JP2012018097A - Pattern measurement method and pattern measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in which a measurement pattern structure sometimes cannot be measured accurately because some part of the structure cannot be measured with sufficient measurement sensitivity when the measurement pattern structure having a thin resist is measured using the scatterometry method.SOLUTION: A right source 201 irradiates a measurement pattern 301 with a light beam. A spectrum measurement part 204 detects an actual spectrum that is a spectrum of a reflected diffraction light of the light beam by means of the measurement pattern 301. A control part 205 performs waveform fitting between the actual spectrum and a theoretical spectrum calculated from a preliminarily prepared model pattern for each of a plurality of wavelength areas within the actual spectrum, and measures a measurement pattern structure.

Description

  The present invention relates to a pattern measuring method and a pattern measuring apparatus for measuring the structure of a measurement pattern formed on a substrate using a scatterometry (light wave scattering measurement) method.

  In recent years, ArF (argon fluoride) resist is often used as a mask material for processing a fine pattern such as a gate wiring in a semiconductor device. However, the ArF resist has a problem that the damage resistance against the electron beam is low. For this reason, secondary electron emission type measurement devices such as CDSEM (Critical Dimension-Scanning Electron Microscope) are used in semiconductor device manufacturing processes to measure the structure (dimensions and shape) of patterns including registry patterns. Then, the incident position of the electron beam in the ArF resist may be reduced, resulting in a measurement error.

  On the other hand, the scatterometry method, which is an optical pattern measurement method that does not cause electron damage to the resist, has attracted attention (see Patent Documents 1 and 2).

  In the scatterometry method, generally, a measurement beam, which is a measurement target pattern, is irradiated with a light beam, and is calculated from an actual spectrum that is a spectrum of reflected diffracted light from the measurement pattern and a model pattern prepared in advance. The structure of the measurement pattern is measured by performing waveform fitting with the theoretical spectrum. Here, waveform fitting refers to comparing the actual spectrum with the theoretical spectrum while changing the variable parameter of the measurement model, and calculating the variable parameter when the actual spectrum matches the theoretical spectrum with the highest accuracy by numerical calculation. It is.

Special table 2004-513509 gazette JP 2006-226994 A

  In recent years, miniaturization of nodes in semiconductor devices has progressed, and accordingly, miniaturization of resist masks has progressed. At this time, the resist may need to be thinned due to the resolution limit of lithography.

  When the structure of a measurement pattern having a thin resist is measured by a scatterometry method, there may be a portion where the structure cannot be measured with sufficient measurement sensitivity, and the structure of the measurement pattern may not be accurately measured.

  As a method for improving the measurement accuracy of the structure of the measurement pattern, there is a method of increasing the number of wavelength divisions that is the number of sampling points of the theoretical spectrum. However, if the number of wavelength divisions is increased, the size of the database of theoretical spectra called a library that is constructed during waveform fitting exceeds the upper limit that can be calculated, and the structure of the measurement pattern cannot be calculated. is there.

  The pattern measurement method according to the present invention is a pattern measurement method for measuring the structure of a measurement pattern formed on a substrate, irradiating the measurement pattern with a light beam, and reflecting reflected diffracted light by the measurement pattern of the light beam. An actual spectrum that is a spectrum is detected, and waveform fitting between the actual spectrum and a theoretical spectrum calculated from a model pattern prepared in advance is performed for each of a plurality of wavelength regions in the actual spectrum, and Measure the structure.

  A pattern measuring apparatus according to the present invention is a pattern measuring apparatus for measuring a structure of a measurement pattern formed on a substrate, and a light source for irradiating the measurement pattern with a light beam, and reflection diffraction of the light beam by the measurement pattern A spectrum measurement unit that detects a real spectrum that is a spectrum of light, and a waveform fitting between the real spectrum and a theoretical spectrum calculated from a model pattern prepared in advance for each of a plurality of wavelength regions in the real spectrum. And a controller that measures the structure of the measurement pattern.

  According to the present invention, since the waveform fitting between the actual spectrum and the theoretical spectrum is performed for each of the plurality of wavelength regions, it is possible to increase the pattern only by increasing the number of wavelength divisions in the wavelength region corresponding to the region having low measurement sensitivity. It is possible to accurately measure the structure of Therefore, it is possible to accurately measure the structure of the pattern while making the size of the library smaller than the upper limit that can be calculated.

It is a figure which shows the structural example of the word line after application | coating of resist, exposure, and image development. It is a figure which shows the structural example of the word line after the dry etching of a lower resist layer. It is a figure which shows the structural example of the word line after the dry etching of a P-SiN layer and a P-SiO layer. It is a figure which shows the structural example of the word line after plasma ashing. It is a figure which shows the structural example of the word line after the dry etching of W / WN / WSi. It is a figure which shows the structural example of the word line after film-forming of a protective film. It is a figure which shows the structural example of the word line after the dry etching of a DOPOS layer. It is a figure which shows the structural example of a pattern measuring apparatus. It is a figure which shows an example of a measurement model. It is a figure for demonstrating an example of the waveform fitting which uses all the wavelength ranges. It is a figure which shows an example of the measurement site | part in the resist layer by a scatterometry method. It is a figure for demonstrating an example of the waveform fitting which used all the wavelength ranges and increased the number of wavelength divisions. It is a figure which shows the example of the waveform fitting which used the short wavelength area | region and increased the number of wavelength divisions. It is a figure for demonstrating an example of the scatterometry method which performs a waveform fitting twice. It is a figure for demonstrating the other example of the scatterometry method which performs a waveform fitting twice.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, components having the same function may be denoted by the same reference numerals and description thereof may be omitted.

  Hereinafter, as a first embodiment of the present invention, a pattern measurement method for measuring the structure of a measurement pattern formed on a substrate using a scatterometry method will be described.

  FIG. 1 is a diagram showing a vertical structure of a measurement pattern whose structure is measured by the pattern measurement method of the present embodiment.

  The measurement pattern shown in FIG. 1 is a word line after the application, exposure and development of a bi-layer resist for etching the hard mask. In FIG. 1, on a Si substrate 1, an SiO layer 2, a DOPOS (doped doped silicon) layer 3, a W / WN / WSi layer 4, a P-SiN layer 5, a P-SiO layer 6, a lower resist layer 7, a resist (PR: Photo Resist) layer 8 is laminated in order from the bottom. The W / WN / WSi layer 4 is a stacked structure of a W layer, a WN layer, and a WSi layer. The resist layer 8 is a thin film made of ArF.

  Here, the word line is formed of the DOPOS layer 3 and the W / WN / WSi layer 4. However, in the following, in addition to the SiO layer 2, the DOPOS layer 3, and the W / WN / WSi layer 4, the word including the P-SiN layer 5, the P-SiO layer 6, the lower resist layer 7 and the resist layer 8 is used as a word. Called a line. The word line shown in FIG. 1 is used as a PolyMetal-Gate electrode.

  The dimensions (film thickness) of each layer are as follows: Si0 layer 2 “6 nm”, DOPOS layer 3 “80 nm”, W / WN / WSi layer 4 “70 nm”, P—SiN layer 5 “140 nm”, and P—SiO layer 6 “80 nm”. ”, Lower resist layer 7“ 300 nm ”, and resist layer 8“ 80 nm ”. In the W / WN / WSi layer 4, the W layer is “55 nm”, the WN layer is “10 nm”, and the WSi layer is “5 nm”.

  The word line forming process will be described below with reference to FIGS.

  First, as shown in FIG. 2, the lower resist layer 7 is processed by dry etching using the resist layer 8 as a mask for the word line shown in FIG. Subsequently, as shown in FIG. 3, the P—SiN layer 5 and the P—SiO layer 6 are processed by dry etching using the lower resist layer 7 as a mask. Further, as shown in FIG. 4, the lower resist layer 7 is removed by plasma ashing and removed. Thereafter, as shown in FIG. 5, the W / WN / WSi layer 4 is processed by a dry etching method using the P—SiN layer 5 and the P—SiO layer 6 as a mask. At this time, the surface layer of the DOPOS layer 3 is etched by about 10 nm. Next, as shown in FIG. 6, a protective film 9 made of SiN is formed on the surface of the word line. The thickness of the protective film 9 is 14 nm. Then, as shown in FIG. 7, the DOPOS layer 3 is processed by a dry etching method.

  In the above word line formation process, the structure measurement of the word line shown in FIG. 1 is important in controlling the final dimension of the word line. If a secondary electron emission type measuring device is used for this structure measurement, the resist layer 8 at the incident site of the electron beam may be reduced, resulting in a measurement error and a word line defect. Therefore, in the following, a scatterometry method that is an optical pattern measurement method that does not cause electron damage to the resist layer 8 will be considered.

  FIG. 8 is a diagram illustrating a configuration example of a pattern measurement apparatus that measures the structure of a measurement pattern using the present scatterometry method. In FIG. 8, the pattern measurement apparatus includes a light source 201, a polarizer 202, an analyzer 203, a spectrum measurement unit 204, and a control unit 205. The spectrum measuring unit 204 includes a spectroscope 204A and a detector array 204B.

  Note that the measurement pattern 301 that is a measurement target of the pattern measurement apparatus is a measurement-dedicated pattern (50 um mouth) having no pattern in each underlying layer on the scribe. However, the measurement pattern 301 is not limited to such a measurement-specific pattern.

  The light source 201 irradiates the measurement pattern 301 with a light beam via the polarizer 202. Note that the entire wavelength region of the light beam is determined in advance. For example, an Xe lamp can be used as the light source 201. In this case, the entire wavelength region of the light beam is about 250 to 750 nm. The light beam spot 302 on the measurement pattern is, for example, 30 μm.

  The catadioptric light of the light beam irradiated onto the measurement pattern 301 by the measurement pattern 301 is incident on the spectroscope 204A via the analyzer 203.

  The spectroscope 204A splits the incident catadioptric light and emits it to the detector array 204B. The detector array 204B detects the actual spectrum that is the spectrum of the catadioptric light by detecting the light intensity of each spectroscopic light from the spectroscope 204A. Thereby, the spectrum measuring unit 204 having the spectroscope 204A and the detector array 204B detects an actual spectrum that is a spectrum of catadioptric light by the measurement pattern 301 of the light beam emitted from the light source 201. The detector array 204B can be constituted by, for example, a CCD (Charge Coupled Device) image sensor.

  The control unit 205 causes the light source 201 to irradiate the measurement pattern 301 with a light beam. Then, the control unit 205 measures the structure of the measurement pattern from the actual spectrum detected by the spectrum measurement unit 204.

  Hereinafter, prior to describing a measurement pattern measurement method by the control unit 205, a conventional scatterometry method will be described in order to facilitate understanding of the present invention.

  In the conventional scatterometry method, as described above, the structure of the measurement pattern is numerically calculated by performing waveform fitting between a real spectrum and a theoretical spectrum calculated from a measurement model prepared in advance. Here, waveform fitting refers to comparing the actual spectrum with the theoretical spectrum while changing the variable parameter of the measurement model, and calculating the variable parameter when the actual spectrum matches the theoretical spectrum with the highest accuracy by numerical calculation. It is.

  When the measurement pattern is the word line shown in FIG. 1, for example, the measurement model shown in FIG. 8 is used as the measurement model. 9, in the measurement model, the Si substrate 101, the SiO layer 102, the DOPOS layer 103, the W / WN / WSi layer 104, the P-SiN layer 105, the P-SiO layer 106, the lower resist layer 107, and the resist layer 108 are below. Are stacked in order.

  In the measurement model shown in FIG. 9, the film thicknesses of the P—SiN layer 105, the P—SiO layer 106, the lower resist layer 107, and the resist layer 108, and the center of the resist layer 108 in the vertical direction indicated by the arrows in the figure. The width of the portion and the side wall angle of the resist layer 108 are variable parameters.

  In the conventional scatterometry method, the waveform fitting between the actual spectrum S1 of the reflected diffracted light from the word line shown in FIG. 1 and the theoretical spectrum S2 calculated from the measurement model shown in FIG. This is performed only once for the region, and a theoretical spectrum (variable parameter) is calculated by numerical calculation as shown in FIG.

  In FIG. 10, the horizontal axis indicates the wavelength, and the vertical axis indicates the light intensity. The solid line shows the real spectrum. Circles indicate the number of wavelength divisions that are sampling points of the theoretical spectrum, and the number of circles is the number of sampling points of the theoretical spectrum. The actual spectrum differs depending on the deflection direction of the light beam applied to the word line. FIG. 10 shows the actual spectrum S1 and the theoretical spectrum S2 for two different deflection directions α and β.

  In the scatterometry method described above, an arbitrary portion of the word line cannot be measured with the same degree of measurement sensitivity. Due to the fact that the resist layer 8 is a thin film, there are portions with high and low measurement sensitivity. Arise. For example, as shown in FIG. 11, the measurement sensitivity with respect to the width L of the middle portion (middle portion) in the vertical direction of the resist layer 8 is high, but the measurement sensitivity with respect to the sidewall angle m of the resist layer 8 is low. For this reason, when the number of wavelength divisions of the theoretical spectrum is about the same as when the resist layer 8 is not a thin film, the error of the side wall angle m becomes large, and the width n and the upper bottom portion (bottom portion) of the lower bottom portion (Bottom portion) ( The width o of the (Top part) cannot be measured with high accuracy.

  As a method for improving the measurement sensitivity with respect to the sidewall angle m, a method of increasing the number of wavelength divisions of the theoretical spectrum in the entire wavelength region of the actual spectrum as shown in FIG. However, in this method, since the base layer (Si substrate 1 to lower resist layer 7) of the resist layer 8 has a laminated structure, there are many variable parameters of the measurement model, and this is called a library that is constructed during waveform fitting. In some cases, the structure of the measurement pattern cannot be calculated because the size of the theoretical spectrum database exceeds the upper limit that can be calculated. For this reason, the number of wavelength divisions cannot simply be increased.

  Therefore, as shown in FIG. 13, a wavelength region other than the resist sensitivity wavelength region which is a wavelength region having sensitivity to the resist layer 8 (for example, the short wavelength region 250 nm to 500 nm) among all the wavelength regions of the light beam ( For example, a method of cutting a long wavelength region (500 nm to 750 nm) and increasing the number of wavelength divisions in the resist sensitivity wavelength region is conceivable.

  In the above method, an increase in library size can be suppressed. However, this method cuts the wavelength region (mainly the long wavelength region) that is sensitive to the thickness of each layer of the underlayer (hereinafter referred to as each underlayer), so the measurement accuracy of the thickness of each underlayer Decreases. For this reason, the measurement error component of the film thickness of each underlying layer affects the measured value of the registry pattern, which causes a decrease in the measurement accuracy of the resist pattern.

  In view of the above, this embodiment proposes a scatterometry method and a pattern measurement apparatus that calculate the structure of a measurement pattern by performing waveform fitting in a plurality of steps.

  In this pattern measurement apparatus, the control unit 205 performs waveform fitting between the actual spectrum detected by the detector array 204B and the theoretical spectrum calculated from the measurement model for each of a plurality of wavelength regions in the actual spectrum, A variable parameter indicating the structure of the measurement pattern 301 is measured. At this time, the control unit 205 performs another waveform fitting using the structure of the part measured by the predetermined waveform fitting among the waveform fittings.

  In each waveform fitting, the control unit 205 measures the structure of each different part in the measurement pattern. For this reason, the wavelength region in each waveform fitting is determined according to the part whose structure is measured by the waveform fitting. More specifically, the wavelength region in each waveform fitting is determined so as to include a wavelength region sensitive to the structure of the part measured by the waveform fitting.

  Furthermore, the number of wavelength divisions of the theoretical spectrum used in each waveform fitting is determined according to the site where the structure is measured by the waveform fitting. More specifically, the lower the measurement sensitivity for the structure of the part measured by waveform fitting, the greater the number of wavelength divisions in the waveform fitting.

  Below, the case where waveform fitting is performed twice continuously as a specific example is demonstrated.

  As shown in FIG. 14, in the first step, the control unit 205 calculates the film thickness of each underlying layer by performing waveform fitting for the entire wavelength region of the actual spectrum. In the second step, the control unit 205 includes a wavelength region (long) other than the resist sensitivity wavelength region (short wavelength region 250 nm to 500 nm) having high measurement sensitivity with respect to the structure of the resist layer 8 out of the entire wavelength region of the actual spectrum. The wavelength region 500 nm to 750 nm) is cut, and the number of wavelength divisions in the resist sensitivity wavelength region in the theoretical spectrum is increased. At this time, in the second step, the variable parameter corresponding to the film thickness of each base layer of the measurement model is fixed to the film thickness value of each base layer calculated in the first step, and then waveform footing is performed. Thereby, all the variable parameters can be calculated, so that the structure of the word line can be measured.

  As described above, according to the present embodiment, since the waveform fitting between the actual spectrum and the theoretical spectrum is performed for each of the plurality of wavelength regions, only the number of wavelength divisions in the wavelength region corresponding to the region having low measurement sensitivity is obtained. It is possible to accurately measure the structure of the pattern simply by increasing the number. Therefore, it is possible to accurately measure the structure of the pattern while making the size of the library smaller than the upper limit that can be calculated.

  As described above, the pattern measurement apparatus according to the present embodiment detects a light source (201) that irradiates a measurement pattern (301) with a light beam and an actual spectrum that is a spectrum of reflected diffracted light by the measurement pattern (301) of the light beam. Waveform fitting between the spectrum measurement unit (204), the actual spectrum, and a theoretical spectrum calculated from a model pattern prepared in advance is performed for each of a plurality of wavelength regions in the actual spectrum, and the structure of the measurement pattern is measured. And a control unit (205).

  In addition, the control unit (205) measures the structures of different parts in the measurement pattern (301) in each waveform fitting.

  In addition, the wavelength region where each waveform fitting is performed is determined according to the part whose structure is measured by the waveform fitting.

  In addition, the number of sampling points of the theoretical spectrum used in each waveform fitting is determined according to the part whose structure is measured by the waveform fitting.

  Further, the control unit (205) performs another waveform fitting using the structure of the part measured by the predetermined waveform fitting among the waveform fittings.

  Next, a second embodiment of the present invention will be described.

  In the present embodiment, another example of the wavelength region in each waveform fitting will be described in the case where the waveform fitting is performed twice in succession.

  As shown in FIG. 15, in the first step, the control unit 205 uses only a wavelength region (specifically, a long wavelength region 500 nm to 750 nm) having high measurement sensitivity with respect to the film thickness of each underlying layer. Fitting is performed to determine the film thickness of each underlying layer. In the second step, similarly to the first embodiment, the control unit 205 performs the waveform fitting using only the resist sensitivity wavelength region, and the structure of the resist layer 8 (film thickness, width of the central portion, side wall) Angle).

  Also in this embodiment, as in the first embodiment, the waveform fitting between the actual spectrum and the theoretical spectrum is performed for each of the plurality of wavelength regions, so that the number of wavelength divisions in the wavelength region corresponding to the region with low measurement sensitivity It becomes possible to measure the structure of the pattern with high accuracy only by increasing the number. Therefore, it is possible to accurately measure the structure of the pattern while making the size of the library smaller than the upper limit that can be calculated.

  In each embodiment described above, the illustrated configuration is merely an example, and the present invention is not limited to the configuration.

DESCRIPTION OF SYMBOLS 1,101 Si substrate 2,102 SiO layer 3,103 DOPOS layer 4,104 W / WN / WSi layer 5,105 P-SiN layer 6,106 P-SiO layer 7,107 Lower resist layer 8,108 Resist layer 201 Light source 202 Polarizer 203 Analyzer 204 Spectrum measurement unit 204A Spectrometer 204B Detector array 205 Control unit 301 Measurement pattern 302 Light beam spot

Claims (10)

A pattern measurement method for measuring a structure of a measurement pattern formed on a substrate,
Irradiating the measurement pattern with a light beam,
Detecting a real spectrum which is a spectrum of reflected diffracted light by the measurement pattern of the light beam;
A pattern measurement method, wherein waveform fitting between the actual spectrum and a theoretical spectrum calculated from a model pattern prepared in advance is performed for each of a plurality of wavelength regions in the actual spectrum, and the structure of the measurement pattern is measured.   The pattern measurement method according to claim 1, wherein in each waveform fitting, a structure of each different part in the measurement pattern is measured.   The pattern measurement method according to claim 2, wherein a wavelength region in each waveform fitting is determined according to a site where the structure is measured by the waveform fitting.   The pattern measurement method according to claim 2 or 3, wherein the number of sampling points of the theoretical spectrum used in each waveform fitting is determined according to a site where the structure is measured by the waveform fitting.   The pattern measurement method according to claim 2, wherein another waveform fitting is performed using a structure of a part measured by a predetermined waveform fitting among the waveform fittings. A pattern measuring device for measuring the structure of a measurement pattern formed on a substrate,
A light source for irradiating the measurement pattern with a light beam;
A spectrum measuring unit that detects a real spectrum that is a spectrum of reflected diffracted light according to the measurement pattern of the light beam;
A controller that performs waveform fitting between the actual spectrum and a theoretical spectrum calculated from a model pattern prepared in advance for each of a plurality of wavelength regions in the actual spectrum, and measures the structure of the measurement pattern; A pattern measuring device.   The pattern measurement apparatus according to claim 6, wherein the control unit measures the structure of each different part in the measurement pattern in each waveform fitting.   The pattern measurement apparatus according to claim 7, wherein a wavelength region in each waveform fitting is determined according to a site where the structure is measured by the waveform fitting.   The pattern measurement apparatus according to claim 7 or 8, wherein the number of sampling points of the theoretical spectrum used in each waveform fitting is determined according to a site where the structure is measured by the waveform fitting.   The pattern measurement apparatus according to claim 7, wherein the control unit performs another waveform fitting using a structure of a part measured by a predetermined waveform fitting among the waveform fittings.

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