absorption or transmission of spectral components of different contributing elements in the species of interest may be widely spread over a broad spectral range. Nevertheless, as a consequence of the constructive interference used in the diffraction process, if the spectral range of the spectrometer [λι ,λυ ] spans a large range such that for specific wavelengths also the corresponding half wavelength radiation falls within the range, meaning that λυ>2.λι, special precautions have to be taken to avoid these higher-order diffractions from reaching the detector array. This typically is the case for UV-VIS spectrometers spanning more than one decade in the spectral range, although embodiments are not limited thereto.

Solutions for the above illustrated problem have been found in applying a filter that has a different spectral response for different positions on the detector, hence for different wavelengths of interest, thus filtering the impinging radiation before it reaches the detector and avoiding 2^nd or higher order diffractions from reaching the detector. Typically, a linear variable filter is used, whereby the spectral response changes substantially linearly from one side of the filter to the other side of the filter. These special filters typically are mounted as a replacement for the package glass cover (after removal of this cover). When the filters are mounted as described above, problems typically may occur when radiation is hitting the detector array under a substantially oblique angle. When light is hitting the detector array more or less perpendicularly, the effect of the glass or filter cover will be small. In some spectrometer configurations, however, light hits the detector array under a substantially oblique angle. In this case, incoming light reflecting from the detector surface will be reflected a second time from the bottom of the filter or glass cover and be detected by a pixel that is different from the pixel of the non-reflected light. In extreme cases this can result in a double peak on the detector for monochromatic illumination.

Therefore, there is still room for improvement for these filters and for methods how they can be made and positioned.

Summary of the invention

It is an object of embodiments of the present invention to provide a good spectrometer for characterizing a sample in the ultraviolet and/or visible range.

It is an advantage of embodiments of the present invention that, when applied in a spectrometer topology, 2^nd order or higher order diffractions are filtered before they reach the covered part of the detector.

It is an advantage of embodiments of the current invention that a spectrometer can be provided wherein these higher order diffractions are not detected. When applied in a spectrometer topology, the diffracted light reaches the area of the detector. Part of the area is thereby exposed to higher order diffractions and part of the area does not suffer from higher order diffractions. The present invention solves the problem of detection of 2^nd or higher order diffraction beams, which could otherwise hinder the optical characterization process.

According to embodiments of the present invention, the filter can be positioned such that part of the detector is not covered by the filter. This part, when applied in a spectrometer topology, will typically be the part which is not suffering from higher order diffractions. The other part may be covered by the filter which filters out the higher order diffractions of the signal. It is an advantage of embodiments of the current invention that a shaped filter, e.g. machined or micro-machined filter, can be applied instead of a linear variable filter, as linear variable filters typically have a complex manufacturing process.

It is an advantage of embodiments of the current invention that a high-pass filter (i.e. "high-pass" with reference to wavelength of the radiation) can be used obtaining the same functionality as would be obtained when using a linear variable filter when applied in a spectrometer after diffraction of the signal using a diffraction grating. The functionality of both is to filter out higher order diffractions from the diffracted light. It is an advantage of embodiments of the current invention that light hitting the detector array under a substantially oblique angle is introducing less errors in the resulting measured spectrum than in the case of a linear variable optical filter mounted as a replacement for the package glass cover.

It is an advantage of at least some embodiments of the present invention that the filter can be directly mounted on the surface of the detector, avoiding or reducing reflection between the filter and the detector. Directly mounted may comprise directly applied on the sensing surface of the detector or suspended directly above the sensing surface, without solid or liquid material being between the sensing surface and the filter. When reflection occurs, the reflecting light will travel along the detector area, but since the filter is directly on top of or close to the sensing surface and since the filter can be very thin, the distance travelled by the reflecting wave along the area of the detector is short compared to prior art solutions where the filter is mounted a certain distance from the detector. Moreover it is an advantage of embodiments according to the present invention that the distance travelled by the reflecting wave is small with regard to the pixel size of the detector.

It is an advantage of embodiments of the current invention that a thin foil can be used as filter. In embodiments according to the current invention, the filter is resting on the detector surface and therefore does not need to be very rigid.

It is an advantage of embodiments of the current invention that the complexity for manufacturing of the shaped filter, e.g. machined or micro-machined filter, is smaller than the complexity for manufacturing of a linear variable optical filter. It is an advantage of embodiments of the current invention that the distance between the filter and the detector is fixed. As opposed to prior art solutions, in embodiments according to the present invention, the filter is mounted directly on top of the detector. In the prior art solutions the distance between the detector and the filter typically positioned on a glass of the packaging of the detector, is often difficult to control.

It is an advantage of embodiments of the current invention that the filter can be placed directly on top of the detector. Micro-machining of the filter allows creating gaps in the filter such that there is still place for the wire bonds towards the detector when the filter is mounted.

It is an advantage of embodiments of the current invention that the relative position between the detector and the filter can be accurately tuned, i.e. within 125μιη, advantageously within 60μιη. Micro-machining of the filter allows to create gaps as position indicators for accurately positioning the filter.

It is an advantage of embodiments of the current invention that only higher order diffractions are attenuated and that the attenuation of first order diffractions is small compared to prior art solutions. In the area where second order diffractions are of no influence, the detector is not covered by a filter. In these areas the first order diffractions are even not attenuated by a filter.

The above objective is accomplished by a method and device according to the present invention.

The present invention relates to a spectrometer for optically characterising a species in the ultraviolet and/or visible wavelength range, the system comprising

a filter for reducing or blocking a spectral portion of an impinging radiation, a detector adapted for distinctively detecting spectral components of radiation on a sensing surface,

the filter being directly mounted on the sensing surface of the detector and being a shaped filter having a shape for partly covering the detector surface and partly leaving the sensing surface open, the filter being adapted for blocking a spectral portion of impinging radiation at the covered detector surface. It is an advantage of embodiments of the present invention that the filter results in optical advantages as well as mechanical advantages.

The detector may comprise any of packaging and/or transparent cover layer overlaying both the filter and the detector. The filter thus may be integrated within the package of the detector.

The shaped filter may be a machined shaped filter.

The machined shaped filter may be a micro-machined shaped filter.

The filter may be a laser-ablated filter. The filter may be a femto-second laser ablated filter, i.e. the filter may be made using laser ablation with a femto-second laser.

The filter may be a filter cut using a micro-jet cutting technique.

The shaped filter may be a resist layer.

The filter may be integrated in the detector or may be positioned thereon and/or connected thereto.

The filter may be glued on the sensing surface.

The filter may be suspended directly above the sensing surface. Suspending may be such that there is no solid or liquid material between the filter and the sensing surface of the detector.

The filter may be directly applied to a silicon detector.The shaped filter may be a printed resin pattern.

The system furthermore may comprise a diffraction element for diffracting incident radiation before it reaches the filter and the detector, whereby the filter is aligned with respect to the detector for reducing or blocking 2^nd or higher order diffraction beams from being incident on the detector.

The filter furthermore may comprise openings for allowing wire bonds to pass the filter.

The filter may be such that the filter has alignment openings for alignment of the filter with respect to the detector.

The filter may be a foil.

The filter may have slanted edges, slanted with respect to the filter surface. The thickness of the filter may be thinner than 0.1mm, advantageously below 50μιη, more advantageously below 25μιη.

The filter may be a high-pass filter with a cutoff wavelength between 380nm and 420nm.

The attenuation of the filter may be a transmission of at least 80% for radiation to be passed to the sensor surface and a transmission below 1% for radiation wavelengths to be blocked from the sensor surface.

The present invention also relates to a method for setting up a spectrometer in the ultraviolet and visible wavelength region, the method comprising:

- obtaining a filter

shaping the filter taking into account a detector surface of the spectrometer so as to induce a shape for partly covering the detector surface and partly leaving the detector surface open for filtering out higher order diffractions before reaching the covered part of the detector to prevent detection thereof.

- aligning the filter directly on the surface of a detector, for partly covering the detector surface.

Shaping the filter may comprise machining the filter.

Machining the filter may comprise micro-machining the filter.

The shaping step may include forming openings in the filter such that mounting the filter on the detector is not obstructed by the presence of wire bonds.

The shaping step may include forming alignment openings for alignment of the filter with the detector.

Machining the filter may comprise laser ablating the filter.

Laser ablation may comprise laser ablating the filter using a femto-second laser.

Machining the filter may comprise micro-jet processing of the filter.

The method may comprise providing a detector by first providing a sensing surface, mounting a filter thereon and packaging the sensor with the filter mounted on the sensing surfaces in a packaging material.

The present invention also relates to the use of a system as described above for characterizing a sample of interest. The present invention furthermore relates to a detector for use in a spectrometer, the detector comprising a sensing element for distinctively detecting spectral components of radiation on a sensing surface and a filter for reducing or blocking a spectral portion of an impinging radiation, the filter being directly mounted on the sensing surface of the detector and being a shaped filter having a shape for partly covering the detector surface and partly leaving the sensing surface open, the filter being adapted for blocking a spectral portion of impinging radiation at the covered detector surface. The detector furthermore may comprise any of a packaging material and/or a cover glass, overlaying the filter and the sensing surface or embedding the filter and the sensing surface to form a packaged detector.

Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

Brief description of the drawings

FIG. 1 schematically illustrates a front view (top of the drawing) and a top view (bottom of the drawing) of a system according to an embodiment of the present invention.

FIG. 2 schematically illustrates a detector array package with glass cover, as known from prior art.

FIG. 3 schematically illustrates a detector array package with glass cover removed, as known from prior art.

FIG. 4 schematically illustrates an exploded view of a detector array with shaped filter according to an embodiment of the current invention.

FIG. 5 schematically illustrates an exploded view of a detector array with package and with shaped filter according to an embodiment of the current invention.

FIG. 6 schematically illustrates a detector array with package and with shaped filter mounted according to an embodiment of the current invention. FIG. 7 and FIG. 8 schematically illustrate a detector array with glass cover and perpendicularly respectively oblique incoming radiation, illustrating a problem solved by embodiments of the present invention.

FIG. 9 shows the spectral response from a monochromatic light source when using the detector array in a spectrometer set-up, for a detector without glass cover (top), a detector with glass cover and for perpendicular impinging radiation, and a detector with glass cover and with oblique impinging radiation.

FIG. 10 illustrates an exemplary method for making a system for measuring the spectrum of a signal, according to an embodiment of the current invention.

FIG. 11 illustrates a representation of the spectral behavior of a filter as can be used in embodiments according to the present invention.

FIG. 12 illustrates the possibility of providing slanted edges at the filter, as can be used in an embodiment according to the present invention.

FIG. 13 illustrates an embodiment of the present invention whereby a filter is suspended above the sensing surface of the detector.

The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.

Any reference signs in the claims shall not be construed as limiting the scope.

In the different drawings, the same reference signs refer to the same or analogous elements.

Detailed description of illustrative embodiments

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

Moreover, the terms top, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Where in embodiments of the present invention reference is made to ultraviolet light, reference is made to light with a wavelength in between 10 nm and 400 nm.

Where in embodiments of the present invention reference is made to visible light, reference is made to light with a wavelength in between 400 nm and 700 nm.

Where in embodiments of the current invention reference is made to the spectral span or spectral range of a spectrometer, reference is made to the spectral range wherein spectrometric characterization can be performed.

Where in embodiments according to the present invention reference is made to a filter being directly mounted on the sensing surface, reference is made to direct application of the filter on the sensing surface, i.e. creating a direct contact between the two, without cover glass or packaging materials being in between or suspension of the filter over the sensing surface, without solid or liquid materials such as cover glasses or packaging materials being in between. Packaging materials and/or cover glasses may be overlaying both the sensing surface and the filter.

In other words, the machined filter may be integrated inside the package of the detector. In a first aspect, the present invention relates to a spectrometer 100 for measuring the spectrum of a signal in the ultraviolet and/or visible frequency range. The spectrometer may be especially suitable for optically characterizing a sample. According to embodiments of the present invention, the spectrometer comprises a filter for reducing or blocking a spectral portion of an impinging radiation. The spectrometer also comprises a detector adapted for distinctively detecting spectral components of impinging radiation. The filter according to embodiments of the present invention is directly mounted on a surface of the detector and is a shaped filter, e.g. micro-machined or machined filter, having a shape for partly covering the detector surface and partly leaving the sensing surface open, the filter being adapted for blocking a spectral portion of impinging radiation at the covered sensing surface. The filter thus may be adapted for filtering a spectral portion of radiation before it reaches a detector surface, e.g. a detector array 120. In certain embodiments of the current invention the detector array 120 can be a CMOS array or a CCD array or a line camera. Typically, the filter characteristics may be selected in function of the spectral range of the spectrometer. The filter may be adapted for filtering out second or higher order diffraction radiation, thus preventing that such radiation reaches the detector surface.

By way of illustration, embodiments of the present invention not being limited thereto, a schematic representation of the central portion of the spectrometer is shown in FIG. 1, illustrating both a front view and a top view of the detector.

In certain embodiments of the present invention, the filter 110 is a thin foil 410 with a sharp transmission characteristic. The sharp transmission characteristic is such that all light below a certain wavelength is blocked and all light above a certain wavelength is transmitted (except for the Fresnel losses). As a consequence of this spectral response, the foil 410 can function as a high-pass optical filter. In a particular embodiment, the foil transmission should have three wavelength regions. A first wavelength region where all visible light is transmitted (e.g. having a transmission of more than 80%), one transition region, and one where almost all other radiation wavelengths are blocked, e.g. with a transmission for these wavelengths below 1%, preferably 0.1%. The transition region advantageously is shorter than 50nm, preferably shorter than 25nm. By way of illustration, embodiments of the present invention not being limited thereto, a possible transmission characteristic as can be used is shown in FIG. 11 illustrating an ideal (dashed line) and a measured (full line) spectral behavior of the filter.

According to embodiments of the current invention the filter 110, which can be a foil 410, is a high-pass filter. The filter may be made of any suitable filtering material such as for example a plastic, a polyester filter made from a deep-dyed PET material, a polycarbonate, pmma, pet, resist, printing resin, etc.

Filtering may be performed based on inherent characteristics of the material or the material may be tuned to block certain wavelengths or wavelength regions.

The spectrometer 100 may comprise a diffraction element, for diffracting an incoming radiation beam in its spectral components, such that different wavelengths can be detected at different positions of the detector surface. Such a diffraction element typically may be a diffractive grating. The diffractive grating may comprise a plurality of lines or similar diffraction features, allowing to spectrally spread the incident radiation beam. As will be appreciated by the skilled person in the spectrometer typically the diffraction element will be positioned before the filter and the detector in the radiation path.

The spectrometer 100 according to embodiments of the present invention also comprises a detector, e.g. a detector array 120 wherein each detector allows to detect the radiation at a wavelength or wavelength range. The detector thus may be adapted for detecting radiation substantially over a wavelength range. The wavelength span of the detector in combination with the diffraction element may for example be from lOOnm to 900nm, e.g. from 200nm to 750nm. By covering the detector 120, e.g. the detector array, selectively with the foil 410, the higher-order diffractions are prevented from reaching the detector array. In some embodiments, more than one shaped filter may be used.

FIG. 2 and FIG. 3 illustrate a detector package as known from prior art, which can be used as a starting configuration for obtaining a system according to an embodiment of the present invention. In embodiments of the present invention, a detector package as shown in FIG. 2 and FIG. 3 can be used whereby additionally a shaped filter is applied to the detector surface.

FIG. 4 shows the detecting surface 120 (silicon chip) and the shaped filter 410 according to an exemplary embodiment of the current invention. An opening 130 is shaped in the filter for letting through the high frequency (low wavelength) signals in the low wavelength region of the detector, which would be blocked if the opening 130 was not there. According to one embodiment, recesses 150 are shaped in the filter 410 such that placing of the filter is not obstructed by the presence of the bond wires. Such bond wires may typically be provided for contacting the detector.

FIG. 5 illustrates an exploded view of the configuration shown in FIG. 4, wherein the shaped filter and the detector with its package is shown. FIG. 6 shows the final configuration wherein the shaped filter is in direct contact with the detector surface.

According to embodiments of the present invention, the shaped filter is applied directly on the detector, e.g. by positioning it directly on the detector, by sticking it to the detector surface, by glueing it to the detector surface, by laminating it to the detector surface or by applying a similar technique or deposition. In an alternative embodiment, the filter is directly suspended above the sensing surface, without a solid material or a fluid being present. The latter is shown by way of illustration in FIG. 13, illustrating the sensor surface 120, the filter 110 and a glass cover 1310. Further features may be similar to those in other embodiments of the present invention.

It is an advantage of embodiments of the present invention that 2^nd order and higher order diffractions are filtered such that substantially only first order diffractions are detected in the detector. Furthermore, as the shaped filter is in contact, e.g. direct contact, with the detector surface, the effect of additional reflections between the filter and the detector surface, which may result in unwanted ghost signals, can be reduced. The latter is advantageous as such ghost signals can result in inaccurate interpretation of the spectrum obtained. In order to illustrate the creation of ghost signals as can occur in prior art systems and as are reduced or even avoided in embodiments according to the present invention, such reflections are discussed below.

In prior art systems, where a filter typically is positioned on the packaging glass cover of the package of the detector, two distinct situations may occur. When radiation is hitting the detector array more or less perpendicularly, the effect of the glass or filter cover will be small as is also illustrated in FIG. 7. The radiation hitting the detector reflects against the filter and again reflects back against the detector. At perpendicular incidence, the reflections however substantially remain within the same pixel of the detector. In some spectrometer configurations, however, light hits the detector 120 array under a substantially oblique angle as illustrated in FIG. 8. In this case, incoming light reflecting from the detector surface will be reflected a second time from the bottom of the filter or glass cover and be detected by a pixel that is different from the pixel of the non-reflected light. In extreme cases this can result in a double peak on the detector for monochromatic illumination. A substantial distance between the detector array and the glass cover will contribute strongly to this problem.

The spectra of the exemplary detectors being exposed to a monochromatic light source when using the detector array in a prior art spectrometer set-up are shown in FIG. 9. The top graph shows the spectrum measured by a detector array not having a glass cover. The middle graph shows the spectrum measured by a detector array with a glass cover and the light being perpendicular to the glass cover and the detector. The reflections hit the detector always in the same pixel and therefore only one peek is shown in the spectrum: the frequency of the monochromatic illumination. The bottom graph shows the spectrum measured by a detector having a glass cover and oblique light. Due to the reflections the light will hit the detector on several pixels resulting in at least 2 peaks in the measured spectrum.

In embodiments according to the present invention the distance between the filter and the detecting surface thus is substantially decreased, in preferred embodiments according to the present invention, the distance is even reduced to substantially zero. The latter is e.g. obtained by putting the filter directly on the detecting surface.

According to embodiments of the present invention, the filter is provided with openings through which the bond wires for wiring the detector can be guided. Such openings can be easily introduced during the shaping of the filter. In embodiments according to the present invention, the filter 110 thus may be adapted through shaping such that it additionally comprises openings 150 to make the filter 110 fit around the wire bonds.

Furthermore, according to preferred embodiments of the current invention, the shaped filter allows better control of the exact alignment between the filter and the detecting surface, and offering more possibilities to include extra functionality into the filter. In embodiments of the current invention alignment openings 140 for aligning the filter 110 with the detector 120 also can be introduced in the filter 110 via micromachining. The alignment opening may for example be aligned with alignment features introduced in the detector. Such alignment features may for example be alignment pins.

Putting the filter 110 directly on top of the detector surface 120, according to an embodiment of the present invention, furthermore has as a consequence that it does not need to be rigid or mechanically strong. Instead of the classical filter, namely deposited layers on top of a glass support, the filter therefore may be a thin foil 410 in exemplary embodiments according to the present invention. Since the foil can become thin, when compared to the pixel size, the optical effects at the edge of the filter 410 can become small or can be restricted to one or a few pixels. The thickness of the foil used advantageously may be below 0.1mm, e.g. below 50μιη or below 25 μιη. Moreover as in certain embodiments of the current invention the foil 410 is put directly on top of the detector 120, the optical effects of reflection are even more reduced and restricted to one or a few pixels.

The filter 110 also may be machined such that the edges are slanted with respect to the main filter surface. The latter may advantageously be used for obstructing less radiation near the edge side. An example of straight edges and slanted edges is shown in FIG. 12.

In the above description the detector used in the spectrometer according to embodiments of the present invention are described in detail. It will be clear to the person skilled in the art that other standard and optional components also may be present in the spectrometer, such as for example a radiation source, a sample holder, additional optical elements, ....

According to particular embodiments of the present invention, the machined filter is made using a machining technique allowing to reduce debris. It was found that advantageously micro-jet cutting as well as laser ablation with a laser with short pulses, e.g. a femto-second laser, results in machining of the filter without creating debris. Such techniques thus allow accurate processing for defining accurate, straight or other shaped edges, without generating particles remaining from the machining process and introducing accuracy problems.

In a second aspect the current invention relates to a method for manufacturing, assembling or setting up a spectrometer operative in the ultraviolet and visible wavelength region. The method according to embodiments of the present invention comprises obtaining a filter, micro-machining the filter, thereby taking into account a detector surface of the spectrometer so as to induce a shape of the shaped filter for partly covering the detector surface and partly leaving the detector surface open for filtering out higher order diffractions before reaching the covered part of the detector to prevent detection thereof. The method also may comprise positioning the filter directly on the surface of a detector, for partly covering the detector surface. The positioning may be aligning. Such alignment may be performed using alignment features, although embodiments of the present invention are not limited thereto. FIG. 10 illustrates a schematic representation of a method for manufacturing a spectrometer. The steps of obtaining a filter, shaping it and positioning the filter in contact with the detector surface are indicated. In certain embodiments of the current invention, during the micro-machining step openings 150 may be made in the filter 110 so that when placing the filter on a detector 120 there is still room for the wire bonds coming from the detector 120. Positioning the filter thus may be providing the filter on top of the detector surface while making sure that the bond wires are positioned through the openings in the filter.

In certain embodiments of the current invention, during the micromachining step, alignment openings 140 may be made in the filter 110 so that when placing the filter 110 on a detector 120 the openings help in positioning the filter 110 relative to the detector 120. As indicated above, alternatively such shaping also may be performed using a lithographic process using resist, for directly depositing on the photodetector. The filter may be processed during the same processing cycle as the photodetector. Another alternative for providing a shaped filter which is also envisaged within the present invention is printing of the filter on the detector, e.g. polymer jet printing. Where in embodiments of the present invention reference is made to machining or micromachining, reference may be made to laser processing, punching, laser cutting, laser ablating, ....

In particular embodiments, the machining is selected so that accurate definition of the edges can be obtained, without introduction or reducing introduction of debris. It was found that advantageously micro-jet cutting as well as laser ablation with a laser with short pulses, e.g. a femto-second laser, results in machining of the filter without creating such debris. Examples of lasers that could be used are pulsed C0₂ lasers, pulsed YAG lasers, .. Pulsed excimer lasers can be beneficial on plastic-based filters as the deep UV wavelength of excimer lasers as ArF and KrF correspond to high absorption coefficients in the plastic and thus lead to highly confined pulse energy absorption within the beam area. Typically little to no debris results from machining with these lasers. Femtosecond pulse systems as Ti-Sapphire can be advantageous to machine even more accurately and with very low to no debris formation.

As indicated above, after shaping the filter, the filter is positioned directly on the surface of the detector 120 such that the filter 110 partly covers the surface of the detector 120 whereby higher order diffractions are filtered before reaching the covered part of the detector 120 to prevent detection of them. When, in a spectrometer setup, the detector has areas which are subject to higher order diffractions and areas which are not, the filter is positioned such that the areas which are not suffering from higher order diffractions are not covered by the filter 110. The latter is advantageous, as it results in less absorption and therefore an improved detection behavior.

In a third aspect the current invention relates to the use of a system 100 according to the present invention for performing spectrometry. The technique may be used for characterizing a specimen of interest. As ghost detections can be reduced or avoided, the characterization can be performed with improved accuracy.

In yet another aspect, the present invention also relates to a detector for use in a spectrometer, the detector comprising a sensing element for distinctively detecting spectral components of radiation on a sensing surface and a filter for reducing or blocking a spectral portion of an impinging radiation, the filter being directly mounted on the sensing surface of the detector and being a shaped filter having a shape for partly covering the detector surface and partly leaving the sensing surface open, the filter being adapted for blocking a spectral portion of impinging radiation at the covered detector surface. The detector furthermore may comprise any of a packaging material and/or a cover glass, overlaying the filter and the sensing surface or embedding the filter and the sensing surface to form a packaged detector. Other features and advantages may be as described in one or more of the aspects above.

Claims

1. A spectrometer (100) for optically characterising a species in the ultraviolet

and/or visible wavelength range, the system comprising:

a filter (110) for reducing or blocking a spectral portion of an impinging radiation, - a detector (120) adapted for distinctively detecting spectral components of

radiation on a sensing surface,

the filter (110) being directly mounted on the sensing surface of the detector and being a shaped filter having (110) a shape for partly covering the detector surface and partly leaving the sensing surface open, the filter being adapted for blocking a spectral portion of impinging radiation at the covered detector surface.

2. A spectrometer (100) according to claim 1, the system furthermore comprising a diffraction element for diffracting incident radiation before it reaches the filter and the detector, whereby the filter (110) is aligned with respect to the detector for reducing or blocking 2^nd or higher order diffraction beams from being incident on the detector.

3. A spectrometer (100) according to any of the previous claims, the detector (120) comprising any of packaging and/or a transparent cover layer overlaying both the filter (110) and the detector (120).

4. A spectrometer (100) according to any of the previous claims, the filter (110) furthermore comprising openings (150) for allowing wire bonds to pass the filter (110).

5. A spectrometer (100) according to any of the previous claims, whereby the filter (110) is such that the filter has alignment openings (140) for alignment of the filter (110) with respect to the detector (120).

6. A spectrometer (100) according to any of the previous claims, wherein the shaped filter is a machined shaped filter, a printed filter or a lithographic resist layer.

7. A spectrometer (100) according to claim 6, wherein the machined shaped filter is a micro-machined shaped filter.

8. A spectrometer (100) according to claim 7, wherein the micro-machined shaped filter is a laser ablated filter.

9. A spectrometer (1000) according to claim 8, wherein the laser ablated filter is a femto-second laser ablated filter.

10. A spectrometer (1000) according to an of claims 6 to 7, wherein the filter is cut by micro-jet cutting.

11. A spectrometer (100) according to any of the previous claims, whereby the filter (110) is a foil (410).

12. A spectrometer (100) according to any of the previous claims, whereby the filter is glued on the sensing surface.

13. A spectrometer (100) according to any of the previous claims, whereby the filter is suspended directly above the sensing surface.

14. A spectrometer (100) according to any of the previous claims, whereby the filter has edges and wherein the edges are slanted with respect to the filter surface.

15. A spectrometer (100) according to any of the previous claims, whereby the thickness of the filter (110) is thinner than 0.1mm, advantageously below 50μιη, more advantageously below 25μιη.

16. A spectrometer (100) according to any of the previous claims whereby the filter (110) is a high-pass filter with a cutoff wavelength between 380nm and 420nm.

17. A spectrometer (100) according to any of the previous claims whereby an attenuation of the filter (110) is a transmission of at least 80% for radiation to be passed to the sensor surface and a transmission below 1% for radiation wavelengths to be blocked from the sensor surface.

18. A method (1000) for setting up a spectrometer in the ultraviolet and visible wavelength region, the method comprising:

obtaining a filter (110)

shaping (1010) the filter (110) taking into account a detector surface of the spectrometer so as to induce a shape for partly covering the sensing surface and partly leaving the sensing surface open for filtering out higher order diffractions before reaching the covered part of the detector (120) to prevent detection thereof.

aligning (1020) the filter (110) directly on the sensing surface of a detector (120), for partly covering the detector surface.

19. A method (1000) according to claim 18, wherein shaping the filter comprises machining the filter, printing the filter or introducing the filter using lithographic processing steps.

20. A method (1000) according to claim 19, wherein machining the filter comprises micro-machining the filter.

21. A method (1000) according to any of claims 19 to 20, wherein machining the filter comprises laser ablating the filter.

22. A method (1000) according to claim 21, wherein laser ablation comprises laser ablating the filter using a femto-second laser.

23. A method (1000) according to any of claims 19 to 20, wherein machining the filter comprises micro-jet processing of the filter.

24. A method (1000) according to any of claims 18 to 23, whereby the shaping step (1010) includes forming openings (150) in the filter (110) such that mounting the filter (110) on the detector (120) is not obstructed by the presence of wire bonds.

25. A method (1000) according to any of claims 18 to 24, whereby the shaping step (1010) includes forming alignment openings (140) for alignment of the filter (110) with the detector (120).

26. A method according to any of claims 18 to 25, wherein aligning a filter comprises suspending the filter directly above the sensing surface.

27. A method according to any of claims 18 to 25, wherein aligning a filter comprises glueing a filter onto the sensing surface.

28. A detector for use in a spectrometer, the detector comprising a sensing element for distinctively detecting spectral components of radiation on a sensing surface and a filter for reducing or blocking a spectral portion of an impinging radiation, the filter being directly mounted on the sensing surface of the detector and being a shaped filter having a shape for partly covering the detector surface and partly leaving the sensing surface open, the filter being adapted for blocking a spectral portion of impinging radiation at the covered detector surface.

29. A detector according to claim 28, the detector furthermore comprising any of a packaging material and/or a cover glass, overlaying the filter and the sensing surface or embedding the filter and the sensing surface to form a packaged detector.

30. A detector according to any of claims 28 to 29, the filter (110) furthermore comprising openings (150) for allowing wire bonds to pass the filter (110).

31. A detector according to any of claims 28 to 30, the filter having alignment openings (140) for alignment of the filter (110) with respect to the sensing surface (120).

32. A detector according to any of claims 28 to 31, wherein the shaped filter is a machined shaped filter, a printed filter or a lithographic resist layer.

33. A detector according to any of claims 28 to 32, wherein the machined shaped filter is a micro-machined shaped filter.

34. A detector according to claim 33, wherein the micro-machined shaped filter is a laser ablated filter, a femto-second laser ablated filter or a filter that is cut by micro-jet cutting.

35. A detector according to any of claims 28 to 34, whereby the filter (110) is a foil (410).

36. A detector according to any of claims 28 to 35 wherein the filter is glued on the sensing surface or wherein the the filter is suspended directly above the sensing surface.

37. A detector according to any of claims 28 to 36, the filter having edges being

slanted with respect to the filter surface.

38. A detector according to any of claims 28 to 37, wherein the thickness of the filter (110) is thinner than 0.1mm, advantageously below 50μιη, more advantageously below 25μιη and/or wherein the filter (110) is a high-pass filter with a cutoff wavelength between 380nm and 420nm and/or wherein an attenuation of the filter (110) is a transmission of at least 80% for radiation to be passed to the sensor surface and a transmission below 1% for radiation wavelengths to be blocked from the sensor surface.

The use of a system (100) according to any of the claims 1 to 17 or a detector according to any of claims 28 to 39 for characterizing a sample of interest.