The present invention relates to an autofocus (AF) system and method that maps the topography of a substrate such as a semiconductor wafer, in a manner that corrects for Goos Hanchen (GH) effect. In addition, the present invention relates to a new and useful detector that is particularly useful in an AF system. The detector preferably has both color and polarization filtering integrally associated with the detector, so that polarization and color filtering is provided at the detector, on a pixel by pixel basis.
The present invention is particularly useful in the manner in which it builds on, and further develops autofocus concepts shown and described in application Ser. Nos. 12/884,890 and 13/066,741, each of which are is incorporated by reference herein.
Application Ser. Nos. 12/884,890 and 13/066,741 explain the basic concept of an autofocus (AF) system that preferably uses fringe projection, and also provides for compensating errors due to the Goos-Hanchen (GH) effect. As explained in those applications, reflected light from the substrate is provided at a plurality of wavelengths and polarizations, detected and used to make corrections that compensate for the errors due to the GH effect. The GH effect produces a shift of a beam when incident on an optical interface (e.g. a substrate that is imaged by an imaging optical system). The substrate surface will produce different phases on reflection for different angles of incidence, polarizations or wavelengths. In an imaging optical system which includes auto focus (AF) illumination of a substrate that is being imaged, this becomes a tilt in the pupil and a shift on the sensor (detector), which in turn translates into an error in the estimate of the z-position of the substrate.
Application Ser. Nos. 12/884,890 and 13/066,741 show and describes wavelength color filtering, utilizing, e.g., a plurality of mirrors, and polarization filtering, as ways of enabling the system to compensate GH errors. In both types of filtering, optical components are provided spatially separated from the detector (in the sense that they are not in direct mechanical contact with the detector. The applications also describe the manner in which processing software is used to provide topography mapping that compensates for GH errors. This processing is basically a weighted combination of the measurements made at different wavelengths and/or polarizations to obtain a surface measurement with minimal errors due to the Goos-Hanchen effect.
In a fringe projection AF system of the type disclosed in U.S. application Ser. Nos. 12/884,890 and 13/066,741 (also see, e.g.
Applicants currently believe using spatially separated filtering may limit the region on the detector along the scan direction that can be used. With a detector having a plurality of pixels (e.g. a charge-coupled-device, CCD detector) the more pixels that are used to make topography measurements, the more averaging that can be done to reduce the random component of a fringe projection measurement.
Therefore, in the present invention, applicants want to utilize as many pixels of the detector as possible. The present invention builds on the concept of application Ser. Nos. 12/884,890 and 13/066,741 by providing appropriate filters that are integrally associated with the CCD when the detector is fabricated. This allows the different wavelengths and polarizations to be sensed simultaneously and on the same detector without spatially separating the filtering ahead of the detector. According to the present invention, a CCD detector has filters that are integrally associated with the detector and designed preferably to allow different wavelengths and polarizations to be sensed simultaneously on the same detector, at the different wavelengths and polarizations, without spatially separating the filtering from the CCD, and producing sensitivity to each wavelength and polarization on a pixel by pixel basis.
Other advantages of the present invention include
According to the present invention, an image projected from a substrate is detected by
According to a preferred embodiment, the detector comprises a component (e.g. a CCD) with a plurality of pixels and also has either or both of polarization state or color filtering integrally associated with each pixel, so that either or both polarization state or color filtering is produced on a pixel by pixel basis at the detector. In this application, reference to a polarization or color filter being “integrally associated” with a detector means that the polarization or color filter is formed as part of the detector component (e.g. as a coating, film or covering plate on a CCD), or otherwise in direct contact with one or more of the elements that make up the detector component.
In an AF system and method that utilizes fringe projection and a detector configured according to the present invention, reflected light imaged to the detector can be, e.g. white light which has a plurality of wavelengths, and the color filtering for each pixel of the CCD component is for a specific subset of the wavelengths of the light reflected from the substrate. The color filtering for each pixel of the CCD component is done in a predetermined pattern on the CCD.
The light reflected from the substrate may also have a plurality of polarizations, and the polarization filtering for each pixel of the CCD component is for a specific subset of the polarizations of the light reflected from the substrate, and produces sensitivity to each wavelength and polarization at the CCD, on a pixel by pixel basis. With such a detector, the polarization filtering for each pixel of the CCD component is done in a predetermined pattern on the CCD. In addition, compensation for GH errors can be readily provided, according to the discloser of application Ser. Nos. 12/884,890 and 13/066,741, which are incorporated by reference herein.
Further features of the present invention will be apparent from the following detailed description and the accompanying drawings.
As described above, the present invention relates to an autofocus system and method that maps the topography of a substrate such as a semiconductor wafer, and in a manner designed to correct for GH effect. In addition, the present invention relates to a new and useful detector that has both color and polarization filtering integrally associated with the detector, so that polarization and color filtering is provided at the detector, on a pixel by pixel basis. The invention builds on the concepts shown and described in U.S. application Ser. Nos. 12/884,890 and 13/066,741, particularly for an AF system. The invention is described herein in relation to such an AF system and method, and in connection with a detector that comprises a charge-coupled device (CCD). From that description, the manner in which the present invention can be employed with various types of AF systems and methods, and with other forms of detectors will be clear to those in the art.
Initially, it is believed useful to describe the basic system and operating principles of the AF system and method of application Ser. Nos. 12/884,890 and 13/066,741, and to then describe the manner in which the present invention builds on such an AF system and method.
Thus,
In
Thus, in the autofocus system and method of application Ser. Nos. 12/884,890 and 13/066,741, light is directed at the substrate 101, and light reflected from the substrate is imaged to a detector 102 to produce the data that is useful for mapping the topography of the substrate (and enables GH correction).
In a system and method of the type disclosed in U.S. application Ser. Nos. 12/884,890 and 13/066,741 (also see, e.g.
As described in U.S. application Ser. Nos. 12/884,890 and 13/066,741, the GH effect produces a shift of a beam when incident on an optical interface (e.g. a substrate that is imaged by an imaging optical system). The substrate surface will produce different phases on reflection for different angles of incidence, polarizations and wavelengths. In an imaging optical system which includes auto focus (AF) illumination of a substrate that is being imaged, this becomes a tilt in the pupil and a shift on the sensor (detector), which in turn translates into an error in the estimate of the z-position of the substrate.
In U.S. application Ser. Nos. 12/884,890 and 13/066,741, providing polarization and/or color filtering between the last optic and the detector is useful in providing GH correction. With the approach of
The present invention builds on the concept of application Ser. Nos. 12/884,890 and 13/066,741 by building in the appropriate filters to the CCD detector component 102a (see also
According to the present invention, the CCD detector component 102a comprises a plurality of pixels and also has either or both of polarization state or color filtering integrally associated with each pixel, so that polarization state or color filtering is produced on a pixel by pixel basis at the detector. In this application, reference to a polarization or color filter being “integrally associated” with a detector means that the polarization or color filter is formed as part of the detector component (e.g. as a coating, film or covering plate on a CCD), or otherwise in direct contact with one or more of the elements that make up the detector component.
The detector 102 comprises a camera, and preferably a camera that includes a CCD detection component 102a. The light reflected from the substrate 101, can be, e.g. white light which has a plurality of wavelengths, and the color filtering for each pixel of the CCD component 102a is for a specific subset of the wavelengths of the light reflected from the substrate. The color filtering for each pixel of the CCD component 102a is done in a predetermined pattern on the CCD, as explained herein in connection with the embodiments of
The light reflected from the substrate 101 may also have a plurality of polarizations, and the polarization filtering for each pixel of the CCD component 102a is for a specific subset of the polarizations of the light reflected from the substrate 101. With such a detector, the polarization filtering for each pixel of the CCD component 102a is done in a predetermined pattern on the CCD.
The present invention is particularly useful with an autofocus system and method that comprises a fringe projection system in which light fringes are projected at the substrate, and the reflected light fringes are imaged to the detector through the polarization or color filtering integrally associated with the detector.
There are several ways that color and/or polarization filtering can be integrally connected with the CCD component 102a. For example, materials such as dielectrics or metals that absorb or reflect at different wavelengths, can be deposited on top of the pixels of the CCD component 102a (e.g. by lithography) that will change (filter) the spectral response of different pixels. Polarization filtering can be accomplished by using a steep angle of incidence on the substrate, coupled with a film or cover plate for each pixel of the CCD detector 102a.
As an example, with the present invention, the fringe projection (FP) system can use 4 wavelengths sampled at two orthogonal linear polarization states, for a total of 8 different signals. In the simplest approach, each row of pixels could be coated to accept one of the 8 signals, such that all 8 signals are measured every 8 pixel rows. For an 8192 row CCD, this allows >1000 pixels per signal across the wafer diameter, or more than 2 measurements at each wavelength within a 1 mm region on the substrate.
Also, the present invention is designed such that each wavelength/polarization is measured at every frame collected by the CCD. The reference light could also be interleaved on the sensor, assuming it is incident at a specific wavelength that is exclusive of the measurement wavelengths.
It should be noted that the present invention is designed to work particularly well when custom sensors are being fabricated for mass production.
Another advantage of the present invention is that the illumination system could be vastly simplified. It should be possible to illuminate with a white light source since there is no longer a need to spatially separate the multiple wavelengths in the pupil. Also, the source could contain both polarizations simultaneously. Perhaps the best combination would be to use a white light source for the reference also and alternate reference and measurement frames in time, so any thermal drift or other issues from the CCD are compensated by the reference.
The measurements at multiple wavelengths and polarizations are not made at exactly the same location on the substrate, which could lead to issues with the Goos Hanchen (GH) correction. However, in practice, two signals could be interleaved along the column direction (for example, same wavelength but both polarizations), which reduces the effects of this potential problem.
Two options for providing a CCD component 102a according to the present invention are shown in
In option 2, shown in
It should be noted that in addition to the two options described herein, there may be many other ways to arrange the filters; the two options described and shown in
Thus, the present invention provides a concept for multiplexing measurement beams (multiple wavelengths and polarizations) and reference beams on the detector, which simplifies the overall optical system for a fringe projection autofocus system by using a CCD detector that has filters designed to allow different wavelengths and polarizations to be sensed simultaneously on the same detector, at the different wavelengths and polarizations, without spatially separating the polarization and color filtering from the detector, thereby producing sensitivity to each wavelength and polarization. Moreover, the present invention provides a CCD detector that allows for a relatively simple illumination system and simple optics.
Other advantages of the present invention include
With the foregoing disclosure in mind, the manner in which various types of AF systems and methods can be designed to provide topography mapping including GH correction, and the manner in which polarization and color filtering can be provided in a CCD component, on a pixel by pixel basis, will be apparent to those in the art.
This application is related to and claims priority from provisional application Ser. No. 61/575,330, entitled “Custom color or polarization sensitive CCD for separating multiple signals in fringe projection system”, and filed Aug. 18, 2011, which provisional application is incorporated by reference herein.
Number | Name | Date | Kind |
---|---|---|---|
5440648 | Roberts et al. | Aug 1995 | A |
5448332 | Sakakibara et al. | Sep 1995 | A |
5521706 | Green et al. | May 1996 | A |
5870176 | Sweatt et al. | Feb 1999 | A |
6337759 | Yamamoto | Jan 2002 | B1 |
RE37752 | Wolff | Jun 2002 | E |
6671047 | Opsal et al. | Dec 2003 | B2 |
6714243 | Mathur et al. | Mar 2004 | B1 |
6771374 | Rangarajan et al. | Aug 2004 | B1 |
6934032 | Subramanian et al. | Aug 2005 | B1 |
7265364 | Teunissen et al. | Sep 2007 | B2 |
7280205 | Bouzid et al. | Oct 2007 | B2 |
7330274 | Hill | Feb 2008 | B2 |
7554596 | Nayar et al. | Jun 2009 | B2 |
7575325 | Suzuki et al. | Aug 2009 | B2 |
7772555 | Hollingsworth | Aug 2010 | B2 |
7982884 | Smith | Jul 2011 | B2 |
8089616 | Owa | Jan 2012 | B2 |
8243285 | Fishbaine | Aug 2012 | B2 |
8319960 | Aiko et al. | Nov 2012 | B2 |
20040012775 | Kinney et al. | Jan 2004 | A1 |
20040165169 | Teunissen et al. | Aug 2004 | A1 |
20040207836 | Chhibber et al. | Oct 2004 | A1 |
20040233435 | Opsal et al. | Nov 2004 | A1 |
20060132773 | Ebert et al. | Jun 2006 | A1 |
20060164657 | Chalmers et al. | Jul 2006 | A1 |
20070056940 | Salem et al. | Mar 2007 | A1 |
20070146697 | Noguchi et al. | Jun 2007 | A1 |
20070247622 | Sun | Oct 2007 | A1 |
20080059218 | Sottery et al. | Mar 2008 | A1 |
20080186491 | Baxter et al. | Aug 2008 | A1 |
20080243412 | Horie et al. | Oct 2008 | A1 |
20090073414 | Tanitsu et al. | Mar 2009 | A1 |
20090073441 | Tanitsu et al. | Mar 2009 | A1 |
20090108483 | Suehira et al. | Apr 2009 | A1 |
20090135437 | Smith | May 2009 | A1 |
20090159799 | Copeland et al. | Jun 2009 | A1 |
20090168062 | Straaijer | Jul 2009 | A1 |
20090316132 | Tanitsu et al. | Dec 2009 | A1 |
20100118398 | Grau | May 2010 | A1 |
20100209832 | Matsuda | Aug 2010 | A1 |
20100282945 | Yokogawa | Nov 2010 | A1 |
20110058038 | Twede | Mar 2011 | A1 |
20110071784 | Smith et al. | Mar 2011 | A1 |
20110075134 | Uto et al. | Mar 2011 | A1 |
20110141309 | Nagashima et al. | Jun 2011 | A1 |
20110320149 | Lee et al. | Dec 2011 | A1 |
20120008150 | Smith et al. | Jan 2012 | A1 |
20120044495 | Straaijer | Feb 2012 | A1 |
20120142122 | Markwort et al. | Jun 2012 | A1 |
20130308140 | Goodwin et al. | Nov 2013 | A1 |
Number | Date | Country |
---|---|---|
201217763 | Sep 2012 | WO |
Number | Date | Country | |
---|---|---|---|
20130208104 A1 | Aug 2013 | US |
Number | Date | Country | |
---|---|---|---|
61575330 | Aug 2011 | US |