CN116429257A - Spectrum measurement system and spectrum type thickness measurement system - Google Patents
Spectrum measurement system and spectrum type thickness measurement system Download PDFInfo
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- G—PHYSICS
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- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/28—Investigating the spectrum
- G01J3/2823—Imaging spectrometer
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
- G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
- G01B11/0675—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating using interferometry
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- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
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Abstract
The invention provides a spectrum measuring system and a spectrum type thickness measuring system, wherein the spectrum measuring system comprises a light source module, a dispersion element, a detector, a displacement table controller and a displacement table; the light source module provides incident light, the incident light irradiates a first area on the sample to generate first interference light, and the first interference light is incident to the detector through the dispersive element to generate a first coherent spectrum; the displacement table controller controls the displacement table to move the sample so that incident light irradiates a second area on the sample to generate second interference light, the second area is partially intersected with the first area, and the second interference light is incident to the detector through the dispersive element to generate a second interference spectrum; the first coherence spectrum is compensated based on the second coherence spectrum. The spectral thickness measurement system comprises a spectral measurement system and obtains the thickness of the first region based on the spectral database and the compensated first coherence spectrum. The invention moves the position of the sample through the displacement table to compensate the missing spectral information on the sample due to the limitation of the spatial resolution of the detector.
Description
Technical Field
The invention relates to the field of optical measurement, in particular to a spectrum measurement system and a spectrum thickness measurement system.
Background
The spectrum measuring system is capable of measuring the spectrum of the resulting sample. When a spectroscopic measurement system is used to measure the thickness of a sample, it is referred to as a spectroscopic thickness measurement system, which is capable of obtaining a thickness associated with the sample from the spectrum, which may be the film thickness on the sample or the absolute thickness of the sample. The existing spectral thickness measurement system of the line light source is shown in fig. 1, and mainly comprises a line light source, a beam splitter, a displacement table (not shown), a CCD camera, a dispersive element (such as a grating or a prism), and a spectral detector (such as a CCD array spectrometer), wherein the measurement method is as follows:
1. the linear light source irradiates the sample after passing through the beam splitter and the objective lens, wherein the sample is a wafer, and the sample can be a wafer without a film layer or a wafer with a film layer, and as shown in fig. 2A, the incident light provided by the linear light source is broad spectrum incident light with the wave band of 193-1700 nm;
2. light reflected on the surface of the wafer and light reflected on the surface of the wafer after entering the wafer form interference light, the interference light returns to the beam splitter and then reaches the dispersion element through the reflection slit, the light reflected by the reflection slit reaches the CCD camera through the plane mirror, and the CCD camera can observe the surface of a sample;
3. The complex light is decomposed into light beams with different reflection angles according to the wavelength by a dispersion element, and the light beams are reflected by a plane mirror to reach a spectrum detector (such as a CCD array spectrometer);
4. the CCD array spectrometer collects R (lambda) -lambda spectrums of sampling points on a collection line of the surface of a wafer, and receives and obtains coherent spectrums of each point on a line light source under the spatial resolution of the CCD array spectrometer under the composite wavelength, as shown in figure 2B, wherein R is reflectivity, lambda is wavelength, a spectrum axis is wavelength of a complex color, a spatial axis is the spatial position of the sampling point, and the reflectivity R (lambda) is positively correlated with the collected light intensity;
5. when the spectrum measuring system is used for measuring the thickness of a sample, the spectrum detected by the CCD array spectrometer is fitted with a spectrum database (theoretical spectrum or known spectrum) to obtain a material dispersion coefficient (n (lambda), k (lambda)), and then a table is searched or a model is matched to obtain the thickness of a sample sampling point, wherein the thickness can be the absolute thickness of a wafer without a film layer or the thickness of the wafer with the film layer. Where n is the refractive index of the medium and k is the extinction coefficient, the theoretical spectrum can be obtained by spectral modeling, and the known spectrum can be obtained by measuring the spectrum of a sample having a known thickness.
The spectrum measurement system has high requirements on the spatial resolution of the detector, and if spectrum information is missed due to limited spatial resolution of the detector, the spatial resolution of the measured spectrum and the thickness of the sample is limited.
Disclosure of Invention
The invention provides a spectrum measuring system and a spectrum thickness measuring system aiming at the technical problems existing in the prior art.
According to a first aspect of the present invention, there is provided a spectral measurement system comprising a light source module, a dispersive element, a detector, a displacement stage controller and a displacement stage for placing a sample, the light source module comprising a line light source or a surface light source;
the light source module provides incident light, a first area on the sample is irradiated by the incident light, the first area is reflected by different interfaces to generate first interference light, and the first interference light is incident to the detector through the dispersion element to generate a first coherent spectrum;
the displacement table controller controls the displacement table to move the sample so that the incident light irradiates a second area on the sample to generate second interference light after being reflected by different interfaces, the second area is partially intersected with the first area, and the second interference light is incident to the detector through the dispersion element to generate a second interference spectrum;
And compensating the first coherent spectrum based on the second coherent spectrum to obtain a compensated first coherent spectrum so as to improve the spatial resolution of the detector.
According to the spectrum measuring system provided by the invention, the position of the sample is moved by the displacement table to compensate the spectrum information on the sample which is missed due to the limitation of the spatial resolution of the detector, so that the spectrum with high spatial resolution of the first area on the sample is measured.
According to a second aspect of the present invention, there is provided a spectral thickness measurement system comprising the spectral measurement system, the spectral measurement system deriving the thickness of the first region based on a spectral database and the compensated first coherence spectrum.
According to the spectral thickness measuring system provided by the invention, the position of the sample is moved by the displacement table to compensate the spectral information on the sample, which is missed due to the limitation of the spatial resolution of the detector, so that the thickness of the first area on the sample with high spatial resolution is measured.
Drawings
FIG. 1 is a schematic diagram of a system architecture of a conventional spectrum measuring system;
FIG. 2A is a schematic diagram of a prior art signal acquisition system for a spectral measurement system;
FIG. 2B is a schematic diagram of a spectrum collected by a conventional spectrum measurement system;
FIG. 3 is a schematic diagram of a spectrum measuring system according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a moving scan of the displacement stage;
FIG. 5A is a schematic diagram of a spectral measurement system including a reflective grating according to one embodiment of the present invention;
FIG. 5B is a schematic diagram of a spectroscopic measurement system comprising a transmissive grating according to one embodiment of the present invention;
FIG. 6 is a schematic diagram showing the comparison of the pixel positions on the surface of the sample after the displacement stage is moved;
FIG. 7 is a schematic diagram of two adjacent light sources of a plurality of light sources;
FIG. 8 is a schematic diagram of a spectrum measuring system according to an embodiment of the present invention;
FIG. 9 is a schematic diagram of a spectrum measuring system according to an embodiment of the present invention;
fig. 10 is a schematic structural diagram of a spectrum measurement system according to an embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention. In addition, the technical features of each embodiment or the single embodiment provided by the invention can be combined with each other at will to form a feasible technical scheme, and the combination is not limited by the sequence of steps and/or the structural composition mode, but is necessarily based on the fact that a person of ordinary skill in the art can realize the combination, and when the technical scheme is contradictory or can not realize, the combination of the technical scheme is not considered to exist and is not within the protection scope of the invention claimed.
Fig. 3 is a schematic diagram of a spectrum measuring system according to an embodiment of the present invention, in which an optical element is not required to be added to the existing spectrum measuring system, but the position of the sample is slightly moved by the displacement stage to compensate the spatial resolution of the detector, so that a spectrum with high spatial resolution can be obtained even if a detector with low spatial resolution is used, but a detector with high spatial resolution can be used, and a spectrum with high spatial resolution can be obtained similarly.
In this embodiment, the high spatial resolution detector refers to a detector whose spatial resolution satisfies the spectral measurement resolution required by the spectral measurement system, that is, a detector whose spatial resolution is less than or equal to the spectral measurement resolution required value is a high spatial resolution detector. A low spatial resolution detector refers to a detector whose spatial resolution does not meet the spectral measurement resolution required by the spectral measurement system, i.e. a detector whose spatial resolution is greater than the spectral measurement resolution requirement is a low spatial resolution detector. For example, if the spectral measurement resolution requirement value is 1um, the detector whose spatial resolution is less than or equal to the value is a high spatial resolution detector, and the detector whose spatial resolution is greater than the value is a low spatial resolution detector.
In some embodiments, a detector with low spatial resolution is used because using a detector with high spatial resolution would result in higher costs. For a detector with low spatial resolution, due to the fact that the spatial resolution of the detector is low and spectrum information is omitted, the spatial resolution of the measured thickness of the sample is low, namely, sampling points are sparse, and the thickness information of enough points on the sample cannot be obtained.
In some embodiments, as shown in fig. 3, the spectral measurement system mainly includes a light source module including a linear light source or a surface light source, a dispersive element (e.g., a grating or a prism), a detector, a displacement stage controller (not shown), and a displacement stage (not shown) for placing a sample.
The light source module provides incident light, a first area on the sample is irradiated by the incident light, and the first area is reflected by different interfaces to generate first interference light, and the first interference light is incident to the detector through the dispersion element to generate a first coherent spectrum; the displacement table controller controls the displacement table to move the sample so that the incident light irradiates a second area (also called as a compensation area) on the sample to generate second interference light after being reflected by different interfaces, the second area is partially intersected with the first area, and the second interference light is incident to the detector through the dispersion element to generate a second interference spectrum; and compensating the first coherent spectrum based on the second coherent spectrum to obtain a compensated first coherent spectrum serving as a spectrum of the first region, so that the spatial resolution of the detector is improved, and the spatial resolution of the first coherent spectrum of the first region can be improved.
In some embodiments, referring to fig. 3, the spectrum measurement system in fig. 3 further includes a beam splitter, and the light source module (for example, including a line light source) irradiates the sample after passing through the beam splitter and the objective lens, where the sample is, for example, a wafer, and may be a wafer without a film layer or a wafer with a film layer. The displacement table moves to an initial acquisition position, or the initial position of the displacement table is used as the initial acquisition position, the initial acquisition position is the position of the displacement table and has a corresponding relation with the position on the sample, the initial acquisition position is set by a user, the displacement table controller controls the displacement table according to the initial acquisition position, the light source module irradiates a first area on the sample through the beam splitter, light reflected on the surface of the sample and light reflected after entering the sample form first interference light, the first interference light returns to the beam splitter and reaches the dispersive element, and the first interference light is polychromatic light (light with a composite wavelength); the chromatic dispersion element decomposes the complex-color light into light beams with different reflection angles according to the wavelength, the light beams reach the detector after being reflected by the plane mirror, and the detector detects a first coherent spectrum of a first area on the sample; the sample is moved by the displacement stage, the detector detects the second coherence spectrum again based on the moved acquisition position, and the first coherence spectrum is compensated based on the second coherence spectrum.
In one embodiment, the second coherence spectrum is used to compensate for the spectrum in the first region that was missed by the first coherence spectrum, and the remainder of the second coherence spectrum is discarded to obtain a compensated first coherence spectrum.
Illustratively, compensating the first coherence spectrum based on the second coherence spectrum comprises:
and traversing each pair of adjacent sampling points on the sample corresponding to the first coherent spectrum, judging whether gaps exist between the adjacent sampling points, responding to the gaps to search the corresponding spectrum in the second coherent spectrum according to the positions of the gaps by the spectrum measurement system, and compensating the searched spectrum to the first coherent spectrum.
In some embodiments, each of the collected coherent spectra may be referred to in fig. 2B, each of which is a three-dimensional spectrum illustrated by the reflectivity axis-the wavelength axis-the spatial axis. Wherein there are a plurality of discrete sampling points on the sample, these sampling points are distributed on a spatial axis as shown in fig. 2B, and the direction of the spatial axis is, for example, the x direction in the present embodiment, and each sampling point corresponds to a schematic diagram of reflectivity and wavelength. For example, if a gap exists between adjacent sampling points in the first coherent spectrum, a sampling point with the same coordinate is found in the second coherent spectrum according to the coordinate of the gap, and if the sampling point is found, the spectrum of the sampling point in the second coherent spectrum is added to the first coherent spectrum, so as to realize spectrum compensation.
In an embodiment, determining whether a gap exists between adjacent sampling points includes:
acquiring adjacent pixels on the detector corresponding to the adjacent sampling points, and according to the pixel interval d between the adjacent pixels d And width w of single pixel d Judging whether a gap exists between the adjacent sampling points, wherein if the pixel interval d d A width w greater than a single pixel d Then it is assumed that there is a gap between adjacent ones of the sampling points and the pixels of the detector are the same size.
Referring to fig. 6, in another embodiment, determining whether a gap exists between adjacent sampling points includes:
obtaining the amplification factor between the pixel of the detector and the sampling point on the sample, obtaining the corresponding area width w of the single sampling point on the sample according to the width and the amplification factor of the single pixel, obtaining the corresponding sampling interval d on the sample according to the pixel interval and the amplification factor, and judging whether a gap exists between the adjacent sampling points according to the comparison of the sampling interval d corresponding to the adjacent sampling points and the area width w, wherein if the sampling interval d is larger than the area width w, the gap exists between the adjacent sampling points, and the sizes of the pixels of the detector are the same.
And acquiring the magnification according to the pixel distribution of the detector and the distribution of sampling points on the sample. Illustratively, a sampling length L is provided on the sample w Which is a preset value, is obtained on the detector and the sampling length L w Corresponding detection length L d The magnification is L w /L d . From this, it can be seen that the area width w=l of a single sampling point on the sample w /L d *w d Sampling interval d=l w /L d *d d 。
It can be appreciated that, referring to fig. 3, the spectrum measurement mechanism is:
1. the linear light source irradiates the sample after passing through the beam splitter and the objective lens;
2. light reflected on the surface of the sample and light reflected after entering the sample form interference light, the interference light returns to the beam splitter and then reaches the dispersion element through the reflection slit, the light reflected by the reflection slit reaches the CCD camera through the plane mirror, and the CCD camera can observe the surface of the sample such as a wafer;
3. the complex light is decomposed into light beams with different reflection angles according to the wavelength by the dispersive element, and the light beams are reflected by the plane mirror to reach the detector;
4. the detector collects R (lambda) -lambda spectrums of each point on a line on the surface of the sample, and receives and obtains coherent spectrums of each point on the sample of the line light source under the spatial resolution of the detector under the composite wavelength, for example, a first coherent spectrum of a first area is obtained, wherein R is reflectivity, and lambda is wavelength;
5. Repeating the steps 2 to 4 after the displacement table moves a trace distance to perform measurement, so as to detect the coherent spectrum again through the detector, for example, obtain a second coherent spectrum of a second area;
6. and compensating the coherent spectrum (such as the first coherent spectrum) measured before the displacement table is moved by using the coherent spectrum (such as the second coherent spectrum) measured after the displacement table is moved according to the position sequence on the sample, so as to obtain a compensated spectrum.
In some embodiments, when the spectrum measurement system is used to measure the thickness of the sample, i.e., the spectrum measurement system is a spectrum thickness measurement system, the compensated spectrum is fitted to a spectrum database to obtain the material dispersion coefficient (n (λ), k (λ)), and a table look-up or model matching is performed to obtain the thickness of the sample, for example, the absolute thickness of the sample or the film thickness of the sample, where the thickness may be the absolute thickness of the wafer without the film layer or the film thickness of the wafer with the film layer. Where n is the refractive index of the medium and k is the extinction coefficient, the spectral database is a theoretical spectrum, which can be obtained by spectral modeling, or a known spectrum, which can be obtained by measuring the spectrum of a sample of known thickness.
Wherein, as an embodiment, the first area and the second area are both smaller than or equal to the maximum irradiation area of the light source module. The spectral measurement system is configured to acquire a region to be measured on a sample, the region to be measured including at least one first region, the displacement stage controller obtains a plurality of sets of positions of a displacement stage, any one of the sets of positions including an acquisition position at which a first coherent spectrum is obtained and a compensation position, the spectral measurement system is responsive to the displacement stage moving to the compensation position to obtain the second coherent spectrum based on the detector, a spectrum of the region to be measured is obtained from each set of the first coherent spectrum and the second coherent spectrum.
In this embodiment, the maximum irradiation area is the maximum area that the light source module can cover on the sample. Taking the line source as an example, the maximum irradiation area is a rectangular area, and since the line width of the line source is generally much smaller than the line length, the rectangular area may also be referred to as a line segment, and the maximum irradiation area is the maximum measured line length of the line source.
In some embodiments, the region under test includes a plurality (i.e., at least two) of first regions. Since the size of the first region is not limited, the region to be measured can be divided into a plurality of first regions, for example, two first regions different in size.
In some embodiments, the acquisition position and the compensation position are both positions of the displacement table and are both set by a user, and the displacement table controller controls the displacement table according to the acquisition position and the compensation position. The acquisition position is related to a scanning path of the displacement stage set by the user, in particular the acquisition position corresponds to a first region of the sample, which comprises a plurality of discrete points on the scanning path, which are sampling points, because of the limited spatial resolution of the detector. In an embodiment, the scanning path of the displacement stage may be a curved scanning path or a linear scanning path, as shown in fig. 4, and the scanning path is, for example, a serpentine scanning path, a spiral scanning path or a linear scanning path.
In some embodiments, as shown in fig. 3 and 4, when the displacement stage controller controls the displacement stage to move along a serpentine scanning path, the displacement stage controller completes a linear scan along the x-direction, then moves a distance along the y-direction, then completes another linear scan along the x-direction, and so on; as shown in fig. 4, when the displacement stage controller controls the displacement stage to move along the linear scanning path, the linear scanning is completed along the x direction, then the position of the displacement stage is changed, then another linear scanning along the x direction is completed, and so on.
In some embodiments, the displacement stage controller controls the displacement stage to move in a serpentine scan path, the displacement stage controller controls the displacement stage to move in the x-direction, and the spectral measurement system performs spectral measurements in the x-direction to achieve spectral compensation for the detector (also applicable to later compensation for beam spacing) without performing spectral measurements in the y-direction.
Wherein each set of positions includes a collection position corresponding to a first region of the sample and a compensation position corresponding to a second region of the sample. The spectrum of the corresponding first region can be obtained from a set of the first coherence spectrum and the second coherence spectrum.
The region to be measured comprises two first regions adjacent in the x direction, the spectrum of one first region is obtained according to one set of the first coherent spectrum and the second coherent spectrum, the spectrum of the other first region is obtained according to the other set of the first coherent spectrum and the second coherent spectrum, and the spectrum of the region to be measured is obtained according to the spectrums of the two first regions.
In this embodiment, the description of the execution of C by a in response to B means that a executes C immediately after B execution is completed or that a executes C after a period of time, where a is an execution body, B is an action, C is another action, and the term "execute" may be omitted.
The type of the detector is not limited, and the spectral information may be detected, for example, a spectral detector, specifically, a matrix spectrometer, a linear spectrometer, or the like. The beam shape of the light source module is not limited, and the light source module may include a linear light source or a surface light source. The type of objective lens is not limited, and both large FOV and small FOV may be used.
In some embodiments, the incident light provided by the light source module is not limited to the incident light, including but not limited to normal incidence and oblique incidence, as shown in fig. 3, which illustrates a normal incidence type spectrum measurement system, as shown in fig. 5A and 5B, which illustrate oblique incidence type spectrum measurement systems, respectively. The grating in fig. 5A is a reflective grating, and the grating in fig. 5B is a transmissive grating.
In an embodiment, referring to fig. 5A and 5B, the measurement method of oblique incidence of the linear light source is as follows: the linear light source is obliquely incident and focused on the wafer through a columnar mirror (not labeled) to generate interference light, the interference light is converged into a quasi-linear light beam through an objective lens (not labeled, such as a columnar mirror), and then is decomposed into monochromatic light with different angles due to different wavelengths through a transmission grating or a reflection grating, and then is reflected through a plane mirror to reach a detector, so that a three-dimensional spectrum formed by a reflectivity axis-a wavelength axis-a space axis (position on a sample) is formed. In one embodiment, the illumination device includes a CCD camera and illumination (i.e., illumination light source), where the illuminated beam is incident perpendicularly to the wafer, and the CCD camera captures an image of the surface of the wafer, which can be used to see if the wafer surface is defective or to see if the line source is in focus.
As an embodiment, the displacement table controller moves the displacement table based on a preset number of movements and a preset movement step length, so as to obtain one or more second areas, where the number of movements is the same as the number of second areas.
In some embodiments, after the detector acquires the first coherent spectrum corresponding to the first area on the sample irradiated by the light source module, the displacement table controller controls the displacement table to move the position of the sample to acquire one or more second areas on the sample. And acquiring a second area when the displacement table controller moves once, so that the number of the movement times is the same as the number of the second areas. For each second region, the detector again detects a second correlation spectrum; the second coherent spectrum detected by the detector one or more times is compensated for the first coherent spectrum to obtain a compensated first coherent spectrum.
In an embodiment, when a plurality of different second regions intersecting the first regions partially are obtained, the first coherent spectrum is compensated based on a plurality of second coherent spectrums corresponding to the plurality of second regions, so as to further improve the spatial resolution of the detector.
It can be understood that when detecting spectral information on a sample, whether it is a low spatial resolution or a high spatial resolution detector, because the spatial resolution of the detector is limited, there is a space between two pixels of the detector corresponding to two sampling points on a wafer, and there is often a situation that omission results in spectral information, which further affects the spatial resolution of the wafer spectral measurement. Therefore, the embodiment of the invention changes the relative position between the light source module and the sample by moving the displacement table, thereby compensating the measurement spectrum and improving the spatial resolution of the detector.
Taking the light source module including a line light source as an example, fig. 6 shows that the position on the wafer corresponding to the spectral information acquired by the detector for the first time is a row of sampling points on the wafer, where a row of sampling points are distributed along the x direction to form a first area, and after the displacement table moves by Δx along the x direction, the detector acquires the position on the wafer corresponding to the spectral information again, that is, another row of sampling points on the wafer, where another row of sampling points are distributed along the x direction to form a second area. Fig. 6 illustrates the transverse relative positions of the two rows of sampling points on the wafer before and after the displacement stage moves, and it should be noted that, for convenience in viewing, the shapes of the sampling points on the wafer corresponding to the two measurement pixels of the detector are simplified to be square, and the positions on the wafer corresponding to the two measurement pixels of the detector are longitudinally separated to only display the transverse relative positions.
The moving mode of the displacement table can be equal-spacing measurement, namely the moving step sizes of the displacement table (single time) are equal, or unequal-spacing measurement, namely the moving step sizes of each moving of the displacement table can be unequal. Illustratively, equidistant measurements are typically used when it is desired to measure the spectrum of all locations on the sample. Non-equidistant measurements are typically used when only a certain area of the spectrum on the sample needs to be of great interest.
In some embodiments, the number of movements is one or more, the displacement stage controller controls the displacement stage to move in a straight scan path or a serpentine scan path, the movement step is nΔx, and:
w is the width of the area on the sample corresponding to the single pixel of the detector, and n is a positive integer. The width is in the distribution direction of the sampling points on the sample corresponding to the pixels of the detector.
The displacement stage controller controls the displacement stage to move along a linear scanning path or a serpentine scanning path, and the optimal number of movements of the displacement stage is as follows
Get->
Is recommended to move by a step of +.>
The actual moving step length and the number of times are not limited, and d is the sampling interval of two adjacent pixels of the detector corresponding to two sampling points on the sample. In one embodiment, the setting Δx is not suggested <1/2w, because the detector is over-sampled at this time, too many measurements will take unnecessary measurement time and too few measurements will not achieve the required spectral measurement accuracy.
In an embodiment, the light source module includes a light source controller and a plurality of light sources, the plurality of light sources are arranged along a first direction, a beam interval exists between at least one pair of adjacent light sources along the first direction, so that a beam interval region exists on a sample, the light source controller controls on or off of each light source, the displacement table controller controls the displacement table to move along the first direction according to a linear scanning path or a serpentine scanning path, so as to obtain a third interference spectrum (in the same way, the first region and a third region on the sample corresponding to the third interference spectrum intersect) for compensating the spectrum of the beam interval region based on the detector and the currently operated light source, and the first coherent spectrum is compensated based on the second coherent spectrum and the third interference spectrum, so as to obtain a spectrum of the first region.
In this embodiment, the first direction is a straight direction, and the word "arrangement" may be a row or a column. Illustratively, the plurality of light sources form a row along a first direction, as shown in fig. 7 and 8, the plurality of light sources form a row along an x-direction, the first direction being the x-direction; in addition, the plurality of light sources may be formed in a row, i.e., a column, along the z-direction, with the first direction being the z-direction. It should be noted that the above description describes a plurality of light sources arranged in the first direction and describes an example of forming one row, but does not exclude a case where all light sources are formed in a plurality of rows, because the number of the plurality of light sources in one row is smaller than or equal to the number of all light sources, for example, the number of all light sources is 8, 4 light sources are formed in one row in the x-direction, and 4 light sources are formed in another row in the x-direction.
It can be understood that, for the spectrum measuring system in fig. 3, using a plurality of individually switchable light sources as the incident light source can increase the single maximum irradiation area, for example, the line light source can increase the single maximum measuring line length, so as to further improve the measuring efficiency, as shown in fig. 7. Because of the beam interval between the adjacent line light sources, when the spectrum information is detected by the detector, a beam interval area is present on the sample, and the beam interval area is an undetectable area. Therefore, the embodiment of the invention provides a spectrum measuring system based on a plurality of light sources, wherein the plurality of light sources form a row, the number of the light sources is the same as that of all the light sources, and the description is given by taking a plurality of linear light sources as an example, as shown in fig. 8.
In one embodiment, there is a physical separation between two adjacent light sources; in an embodiment the housings of the two adjacent light sources are in contact, i.e. the possibility of contact of the two adjacent light sources is not precluded, since the light sources typically have housings, even if there is a case where the housings of the two adjacent light sources are in contact, there is a beam separation between the two adjacent light sources due to the wall thickness of the housing.
In fig. 7 and 8, there is a beam interval between the line light sources, so that there is omission in a single detection process of the detector, and a beam interval region on the sample cannot be detected, and a displacement table moving mode can be used to compensate the spatial resolution of the detector and simultaneously compensate the spectrum corresponding to the beam interval. L is the total length of a single line light source, D is the beam spacing of adjacent line light sources, and square is the simplified shape of the sampling point on the wafer corresponding to the pixel of the detector.
When the light spectrum corresponding to the light beam interval of the compensation line light source is realized, the light source controller controls all the light sources to work so as to obtain a first coherent light spectrum based on the detector, the light source controller responds to the detector to obtain the first coherent light spectrum so as to turn off part of the light source, and the displacement table controller responds to the light source controller to turn off part of the light source so as to control the displacement table to move and obtain the third coherent light spectrum based on the detector.
Referring to fig. 8, the spectroscopic measurement system includes a plurality of individually switchable rows of light sources, beam splitters, dispersive elements, detectors (e.g., CCD array spectrometers), and a displacement stage on which a sample is placed.
In some embodiments, the displacement stage is moved to the initial collection position, or the initial position of the displacement stage is taken as the initial collection position, all light sources in a row are turned on, all light sources irradiate the sample through the beam splitter, and light reflected on the surface of the sample and light reflected after entering the sample form interference light, and the interference light returns to the beam splitter and reaches the dispersive element; the dispersion element decomposes interference light into light beams with different reflection angles according to wavelength, and the light beams are reflected by the reflecting mirror to reach the detector, and the detector detects a first coherent spectrum; and turning off part of the light sources in all the light sources, moving through the displacement table, and detecting the third coherent spectrum again by the detector based on the moved position so as to be used for compensating the spectrum of the beam interval region on the sample corresponding to the beam interval.
Wherein the light source controller is responsive to the detector to obtain a first coherence spectrum to turn off one edge light source of the plurality of light sources. In an embodiment, the dimensions of the light sources are the same, the displacement stage is moved once to obtain the third coherence spectrum when the beam interval D is smaller than or equal to the length L of a single light source in the beam interval direction, and the displacement stage is moved multiple times to obtain the third coherence spectrum after each movement when the beam interval D is larger than the length L.
It will be appreciated that a third correlation spectrum is acquired by the detector by controlling the displacement stage to move the sample and to switch off some of all of the light sources. The third coherence spectrum is acquired by turning off one of the edge light sources among all the light sources, for example, turning off the first light source or the last light source sequentially arranged in the first direction, and determining the number of movements of the displacement stage according to the magnitude relation of the beam interval D and the length L of the single light source in the beam interval direction, for example, every time the displacement stage is moved.
On the basis of obtaining a third interference spectrum, the light source controller responds to the detector to obtain the third interference spectrum so as to select any one of the light sources to work, and the displacement table controller responds to the light source controller to select any one of the light sources to work so as to control the displacement table to move and obtain the second interference spectrum based on the detector.
It can be appreciated that the third coherent spectrum is used to compensate the spectrum of the missing light beam interval region in the first coherent spectrum, and the first coherent spectrum is also used to compensate the second coherent spectrum, when the spectrum measurement system is a spectrum type thickness measurement system, the thickness of the sample in the first region is obtained based on the first coherent spectrum and the spectrum database after the third coherent spectrum and the second coherent spectrum are compensated.
Illustratively, the displacement stage is moved to compensate for beam gaps between adjacent light sources, and then moved to compensate for the spatial resolution of the detector.
The specific measurement process is as follows: first, all line light sources in a row are turned on, and the detector detects the first coherent spectrum, and at this time, the first coherent spectrum detected by the detector is missed because of the beam interval between the adjacent light sources. Thus, turning off one of the light sources later, preferably turning off the first light source or the last light source, and moving the displacement stage in a first direction (e.g., x-direction) and in a direction of the turned-off light source, such as the two linear light sources in fig. 8, when the first light source on the left is turned off, the displacement stage moves to the left; when the second light source on the right is turned off, the displacement table moves to the right, and the detector detects again to obtain a third coherent spectrum, wherein the third coherent spectrum can compensate the spectrum of the first coherent spectrum, which is missing due to the light beam interval.
The above-mentioned movements of the displacement stage only compensate for the spectrum of the beam-spaced region corresponding to the beam spacing, and may further compensate for the spatial resolution of the detector. In an embodiment, when the displacement stage is moved to compensate the spatial resolution of the detector, only a single linear light source is turned on, and any one of all the light sources can be used, and the foregoing embodiment has described the step size and the number of movements of the displacement stage, and also described the measurement mechanism when compensating the spatial resolution of the detector, and will not be repeated here.
In an embodiment, the third coherence spectrum is used to compensate for the spectrum in the first region that was missed by the measurement of the first coherence spectrum, and the remainder of the third coherence spectrum is discarded to achieve the spectral compensation.
As can be seen from the foregoing analysis, when a plurality of light sources are provided, there is a beam separation between at least one pair of adjacent light sources, resulting in a beam separation region on the sample.
Illustratively, compensating the first coherence spectrum based on the third coherence spectrum comprises:
and the spectrum measuring system searches the corresponding spectrum in the third coherent spectrum according to the position of the beam interval region and compensates the searched spectrum to the first coherent spectrum.
The spatial distribution and the size of the light sources are known information, so that the position of the beam interval between the adjacent light sources can be obtained, and the position of the beam interval region on the sample corresponding to the beam interval can be known by combining the position conversion relation between the light sources and the corresponding irradiation region on the sample.
In one embodiment, the detector performs three detections, and the third coherent spectrum compensates for the missing spectrum of the first coherent spectrum due to the beam spacing, and the second coherent spectrum compensates for the spatial resolution of the first coherent spectrum. When the spectrum measuring system is a spectrum type thickness measuring system, fitting is carried out according to the compensated first coherent spectrum and a spectrum database to obtain a material dispersion coefficient (n (lambda), k (lambda)), and then table lookup or model matching is carried out to obtain the thickness of the sample.
Illustratively, based on the spectral measurement system of fig. 8, the measurement is described as follows:
1. the multi-probe line light source irradiates the sample after passing through the beam splitter and the objective lens;
2. light reflected on the surface of the sample and light reflected after entering the sample form interference light, the interference light returns to the beam splitter and then reaches the dispersion element through the reflection slit, the light reflected by the reflection slit reaches the CCD camera through the plane mirror, and the CCD camera can observe the surface of the sample such as a wafer;
3. The dispersive element decomposes the light with the composite wavelength into light beams with different reflection angles, and the light beams are reflected to the detector by the plane mirror;
4. the method comprises the steps that a detector collects R (lambda) -lambda spectrums of all points on a measuring line, and receives and obtains coherent spectrums of all points on the measuring line under the composite wavelength under the spatial resolution of the detector, so that a first coherent spectrum is obtained;
5. and (3) repeating the steps 1-4 after the displacement table moves a distance, and completing the measurement of the spectrum of the compensating beam interval region so as to obtain a third coherent spectrum.
6. Using a single linear light source, the displacement table returns to the measuring starting point in the step 1, and moves for a distance Deltax along the direction of the linear light source (namely, the direction of the spatial resolution to be compensated, if the displacement table is a surface light source, and the direction of the spatial resolution to be compensated is the same), and then the steps 1-4 are repeated to obtain a second coherent spectrum for compensating the spatial resolution of the detector. n is a positive integer, where the purpose of the moving distance is to make the spot compensate for the beam interval D, for example, first move by L distance, if the beam interval D cannot be compensated by moving by L distance once, then move by L distance again until the compensation is possible;
7. and compensating the first coherent spectrum by using the second coherent spectrum and the third coherent spectrum to obtain a compensated first coherent spectrum.
In some embodiments, when the spectral measurement system is used to measure the thickness of the sample, i.e., the spectral measurement system is a spectral thickness measurement system, the compensated first coherent spectrum is fitted to a spectral database to obtain the material dispersion coefficient (n (λ), k (λ)), and then a look-up table or model matching is performed to obtain the thickness of the sample.
In this embodiment, since the total length of the multiple line light sources is larger, optical components with dimensions adapted to the multiple light sources, such as a longer beam splitter and a dispersive element, are used. The displacement table moves to compensate the spatial resolution of the detector and the light beam interval of the light source, so that the spectrum with high spatial resolution can be measured.
As an embodiment, the detector comprises a spectral detector; or the detector comprises a light intensity detector and the spectrum measuring system further comprises a wavelength controller and a wavelength modulator, wherein the wavelength controller is configured to change the output wavelength of the wavelength modulator, and the light intensity detector detects the light intensities corresponding to different output wavelengths so as to form a spectrum with discrete wavelengths according to the output wavelength and the light intensities.
Wherein, as shown in fig. 9 and 10, the spectrum measuring system with the detector being the light intensity detector further comprises a wavelength controller and a wavelength modulator for modulating the output wavelength if the detector is the light intensity detector. The spectrum measuring method is similar to the spectrum measuring method when the detector is a spectrum detector, and specifically comprises the following steps:
The displacement table controller controls the displacement table to move to an initial acquisition position, or the initial position of the displacement table is used as the initial acquisition position, the light source module irradiates a sample through the beam splitter, light reflected on the surface of the sample and light reflected after entering the sample form interference light, the interference light returns to the beam splitter and reaches the wavelength modulator, the output wavelength of the wavelength modulator is changed through the wavelength controller, so that the wavelength modulator outputs quasi-monochromatic light with different wavelengths (namely, near monochromatic light) to reach the dispersion element, monochromatic light with each wavelength is formed to reach the light intensity detector, and the light intensity detector detects a first coherent spectrum; and moving the sample position through the displacement table, and detecting the second coherent spectrum again by the detector based on the moved acquisition position, wherein the second coherent spectrum compensates the first coherent spectrum so as to improve the spatial resolution of the light intensity detector. For other contents, please refer to the foregoing embodiments, and the description is omitted herein.
It will be appreciated that referring to fig. 9, the replacement of the spectral detector with an optical intensity detector in the displacement stage movement of fig. 3 further reduces costs, with the advantage that a particular discrete wavelength can be used to simplify subsequent processing, i.e. to view only characteristic spectral lines, as in fig. 9, wavelength modulators including but not limited to monochromators, filters, multi-filters, spatial light modulators, etc. The position of the wavelength modulator is not limited, and can be any position from the light source module to the detector; the slit behind the dispersive element is optional, and the placement position can be increased or decreased and adjusted as required, and the wavelength modulator in fig. 9 is located in front of the dispersive element, and the wavelength modulator in fig. 10 is located behind the light source module.
By way of example, taking fig. 9 as an example, the measurement is described as follows:
1. the linear light source irradiates the sample after passing through the beam splitter and the objective lens;
2. the interference light reaches the wavelength modulator through the beam splitter and the reflection slit and passes through the linear light under a certain wavelength;
3. the linear light generates monochromatic light after passing through the dispersive element, and the monochromatic light passes through the slit, is further filtered by the wavelength and reaches the light intensity detector after being reflected by the plane mirror;
4. the detector collects R (lambda) -lambda spectra of each point on the line, and receives and obtains coherent spectra of each point on the measuring line under the composite wavelength under the spatial resolution of the detector.
Wherein the multi-wavelength light passes through the wavelength modulator and then only passes through approximately a single wavelength of light. The light wavelength range is further reduced after passing through the rotatable dispersion element and the slit to obtain single-wavelength light, namely single-color light, and the single-wavelength light is reflected to the detection surface of the light intensity detector through the rotatable plane mirror to obtain the light intensity distribution of the light source with the single wavelength carrying the information of the sample (such as a wafer). At this time, the hardware and the displacement table are fixed, and the wavelength which can be passed by the wavelength modulator is adjusted so that the other wavelength reaches the rotatable dispersion element and the slit, and finally reaches the detector to finish the measurement under the wavelength; and repeatedly adjusting the wavelength to obtain the coherent spectrum of the composite wavelength at the measuring position.
5. Repeating the steps to measure after the displacement table moves a trace distance, wherein the moving mode of the displacement table is consistent with the moving mode of the spectrum detector;
6. the coherent spectrum (such as the second coherent spectrum) measured after the displacement stage is moved is compensated for the spectrum (such as the first coherent spectrum) measured before the displacement stage is moved according to the position sequence on the sample, and the compensated spectrum is obtained.
In some embodiments, when the spectral measurement system is used to measure the thickness of a sample, i.e., the spectral measurement system is a spectral thickness measurement system, the compensated spectrum is fitted to a spectral database to obtain the material dispersion coefficient (n (λ), k (λ)), and then a look-up table or model matching is performed to obtain the thickness of the sample.
The type of the detector is not limited, and the light intensity information of the light can be detected. When the detection surface of the detector is in a dot shape, the plane mirror is rotated along the length direction of the linear light source to enable each point on the linear light source under the wavelength to sequentially pass through the detector, so that the dot-shaped detector can still obtain the light intensity information of any point on the line.
The spectrum measuring system provided by the embodiment of the invention has the following advantages:
(1) The spatial resolution of the detector is compensated by micro-movement of the displacement table without adding additional optical elements;
(2) When a plurality of light sources form a row, the displacement table moves to compensate the beam interval area on the sample corresponding to the beam interval between the light sources;
(3) Not only for the spectral detector but also for the intensity detector, when using the intensity detector, a wavelength controller and a wavelength modulator are added, optionally a slit is also added.
The embodiment of the invention also provides a spectrum thickness measuring system comprising the spectrum measuring system, so as to obtain the thickness related to the sample based on the spectrum measurement of the sample, wherein the thickness can be the film thickness on the sample or the absolute thickness of the sample. As described above, when the spectrum measuring system is used for measuring the thickness of the sample, the spectrum measuring system is a spectrum type thickness measuring system, and the thickness of the first region is obtained based on the spectrum database and the compensated first coherence spectrum. Wherein the spectrum database may be a theoretical spectrum or a known spectrum.
In this example, the word "absolute thickness" is used to distinguish from the word "film thickness", for samples without a film layer, the absolute thickness of the sample being the thickness of the sample; for a sample with a film layer, the sample comprises a substrate and the film layer, the absolute thickness of the sample can be the thickness of the substrate, or the sum of the thickness of the substrate and the thickness of the film layer, and the spectral thickness measurement system can measure and obtain the film thickness of the film layer and/or the thickness of the substrate.
Illustratively, when a spectral thickness measurement system is used to measure the film thickness of a sample, such as the spectral reflectance type film thickness meter shown in fig. 3, light reflected by the upper surface of the film layer from incident light and light reflected by the lower surface of the film layer from incident light form interference light.
Illustratively, a spectroscopic thickness measurement system is used to measure the absolute thickness of the sample. Taking a wafer as an example, it is known by those skilled in the art that a silicon wafer has better transparency to light in the wavelength band of about 1000nm to about 6000nm, so that the absolute thickness of the silicon wafer can be measured by selecting a light source in a suitable wavelength band. In one embodiment, the light source is a light source with near infrared band of 780-2526 nm; in one embodiment, the light source is a light source in the near infrared band of 1000 to 1700 nm.
Illustratively, when a spectroscopic thickness measurement system is used to measure the absolute thickness of a sample, the spectroscopic thickness measurement system is, for example, a spectroscopic reflectance absolute thickness gauge as shown in FIG. 3.
Taking a wafer without a film layer as an example, light reflected by the upper surface of the wafer by incident light and light reflected by the lower surface of the wafer after the incident light enters the wafer form interference light, and the absolute thickness of the wafer can be obtained by processing the interference light.
Taking a wafer with a film layer as an example, light reflected by the upper surface of the film layer by incident light and light reflected by the lower surface of the film layer after the incident light enters the film layer form interference, light reflected by the upper surface of the substrate by the incident light and light reflected by the lower surface of the substrate after the incident light enters the substrate also form interference, and a detector collects the interference light, wherein the film thickness of the film layer and the absolute thickness of the substrate can be obtained by processing the interference light, and the wafer comprises the substrate and the film layer positioned on the substrate.
Because the spectral thickness measurement system includes the spectral measurement system of the foregoing embodiment, the spectral thickness measurement system obtains a high spatial resolution thickness of the first region on the sample when the spectral measurement system obtains a high spatial resolution spectrum of the first region on the sample.
In the foregoing embodiments, the descriptions of the embodiments are focused on, and for those portions of one embodiment that are not described in detail, reference may be made to the related descriptions of other embodiments.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (11)
1. A spectrum measurement system, comprising a light source module, a dispersion element, a detector, a displacement table controller and a displacement table for placing a sample, wherein the light source module comprises a linear light source or a surface light source;
the light source module provides incident light, a first area on the sample is irradiated by the incident light, the first area is reflected by different interfaces to generate first interference light, and the first interference light is incident to the detector through the dispersion element to generate a first coherent spectrum;
the displacement table controller controls the displacement table to move the sample so that the incident light irradiates a second area on the sample to generate second interference light after being reflected by different interfaces, the second area is partially intersected with the first area, and the second interference light is incident to the detector through the dispersion element to generate a second interference spectrum;
and compensating the first coherent spectrum based on the second coherent spectrum to obtain a compensated first coherent spectrum so as to improve the spatial resolution of the detector.
2. The spectroscopic measurement system of claim 1, wherein the first and second regions are each less than or equal to a maximum illumination area of the light source module.
3. The spectroscopic measurement system of claim 1 wherein the displacement stage controller moves the displacement stage based on a preset number of movements and movement steps to obtain one or more of the second regions, the number of movements being the same as the number of second regions.
4. A spectral measurement system according to claim 3, wherein the displacement stage controller controls the displacement stage to move in a linear scan path or a serpentine scan path, the movement step being nΔx, and:
w is the width of the area on the sample corresponding to the single pixel of the detector, and n is a positive integer.
5. The spectral measurement system of claim 1, wherein the light source module comprises a light source controller and a plurality of light sources, the plurality of light sources being arranged along a first direction, and a beam spacing exists between at least one pair of adjacent light sources such that a beam spacing region exists on the sample, the light source controller controlling the on or off of each light source, the displacement stage controller controlling the displacement stage to move along the first direction in a linear scan path or a serpentine scan path to obtain a third coherent spectrum based on the detector and the currently operating light source for compensating the spectrum of the beam spacing region, and compensating the first coherent spectrum based on the second coherent spectrum and the third coherent spectrum to obtain the spectrum of the first region.
6. The spectral measurement system of claim 5, wherein the light source controller controls operation of all light sources to obtain a first coherent spectrum based on the detector, wherein the light source controller is responsive to the detector to obtain the first coherent spectrum to turn off a portion of the light sources, wherein the displacement stage controller is responsive to the light source controller to turn off a portion of the light sources to control the displacement stage movement and to obtain the third coherent spectrum based on the detector.
7. The spectral measurement system of claim 6, wherein the light source controller is responsive to the detector to obtain a third coherent spectrum to select any of the light source operations, and wherein the displacement stage controller is responsive to the light source controller to select any of the light source operations to control the displacement stage movement and to obtain the second coherent spectrum based on the detector; the light source controller is responsive to the detector to obtain a first coherent spectrum to turn off one edge light source of the plurality of light sources; the size of each light source is the same, when the beam interval D is smaller than or equal to the length L of a single light source along the beam interval direction, the displacement table moves once to obtain the third coherence spectrum, and when the beam interval D is larger than the length L, the displacement table moves multiple times to obtain the third coherence spectrum after each movement.
8. The spectral measurement system of claim 5, wherein compensating the first coherence spectrum based on the third coherence spectrum comprises:
and the spectrum measuring system searches the corresponding spectrum in the third coherent spectrum according to the position of the beam interval region and compensates the searched spectrum to the first coherent spectrum.
9. The spectral measurement system of any of claims 1-8, wherein compensating for a first coherence spectrum based on the second coherence spectrum comprises:
and traversing each pair of adjacent sampling points on the sample corresponding to the first coherent spectrum, judging whether gaps exist between the adjacent sampling points, responding to the gaps to search the corresponding spectrum in the second coherent spectrum according to the positions of the gaps by the spectrum measurement system, and compensating the searched spectrum to the first coherent spectrum.
10. The spectroscopic measurement system of claim 9, wherein determining whether a gap exists between adjacent ones of the sampling points comprises:
acquiring adjacent pixels on the detector corresponding to the adjacent sampling points, and judging whether gaps exist between the adjacent sampling points according to comparison of pixel intervals between the adjacent pixels and the width of a single pixel, wherein if the pixel intervals are larger than the width of the single pixel, the gaps exist between the adjacent sampling points, and the sizes of the pixels of the detector are the same;
Or acquiring the amplification factor between the pixel of the detector and the sampling point on the sample, acquiring the corresponding area width of the single sampling point on the sample according to the width and the amplification factor of the single pixel, acquiring the corresponding sampling interval on the sample according to the pixel interval and the amplification factor, and judging whether a gap exists between the adjacent sampling points according to the comparison of the sampling interval corresponding to the adjacent sampling points and the area width, wherein if the sampling interval is larger than the area width, the gap exists between the adjacent sampling points, and the sizes of the pixels of the detector are the same.
11. A spectral thickness measurement system comprising a spectral measurement system according to any of claims 1-10, wherein the spectral measurement system derives the thickness of the first region based on a spectral database and the compensated first coherence spectrum.
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