JP2005535882A - Determination of sample topography and composition using interferometers - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique related to a pre-established reference scale for interference phase measurement.
The topography of a sample (460) is measured using an interferometer having a beam splitter (402), a tilted reference mirror (404), and a detector (405). The data processing unit measures a first set of fringe line disturbances and maps to a trace extending across the first axis of the sample to generate a first set of profiles describing the sample topography; Adjusting the position relative to the sample to generate a second set of fringe line disturbances and measuring the second set of interferometer fringe line disturbances to generate a second set of profiles describing the topography Then, the topographic description with improved resolution is generated by interleaving the first and second sets of profiles. The method may further involve characterizing the sample as consisting of a certain material by fitting a reflectance versus wavelength curve.

Description

Priority Claim This application is filed on Aug. 9, 2002, US patent application Ser. No. 10 / 215,894, entitled “Method and Apparatus for Determining Sample Composition Using an Interferometer”. No. 10 / 215,897 entitled “Pre-established Reference Scale for Interferometric Phase Measurements” dated August 9, 2002, filing date “August 9, 2002” No. 10 / 215,801 entitled “Interferometric Phase Measurements Using Reference Scale” and the filing date of August 9, 2002 “Flying line disturbance sample height at a specific position above the sample stage of the interferometer Claims priority to No. 10 / 215,905, entitled "Advanced Signal Processing Technology to Change to".
The field of the invention relates generally to measurement techniques, and more particularly to pre-established reference scales for interferometric phase measurement.

1.0. Basic interferometry Interferometry involves the analysis of interference waves to measure distance. An interferometer is a measuring instrument that performs interferometry and generally reflects a first series of light waves from a first reflective surface and reflects a second series of light waves from a second reflective surface. The first and second series of waves are substantially combined to form a combined waveform. The signal generated through the combined waveform sensing is then processed to understand the relative placement of the reflective surfaces. FIG. 1 shows an embodiment of an interferometer of the type often known as a Michelson interferometer.

  Referring to FIG. 1, a light source 101 and a splitter 102 are used to form a first group of light waves directed to the reference mirror 104 and a second group of light waves directed to the plane mirror 103. Splitter 102 substantially splits light 106 from light source 101 to form these groups of light waves. In general, the splitter 102 has the light 106 from the light source 101 such that 50% of the optical intensity from the light source 101 is directed to the reference mirror 104 and 50% of the optical intensity from the light source 101 is directed to the flat mirror 103. Is designed to be divided evenly.

  At least a portion of the light directed to the plane mirror 103 is reflected back to the splitter 102 (by traveling in the + z direction after reflection), and at least a portion of the light directed to the reference mirror 104 is reflected to the splitter 102. Back (by traveling in the -y direction after reflection). The light reflected from the reference mirror 104 and the plane mirror 103 is substantially combined by the splitter to form a third group of light waves that propagate in the y direction and impinge on the detector 105. The pattern of optical intensity observed by the detector 105 is then analyzed to measure the difference between the distances d1 and d2 that exist between the plane mirror 103 and the reference mirror 104, respectively.

  In other words, for a plane wavefront, if the distance d2 is known, the distance d1 can be measured by measuring the brightness of the light received at the detector 105. Here, according to the principle of wave interference, if the distance d1 is equal to the distance d2, the reflected waveforms will interfere constructively with each other when combined by the splitter 102 (thus their amplitudes are Added). Similarly, if the difference between distance d1 and distance d2 is half the wavelength of light emitted from light source 101, the reflected waveforms will interfere destructively with each other when combined by splitter 102 (thus, Are subtracted from each other).

  The former situation (constructive interference) produces a relative maximum optical intensity (ie, relatively “brightest” light) at the detector 105, and the latter situation (destructive interference) is the relative minimum optical intensity. (Ie relatively “darkest” light). When the difference between distance d1 and distance d2 is somewhere between zero and half the wavelength of the light emitted by light source 101, the brightness of the light observed by detector 105 is from constructive interference. Smaller than the brightest light, but larger than the darkest light from destructive interference (eg, in a “medium” tone between the relatively “brightest” and “darkest” optical intensities) is there). The exact “halftone” observed by detector 105 is a function of the difference between distance d1 and distance d2.

  In particular, when the difference between distance d1 and distance d2 is far from zero and approaches half the wavelength of light emitted by light source 101, the light observed by detector 105 becomes darker. Therefore, the difference between the distance d1 and the distance d2 can be accurately measured by analyzing the optical intensity observed by the detector 105. For a planar optical wavefront, the optical intensity should be “constant” across the surface of the detector 105, whatever the difference between the distances d1 and d2 (from a simplified point of view). This is because the same “effect” will be applied to each optical path length followed by any pair of reflected rays that are combined by splitter 102 to form a ray toward detector 105 (even if zero). .

  It should be noted here that due to the 45 ° orientation of the splitter 102, the portion of the reference mirror and plane mirror guided light travels an equal distance within the splitter 102. For example, from the analysis of FIG. 1, the reference mirror and plane mirror guide portions of light beam 107 travel an equal distance in splitter 102, and the reference mirror and plane mirror guide portions of light beam 108 travel an equal distance in splitter 102. Becomes clear. Since all rays traveling from the splitter 102 to the detector 105 should travel the same distance d3, the plane mirror and reference mirror guiding portions of the light (these are combined common rays that impinge on the detector 105). Only the optical path length difference, such as between the first and second) should result from the difference between d1 and d2, and similarly, for a plane wavefront, the difference between d1 and d2 It should be clear that the rays should be equally affected. Thus, ideally, the same “halftone” should be observed throughout the detector, and the specific “halftone” is used to determine the difference between the distances d1 and d2 from the wave interference principle. can do.

2.0. Interferometer with “Inclined” Reference Mirror Referring to FIG. 2, when the reference mirror 204 is tilted (eg, θ is greater than 0 ° as seen in FIG. 2), the light plane mirror 203 and the reference Since the optical path length difference, such as between the guiding portions of the mirror 204, is no longer uniform, the optical intensity observed at the detector 205 will not be uniform across the surface of the detector 205. In other words, the “tilt” of the reference mirror 204 causes the optical path length to fluctuate between the light waves toward the reference mirror 204, which in turn leads to variations in the optical intensity observed by the detector 205.

  Here, since the wave interference principle will still be applied at the detector 205, the variation in optical path length caused by the tilted reference mirror 204 is the difference in optical path length encountered by light impinging on the detector 202. Can be seen to be the cause of traveling substantially through distances such as λ / 2, λ, 3λ / 2, 2λ, 5λ / 2, 3λ, where λ is the wavelength of the light source. This in turn corresponds to a continuous mutual transition between constructive and destructive interference along the z-axis of detector 205. FIG. 3a shows an example of an optical intensity pattern 350 observed by the detector 305 when the interferometer reference mirror is tilted (as seen in FIG. 2).

  Here, it should be noted that the optical intensity pattern 350 includes local minimums 352a, 352b, and 352c, and local maximums 351a, 351b, 351c, and 351d. The local minimums 352a, 352b, and 352c that should appear as the "darkest" shade within that area of the detector 305 are called "fringe lines". FIG. 3b depicts the fringe lines that appear on the detector when the interferometer reference mirror is tilted. Here, ideally, fringe lines extending along the x-axis will repeatedly appear as moving across the z-axis of the detector. Fringe line separation is a function of both the wavelength of the light source and the tilt angle of the reference mirror. More specifically, the fringe line separation is proportional to the wavelength of the light source and inversely proportional to the tilt angle. Therefore, the fringe line separation can be expressed as ~ λ / θ.

  The present invention is illustrated by way of example and is not limited to the accompanying drawings.

US patent application Ser. No. 10 / 215,894 US patent application Ser. No. 10 / 215,897 US patent application Ser. No. 10 / 215,801 US patent application Ser. No. 10 / 215,905

  As explained below, the principles of interferometry are utilized so that an accurate description of the surface topology of the sample can be obtained. More particularly, the fringe line disturbances observed on the detector of the interferometer (which are caused by the introduction of the sample into the interferometer) are measured against a pre-established reference scale. As a result, the height of the sample can be mapped to a specific location on the surface of the sample, which in turn allows for the creation of an accurate description of the topographic shadow of the sample.

1.0. Mapping of detector surface positions to sample stage surface traces FIGS. 4a and 4b show the fringe lines that appear on the detector 405 of an interferometer with a tilted reference mirror and the corresponding “traces” of these fringe lines on the sample stage 403. Both of the “mapping” embodiments that exist between are shown. Here, the sample stage 403 can have a reflective coating and thus operates by itself in the same way (or at least similar) as the flat mirror 103 described in the background section above. . With reference to FIG. 4 a, for a 45 ° splitter 402 orientation, each fringe line substantially “maps” to a trace extending parallel to the x-axis at a particular y-axis location on the sample stage 403. . In other words, each fringe line “maps” to its 90 ° reflection from the splitter 402 towards the sample stage 403. Here, the z-axis positioning (eg, z-axis position z _k ) of the fringe line on the detector is radiated to the splitter 402 (through the projection 491) and “reflected from the splitter 402 at an angle of 90 ° with respect to the sample stage 403. "(To form the projection 492), the projection 492 on the sample stage 403 will collide with a particular y-axis position of the sample stage 403 (eg, y _k as seen in FIG. 4a).

  Referring to FIG. 4b, when a sample whose topography is to be measured (eg, sample 460) is placed on the sample stage 403, there is a disturbance to the fringe line (compared to the original appearance of the fringe line before the appearance of the sample). Will appear. For each fringe line, the disturbance follows the topography of the sample 460 along its “mapped” trace that extends along the sample stage 403 parallel to the x-axis, as shown in FIG. 4a. Thus, referring to FIG. 4b, fringe lines 451b, 451c, 451d on detector 405 "map" to traces 452b, 452c, 452d on sample stage 403, respectively. Since sample 460 does not cover traces 452a and 452e of sample stage 403, fringe lines 451a and 451e remain undisturbed on detector 405.

3.0. Interferometry technique using a pre-established measurement scale FIG. 5 illustrates an optical fringe line disturbance (which occurs in response to a sample placed on the sample stage of the interferometer) on a pre-established measurement scale. Fig. 4 illustrates an embodiment of a method for creating a sample topographic description by measuring against. According to the method of FIG. 5, a measurement scale (sometimes referred to as a reference scale, scale, etc.) is first established (501). The measurement scale can be viewed as similar to a ruler for measuring fringe line disturbances. Thus, once the sample is introduced into the interferometer and an interferogram of the sample is generated (502), the sample topography is accurately understood by measuring the fringe line against a pre-established measurement scale (503). can do.

  In other words, disturbances encountered by the fringe line in response to a sample being introduced into the interferometer can be accurately translated to a sample height along a known location in the xy plane of the sample stage. Pre-establishing a reference scale allows not only a highly accurate description of surface topography, but also an efficiently generated description of surface topography (eg from the perspective of device sophistication and / or time consumption) Enable. Figures 6 to 9a and 9b relate to the establishment of a measurement scale, and a description of each of these figures follows.

4.0. Establishing Measurement Scale FIG. 6 shows a method for establishing a measurement scale. It should be noted that the method of FIG. 6 includes an “xy plane accuracy” component 610 and a “z-direction accuracy” component 611. Referring now to FIGS. 4 b and 6, setting the accuracy of the xy plane 610 corresponds to generating a measurement scale that can derive an accurate position along the plane of the sample stage 403. Similarly, z-direction accuracy setting 611 corresponds to the generation of a measurement scale that can track the exact change in the topographic profile of sample 460. A three-dimensional description of the sample that accurately tracks the sample height (in the z direction) across multiple x and y positions on the surface of the sample 460 and sample stage 403 by a combination of establishing accuracy in the xy plane and z direction. Can be generated.

  According to the method of FIG. 6, the accuracy of the xy plane can be established by aligning (610) the fringe lines observed on the detector 405 to be equidistant from that of the calibration standard (FIG. 6). Note that in connection with 4b, the calibration standard is presented to stage 403, not sample 460). With the fringe lines aligned (610), the “sample height measurement per pixel” parameter is calculated (611).

  Here, an array of optically sensitive elements (eg, an array of charge coupled devices (CCD)) can be used to implement the detector 405. The location of each array may be referred to as a “pixel”. Because of this array, each optically sensitive element that extends across a disturbed fringe line configuration corresponds to a unique x, y, z position (above the surface of detector 405) along the sample topography. Become. In other words, setting the accuracy of the xy plane (610) causes the detector pixel to “map” to a specific location in the xy plane of the sample stage. Thus, if the fringe line is disturbed when the sample is introduced into the interferometer, the distance that the fringe line travels from its original undisturbed pixel location on the detector is mapped to the original undisturbed pixel location. Will correspond to the sample height at those particular x, y sample stage positions.

  That is, each of the optically sensitive elements that make up the array uses a surface area that is quantifiable on the plane of the detector 405 (ie, each pixel has a “size”), so a wide area of fringe line disturbance. , Each pixel will generally correspond to a specific “height” unit above the sample stage measured along the detector z-axis. In other words, recalling the explanation of FIG. 4b that a fringe line disturbance results from placement of the sample 460 on the interferometer sample stage 403, a particular change in fringe line position can translate to a particular sample height. it can.

  Here, the height of the sample is the z-axis where the fringe line area or portion will be “moved” along the surface of the detector 405 by introducing the sample 460 into the interferometer. Can be derived from the distance along Thus, each pixel location can be correlated to a specific unit distance along the z-axis above the surface of the sample stage 403, which in turn will “determine” the sample height above the sample stage 403. Can be used for This is further explained below in connection with FIGS. 9a and 9b.

  However, to explain FIG. 6, the amount of unit distance along the z-axis above the sample stage 403 that a pixel represents may be referred to as a “sample height measurement per pixel unit” 611. For example, if the sample height measurement per pixel unit is 20 nm when the sample is placed on the sample stage and the fringe line is observed to move 3 pixels along the z-axis of the detector 405, the sample height This is calculated as 60 nm. As a side note, the optically sensitive element of each pixel is set so that the optical intensity impinging on its unique xz position of the detector is provided as a digital signal. For example, each optically sensitive element in the array is set to provide 1 byte of information that indicates the optical intensity observed at that particular unique xz position on the surface of detector 405.

  With the fringe line aligned to the calibration standard (610) and the sample height measurement per pixel unit calculated (611), the pre-established measurement scale (1) places the sample on the sample stage. Information relating to the mapping of the detector fringe line to the sample stage 403 (e.g., for each fringe line observed on the detector 405 when the sample is not placed on the stage, (a) the detector Record its x, z pixel location on 405, (b) recognize how x, z location on detector 405 maps to x, y location on sample stage 403), and (2) pixel units It can be formed by recording (612) the per-sample height measurement.

  It should be noted that the sample is the “object” whose surface topography is measured. Next, according to the method of FIG. 6, the unperturbed fringe lines are aligned, their mapping positions are recorded, and the sample height measurement per pixel unit is calculated and recorded. Information suitable for creating a measurement scale that can be used to measure the topography of the sample is stored (612).

3.1. Alignment of Fringe Line with Calibration Standard FIGS. 7a-7c and FIG. 8 relate to the technique for aligning (610) the fringe line described in FIG. 6 with the calibration standard. A calibration standard is a device with markings spaced at a high degree of accuracy. For example, the National Institute of Standards and Technology (NIST) provides a longitudinal grid calibration standard that is evenly spaced (eg, each grid spaced 1 micron apart). An example of a calibration standard can be seen in FIGS. 7a and 7b. Here, each grid (or other marking) is placed on the surface of the calibration standard with a uniform spacing of distance “Y”. FIG. 7 a is a “comprehensive” view of an exemplary calibration standard 700, while FIG. 7 b is a perspective view of the exemplary calibration standard 700.

  FIG. 7c is a display 701 of an optical image that appears on the detector of an interferometer with a tilted reference mirror when the calibration standard is placed on its sample stage. Here, the optical image will include an image of the calibration standard marking and a fringe line resulting from the tilted interferometer reference mirror. In the depiction of FIG. 7c, calibration markings and fringe lines are shown in accordance with the “split screen” depiction for simplicity of illustration. In other words, the appearance of calibration standard markings 710a to 710f is shown on the left side 702 of the optical image display 701, and the appearance of fringe lines 711a to 711e is shown on the right side 703 of the optical image display.

  It should be noted that in the exemplary depiction of FIG. 7c, a calibration standard should be set on the sample stage such that the calibration marking extends along the x-axis. FIG. 8 shows a technique for aligning fringe lines 711a to 711e with calibration markings 710a to 710e in the optical image displayed in FIG. 7c. According to the technique of FIG. 8, and with reference to FIGS. 4b and 8 (note that sample 460 of FIG. 4b should be replaced by a calibration standard), it can be seen in the depiction of 801a. To set the spacing of fringe lines 810a to 810e equidistant from the spacing of calibration markings 811a to 811e, the tilt angle of reference mirror 404 is adjusted. Here, it should be recalled from the depiction of FIG. 3 that the fringe line separation is inversely proportional to the tilt angle θ of the reference mirror.

  Since the fringe interval is a function of the inclination angle θ, the fringe line interval can be made equal to the calibration marking interval by appropriately adjusting the inclination angle θ (820). The depiction 801a shows an embodiment in which the spacing between adjacent fringe lines is equidistant from the calibration marking spacing. Accordingly, adjacent calibration markings 810a through 810e have the same spacing (Y) as adjacent fringe lines 811a through 811e. In another embodiment (eg, the density of fringe lines is greater than the density of calibration markings), the number of fixed fringe lines can be set in the calibration markings. For example, in one embodiment, 10 fringe lines can be established per calibration marking, allowing a fringe line density of 10 times the calibration marking density of the calibration standard.

  However, it should be noted that the depiction 801 of FIG. 8 shows a fringe line spacing that is equally spaced from the calibration marking spacing, but the fringe lines 811a through 811e themselves do not align with the calibration markings 810a through 810e. Here, the position of the reference mirror 404 along the y-axis can be adjusted (821). In other words, the fringe line can be moved up and down along the z-axis of the detector by adjusting the y-axis position of the reference mirror 404. According to the technique of FIG. The position of the y-axis can be adjusted so that the fringe lines 811a to 811e “align” with the calibration markings 810a to 810e, as seen in the depiction 801. Note that fringe lines 811a through 811e are shown as being spaced apart by distance Y in depiction 801a. This again dates back to the Y spacing between adjacent markings of the calibration standard as first shown in FIG. 7c. It should be noted that the second process 821 is optional since the setting of the fringe line spacing from process 820 establishes the measurement accuracy in the xy plane of the sample stage.

  Here, with respect to the mapping of fringe lines to traces extending along the sample stage at a particular y-axis position (as described in detail above in connection with FIG. 4a), the calibration standard set in the sample stage 403 The alignment of the fringe lines with respect to allows the relative spacing between the fringe lines along the y-axis of the sample stage 403 to be accurately and accurately correlated to a specific distance. Thus, if a one-to-one fringe line to calibration marking ratio is established (and it is known that the calibration markings are spaced a distance Y apart), the fringe lines are Since it occurs exactly Y apart along the y-axis, it can be used to measure the surface change of the sample. Similarly, as another example, if a 10: 1 fringe line to calibration marking ratio is established (and it is known that the calibration markings are spaced a distance Y apart), the fringe line is , Because they occur exactly 0.1 Y apart along the y-axis of the sample stage, they can be used to measure the surface change of the sample.

  In one embodiment, the understood distance between adjacent fringe lines when the fringe lines map to the xy plane of the sample stage is normalized by the number of pixels between adjacent fringe lines observed on the detector. . This calculation is based on the distance along each sample stage's corresponding y axis (and along the x axis of the sample stage) (ie along both the x and y axes of the detector that each pixel represents). Substantially corresponds to a "per pixel" distance).

  For example, if there are 10 pixels between adjacent fringe lines on the detector, and that the adjacent fringe lines map to sample stage traces spaced by a distance Y as a result of the calibration process Is understood that there is 0.1Y resolution per pixel in both x and y directions. In this case, for example, a series of five consecutive pixels along the x-axis of the detector can be recognized as a mapping to a 0.5Y distance on the surface of the sample stage (or sample), as well A series of five consecutive pixels along the detector z-axis can be recognized as a mapping to a 0.5 Y distance on the surface of the sample stage (or sample).

  Recall that by recording the information related to the mapping of the detector fringe line to the sample stage, a pre-established measurement scale is partly formed. It should be noted that preserving the resolution is recognized as a storage of information that can be used for this purpose. For example, if the resolution per pixel in the x and y directions corresponds to a distance of 0.1 Y, an undisturbed fringe line detected 30 pixels away along the detector z axis will be along the y axis of the sample stage. It can be recognized that the traces arranged at a distance of 3Y are displayed. Similarly, if the fringe lines extend to 100 pixels across the x-axis of the detector, these same fringe lines can be recognized as traces extending over a distance of 10Y along the x-axis of the sample.

  Finally, the “sample height measurements per pixel” described above (and those detailed immediately below) and the “per pixel” along the x and y axes of the sample stage described above. Note that the difference between the distances should be clear. In other words, according to the measurement technique of the present invention, the pixel position is not only for identifying a specific position on the xy surface of the sample stage, but also for identifying the sample height along the z-axis above the sample stage. Can also be used. The “per pixel” distance along the x and y axes of the sample stage is directed to the former, and the “sample height measurement per pixel unit” is directed to the latter.

3.2. Calculation of sample height measurements per pixel Returning to FIG. 6, once the fringe line is aligned to the calibration standard (610) (and possibly “per pixel” resolution in the x and y directions is recorded. Then, the next step in establishing the measurement scale is to calculate 611 the sample height measurement per pixel unit. The “sample height measurement per pixel unit” in FIG. 6 represents the amount of unit distance along the z-axis above the sample stage to which a one-pixel fringe line disturbance along the detector z-axis is translated. You should recall the explanation. Interferometry is based on the difference in optical path length between the light toward the reference mirror and the light toward the sample stage, so introducing a sample into the sample stage substantially reduces the optical path length difference that existed prior to the introduction. It is something that changes. In other words, at least a portion of the light that faces the sample stage (not the tilted reference mirror) will reduce its optical path length because it is reflected from the sample and not from the sample stage.

  This shortened optical path length corresponds to a change in the optical path length difference and then causes disturbances to the position of the fringe line. Thus, in order to calculate the sample height measurement per pixel unit, the amount of disturbance in the fringe line positioning must be correlated to the change in optical path length that occurs when the sample is placed on the sample stage. Here, in order to better understand the change in optical path length, an analysis of an interferometer without a sample is provided, and an analysis of an interferometer with a sample is also provided. 4a and 9a relate to the optics of an interferometer without a sample, and FIGS. 4b and 9b relate to the optics of an interferometer with a sample. Each explanation is made immediately below. A method of comparing the optical conditions present when the sample is present and not present (with particular attention to the change in optical path length) leads to a sample height measurement per pixel unit.

  Referring to FIG. 4a, the first distance 493 represents the distance λ between the reference plane 499 of θ = 0 ° and the tilted reference mirror 404, and the second distance 494 is the reference plane 499 of θ = 0 °. And the tilt reference mirror 404 is assumed to represent a distance 3λ / 2. It can be shown that when the sample is not placed on the sample stage, a fringe line appears at every integer interval of λ / 2 between the tilted reference mirror 404 and the reference plane 499 of θ = 0 °. Thus, for example, the first fringe line 495 appears on the detector 405 as a result of the first distance 493, and the second fringe line 496 appears on the detector 405 as a result of the second distance 494.

  This characteristic is: (1) the “intercept” on the tilt reference mirror 404 at each integer interval of λ / 2 between the tilt reference mirror 404 and the reference plane 499 of θ = 0 °, and (2) the detector 405 itself. It can be seen that there is a “like” relationship with the position of the fringe line. In other words, from the description of FIG. 3, recalling that the fringe lines 495 and 496 are separated from each other by ˜λ / θ, the intercept 497 of the distances 493 and 494 of the tilt reference mirror 404 separated by λ / (2 sin θ). And 498 are also spaced along the plane of the tilted reference mirror 404 (distance 494 is λ / 2 longer than distance 493, and from the basic geometry, the hypotenuse of the right triangle Is because one side of the triangle (λ / 2) is divided by the sine of the angle facing the one side (sin θ).

  Here, since ~ λ / θ coincides with λ / (2 sin θ) (especially when θ is a small angle), (1) each integer λ between the tilt reference mirror 404 and the reference plane 499 of θ = 0 ° A correlation can be imagined between the spacing between the sections on the tilted reference mirror 404 with a / 2 spacing and (2) the spacing between the fringe lines appearing on the detector 405.

  Figures 9a and 9b show the change in fringe line position that occurs when the sample is placed on the sample stage. In particular, FIG. 9a further provides optical analysis when the sample is not placed on the sample stage, and FIG. 9b provides optical analysis when the sample is placed on the sample stage. By comparing analysis sets, a proper understanding of sample height measurements per pixel unit can be formulated.

  Similar to FIG. 4a, FIG. 9a shows an interferometer 910 with no sample on the sample stage 903a. When the interferometer does not have a sample on its sample stage 903a, the variation in the optical path length difference between the light toward the sample stage 903a and the light toward the tilted reference mirror 404a (the appearance of a fringe line on the detector 905) For the most part) is a function of the distance between the reference plane 999a with θ = 0 ° and the tilted reference mirror 904a. Here, when the sample is not placed on the sample stage 903a, all light that the sample is directed to the sample stage 903a travels the same distance d1 as it travels (and returns again) from the splitter 902a to the sample stage 903a.

  Accordingly, the “variation” of the path length from the splitter 902a to the tilt reference mirror 904a is “main” with respect to the “variation” of the optical path length generated between the light toward the sample stage 903a and the light toward the tilt reference mirror 904a. Can be considered "cause", which in turn results in the appearance of multiple fringe lines on detector 905a. Here, the “variation” of the path length from the splitter 902a to the tilt reference mirror 904a obviously occurs in the region between the reference plane 999a of θ = 0 ° and the tilt reference mirror 904a, so θ = 0 °. The area between the reference plane 999a and the tilted reference mirror 904a serves as the main area focused on optical analysis.

  If the sample is not placed on the sample stage 903a, fringe lines appear at every integer interval of λ / 2 between the tilted reference mirror 904a and the θ = 0 ° reference plane 999a, and the detector fringe line spacing. It should be recalled that a correlation can be imagined between and the intercept interval on the tilt reference mirror 404. Accordingly, FIG. 9a shows a first fringe line 995a across the portion of the CCD detector 905a resulting from the λ spacing 993a between the reference plane 999a of θ = 0 ° and the tilted reference mirror 904a, and θ = 0 °. Shown is a first fringe line 996a across the same portion of the CCD detector 905a resulting from a 3λ / 2 spacing 994a between the reference plane 999a and the tilted reference mirror 904a.

  Referring to FIG. 9b, it should be noted that the sample 912 has been placed on the sample stage 903b of the interferometer 911. Here, sample 912 has (1) a height of λ / 4 (measured along the z-axis) and (2) fringe before introduction of sample 912 (as seen in FIG. 9a). It is assumed that it is located at the y-axis position on the sample stage 903b mapped to the line 995a. In this case, an appropriate optical analysis can be performed by superimposing the shape of the sample 912 on the reference plane 999b of θ = 0 ° at the position of the interval 993a that existed before the introduction of the sample 912.

  FIG. 9b shows this superposition, which in turn modifies the shape of the reference plane 999b. Here, the shape of the sample is superimposed at the position of the interval 993a. (1) The sample 912 is arranged at the y-axis position on the sample stage 903b that maps to the fringe line 995a (the interval 993a is the appearance of the fringe line 995a). (2) reflects the fact that a change in the optical path length of λ / 4 is brought into the part of the light that is reflected from the sample at that time (not from the sample stage).

  The change in optical path length results in a disturbance to the position of the fringe line 995a because the difference in optical path length (between the light toward the sample stage and the light toward the reference mirror) has changed with the introduction of the sample. Accordingly, the fringe line 995a moves down to a new position along the detector 905b (as observed in FIG. 9b by the fringe line 995b). The new position of the fringe line 995b corresponds to the same length (ie, λ) as the spacing 993b between the reference plane 999b and the tilted reference mirror 904b that existed prior to sample introduction. However, the modification of the shape of the reference position due to the shape of the sample 912 substantially results in a spacing 993b of the same length at the lower position along the z-axis. Accordingly, the fringe line 995b moves down to a lower position on the detector 905b surface.

  Here, the change of λ / 4 causes the fringe line 995b to fall to its midpoint between its initial position 907 (before the introduction of the sample 912) and the fringe line 996b. This is because the interval 993b can be subdivided into a first segment (length 3λ / 4) and a second segment (length λ / 4) (note that the total length λ of the interval 993b is maintained). It happens naturally when it is considered. The λ / 4 segment helps to form a right angle (observed in FIG. 9b) with the tilted reference mirror 904b, which from the basic geometry results in the spacing of the sample 912 introduced into the interferometer 911. It shows that the intercept of the 993b tilted reference mirror 904b moves by λ / (4 sin θ) along the plane of the reference mirror 904b. Since there is a correlation between the position of the “disturbance” on the tilted reference mirror 904b and the fringe line 995b of the detector 905b itself, this is a fringe line that uses half the distance that is split from the fringe line 996b. Corresponds to the movement of 995b.

  Consistent with the above analysis, it should be noted that the height of the sample 912 that caused the λ / 2 fringe line 995b to drop more than enough to completely overlap the fringe line 996b. It is therefore clear that the “sample height measurement per pixel unit” can be calculated as λ / (2N). Here, N is the number of pixels between adjacent fringe lines on the CCD detector 905a (as shown in FIG. 9a) when no sample is placed on the sample stage 904b. For example, referring to FIG. 9a, it should be noted that there are 10 pixels between adjacent fringe lines 995a and 996a. For a light source with wavelength λ = 20 nm, this corresponds to a “sample height measurement per pixel unit” of 1 nm per pixel (ie 20 nm / 20 pixels = 1 nm / pixel). Thus, in this example, the sample height can be accurately measured as 5 nm due to the introduction of the sample that caused the fringe lines 556a and 556 to move.

  Returning now to FIG. 6, the “sample height measurement per pixel unit” refers to the wavelength λ of the light source and the number of pixels observed to exist between the fringe lines when the sample is not placed on the sample stage. (611). Here, the process of aligning the fringe lines with the calibration standard (610) can adjust the spacing between the fringe lines on the detector, thus calculating the “sample height measurement per pixel” ( It should be noted that 611) should be done after the position of the fringe line is aligned (610).

  In one embodiment, with the “sample height measurement per pixel unit” calculated (611), the information related to the mapping of the detector fringe line to the sample stage is “sample height per pixel unit”. Information ", which is stored (612) along with the" measurement value ", which can be used to substantially construct a measurement scale that can measure the fringe line change and determine the topography of the sample, as described above. Corresponds to saving.

5.0. Apparatus Embodiment FIG. 10A illustrates an implementation of a test measurement system that can determine surface topography by comparing the fringe lines that appear when a sample is placed on the sample stage against a pre-established measurement scale. The form is shown. The test measurement system of FIG. 10A includes a light source 1001 and a splitter 1002. The light source can be implemented using various types of light sources such as, for example, gas lasers, semiconductor lasers, tunable lasers, and the like. A collimator lens or other device can be used to form a plane wavefront from the light of the light source 1001. The splitter 1002 is oriented so that the first portion of light from the light source is directed to the reference mirror 1004 and the second portion of light from the light source is directed to the sample stage 1003. Splitter 1002 can be implemented using a number of different optical components, such as glass or pellicle.

  In order to properly guide the light as described above, the splitter 1002 is disposed at an angle α with respect to the plane in which the surface topography measurement is performed (eg, the xy plane as seen in FIG. 10A). In yet another embodiment, α = 45 °, but one skilled in the art can determine and implement another angle suitable for a particular application. The splitter 1002 can also be designed so that 50% of the light from the light source 1001 faces the reference mirror 1004 and the remaining 50% of the light from the light source 1001 faces the sample stage 1003. However, those skilled in the art will be able to determine other functional percentage ratios.

  More broadly, the reference mirror 1004 can be viewed as an embodiment of a reflective plane that reflects light back to the splitter 1002. The reflective plane can be implemented using a number of different components such as a suitable reflective coating formed on the plane. The reflection plane can be tilted by an angle θ so that an appropriate spacing is constructed along the surface of the detector 1005. As described above, the positioning of θ can be adjusted to align the fringe line with the calibration standard.

  The sample stage 1003 supports a test sample whose surface topography is to be measured. After light is reflected from the sample stage 1003 and / or the sample placed on the sample stage 1003, the light is combined with the light reflected from the reference mirror 1004. The combined light is then directed to the detector. More broadly, the detector 1005 can be viewed as an optoelectronic transducer that converts an optical intensity pattern into an electronic display on the surface of the detector. For example, as described above, the detector 1005 can be implemented as a charge coupled device (CCD) array that is divided into a plurality of pixels on the surface where light is received. Here, an output signal is provided for each pixel representing the luminance received by the pixel.

  The fringe detection unit 1006 processes the data generated by the detector 1005. The fringe detection unit 1006 plays a role of detecting positions of various fringes appearing on the detector 1005. Although embodiments of the fringe detection unit 1006 are described in more detail below in connection with FIGS. 11a to 11c, it is important to recognize that the fringe detection unit 1006 can be implemented in many ways. For example, the fringe detection unit 1006 can be implemented as a motherboard (having a central processing unit (CPU)) inside a computer system (such as a personal computer (PC) or workstation). Here, fringe detection can be accomplished using a software program executed by the motherboard. In another embodiment, the fringe detection unit 1006 can be implemented using dedicated hardware (eg, one or more semiconductor chips) instead of a software program. In another embodiment, some combination of dedicated hardware and software can be used to detect fringes.

  Figures 11a to 11c describe in more detail at least one embodiment of a fringe detection unit. FIG. 11a provides a method 1100 for performing fringe detection. FIG. 11b provides an embodiment of a dedicated hardware circuit 1150 that effectively performs the method of FIG. 11a. FIG. 11c shows waveforms that can be applied to the circuit of FIG. 11b. In accordance with the method of FIG. 11a, fringes are detected by taking the first derivative 1104 of a column of detector array data. A column of detector array data is a collection of optical intensity values from pixels extending along the same column of the detector pixel array. For example, if the array 1101 of FIG. 11a is considered an interferometer CCD detector, the first column 1102 across the array surrounds the “first” column of CCD data and the second column 1103 across the array is , Surrounding the “second” row of CCD data, etc.

  The optical intensity value from the row of CCD data should show a series of local minimum values. In other words, each column of CCD data corresponds to a “series” of optical intensity values that collide with the CCD detector at the same x-axis position along the z-axis, so that the optical intensity values are relative to their z-axis position A set of local minima should appear. For example, referring back to FIG. 3, a series of local minimums are revealed by moving in the + z direction with the x coordinate fixed along the optical intensity pattern 350 (eg, fringe lines 352a, 352b, Recognizing (at a position corresponding to 352c) naturally results. FIG. 11 c provides another example where a typical distribution 1112 of optical intensity values at the same fixed x position along the detector z-axis is presented.

From the depiction in FIG. 1, each local minimum value (eg, at points z ₂ , z ₄ , z ₆ , z _8, etc.) will correspond to a fringe line (as a result of destructive interference, the fringe line is minimal optical). Recall that it corresponds to strength). Therefore, the pixel position on the detector where the fringe line appears can be accurately identified. In other words, the x-coordinate of the column of CCD data to be analyzed is known (eg, x _n ), and the fringe detection is performed at the place where the fringe line appears (eg, z ₂ , z ₄ , z ₆ , z _8, etc.). Since the process identifies specific z-axis coordinates, a set of pixel coordinates (eg, (x _n , z ₂ ), (x _n , z ₄ ), (x _n , z ₆ ), (x _n , z ₈ ), etc.) can be easily identified for each analysis of a column of CCD data.

  Taking the first derivative 1104 of the column of CCD data (with respect to the z-axis) and then determining 1105 that the first derivative changes from a negative polarity to a positive polarity will result in a particular column of CCD data A method for identifying the z-coordinate of each pixel that receives a fringe line. Such an approach could be done in software, hardware, or a combination of the two, but FIGS. 11b and 11c relate to an approach that uses dedicated hardware. Here, a string of CCD data indicated by waveform 1112 is provided at input 1108. The column of CCD data 112 is then presented to both the comparator 1106 and the delay unit 1107. The delay unit substantially provides a delayed or shifted version of the column of CCD data 1112 (observed as waveform 1113).

The comparator 1109 displays which of the waveform 1112 and 1113 pairs is larger. Waveform 1114 provides an example of the comparator output 1109 signal generated for waveforms 1112 and 1113. Note that a rise is induced for each local minimum (eg, at points z ₂ , z ₄ , z ₆ , z _8, etc.). Those skilled in the art will recognize that mathematically indicating which of the pair of waveforms 1112 and 1113 is larger corresponds to taking the first derivative 1105 of waveform 1112 and determining its polarity. . Here, determining where the polarity changes from negative to positive corresponds to identifying the minimum value (because the slope of the waveform changes from negative to positive at the minimum value). Therefore, as seen in FIG. 11c, each rising edge of the output signal of the comparator needs to be aligned with each local minimum value in the column of CCD data.

4.0. Embodiment of Pre-Established Measurement Scale and Topography Measurement Based on it Returning to FIG. 10A and having finished the description of the embodiment of the fringe detection unit 1006 (as described above in connection with FIGS. 11a to 11c), this section will An embodiment of the operation of the measurement unit 1007 will be considered in detail. The operation of the topography measurement unit is considered to explain how to create an accurate topography description. However, before beginning such an explanation, a brief discussion of the overall method and certain details regarding the establishment of a measurement scale, although somewhat derailed, are provided.

  Returning to FIG. 5, it is recalled that the measurement scale is first established (501) before the topographic measurement is performed (503). Here, FIGS. 6 to 9b show that the measurement scale (1) aligns the fringe line to the calibration standard without placing the sample on the sample stage, and (2) recognizes the mapping of the detector fringe line to the sample stage. And (3) helped to illustrate that it can be made by recognizing sample height measurements per pixel unit. That is, in one embodiment, storing the measurement scale information involves storing the fringe line position of the interferogram when the sample has not yet been introduced into the interferometer. This essentially acts as a baseline against which fringe line disturbances that occur in response to introduction of the sample into the interferometer are compared.

  From the description of fringe line detection (performed by fringe detection unit 1006) described above in connection with FIGS. 11a through 11c, the position of the fringe line above the entire detector 1005 is fringe relative to each detector row. Obviously, it can be determined by performing an analysis of the detection. That is, the measurement scale (1) aligns the fringe line with the calibration standard without introducing the sample into the interferometer, and (2) determines the pixel location where the fringe line appears on the detector (eg, each detection By performing fringe detection on the instrument), (3) storing these pixel positions, and (4) the distance between traces on the sample stage (eg, x / y direction parameters per pixel resolution) Saved or otherwise recognized), or simply by recording the calibration standard interval, and (5) separation of the fringe line Can be created by saving or otherwise recognizing sample height measurements per pixel unit

  FIG. 12a shows pixel location information that can be stored to help form a stored measurement scale. Here, an array of detector pixel locations is observed and an “X” is placed at each location where a fringe line is detected when the sample is not placed on the sample stage. Accordingly, five fringe lines 1201, 1202, 1203, 1204, and 1205 are detected as seen in the example of FIG. 12a. The elements of information that can be stored and from which the measurement scale can be used are therefore: (1) a trace on the xy plane of the sample stage to which the fringe line separation observed on the detector maps The understood spacing between (and / or a parameter that can determine the spacing such as the per-pixel change in the x and y parameters described above), (2) for each fringe line on the detector Position (eg, (x, y) pixel coordinates of each pixel having “X” in FIG. 12), and (3) “sample height per pixel unit” calculated with the tilt angle of the reference mirror established. Measurement value ". The relevance of each of these will be described below.

  From FIG. 8, the alignment of the fringe lines 811a-811e to the calibration standard markings 810a-810e is the alignment of the fringe lines 811a-811e to the sample stage traces placed a distance "Y" along the y axis of the sample stage. Recall that each mapping is possible. FIG. 12a reveals that the stored measurement scale identifies the separation along the y-axis of each detected fringe line sample. For example, as just one approach, one fringe line (eg, fringe line 203) is a “baseline” with a corresponding (ie, “mapped”) y-axis position on the sampling stage defined by y = 0. It can be recognized as a fringe.

  In an embodiment where each fringe maps along the x-axis of the sample and each fringe maps to a trace spaced Y from the trace of the adjacent fringe line on the sample stage, the trace 1204 is a sample of y = −Y The trace 1202 will correspond to the y-axis position on the sample with y = + Y. Similarly, trace 1205 will correspond to the y-axis position on the sample with y = -2Y, and trace 1201 will correspond to the y-axis position on the sample with y = + 2Y. Returning briefly to FIG. 4a, it should be noted that the “higher” fringe line on the z-axis of detector 405 will map to a “lower” position along the y-axis of the detector. Accordingly, fringe lines 1202 and 1201 located at the bottom of baseline fringe 1203 are given a positive polarity, while fringe lines 1204 and 1205 located at the top of baseline fringe 1203 are negatively polarized. Is given.

  Tracking the position of each fringe line on the detector (eg, the (x, z) pixel coordinates of each pixel having “X” in FIG. 12a) is located at a particular y-axis position along the sample stage surface. Substantially corresponds to the position of several different “lower” measurement scales. FIG. 12b is a diagram along this perspective, where a set of measurement scales are observed, each measuring the sample height along the x-axis at a unique y-axis position. That is, for embodiments in which the fringe line spacing maps to Y distances on the same stage, another view of the pre-established measurement scale is (1) spaced by a distance Y along the y-axis of the sample stage. Placed (2) stand upright on the sample stage (through the “measured height per pixel” parameter) so that the sample height above the sample stage can be measured, and (3) detect A transformation of the information received on the detector for a plurality of measurement scales extending along the x-axis of the instrument.

  Tracking the position of fringe detection corresponds to the degree of data compression because pixel coordinates that are not associated with a fringe line (ie, those that do not have an “X” in FIG. 12) may be discarded. In addition, for further data compression, if all the fringe detections for a particular fringe line (eg, each “X” associated with fringe line 1205) are at the same z-axis coordinate, the entire fringe line is displayed. In order to do so, only one data value (ie z-axis coordinate) should be stored. In order to properly record the measurement scale information, the sample height measurement per pixel unit is recorded as well. If "bending" appears in the fringe line (eg due to imperfect optical properties), a correction factor can be applied to the fringe line data on a per pixel basis to "straighten" the fringe line Should be noted.

  As described above in connection with FIGS. 9a and 9b, and as will be described immediately below, the sample height measurement per pixel unit is used to determine a specific (in response to a sample placed on the sample stage. Considering with disturbances (in pixels) that occur at x, z) coordinate locations, helps to determine the height of the sample at a particular location. In a sense, each pixel on the detector corresponds to a “scale point” along the vertical axis (ie along the z-axis) of all measurement scales observed in FIG. Is the sample height per pixel unit.

  FIG. 13 shows the fringe line display of FIG. 12a after being disturbed, corresponding to the placement of the sample on the sample stage. Here, the fringe line 1301 in FIG. 13 corresponds to the fringe line 1201 in FIG. 12A, the fringe line 1302 in FIG. 13 corresponds to the fringe line 1202 in FIG. The fringe lines 1301-1305 of FIG. 13 also correspond to the fringe lines 451e to 451a of FIG. 4b, which tracks the profile of the trapezoidal sample 460. FIG. 14 shows the result when the difference between the corresponding fringe lines of FIGS. 13 and 12a (ie, fringe line disturbance) is calculated. For example, subtract the fringe lines of FIG. 12a from their corresponding fringe lines of FIG. 13 (ie, subtract fringe line 1205 from fringe line 1305, subtract fringe line 1204 from fringe line 1304, etc.) −1 14 (to correct the transformation topography profile observed in FIG. 13), resulting in profiles 1401 to 1405 in FIG.

  Profiles 1401-1405 each correspond to an accurate description of the sample topography at the y-axis position defined by the measurement scale. The topographic profiles 1401 to 1405 are measured vertically from a pixel perspective, so that the “sample height measurement per pixel” parameter is used to accurately define the sample height at each x-axis position. Note that it can be used. For example, it should be noted that the trapezoidal profile reaches a maximum height of 3 pixels. Here, if the “sample height measurement per pixel” parameter corresponds to 1 nm per pixel, the measured maximum height of the sample would be 3 nm.

  While FIGS. 12a, 13 and 14 serve to illustrate an embodiment of the operation of the topography measurement unit 1007 of FIG. 10A, FIG. 15 illustrates a circuit design embodiment 1507 of the topography measurement unit 1007 observed in FIG. 10A. Show. According to the design of FIG. 15, stored measurement scale data and distributed fringe line data are received at inputs 1522 and 1521, respectively. Here, the information associated with FIG. 12a can be thought of as some stored measurement scale data (excluding the sample height per pixel unit and the y-axis position of the sample stage corresponding to each unperturbed fringe line). The fringe line pattern observed in FIG. 13 can be considered as an example of the fringe line data distributed in response to the samples arranged on the sample stage. In this case, it should be noted that input 1521 in FIG. 15 corresponds to input 1021 in FIG. 10A, and input 1522 in FIG. 15 corresponds to input 1022 in FIG. 10A. It should be noted that in the particular embodiment of FIG. 10A, sample data and stored measurement scale data are extracted from their own memory areas 1024 and 1023. If shared memory is used, inputs 1021 and 1022 are combined into a shared data path.

  The fringe line extraction unit 1501 extracts corresponding fringe lines for comparison of appropriate memory areas 1523 and 1524. Here, the corresponding pair of fringe lines can be extracted in the context of how they were stored. For example, the z-axis pixel coordinates of the first fringe line associated with the measurement scale information (eg, fringe line 1201 in FIG. 12) can be automatically stored in the first area of the memory 1524 (detection unit 1006). The z-axis pixel coordinates of the first distributed fringe line associated with the sample information (eg, fringe line 1301 in FIG. 13) can be automatically saved in the first region of memory 1523 ( If with detection unit 1006), these same pairs of fringe line data can be extracted by automatically referencing these same memory areas using fringe line extraction unit 1501. Thus, fringe lines 1201 and 1301 can be presented together at inputs 1522 and 1521, respectively, fringe lines 1202 and 1302 can be presented together at inputs 1522 and 1521, respectively, and so forth.

  The y-axis position of these fringe line sample stages is such that the analysis of the fringe line pair presented together at inputs 1522 and 1521 can be tracked with respect to the y-axis position of a particular sample stage (for each unperturbed fringe (Saved in memory 1524 along with the pixel position of the line) can be tracked. With a pair of corresponding fringe lines extracted, the difference between the distributed and disturbed positions is calculated and then multiplied by -1 to properly transform the data (the reference mirror tilt angle is the reference angle). Note that a factor of 1 can be omitted if provided at the bottom rather than the top of the mirror (as observed throughout the description of the invention).

  This creates a new set of data (measured in pixels) that represents the profile of the sample at the y-axis position of the sample stage corresponding to a pair of fringe lines (eg, profile 1402 in FIG. 14). Thus, multiplication of the number of pixels in each x-axis coordinate of the “sample height measurement per pixel” parameter should produce an accurate sample profile from the fringe line pair. The topography profile can be stored or displayed beyond the topography measurement unit. They can also be compressed using various data compression techniques to reduce the amount of data processed.

  Returning to FIG. 10A, it is important to recognize that the topography measurement unit 1007 can be implemented in numerous ways and in many different processing schemes. For example, the entire unit 1007 can be implemented in a computer system (personal computer (PC), workstation, etc.) using a motherboard (having a central processing unit (CPU)). Here, the topography profile can be created using a software program implemented on the motherboard. If the functions of both the fringe detection unit 1006 and the topography measurement unit 1007 are implemented in software, the computer system can be used after the O / E converter to perform a complete topography measurement analysis Should be noted.

  Thus, data processing is performed “behind” the detector, regardless of whether (or whatever the extent) data processing is performed using software routines and / or using dedicated hardware. More generally, the processing is considered to be executed by the “data processing unit” 1020. Here, the data processing unit 1020 can be implemented as dedicated hardware (eg, as proposed by FIG. 10A), or alternatively or in combination, using a computer system. . An embodiment of a computer system is shown in FIG. 10B. A general purpose processor, a digital signal processor (DPS), and / or a general purpose / digital signal hybrid processor can be used as appropriately as possible.

  That is, all signal processing techniques described herein can be stored on machine-readable media in the form of executable instructions. Thus, embodiments of the present invention are implemented on or implemented on some form of processing core (such as a “central processing unit (CPU)” of a computer) or on machine-readable media. It should also be understood that it can be used as a software program or as its support. A machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (eg, a computer). For example, machine-readable media can be read-only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagated signals (Eg, carrier wave, infrared signal, digital signal, etc.).

  FIG. 10B illustrates an embodiment of a computer system 1000 capable of executing instructions that reside on machine-readable media, noting that other, eg, more advanced computer system embodiments may be implemented. . In one embodiment, the machine readable media may be fixed media such as hard disk 1002. In another embodiment, it may be a removable medium such as a CDROM 1003, a compact disk, a magnetic tape. The instructions (or portions thereof) stored on the machine-readable medium are loaded into a memory (eg, random access memory (RAM)) 1005, and the processing core 1006 then executes the instructions. Information can be received through the network interface before being loaded into memory 1005.

  In other embodiments, the topography measurement unit 1006 can be implemented using dedicated hardware (eg, one or more semiconductor chips) rather than a software program. In other embodiments, some combination of dedicated hardware and software can be used to create the topography profile. In addition, multiple topographic profiles can be analyzed in parallel (eg, by multiple implementations of the circuit of FIG. 15 operating simultaneously on different sets of fringe line pairs).

6.0. High-resolution topographic descriptions through alternating insertion of multiple topographic measurements 16a, 16b, and 17 relate to techniques for enhancing the overall resolution of topographic measurements along the y-axis of the sample stage. Returning to FIG. 10A, it should be noted that a stepper motor is coupled to a sample stage 1003 that can move the stage along the y-axis. Here, as described in detail above, in the case of Y trace separation, the sample stage can be moved a distance (eg, smaller than Y) to enhance the trace separation resolution.

  For example, if the sample stage is moved by an amount of Y / 2 along the y-axis, the fringe line trace is substantially “moving” so that it can be traced over the new position of the sample. I will. FIG. 16b reveals examples of these new traces. It should be noted that these traces may be compared to the traces originally observed in FIG. 4b so that they can be compared in the way they moved. FIG. 16a provides a “new” sample fringe that is detected in response.

  FIG. 17 provides a more complete topographic description embodiment that occurs when the topographic information from FIGS. 13 and 16a are combined by aligning or otherwise interleaving the profiles at the appropriate y-axis position. To do. More complete topographic information is then stored in volatile memory (eg, a semiconductor memory chip) or non-volatile memory (eg, hard disk storage) and / or on the screen so that the topographic information can be easily viewed. Can be displayed. The control applied to the stepper motor 1008 can be managed by the data processing unit 1020 of FIG. 10A and is therefore consistent with the above description, such control being software, dedicated hardware, or a combination thereof. It should be noted that can be managed by.

  It is important to note that other approaches can be used to substantially achieve the same or similar effects as described above. In other words, other optical techniques can be used to substantially provide a collection of traces that can be interleaved with each other to form a higher resolution image of the entire sample. For example, according to one approach, the phase of the light emitted from the light source is adjusted to “tune” the positioning of the fringe line on the detector. Here, the action of changing the phase of the light will have the same effect as moving the sample stage as described above in connection with FIGS. 16a, 16b and 17. FIG.

  That is, a new relative positioning on the sample of the fringe line trace mapping will occur, which in turn will produce another set of traces (different sample stages and / or light) to form a high resolution topographic image. A new set of traces that can be interleaved with each other (formed by phase positioning). According to another related approach, the position of the tilted reference mirror is moved along the optical path axis (eg, along the y-axis depicted in FIG. 10A) to “adjust” the fringe line positioning.

  Again, a new relative positioning on the fringe line trace mapping sample will occur, which in turn generates a new set of traces that can be interleaved with other sets of traces. Furthermore, different wavelengths of light can be used (eg, different “colors” of light can be used). Here, however, a separate measurement scale should be established for each wavelength of light used.

  Regardless of whether other techniques for creating interleaveable traces are used, or which technique (or combination of techniques) is used, the expansion and fringe lines are also described below. . With respect to magnification, it should be noted that returning to FIG. 10A, a magnification lens 1010 is included. By incorporating magnification into the interferometer, the “sample height measurement per pixel unit” parameter and the “distance per pixel unit along the x and y directions of the sample stage” parameter can be enhanced. For example, in the case of no enlargement, there are 10 pixels between adjacent fringe lines (eg, as observed in FIG. 9a), a 10 × enlargement does not separate adjacent fringe lines by 10 pixels, but 100 pixels. It will move away substantially. Since the fringe lines are still considered to be a distance of λ / 2, the sample height measurement per pixel unit can still be determined from λ / (2N). Therefore, a 10-fold increase in N corresponds to a 10-fold increase per change in sample height.

  It should also be noted that in connection with the fringe line, the fringe line seen in FIG. 3 corresponds to a minimal position observed within the optical intensity pattern 350 (as described above). More generally, a fringe line is an arbitrary sought luminance feature (e.g., a local minimum) within the range of an optical intensity pattern that is disturbed in the manner described above as a result of the sample being introduced into the sample stage. Position, maximum position, etc.). Finally, it should also be noted that the stepper motor 1009 can be used to adjust the position of the reference mirror 1004 along the y-axis and / or adjust the tilt of the reference mirror.

7.0. Characterization of Sample Composition by Analysis of Fringe Line Luminance Information FIGS. 18a to 18b are for the following discussion which explains how to determine the material composition of a sample by analyzing the value of the fringe line luminance detected from the interferometer detector. Related. That is, recalling the description of FIGS. 11a-c and 12a, it should be noted that fringe line detection includes identification of specific pixel locations. Therefore, the optical intensity data used to determine the fringe line in a state where the fringe line is normally detected can be discarded. However, according to the measurement techniques described in this section, optical intensity information is considered useful information because it can create further characterization of the sample beyond the surface topography.

More particularly, the material comprising the surface of the sample can be determined by characterizing the reflectance of the sample surface as a function of the light wavelength of the interferometer light source. The solid line graphic element in the diagram of FIG. 18a provides an exemplary depiction of a “reflectance versus wavelength” curve. Here, reflectivity vs. wavelength is a function of the fine details of the reflective surface, such as conductivity, lattice spacing, lattice type, etc., and also a specific material or substance (eg, cobalt (Co) Pure materials, or alloys or other combinations of materials such as silicon nitride (Si ₃ N ₄ ), “nickel iron” (Ni _100-x Fe _x ), etc., for these same microstructure details Since it has a specific value, the “reflectance vs. wavelength” curve of a specific material or substance often uniquely defines it.

  In other words, different materials or substances tend to exhibit different “reflectivity vs. wavelength” curves, and thus the material from which it (sample) is constructed by creating a “reflectivity vs. wavelength” curve of the sample. Or the substance can be judged. Here, rather than assigning optical intensity values observed at the detector, they can be analyzed so that the specific reflectivity of the sample for a specific wavelength of the interferometer light source can be determined.

  By changing the wavelength of the light source and monitoring the corresponding change in reflectivity of the sample, the “reflectance vs. wavelength” curve of the sample can be measured. This can then be used to determine the material composition of the sample itself. FIG. 18a provides exemplary results from such measurements in which specific measured reflectance data points are plotted against the applied wavelength. Since the data points trace the reflectance curve of the sample, the composition of the sample can be determined.

  In various embodiments, the optical intensity observed at the pixel location where the fringe line was detected is used to perform a reflectance analysis. Thus, in some cases, the pixel location of the detected fringe line is not only used (to create a topographic description of the sample surface), but the same to help characterize the material from which the sample is constructed The optical intensity value of the fringe line is also used.

  However, if it is understood that the fringe line can be interpreted to correspond to something other than a local minimum when appropriate, in some cases the minimum optical intensity value is not sufficient to perform a reflectance analysis. It should also be noted that it may be useful to track the maximum optical intensity value instead. Thus, in some cases, the fringe line used for topography purposes may be the same as the fringe line used for reflectance analysis (eg, both are minimal), while in other cases the topography line The fringe line used for the purpose may be different from the fringe line used for reflectance analysis (for example, one is a minimum and the other is a maximum).

  In a further embodiment, the spatial and / or wavelength dependent interferometer characteristics can also be pre-characterized to ensure that any resulting adverse effects on reflectance measurements can be offset. For example, if it is known that the first pixel location observes light of lower brightness than the second pixel location (due to optical imperfections associated with the interferometer), the skilled person The difference in optical intensity (between pixel pairs) due to meter imperfections can be separated from that based on the intrinsic reflectance characteristics of the sample itself. The same is true for wavelength-related discrepancies or imperfections of the interferometer (if any).

In the simplest case where the topography is seen in FIG. 18b, the sample is composed uniformly with a single composition (eg, the sample is composed uniformly with Co or uniform with Si ₃ N ₄ etc. It is assumed that Because of the uniform composition of the sample, the fringe line “moves freely” across the surface of the detector without affecting the overall reflectance experiment. Here, recalling from the background description that the fringe lines are separated according to ~ λ / θ, the adjustment 1811 of the wavelength (λ) of the light source during the reflectance calculation 1810 (or at least the recording of the optical intensity) is: Move the fringe line over the surface of the detector. However, interferometer spacing and wavelength-related discrepancies can be offset and the “reflectivity vs. wavelength” curve can be recorded regardless of the position of the fringe line because the sample reflectivity is uniform.

  In the more likely scenario shown in detail in FIG. 18c, it may be more desirable to realign the fringe lines with each wavelength change. In other words, after the wavelength has changed (1821), an attempt is made to reposition the fringe line (1822) so that it appears in the same position as it appeared during exposure at the previous wavelength. This allows a measurement to determine the reflectivity of a particular area of the sample due to the method of mapping to that sample stage. Thus, if the sample consists of a different material or mixture of materials (eg, the first region is silicon (Si) and the second region is copper (Cu)), the interferometer will produce a different mixture on a pixel-by-pixel basis. It is possible to identify.

  That is, a first “reflectance vs. wavelength” curve can be measured for the portion of the sample that maps to the first pixel location, and a second “reflectance vs. wavelength” curve can be taken at the second pixel location. Measurements can be made on the portion of the sample to be mapped. By tracking separate curves for different pixels (or possibly different groups of pixels), if the sample has different materials / substances at the mapped location, the different “reflectivity vs. wavelength” curves are themselves It will be clear that it is between different pixel locations. Thus, different materials / substances can be identified at the exact sample location.

  The fringe line can be repositioned (1822), for example by adjusting the tilt angle of the reference mirror, so that the movement caused by the wavelength change can be compensated. Thus, the “new” data points in the “reflectivity vs. wavelength” curve (1) change the wavelength of the light source (1821), (2) the fringe line overlaps those positions that existed before the wavelength change. (1822), (3) generated by calculating and storing the reflectance at the fringe line (or storing the observed luminance so that at least the luminance can be calculated later) (1820) Is done. It should be noted that the reflectance calculation can be easily performed by one skilled in the art, since those skilled in the art will recognize that the observed brightness is proportional to the sample reflectance.

  Similar to the technique described above in connection with FIGS. 16a, 16b, and 17, with the first group of reflectivity curves generated for the first set of fringe line positions (first set of fringes). A second group of reflectivity curves for the second set of fringe line positions can be generated (by multiple loops through the topography of FIG. 18c for the line positions) (second set of fringe line positions). Note that (by multiple loops through the topography of FIG. 18c).

  Corresponding group reflectance curves can then be interleaved so that the composition of the sample can be determined with precise resolution (eg, as in the concept described in connection with FIG. 17). . The procedure for performing a “reflectivity vs. wavelength” analysis of the sample (eg, as described above) can achieve a complete description of the sample measuring both the surface topography of the sample and the composition of the material. It should also be noted that it can be combined (eg, by preceding or following) with a procedure for determining the topography of the sample (eg, as described in the previous section).

  Also, slightly back in FIG. 10a, the data processing unit 1020 can be configured to track the measured “reflectance versus wavelength” curve (eg, through software or hardware). Further, the data processing unit 1020 can determine the measured curve against a database of such curves for known materials or substances so that it can determine that a particular curve matches a known material or substance. Can be set to compare (eg, by correlating measured curves with curves stored in a database). Many of these techniques can be implemented in software and can be incorporated into machine-readable media.

8.0. Signal Processing Technique for Measuring Fringe Line Disturbances Extending Outside Related Reference Fields Returning to FIG. 13, fringe line disturbances “harmonize” in the sense that each fringe line disturbance remains within their corresponding reference field. It should be noted. The reference field corresponds to the field of optical image data that resides adjacent to the fringe line that it will initially project to reveal changes in the sample height when the fringe line is disturbed. For example, referring to FIG. 12a, the field of image data between fringe line 1204 and fringe line 1203 corresponds to the reference field for fringe line 1204, and the field of image data between fringe line 1203 and fringe line 1202 is fringe line. Corresponding to the reference field for 1203, and so on.

  Next, comparing FIGS. 12a and 13, it should be noted that the combination of maximum sample height and fringe line spacing is such that each fringe line disturbance is maintained within its own reference field. . This helps to create a relatively simple sample topography profile as seen in FIG. That is, the pixel position of the entire fringe line and its associated disturbances are partitioned by themselves (ie, without being accompanied by the pixel position of another fringe line) for a particular memory location (eg, a fringe line reference field). Can be easily stored and compared with its corresponding disturbed fringe line position.

  That is, in general, according to various embodiments, the pre-defined maximum measurable / acceptable sample height is designed such that the fringe line disturbance is maintained within the corresponding reference field. Can be recognized. This maintains the signal processing required to derive topographic information that is closer to the lowest degree of sophistication. It should be noted that any such “maximum height” can be easily established by manipulating the fringe line spacing (eg, adjusting the tilt angle θ). In addition, the resolution of the measurement is not lost because a suitable interpolating technique (as described in connection with FIGS. 16a, 16b, and 17) can be used to create the desired resolution topography description.

  However, if it is desirable to easily measure fringe line disturbances that violate the respective reference field, more robust signal processing techniques can be used to accurately “track” specific fringe lines. it can. That is, for example, if the memory resources are re-divided so that data storage can be organized according to the reference field of the image, the pixel positions of the different fringe lines can reside in the common reference field. FIG. 19a shows an exemplary depiction of fringe lines 1951b, 1951c, and 1951d observed on a detector 1905 that violates the corresponding reference field. Correspondingly, segments BC and EF of fringe line 1951b and segments HI and JK of fringe line 1951c reside in the same field of the reference field (located between undisturbed fringe line positions 1913 and 1912). It should be noted.

  FIG. 19b shows an exemplary depiction of a sample 1960 that can produce the fringe line disturbance seen in FIG. 19a. Note that the fringe lines 1951a, 1951b, 1951c, 1951d, and 1951e of FIG. 19a map to the traces 1952a, 1952b, 1952c, 1952d, and 1952e of FIG. 19b, respectively. Comparing sample 1960 in FIG. 19b with sample 460 in FIG. 4b, the taller sample 1960 in FIG. 19b (compared to the shorter sample 460 in FIG. 4b) has fringe lines 1951b, 1951c, and 1951d. Note that it may have violated its respective criteria field.

7.1. Base memory partitioning by reference field Before beginning to describe a more sophisticated signal processing technique suitable for tracking multiple fringe lines within the same reference field, the detected fringe line disturbance (e.g., FIG. A brief description will be given of how memory resources used to store pixel data (such as 15 and 102 memories 1023 and 1523) can be partitioned to store pixel data on a per-reference field basis. At the beginning of this description, it is emphasized that memory partitioning is done on a per-reference field basis, regardless of whether the fringe line "expects" or "unexpected" to violate each reference field. is important. Thus, memory partitioning applies to the signal processing techniques described above in connection with FIGS. 13-15, as well as to that environment in which the fringe line violates its respective reference field as seen in FIG. 19a. can do.

  Analysis of stored image data on a per-reference field basis allows for easy / efficient memory management. That is, the memory resource used to store the disturbed image data (eg, memory resource 1023 in FIG. 10a) can be viewed as being divided into its own reference field area. This in turn allows for easy memory organization / use between measurements and samples regardless of where on the detector the fringe line was detected.

For example, according to one embodiment, saving reference scale information includes saving each z-axis position on a detector where an undisturbed fringe line resides (eg, to memory resource 1024 in FIG. 10a). Accordingly, the first pre-established memory location is scheduled for storage of the z-axis location (eg, “z ₁ ”) relative to the first undisturbed fringe line (eg, fringe line 1205 in FIG. 12a). A second pre-established memory or register area can be located at a z-axis position (eg, “z ₂ ”) relative to a second undisturbed fringe line (eg, fringe line 1204 in FIG. 12a). Can be scheduled for storage, etc.

Thus, the boundary of the reference field (ie, the adjacent undisturbed position) is always stored in the previously defined memory / register area, regardless of whether the boundary itself changes between reference scales. That is, for example, the first reference field may be the first and second of the memory 1024, even if the test device stores different measurement scale embodiments (eg, different fringe line intervals) over its useful life. It can be recognized that it is always bounded by the z-axis values z ₁ and z ₂ stored between the previously established memory locations.

  As a result, the detected fringe line disturbance pixel locations can be discarded according to their particular reference field. In other words, using knowledge of the reference field boundaries, the fringe detection unit 1006 can store the fringe line area in the common area of the memory 1023 within the same reference field area (see, eg, FIG. 19a). The pixel coordinates of the fringe line areas HI, BC, EF, and JK can then be stored in a common memory location in the memory 1023). In addition, these regions of memory 1023 can also be pre-established (eg, the first pre-established region of memory 1023 is within the first reference field regardless of the z-axis boundary of the first reference field). And the second pre-established region of the memory 1023 is a pixel value detected in the second reference field regardless of the z-axis boundary of the first reference field. Etc. are scheduled for).

  In addition, the topography measurement unit 1007 automatically reads from these pre-established areas of the memory 1023 to intentionally extract data within a particular reference field without knowledge of the particular z-axis boundary itself. Can be set as follows. For example, the topography measurement unit 1007 reads (1) reads from a first address (or group of addresses) to obtain the pixel position of the fringe line detected in the “first” reference field; (2) It can be preset such as reading from a second address (or group of addresses) to obtain the pixel position of the fringe line detected in the “second” reference field. Therefore, according to this point of view, access to a specific z-axis boundary value by the topography measurement unit is not required.

7.2. Tracking multiple fringe lines within the same reference field As mentioned above, memory resources are split on a per-reference field basis, regardless of whether the fringe line is expected to violate its corresponding reference field. can do. For example, referring to FIGS. 13 and 12a, (1) fringe lines 1205 and 1305 can be read from memories 1024 and 1023 as a result of undisturbed and disturbed reading of the first reference field (these are And then subtracted from each other to form a topography profile 1405), (2) the fringe lines 1204 and 1304 are read from the memories 1024 and 1023 as a result of the undisturbed and disturbed reading of the first reference field. Can be read (these are then subtracted from each other to form a topography profile 1404), etc.

  If the fringe line is expected to violate the corresponding reference field, more advanced signal processing techniques may be required. In other words, different fringe lines can occupy the same reference space if the fringe line can violate the corresponding reference field. Therefore, techniques that can recognize different fringe lines in the same reference field space should be used so that each disturbance can be properly measured. For example, fringe line segment BC in FIG. 19a represents a higher height above the sample stage than fringe line segment HI. Therefore, a different fringe line should be recognized so that its corresponding undisturbed position can be used as a reference for the topography measurement.

FIG. 20 illustrates a signal processing technique that enhances the tracking of individual slopes (ie, “edges”) of fringe line disturbances to address the presence of different fringe lines within a common reference field. Further, while the edge of a particular fringe line disturbance is tracked, a calculation is performed to convert the position of each fringe line disturbance to its corresponding sample height (z _s ). Using knowledge of a particular location in the xy sample stage space, signal processing techniques can generate an “output” corresponding to a particular x, y, z _s data location. These x, y, z _s data locations can then be saved or plotted to display the overall topography of the sample. Furthermore, as will be described in more detail below, the technique allows further compression of pixel data points to further reduce processing overhead.

  According to the signal processing technique of FIG. 20, track edges from different fringe lines are tracked in a first direction (eg, a “downward” tilt direction as seen in FIG. 19a) across each reference field. (2001). For example, to perform the first tracking sequence 2001, this technique does the following: (1) reads image data corresponding to the reference field between the undisturbed fringe line positions 1914 and 1913 from the memory, and sets the fringe line 1951b The downward edge segment “AB” is tracked, and then (2) the image data corresponding to the reference field between the undisturbed fringe line positions 1913 and 1912 is read from memory and the downward edge segment “BC” of the fringe line 1951b is read. And “HI” of the fringe line 1951c. Eventually, the reference field below the unperturbed fringe line position 1911 will be processed to indicate the end of the sequence 2001.

  Next, while performing the second tracking sequence 2001 in the “upward” direction, this technique (after the reference field under position 1911 and between positions 1911 and 1912 has already been processed) (1 ) Read data from memory corresponding to the reference field between the unperturbed fringe line positions 1913 and 1912 and track the upward segments of “EF” on the fringe line 1951b and “JK” on the fringe line 1951c; (2) Data corresponding to the reference field between the fringe line positions 1913 and 1912 that are not being read may be read from memory, tracking the upward segment of “EF” on the fringe line 1951b, and so on. Eventually, the reference field between reference line positions 1915 and 1914 will be processed to indicate the end of sequence 2002.

  Figures 21a to 21c relate to an embodiment of a method that can be used to process data in either an upward or downward direction. FIG. 21 a shows the method, FIG. 21 b relates to its “downward” direction application, and FIG. 21 c relates to its “upward” direction application. An example of operation in each direction will be described below. Referring to FIGS. 21a and 21b, data corresponding to the reference field is read from its corresponding memory location (2101). Here, the data corresponding to the reference field can be retrieved from the address location (or group of address locations) where the pixel location for the detected fringe line resident in the reference field in question is found in memory (2101). ).

Next, starting from its intercept with the upper boundary of the reference field, each fringe line segment is “tracked” (2102) while converting it to the sample height z _s at the appropriate xy sample stage position ( (For example, by recognizing the presence of adjacent pixel locations). Tracking and transforming (2102) can be viewed as multi-dimensional 2102 ₁ to 2102 _n , where the dimension size depends on the number of different fringe line segments processed. That is, if one segment is required to process in the downward direction (eg, as for the reference field between positions 1914 and 1913), n = 1 and two segments are required to process in the downward direction. (For example, as for the reference field between positions 1913 and 1912) n = 2, and so on.

  A fringe line segment starts at its intercept with its “upper” boundary and looks down or by recognizing the presence (in the reference field data) of the nearest pixel coordinate (E.g., by scanning the data and knowing the closest pixel location that is "down and / or right" of the intercept. In the simple case this is the next highest x It should correspond to simply selecting a pixel location having a value). This process is then repeated continuously until either the next lower reference field intercept is reached or the fringe line moves back and crosses the upper boundary again.

Each pixel location of the fringe line segment can be converted to appropriate x, y, z _s topography information through the use of stored measurement scale information and an understanding of overall geometry and optics. In one embodiment, consistent with the illustration provided herein, for all fringe line pixel locations (x, y), (1) the appropriate sample stage x-coordinate values are “x and y Determined by taking into account the x-coordinate of the pixel by the “resolution per pixel in direction” parameter (eg, as described at the end of section 3.1), and (2) the y-coordinate value of the appropriate sample stage is Determined by reference to the particular fringe line being tracked (eg, fringe line 1951b is understood to be the y-axis position -Y on the sample stage), and (3) the appropriate sample height z _s the relationship: is determined by _{z s = REF2 + (R-} dz), where, (a) REF2 is the "baseline reference" fringe lines have a reference field (B) R is “sample height per reference field violation”, and (c) dz is the pixel z-axis detector position and sample height per pixel unit. The difference from the position of the lower reference field boundary REF1 taking into account the depth parameter (ie, z-REF1). A more complete description of each of these is as follows.

  REF2 can be viewed as a variable to track for each fringe line. In other words, in various embodiments, a separate REF2 variable is maintained for each tracked fringe line. Whenever a fringe line violates another reference field, its corresponding REF2 variable is incremented by N (Δz), where N is the number of pixels between adjacent fringe lines (along the detector z-axis). Yes, Δz is the sample height per pixel unit (described in Section 3.2). Thus, when the fringe line is within its reference field (such as segment AB of fringe line 1951b), the REF2 variable is 0 and has not yet violated the reference field.

  When a fringe line breaks its first reference field and needs to be tracked across a second reference field (such as segment BC of fringe line 1951b), the fringe line's REF2 variable is For the conversion process performed in the second field of the reference, it is incremented to a value of N (Δz). If the fringe line violates into the third reference field, the fringe line REF2 variable is incremented to a value of 2N (Δz) for the conversion process performed in the second field of the fringe line reference. . Thus, the REF2 variable for the fringe line is translated into a corresponding sample height distance for each reference field violation.

  Whereas the REF2 variable displays the amount of sample height measured “to date” for a particular fringe line, R (sample height per reference field violation) is the reference field currently being processed. Displays a field for the sample height position that is affected by tracking the fringe line within. Therefore, R is a constant of N (Δz). Here, for any detector z-axis position, the term R-dz substantially indicates how far the fringe line has been extended in the current reference field. That is, since dz represents the sample height Δz for each pixel unit considering the distance above REF1 to which the specific pixel position corresponds when dz = 0 (see FIG. 21B), the fringe line is the next lower reference. When the reference field is expanded to intersect with a field (eg, point B in FIGS. 21b and 19a), and when dz is R / 2, the fringe line violates half of the current reference field. And so on.

  The “downward” sloped fringe line is being tracked in the reference field, and the topographic loop characteristics of FIG. 21a indicate that data for the next lower reference field is then extracted and analyzed. For example, after the reference field between positions 1914 and 1913 has been analyzed (as tracking segment AB of fringe line 951b), positions 1913 and 1912 are then analyzed (segment BC and fringe line of fringe line 1951b). So that the segment HI of 951c is tracked). Here, during each pair of reference field analysis, for each fringe line that was violated in the next lower reference field (eg, points C and I after the reference field between positions 1913 and 1912 was analyzed). Thus, the intersection of each fringe line is identified / recorded (2103).

  Some form of data compression can be performed on those fringe lines that do not violate the next reference field. For example, in the case of the fringe line 951b, when the reference field between the positions 1912 and 1911 is analyzed, only the edge of the sample is actually measured, and the data tracking process may end at the point D1. Alternatively, the tracking process can be slowed down from point D1 to point D2, such that the density of transformed sample points decreases as it extends across the plane of the sample. Either of these techniques reduces the number of pixel locations used for topographic information, which in turn corresponds to a form of data compression.

  A similar process is repeated after the edge of the fringe line sloping downward is tracked, but in the opposite direction upward. Reference can now be made again to the method of FIG. FIG. 21c relates to the processing of the fringe line segment EF of fringe line 1951b (when the reference field between positions 1913 and 1912 has been analyzed). Here, the upward processing is equivalent to the downward processing.

The biggest difference is that in one embodiment, the appropriate sample height z _s is determined by the formula: z _s = REF2-dz, where REF2 is the number of reference fields that the fringe line has already violated. Is the same “baseline reference”, but whenever a higher reference field is analyzed, it is decremented by N (Δz) in the upward direction. Note that the lower boundary for purposes of determining dz is REF2 in this case. With all the fringe lines being tracked and the tracking process violating the highest reference field, a set of (x, y, z _s ) data points describing the sample topography in three dimensions remains. Those skilled in the art will be able to create software and / or hardware for the topography measurement unit 1007 that can implement the techniques described above.

9.0. In the foregoing specification, the invention has been described with reference to specific exemplary embodiments. However, it will be apparent that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the claims. The specification and drawings are accordingly to be regarded in an illustrative rather than a restrictive sense.

It is a figure which shows an interference measurement system. It is a figure which shows the interference measurement system which has the inclined reference | standard mirror. FIG. 5 is a diagram depicting an optical intensity pattern that occurs when the reference mirror of the interferometer is tilted. It is a figure which shows the fringe line observed with the detector of an interferometer when the reference | standard mirror of an interferometer is inclined. FIG. 6 is a diagram showing how a fringe line maps to a specific y-axis position along a sample stage. FIG. 6 shows the perturbation imparted to the fringe line of an interferometer having a tilted reference mirror as a result of the sample being placed on the sample stage of the interferometer. FIG. 4 illustrates an embodiment of a method that can be used to create a sample topographic description. FIG. 6 illustrates an embodiment of a method for establishing a reference scale with respect to which fringe line changes are measured. It is a figure which shows the "upper surface" of a collation standard device. It is a perspective view of the collation standard of FIG. 7a. FIG. 6 is a diagram showing a display of an image appearing at the detector of an interferometer having an inclined reference mirror when a verification standard is placed on the sample stage. FIG. 5 illustrates an embodiment of a method for aligning a fringe line with a reference line of a reference standard placed on a sample stage of an interferometer. FIG. 6 shows adjacent fringe lines on a CCD array detector of an interferometer having an inclined reference mirror. FIG. 6 is a diagram showing a disturbance that occurs in one of the fringe lines when a sample having a height λ / 4 is placed along its optical path. FIG. 6 shows an embodiment of an interferometer having a tilted reference mirror that measures sample topography relative to a pre-established measurement scale. 1 is a diagram illustrating an embodiment of a computer system. It is a figure which shows the method of detecting fringe. FIG. 6 shows a circuit that can be used to detect fringe lines. FIG. 12 shows signals related to the operation of the circuit of FIG. 11b. FIG. 5 shows an embodiment of a fringe trace used to form a pre-established measurement scale. It is a perspective view of a pre-established measurement scale. FIG. 12b shows an embodiment of the disturbance that occurs in the fringe trace of FIG. 12a when a sample is introduced into the interferometer. FIG. 14 shows sample topography information extracted from the fringe trace analysis of FIGS. 12a and 13; FIG. 10B illustrates an embodiment of a circuit that can be used to implement the topography measurement unit of FIG. 10A. FIG. 6 depicts a “new” pattern of fringe traces after the sample has moved along the y-axis. FIG. 16b depicts a “new” relative placement of samples corresponding to the “new” fringe pattern traces observed in FIG. 16a. FIG. 16 depicts a topographic description of a sample derived from the fringe trace observed in FIGS. 13 and 16a. FIG. 5 is an exemplary depiction of reflectivity versus light source wavelength suitable for characterizing sample composition. FIG. 3 illustrates a first method that can be used to generate a reflectance versus light source curve. FIG. 6 illustrates a second method that can be used to generate a reflectance versus light source curve. FIG. 5 is a diagram illustrating an example of a fringe line disturbance that extends outside a related reference field of the fringe line. FIG. 19b is an exemplary depiction of a sample believed to be able to produce the fringe line disturbance pattern observed in FIG. 19a. FIG. 6 illustrates a method that can be used to follow a disturbed fringe line beyond an associated reference field of the fringe line. FIG. 6 illustrates a method that can be used to track a specific edge of a fringe line disturbance disturbed beyond the associated reference field of the fringe line. FIG. 20 illustrates an exemplary depiction applied to tracking a segment of a downward sloping edge of the fringe line 1951b of FIG. FIG. 20 illustrates an exemplary depiction applied to following the segment of the upward sloping edge of the fringe line 1951b of FIG.

Explanation of symbols

402 Splitter 403 Sample stage 404 Tilt reference mirror 405 Detector 451a, 451b, 451c, 451d, 451e Fringe line 452a, 452b, 452c, 452d, 452e Trace 460 samples

Claims (55)

(A) converting the first set of interferometer fringe line disturbances to predetermined measurement scale information to generate a first set of profiles that describe the topography of the samples placed on the sample stage associated with the interferometer; Measuring stage against,
Including
The first set of profiles maps to a trace extending across a first axis of the sample and the sample stage;
The traces have a perceived spacing between each other along a second axis of the sample and the sample stage;
(B) adjusting the relative position of the trace with respect to the sample to generate a second set of fringe line disturbances;
(C) measuring a second set of interferometer fringe line disturbances against the predetermined measurement scale information to generate a second set of profiles describing the topography of the sample;
(D) interleaving the first set of profiles and the second set of profiles to generate a topographic description of the sample having a resolution along the second axis that is less than the spacing. When,
The method of further comprising.   The method of claim 1, wherein the adjusting further comprises moving the sample stage.   The method of claim 1, wherein the adjusting step further comprises changing the phase of light generated by a light source that is part of the interferometer.   The method of claim 1, wherein the adjusting step further comprises changing a position of a tilted reference mirror that is part of the interferometer.   The method of claim 1, wherein the adjusting is accomplished using different wavelengths.   The method of claim 1, further comprising storing the topographic description.   The method of claim 6, wherein the storing further comprises storing in volatile memory.   The method of claim 6, wherein the storing further comprises storing in a non-volatile memory.   The method of claim 1, further comprising displaying the topography description on a screen so that the topography description can be viewed. Measuring the first set of interferometer fringe line disturbances comprises:
(A) detecting the fringe line from an optical intensity pattern supplied from a detector associated with the interferometer;
(B) comparing the shape of the detected fringe line at its respective position to the predetermined measurement scale information to form the first set of profiles;
Further including
The predetermined measurement scale information further includes a shape at the respective position of the detected fringe line when the fringe line was not disturbed.
The method according to claim 1.   11. The method of claim 10, wherein the predetermined measurement scale information further includes a parameter that converts each range of the disturbance into a measurement of the height of the sample.   The method of claim 10, wherein detecting the fringe line further comprises detecting a local minimum in the optical intensity pattern.   The method of claim 10, further comprising compressing data comprising the first set of profiles. Storing information identifying a trace along the sample stage to which a plurality of fringe lines detected on a detector that is part of the interferometer maps;
(1) due to the sample being placed on the sample stage;
(2) observed on the detector;
Storing parameters that can be used to translate positional disturbances of the fringe line into a plurality of topographic profiles of the sample along the trace;
The method of claim 1, further comprising forming the predetermined measurement scale by:   The method of claim 14, wherein the detector further comprises an array of optically sensitive elements, each array position corresponding to a unique pixel.   Divide the wavelength of the light source used by the interferometer by 2N, where N is the number of pixels between adjacent fringe lines observed on the detector when the sample is not placed on the sample stage. The method of claim 15, further comprising calculating the parameter.   The method of claim 15, wherein storing the information further comprises storing information identifying an interval between the traces.   The information is adjusted after the spacing between the set of fringe lines observed on the detector is adjusted to be equal to the spacing separating the markings on the calibration standard placed on the sample stage. The method of claim 15 further comprising the step of determining.   19. The method of claim 18, further comprising tilting a reference mirror within the interferometer to adjust the fringe line spacing.   The method of claim 14, wherein storing the information further comprises storing a position of the fringe line observed on the detector.   The method of claim 20, wherein the detector further comprises an array of optically sensitive elements, each array position corresponding to a unique pixel.   The method of claim 21, wherein storing the information further comprises storing a pixel location at which a fringe line is observed on the detector.   21. The method of claim 20, further comprising detecting the fringe line from an optical intensity pattern provided by the detector.   The method of claim 23, wherein detecting the fringe line further comprises finding a local minimum along the optical intensity pattern. The measuring step includes
Tracking a fringe line disturbance that violated the fringe line reference field;
When x and y represent the position on the plane of the sample stage of the interferometer, and z _s represents the height of the sample above the x, y position, each pixel position of the tracked fringe line disturbance is represented by x, y, converting to z _s data points;
Further including
The sample is placed on a sample stage of an interferometer to generate the fringe line disturbance;
The fringe line disturbance is observed on a detector of the interferometer;
The method according to claim 1.   26. The method of claim 25, wherein tracking the fringe line disturbance further comprises tracking the fringe line disturbance on a per-reference field basis. Tracking fringe line disturbances on a per-reference basis basis
(A) reading image data for a first reference field;
In addition,
The image data includes a pixel position of a fringe line that is detected in the first reference field and is one of the fringe lines;
(B) starting at a pixel location corresponding to the fringe line intercept with the upper boundary of the first reference field, and transforming each pixel location of the fringe line in a downward direction, which is the step of transforming with respect to each pixel location. The steps to follow,
Further including
26. The method of claim 25. Step of converting for said particular pixel further includes the step of calculating a _{z s = REF2 + (R-} dz) by z _s,
(A) REF2 is a baseline reference that takes into account the number of reference fields that the fringe line has already violated;
(B) R is a parameter indicating the amount of sample height per reference field violation;
(C) dz is the difference between the z-axis position of the pixel on the detector and the position of the lower boundary of the reference field considering the sample height parameter per pixel unit;
28. The method of claim 27.   29. The method of claim 28, further comprising incrementing the REF2 parameter by R each time the fringe line disturbance violates within another reference field.   R = N (Δz) where N is the number of pixel positions between adjacent fringe lines observed on the detector and Δz is a parameter for the sample height per pixel unit. 30. The method of claim 29. Tracking fringe line disturbances on a per-reference basis basis
(A) reading image data for a second reference field;
In addition,
The image data for the second reference field includes a pixel position of a fringe line that is one of the fringe lines detected in the second reference field;
The second reference field is below the first reference field;
(B) starting at a pixel location corresponding to the fringe line intercept with the upper boundary of the second reference field, and transforming each pixel location of the fringe line in a downward direction, which is a transform with respect to each pixel location. The steps to follow,
Further including
26. The method of claim 25. Tracking fringe line disturbances on a per-reference basis basis
(A) reading image data for a first reference field;
In addition,
The image data includes a pixel position of a fringe line that is detected in the first reference field and is one of the fringe lines;
(B) starting at a pixel position corresponding to the fringe line intercept with the lower boundary of the first reference field and transforming each pixel position of the fringe line in an upward direction, the step of transforming with respect to each pixel position; The steps to follow,
Further including
26. The method of claim 25. (A) (1) a sample stage on which a sample is arranged, and (2) a detector for observing a plurality of fringe lines,
An interferometer further comprising:
(B) (1) measuring a first set of fringe line disturbances against predetermined measurement scale information to generate a first set of profiles describing the topography of the sample; The profile of the sample and a trace extending across a first axis of the sample and the sample stage, the trace being a recognized distance between each other along the second axis of the sample and the sample stage Have
(2) adjusting the relative position of the trace with respect to the sample to generate a second set of fringe line disturbances;
(3) measuring a second set of interferometer fringe line disturbances against the predetermined measurement scale information to generate a second set of profiles describing the topography of the sample;
(4) interleave the first set of profiles and the second set of profiles to generate a topographic description of the sample having a resolution along the second axis that is less than the spacing;
A data processing unit;
The apparatus characterized by including.   34. The apparatus of claim 33, wherein the relative position of the trace is adjusted by moving the sample stage.   35. The apparatus of claim 33, wherein the relative position of the trace is adjusted by changing the phase of light generated by a light source that is part of the interferometer.   34. The apparatus of claim 33, wherein the relative position of the trace is adjusted by changing the position of a tilted reference mirror that is part of the interferometer.   The apparatus of claim 33, wherein the relative position of the trace is adjusted by using different wavelengths.   The apparatus of claim 33, wherein the data processing unit is designed to store the topography description.   40. The apparatus of claim 38, wherein the data processing unit is designed to store the topographic description in volatile memory.   The apparatus of claim 38, wherein the data processing unit is designed to store the topography description in a non-volatile memory.   34. The apparatus of claim 33, wherein the data processing unit is designed to display the topography description on a screen so that the topography description can be viewed. The data processing unit is
(A) detecting the fringe line from an optical intensity pattern supplied from a detector associated with the interferometer;
(B) the predetermined measurement scale information further comprising a shape of the detected fringe line at its respective position when the fringe line was not disturbed to form the first set of profiles; In contrast, the shape of the detected fringe line at its respective position is compared.
Measuring the first set of interferometer fringe line disturbances by
34. The apparatus of claim 33.   43. The apparatus of claim 42, wherein the predetermined measurement scale information further includes a parameter that converts each range of the disturbance into a measurement of the height of the sample.   43. The apparatus of claim 42, wherein the data processing unit detects the fringe line by detecting a local minimum in the optical intensity pattern. The data processing unit measures disturbances in the fringe line against previously stored measurement scale information to generate a plurality of profiles describing the sample topography disposed on the sample stage;
The measurement scale information is
(1) information identifying a trace along the sample stage to which the fringe line maps;
(2) a parameter that can be used to convert the disturbance into a plurality of topographic profiles of the sample along the trace;
Further including
34. The apparatus of claim 33.   The apparatus of claim 45, wherein the data processing unit further comprises a computer system.   46. The apparatus of claim 45, wherein the detector further comprises an array of optically sensitive elements such that each pixel forms an array of pixels that convert optical intensity into an electrical signal. The computer system includes:
Divide the wavelength of the light source used by the interferometer by 2N, where N is the number of pixels between adjacent fringe lines observed on the detector when the sample is not placed on the sample stage. Calculating the parameters by
Further comprising software in the form of executable instructions for executing a method comprising:
48. The apparatus of claim 47.   47. The apparatus of claim 46, wherein the information identifying traces along the sample stage to which the fringe line maps further comprises a second parameter identifying the spacing between the traces.   The apparatus of claim 46, wherein the information identifying a trace along a sample stage to which the fringe line maps further comprises the position of the fringe line observed on the detector.   51. The apparatus of claim 50, wherein the detector further comprises an array of optically sensitive elements, each array position corresponding to a unique pixel.   52. The apparatus of claim 51, wherein information identifying a trace along a sample stage to which the fringe line maps further comprises a pixel location at which the fringe line is observed on the detector. The computer system includes:
Detecting the fringe line from an optical intensity pattern supplied by the detector;
Further comprising software in the form of executable instructions for executing a method comprising:
47. The apparatus of claim 46.   54. The apparatus of claim 53, wherein detecting the fringe line further comprises finding a local minimum along the optical intensity pattern.   46. The apparatus of claim 45, wherein the data processing unit further comprises a fringe detection unit formed of dedicated hardware for detecting the fringe line from an optical intensity pattern supplied by the detector.

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