Semiconductor wafer evaluation method and semiconductor wafer production method

Abstract

Provided is a semiconductor wafer evaluation method comprising: determining a film thickness range in which the intensity of scattered light obtained by a defect inspection device is equal to or greater than a prescribed intensity; forming, on a surface of an semiconductor wafer being evaluated, a film which expands a defect present on said surface such that the film has a thickness in the film thickness range; inspecting the surface of the film via a defect inspection device to perform LPD measurement; identifying the position of an observation target LPD on the basis of coordinate data obtained by the LPD measurement, and determining whether the observation target LPD is a film protrusion, which is a hump of the film, by observing this position via a scanning electron microscope; and performing an evaluation regarding the film protrusion.

Description

Semiconductor wafer evaluation method and semiconductor wafer manufacturing method CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2024-055694, filed March 29, 2024, the entire disclosure of which is expressly incorporated herein by reference.

[0002] The present invention relates to a semiconductor wafer evaluation method and a semiconductor wafer manufacturing method.

[0003] As a method for evaluating semiconductor wafers, a method based on light point defects (LPDs) detected by a defect inspection device is widely used (see, for example, Patent Documents 1 and 2 (the entire disclosures of which are specifically incorporated herein by reference)). Patent Document 1: Japanese Patent No. 6414801 Patent Document 2: Japanese Patent Laid-Open Publication No. 2023-061116

[0004] Defects may exist on the surface of a semiconductor wafer. These defects may include minute defects that are below the detection limit size of a defect inspection device. If it becomes possible to evaluate semiconductor wafers that may contain such minute defects, it will be possible to manufacture high-quality semiconductor wafers with fewer minute defects, for example, by changing the manufacturing conditions for the semiconductor wafers based on the evaluation results so as to suppress the occurrence of minute defects.

[0005] An object of one aspect of the present invention is to provide a new evaluation method capable of evaluating defects present on the surface of a semiconductor wafer.

[0006] For example, as described in Japanese Patent No. 6414801 (Patent Document 1) and Japanese Patent Laid-Open Publication No. 2023-061116 (Patent Document 2), in order to evaluate semiconductor wafers, a coating is formed on the surface of the semiconductor wafer to be evaluated, thereby enlarging defects present on the surface. By observing the coating surface using a defect inspection device after forming such a coating, the LPD detection size can be increased compared to before the coating was formed. This is preferable for evaluating semiconductor wafers that may contain minute defects below the detection limit of the defect inspection device. Therefore, the present inventors have conducted extensive research into a semiconductor wafer evaluation method that includes forming such a coating on the surface of the semiconductor wafer to be evaluated. As a result, the present inventors have discovered a new evaluation method that includes setting the thickness of the coating formed on the surface of the semiconductor wafer to be evaluated within a thickness range in which the scattered light intensity obtained by the defect inspection device is equal to or greater than a predetermined intensity, and observing the coating surface using a scanning electron microscope to classify the type of LPD.

[0007] That is, one aspect of the present invention is as follows: [1] A method for evaluating a semiconductor wafer (hereinafter also referred to as a "first evaluation method"), comprising: determining a film thickness range in which the scattered light intensity obtained by a defect inspection device is equal to or greater than a predetermined intensity; forming a film, within the film thickness range, on the surface of a semiconductor wafer to be evaluated, which expands defects present on the surface; inspecting the surface of the film using the defect inspection device and performing LPD measurement; identifying the position of an LPD to be observed based on coordinate data acquired by the LPD measurement, and observing this position with a scanning electron microscope (SEM) to determine whether the LPD to be observed is a film protrusion formed by the film being raised; and performing an evaluation of the film protrusion. [2] The method for evaluating a semiconductor wafer according to [1], wherein determining the film thickness range of the coating includes: preparing a plurality of wafers as experimental wafers; inspecting the surfaces of the plurality of experimental wafers using a defect inspection device to perform LPD measurement; forming coatings of different film thicknesses on the surfaces of the plurality of experimental wafers; inspecting the surfaces of the coatings of the plurality of experimental wafers using a defect inspection device to perform LPD measurement; identifying the positions of LPDs to be observed for each of the plurality of experimental wafers based on coordinate data acquired by LPD measurement after the coating has been formed, and observing these positions using a scanning electron microscope to determine whether the LPDs to be observed are coating protrusions formed by the coating; calculating a ratio between an LPD detection size acquired by LPD measurement before the coating has been formed and an LPD detection size acquired by LPD measurement after the coating has been formed, for LPDs determined to be coating protrusions for each of the plurality of experimental wafers; and determining the film thickness range based on the calculated ratio. [3] The semiconductor wafer evaluation method according to [1] or [2], wherein the coating is a nitride film. [4] The semiconductor wafer evaluation method according to any one of [1] to [3], wherein the defects are particles. [5] The semiconductor wafer evaluation method according to any one of [2] to [4], wherein the coating is a nitride film and the defects are particles.[6] A method for evaluating a semiconductor wafer (hereinafter also referred to as a "second evaluation method"), comprising: forming, on the surface of a semiconductor wafer to be evaluated, a coating that expands defects present on the surface, with a thickness in the range of 70 nm to 140 nm; inspecting the surface of the coating using a defect inspection device and performing LPD measurement; identifying the position of an LPD to be observed based on coordinate data acquired by the LPD measurement, and observing this position using a scanning electron microscope to determine whether the LPD to be observed is a coating protrusion caused by a rise in the coating; and evaluating the coating protrusion. [7] The method for evaluating a semiconductor wafer according to [6], wherein the coating is a nitride film. [8] The method for evaluating a semiconductor wafer according to [6] or [7], wherein the defect is a particle. [9] The method for evaluating a semiconductor wafer according to [7] or [8], wherein the defect is a particle.

[10] The method for evaluating a semiconductor wafer according to any of [1] to [9], further comprising: determining whether the semiconductor wafer to be evaluated is good or bad based on the results of the evaluation of the coating protrusion.

[11] A method for manufacturing a semiconductor wafer, comprising: manufacturing a semiconductor wafer under manufacturing conditions to be evaluated; evaluating the manufactured semiconductor wafer by the evaluation method described in

[10] ; determining, based on the results of the evaluation, manufacturing conditions obtained by modifying the manufacturing conditions to be evaluated as subsequent manufacturing conditions, or determining the manufacturing conditions to be evaluated as manufacturing conditions to be continued; and manufacturing a semiconductor wafer under the determined manufacturing conditions.

[0008] According to one aspect of the present invention, a new evaluation method can be provided that can evaluate defects present on the surface of a semiconductor wafer.

[0009] Figure 1 is a schematic diagram of size expansion due to the lens effect. Figure 2 shows specific examples of SEM images of film protrusions and post-film deposition particles. Figure 3 is a graph obtained by plotting the pre-film deposition LPD detection size on the X axis and the post-film deposition LPD detection size on the Y axis for four experimental wafers in the example. Figure 4 shows the number of film protrusions determined for five levels of evaluation wafers in the example.

[0010] [Semiconductor Wafer Evaluation Method] In this specification, the first evaluation method and the second evaluation method are collectively referred to as "semiconductor wafer evaluation method" or "evaluation method." Unless otherwise specified, the description of the first evaluation method also applies to the second evaluation method, and the description of the second evaluation method also applies to the first evaluation method.

[0011] <Semiconductor wafer to be evaluated> The "semiconductor wafer to be evaluated" is also referred to as the "wafer to be evaluated." Regarding the type of semiconductor wafer, examples of the semiconductor wafer to be evaluated by the above evaluation method include various semiconductor wafers generally used as semiconductor substrates. Specific examples of semiconductor wafers include various silicon wafers. Silicon wafers can be, for example, silicon single crystal wafers that have been cut from a silicon single crystal ingot and then subjected to various processing steps, such as polished wafers that have been polished to have a polished surface on the surface, and epitaxial wafers on which an epitaxial layer has been formed. The diameter of the semiconductor wafer to be evaluated is, for example, 200 mm or less or 200 mm or more (e.g., 200 mm, 300 mm, or 450 mm), but is not particularly limited.

[0012] Defects exist on the surface of a semiconductor wafer to be evaluated. Such defects can be protrusion-like defects. A specific example of a protrusion-like defect is a particle. A particle is a foreign substance that adheres to the wafer surface during the wafer manufacturing process.

[0013] <LPD Measurement Using a Defect Inspection Device> In the above evaluation method, LPD measurement is performed on the coating surface at least after the coating film described below is formed. Alternatively, LPD measurement can be performed on the semiconductor wafer surface before the coating film is formed. Hereinafter, LPD measurement on the coating surface after the coating film is formed will also be referred to as "LPD measurement after film formation on the evaluation target wafer" or "LPD measurement after film formation," and LPD measurement on the wafer surface before the coating film is formed will also be referred to as "LPD measurement before film formation on the evaluation target wafer" or "LPD measurement before film formation."

[0014] The defect inspection device can be a known defect inspection device capable of irradiating light onto the surface of an object to be inspected and detecting scattered light from the surface. Such defect inspection devices are generally referred to as light scattering defect inspection devices, surface inspection machines, etc. A specific example of a defect inspection device is a laser defect inspection device. A laser defect inspection device typically scans the surface of an object to be inspected with laser light and detects protrusions on the surface of the object to be inspected as bright spots (LPDs) using scattered light. Furthermore, by measuring the scattered light from the LPDs, the position (specifically, coordinate points) of the protrusions on the surface of the object to be inspected and the size detected as an LPD (LPD detection size) can be determined. The LPD detection size is output by an analysis unit of the defect inspection device by comparing the intensity of the scattered light from the LPDs with the scattered light intensity of standard particles such as silica particles. The laser light can be ultraviolet light, visible light, or the like, and its wavelength is not particularly limited. Ultraviolet light refers to light in a wavelength range of less than 400 nm, and visible light refers to light in a wavelength range of 400 nm to 600 nm. The analysis unit of a laser defect inspection device typically acquires information on two-dimensional position coordinates (X and Y coordinates) on the surface of the object to be inspected for each of the detected LPDs, and can create an LPD map showing the in-plane distribution of LPDs on the surface of the object to be inspected from the acquired two-dimensional position coordinate information. Specific examples of commercially available laser defect inspection devices include the Surfscan series SP1, SP2, SP3, SP5, and SP7 manufactured by KLA-TENCOR Corporation. However, these devices are merely examples, and various other defect inspection devices can also be used. In the post-film-deposition LPD measurement of the evaluation target wafer and the pre-film-deposition LPD measurement of the evaluation target wafer, the inspection area by the defect inspection device can be the entire in-plane area of ​​the wafer surface or a partial area of ​​the in-plane area. In the post-film-deposition LPD measurement of the evaluation target wafer, it is preferable that the inspection area on the wafer surface be the same area as the inspection area in the pre-film-deposition LPD measurement of the evaluation target wafer, or an area including the same area as the inspection area in the pre-film-deposition LPD measurement of the evaluation target wafer.This allows LPDs detected in the pre-film deposition LPD measurement of the evaluation target wafer to be detected in the post-film deposition LPD measurement of the evaluation target wafer as well. The defect inspection system can acquire scattered light intensity (more specifically, the LPD detection size determined as described above from the scattered light intensity) and coordinate data for LPDs within the inspection area. For example, if an LPD is detected in the post-film deposition LPD measurement of the evaluation target wafer at the same coordinate position as the coordinate position at which an LPD was detected in the pre-film deposition LPD measurement of the evaluation target wafer, it can be determined that a defect of a size equal to or larger than the detection limit of the defect inspection system exists at that position on the surface of the evaluation target wafer. If an LPD is detected in the post-film deposition LPD measurement of the evaluation target wafer at a coordinate position at which no LPD was detected in the pre-film deposition LPD measurement of the evaluation target wafer, it can be determined that a defect of a size below the detection limit of the defect inspection system exists at that coordinate position on the surface of the evaluation target wafer.

[0015] <Formation of Coating> The coating formed on the surface of the semiconductor wafer to be evaluated can be any of various coatings formed by known film formation methods, including nitride films, oxide films, polysilicon films, amorphous silicon films, and metal films.

[0016] In one embodiment, the coating can be a deposited film in which a film-forming material is deposited on the surface of a semiconductor wafer. Examples of the deposition method for forming the deposited film include various film-forming methods that can deposit a film-forming material on the surface of a semiconductor wafer by vapor phase growth, such as CVD (Chemical Vapor Deposition) and ALD (Atomic Layer Deposition). Examples of the CVD method include LP (Low Pressure)-CVD and plasma CVD.

[0017] Regarding the film thickness, in a first evaluation method, a film thickness range is determined in which the scattered light intensity obtained by a defect inspection device is equal to or greater than a predetermined intensity. The process of making such a determination is hereinafter referred to as a "film thickness determination process." In a second evaluation method, a film having a thickness within a range of 70 nm to 140 nm is formed on the surface of a semiconductor wafer to be evaluated. The film thickness range of 70 nm to 140 nm can be the film thickness range in which the scattered light intensity obtained by a defect inspection device is equal to or greater than a predetermined intensity. In the present invention and this specification, the film thickness can be a value determined by a known film thickness measurement method, or it can be a set film thickness set in a film formation device.

[0018] In the second evaluation method, the thickness of the coating formed on the surface of the semiconductor wafer to be evaluated is 70 nm or more, preferably 80 nm or more, with 90 nm or more, 100 nm or more, and 110 nm or more being more preferred in this order, from the viewpoint of increasing the scattered light intensity obtained by the defect inspection device. Furthermore, in the second evaluation method, the thickness of the coating formed on the surface of the semiconductor wafer to be evaluated is 140 nm or less, preferably 130 nm or less, from the above viewpoint. In the first evaluation method, the thickness of the coating formed on the surface of the semiconductor wafer to be evaluated is only required to be within a thickness range in which the scattered light intensity obtained by the defect inspection device is equal to or greater than a predetermined intensity, and may be outside or within the range described above for the second evaluation method. In one embodiment, the thickness of the coating formed on the surface of the semiconductor wafer to be evaluated in the first evaluation method is preferably 70 nm or more, more preferably 80 nm or more, with 90 nm or more, 100 nm or more, and 110 nm or more being even more preferred in this order. In one embodiment, the thickness of the coating formed on the surface of the semiconductor wafer to be evaluated in the first evaluation method is preferably 140 nm or less, and more preferably 130 nm or less.

[0019] The coating can expand defects present on the surface of the semiconductor wafer. By "expanding," protrusions larger in size than the defects on the surface of the semiconductor wafer are formed on the surface of the coating. This is due to the so-called "lens effect." The "lens effect" is a phenomenon in which, starting from a protrusion, a coating protrusion with a diameter several times larger than the protrusion is formed on the coating surface directly above it. In this invention and this specification, "coating protrusion" refers to a portion of the coating surface that is raised due to the presence of a protruding defect directly below it.

[0020] Figure 1 is a schematic diagram of size expansion due to the lens effect. In the example shown in Figure 1, films with different thicknesses (T1<T2<T3) are formed on the surfaces of each wafer.

[0021] The defect inspection system detects LPDs by irradiating light onto the surface of the object to be inspected and receiving the scattered light from the surface as a signal from the protrusions. The intensity of the scattered light is mainly based on Rayleigh scattering, as shown in Equation (1).

[0022]

[0023] (In formula (1), Is: scattered light intensity, λ: wavelength of light incident on the surface of the object to be inspected, Ii: incident intensity, r: distance between the scatterer and the detector, d: diameter of the scatterer (defect), n: complex refractive index (including attenuation coefficient), θ: scattering angle (angle between the incident direction and the detector))

[0024] Rayleigh scattering explains that the larger the diameter of the spherical scatterer, the greater the scattered light intensity. Defect inspection systems also follow this principle, making larger scatterers easier to detect. For example, as shown in Figure 1, the film protrusions are larger when the film thickness is T2 compared to T1, resulting in stronger scattered light intensity. However, if the shape of the scatterer differs significantly from a spherical shape, the scattering characteristics are likely to differ. As the film thickness increases, the shape of the film protrusions becomes smoother and significantly different from a spherical shape, resulting in less scattered light. For example, as shown in Figure 1, the scattered light intensity is weaker when the film thickness is T3 compared to T2, making it difficult to detect as an LPD. Therefore, LPD detection is facilitated by forming a coating on the surface of the semiconductor wafer to be evaluated within a film thickness range that results in a scattered light intensity measured by a defect inspection system that is equal to or greater than a predetermined intensity. In the first evaluation method, such a film thickness range is determined in the film thickness determination process.

[0025] <Film Thickness Determination Step> The film thickness determination step in the first evaluation method includes the steps of: preparing a plurality of wafers as experimental wafers (hereinafter referred to as an "experimental wafer preparation step"); inspecting the surfaces of the plurality of experimental wafers using a defect inspection device and performing LPD measurements (hereinafter referred to as "pre-film-deposition LPD measurements of experimental wafers" or "pre-film-deposition LPD measurements"); forming coatings with different film thicknesses on the surfaces of the plurality of experimental wafers (hereinafter referred to as an "experimental wafer deposition step"); inspecting the surfaces of the coatings of the plurality of experimental wafers using a defect inspection device and performing LPD measurements (hereinafter referred to as "post-film-deposition LPD measurements of experimental wafers" or "post-film-deposition LPD measurements"); The process may include: identifying the position of the LPD to be observed for each of the plurality of experimental wafers based on coordinate data obtained by LPD measurement after the film formation, and observing this position using a scanning electron microscope to determine whether the LPD to be observed is a film protrusion caused by a raised portion of the film (hereinafter referred to as the "LPD classification process for experimental wafers"); calculating, for each LPD determined to be a film protrusion on each of the plurality of experimental wafers, a ratio between the LPD detection size obtained by LPD measurement before the film formation and the LPD detection size obtained by LPD measurement after the film formation (hereinafter referred to as the "ratio calculation process"); and determining the film thickness range based on the calculated ratio (hereinafter referred to as the "film thickness range determination process").

[0026] The above steps will be explained below in order.

[0027] (Experimental Wafer Preparation Process) For the experimental wafer, the above description regarding the semiconductor wafer to be evaluated can be referenced. However, the experimental wafer does not need to be the same type of wafer as the evaluation target wafer, nor does it need to be a wafer with the same diameter. Epitaxial wafers tend to have fewer types of defects present on the wafer surface (specifically, the epitaxial layer surface) than polished wafer surfaces. Therefore, when comparing polished wafers and epitaxial wafers, it is preferable to use epitaxial wafers as experimental wafers. However, polished wafers can also be used as experimental wafers. Furthermore, the multiple experimental wafers are not limited to wafers cut from the same ingot. The number of experimental wafers can be two or more, three or more, or four or less. The number of experimental wafers can be, for example, eight or less, seven or less, six or less, or five or less. However, the number of experimental wafers is not limited to the above range. It is preferable that the multiple experimental wafers be wafers that have been subjected to cleaning processing under the same cleaning conditions, because there is little or no difference in the defect types present on the wafer surfaces among the multiple experimental wafers. In the present invention and this specification, "the same cleaning conditions" is not limited to being completely the same, and it is understood that normal variations (e.g., changes in the concentration of the cleaning solution over time) and / or variations caused by operators or equipment may occur.

[0028] (Pre-film deposition LPD measurement of experimental wafers) The surfaces of the multiple experimental wafers are inspected using a defect inspection device to measure LPDs. For LPD measurement, please refer to the previous description regarding LPD measurement of semiconductor wafers to be evaluated. When inspecting the surfaces of the multiple experimental wafers using the defect inspection device, the areas of the inspection regions may be the same or different. In order to create a linear equation, as described below, it is preferable to detect multiple LPDs on the surface of each experimental wafer. The number of LPDs to be detected may be two or more, and may be three or more, five or more, ten or more, twenty or more, thirty or more, forty or more, or fifty or more, or may be 100 or less, 90 or less, or 80 or less.

[0029] (Film formation process for experimental wafers) Next, a coating is formed on the surfaces of the plurality of experimental wafers on which pre-film formation LPD measurement was performed. The thickness of the coating formed here is different for the plurality of experimental wafers. The type of coating formed on the surface of each of the plurality of experimental wafers may be the same or different. Furthermore, the type of coating formed on the surface of the plurality of experimental wafers may be the same as or different from the type of coating formed on the surface of the semiconductor wafer to be evaluated. For the formation of the coating, please refer to the previous description regarding the formation of a coating on the semiconductor wafer to be evaluated.

[0030] (Post-Film Deposition LPD Measurement of Experimental Wafers) After forming a film on each surface of the plurality of experimental wafers, the film surface is inspected using a defect inspection device to perform LPD measurement. In the post-film deposition LPD measurement of the experimental wafers, the inspection area on the film surface of each experimental wafer is preferably the same as the inspection area used in the pre-film deposition LPD measurement of the experimental wafers, or an area including the same area as the inspection area used in the pre-film deposition LPD measurement of the experimental wafers. This allows LPDs detected in the pre-film deposition LPD measurement of the experimental wafers to also be detected in the post-film deposition LPD measurement of the experimental wafers. For LPD measurement, please refer to the previous description regarding LPD measurement of the semiconductor wafers to be evaluated.

[0031] (LPD Classification Process for Experimental Wafers) For each of the multiple experimental wafers, the position of the LPD to be observed is identified based on the coordinate data acquired by the LPD measurement after film formation, and this position is observed using a scanning electron microscope (SEM). By performing morphological observation using the SEM, it is possible to determine whether the LPD detected by the defect inspection device at the observation position is a film protrusion (a raised portion of the film surface due to the presence of a protruding defect directly below the surface of the film). Foreign matter adhering to the film surface after film formation (i.e., post-film formation particles) and film protrusions can be easily classified by morphological observation using the SEM. SEM observation can be performed using a method typically used for semiconductor wafers.

[0032] (Ratio Calculation Step) For each LPD determined to be a film protrusion on each of the multiple experimental wafers, a ratio is calculated between the detected LPD size obtained by the pre-film-deposition LPD measurement (hereinafter also referred to as "pre-film-deposition LPD detection size") and the detected LPD size obtained by the post-film-deposition LPD measurement (hereinafter also referred to as "post-film-deposition LPD detection size"). The LPDs for which the ratio is calculated may be some or all of the LPDs determined to be film protrusions. The ratio may be "post-film-deposition LPD detection size / pre-film-deposition LPD detection size" or "pre-film-deposition LPD detection size / post-film-deposition LPD detection size," and is preferably "post-film-deposition LPD detection size / pre-film-deposition LPD detection size." Hereinafter, "post-film-deposition LPD detection size / pre-film-deposition LPD detection size" will also be referred to as "size expansion ratio." The size expansion ratio can be calculated, for example, as follows. For each of the plurality of experimental wafers, the detected LPD size before film formation was plotted on the X axis and the detected LPD size after film formation was plotted on the Y axis for the plurality of LPDs determined to be film protrusions, and a line Y = aX was fitted using a known fitting method. The slope "a" of this line was taken as the size enlargement rate.

[0033] (Film Thickness Range Determination Process) Regarding the lower measurement limit set in the defect inspection device, it is preferable to set the lower measurement limit of the LPD detection size when performing LPD measurement of a coating formed on a wafer surface (post-film LPD measurement) higher (i.e., a larger value) than the lower measurement limit of the LPD detection size when performing LPD measurement of a wafer surface before a coating is formed (pre-film LPD measurement). This is because the coating surface is typically rougher and has a higher haze than the wafer surface. If the lower measurement limit in the post-film LPD measurement is set to "A" and the lower measurement limit in the pre-film LPD measurement is set to "B" (A > B), the size magnification ratio is preferably "A / B" or greater in order to increase the scattered light intensity and thereby enable detection of even smaller LPDs. Therefore, for example, the above-mentioned "A / B" value can be used as an index to determine the "film thickness range within which the scattered light intensity obtained by the defect inspection device is equal to or greater than a predetermined intensity." For example, the smallest coating thickness among the multiple experimental wafers for which the size expansion ratio was within the range of "A / B" or more can be set as the lower limit of the above-mentioned thickness range, and the largest coating thickness for which the size expansion ratio was within the range of "A / B" or more can be set as the upper limit of the above-mentioned thickness range. In the first evaluation method, for example, a coating having a thickness within the thus determined thickness range can be formed on the surface of the semiconductor wafer to be evaluated. As an example, the same thickness as the coating of the experimental wafer for which the size expansion ratio was the largest within the above-mentioned thickness range can be determined as the film thickness to be formed on the surface of the semiconductor wafer to be evaluated, but this is merely an example, and the first evaluation method is not limited to such an example.

[0034] <LPD Classification for Semiconductor Wafer to be Evaluated> In the above evaluation method, the position of the LPD to be observed is identified based on the coordinate data obtained by performing LPD measurement after forming a coating on the semiconductor wafer to be evaluated, and this position is observed using a scanning electron microscope (SEM). By performing morphological observation using the SEM here, it is possible to determine whether the LPD detected by the defect inspection device at the above observation position is a coating protrusion (a raised portion of the coating surface due to the presence of a protruding defect directly below the surface of the coating). For details about SEM observation, please refer to the above description.

[0035] <Evaluation and Pass / Fail Determination of Coat Protrusions on a Semiconductor Wafer to be Evaluated> In the evaluation method described above, for example, one or more of the LPD detection size, number, and in-plane distribution (in-plane number distribution, in-plane size distribution, etc.) on the wafer surface of LPDs determined to be coat protrusions according to the LPD classification described above can be determined. Then, using one or more of these as indicators, the pass / fail determination of the semiconductor wafer to be evaluated can be performed. Alternatively, from the LPD detection size and size magnification ratio of the coat protrusions, it is possible to estimate the size of the LPDs on the wafer surface before film formation that correspond to the LPD detection size determined by LPD measurement after film formation. For an example of a calculation method for such an estimation, please refer to the description of the Examples below. For example, the defect size calculated in this way can also be used as an indicator for pass / fail determination. The pass / fail determination threshold can be set according to the quality desired for the product wafer. For specific examples of pass / fail determination, please refer to the description of the semiconductor wafer manufacturing method described below.

[0036] According to the above evaluation methods (i.e., the first evaluation method and the second evaluation method), the expansion (lens effect) of the coating makes it possible to detect and evaluate minute protrusion-like defects that cannot be detected by inspecting the surface of a semiconductor wafer with a defect inspection device.

[0037] [Method for Manufacturing Semiconductor Wafer] One aspect of the present invention relates to a method for manufacturing a semiconductor wafer, including manufacturing a semiconductor wafer under manufacturing conditions to be evaluated, evaluating the manufactured semiconductor wafer using the semiconductor wafer evaluation method, determining, based on the results of the evaluation, manufacturing conditions obtained by modifying the manufacturing conditions to be evaluated as subsequent manufacturing conditions, or determining the manufacturing conditions to be evaluated as manufacturing conditions to be subsequently adopted, and manufacturing a semiconductor wafer under the determined manufacturing conditions.

[0038] Specific examples of the above-mentioned manufacturing method include the following: Semiconductor wafers are manufactured under manufacturing conditions A. Separately, semiconductor wafers are manufactured under manufacturing conditions B, which are different from manufacturing conditions A. The manufacturing conditions to be evaluated are designated "manufacturing conditions B." Evaluation wafers are sampled from each of a group of wafers manufactured under manufacturing conditions A and a group of wafers manufactured under manufacturing conditions B, and evaluated using the evaluation method described above. For example, if the evaluation results show that the total number of coating protrusions determined by the evaluation method described above is smaller in the evaluation wafers sampled from the group of wafers manufactured under manufacturing conditions A than in the evaluation wafers sampled from the group of wafers manufactured under manufacturing conditions B, manufacturing conditions A can be determined to be manufacturing conditions that are less likely to cause defects on the semiconductor wafer surface than manufacturing conditions B. In this case, manufacturing conditions B can be changed to approach manufacturing conditions A, and the modified manufacturing conditions can be designated as improved manufacturing conditions B, and subsequent semiconductor wafer manufacturing can be performed using these modified manufacturing conditions. Furthermore, for example, if the evaluation results show that the in-plane distribution (in-plane size distribution, in-plane number distribution, etc.) of coating protrusions determined by the evaluation method described above is more distant from the in-plane distribution desired for the product in an evaluation wafer sampled from a group of wafers manufactured under manufacturing condition B than in an evaluation wafer sampled from a group of wafers manufactured under manufacturing condition A, then manufacturing condition A can be determined to be a more desirable manufacturing condition than manufacturing condition B. In this case, manufacturing condition B can be changed to approach manufacturing condition A, and the changed manufacturing condition can be designated as improved manufacturing condition B, and subsequent semiconductor wafer manufacturing can be performed using this modified manufacturing condition. In the above example, the manufacturing conditions are determined by comparing two manufacturing conditions (manufacturing conditions A and B), but the number of manufacturing conditions compared may be three or more.

[0039] Further, the following can be exemplified as specific embodiments of the above-mentioned manufacturing method. First, test manufacturing conditions are determined in order to determine the manufacturing conditions (hereinafter referred to as "actual manufacturing conditions") for manufacturing semiconductor wafers to be actually shipped as products. Semiconductor wafers are manufactured under these test manufacturing conditions. The semiconductor wafers manufactured under the test manufacturing conditions are evaluated using the evaluation method described above. Based on the results of the evaluation, manufacturing conditions obtained by modifying the test manufacturing conditions can be determined as the actual manufacturing conditions, or the test manufacturing conditions themselves can be determined as the actual manufacturing conditions. Then, semiconductor wafers can be manufactured under the determined actual manufacturing conditions. For example, if the evaluation results show that the total number of coating protrusions determined by the evaluation method described above for semiconductor wafers manufactured under the test manufacturing conditions exceeds a predetermined target value, manufacturing conditions obtained by modifying the test manufacturing conditions so as to suppress the occurrence of defects on the wafer surface can be determined as the actual manufacturing conditions. Furthermore, for example, even if the evaluation results show that the in-plane distribution (in-plane size distribution, in-plane number distribution, etc.) of coating protrusions determined by the evaluation method described above in a semiconductor wafer manufactured under test manufacturing conditions is significantly different from the desired in-plane distribution, manufacturing conditions in which the test manufacturing conditions have been modified so as to suppress the occurrence of defects on the wafer surface can be determined as actual manufacturing conditions.

[0040] Regarding the manufacturing process of semiconductor wafers, for example, the manufacturing process of polished wafers can be produced by a manufacturing process including cutting (slicing) wafers from semiconductor ingots such as silicon single crystal ingots, chamfering, rough polishing (e.g., lapping), etching, mirror polishing (finish polishing), and a cleaning process performed between or after the above processing steps. Particles, which are a type of protruding defect on the surface of a semiconductor wafer, are foreign matter attached to the wafer surface and can be removed by cleaning. Therefore, in one embodiment, the manufacturing conditions to which the above-mentioned changes are made can be cleaning conditions. To reduce particles, for example, the cleaning conditions can be strengthened. Specifically, measures for reducing particles include increasing the number of cleanings, lengthening the cleaning time, and using a cleaner with stronger cleaning power.

[0041] The present invention will be further described below based on examples, although the present invention is not limited to the embodiments shown in the examples.

[0042] The defect inspection device used below is a Surfscan series SP7 manufactured by KLA-TENCOR Corp. In the pre-film LPD measurement, the lower measurement limit of the SP7 was set to 15 nm, and in the post-film LPD measurement, the lower measurement limit of the SP7 was set to 24 nm.

[0043] The thickness of the coating described below is the set thickness set in the film forming apparatus.

[0044] [Measurements on Experimental Wafers] <Experimental Wafer Preparation Step> Four silicon single crystal wafers (epitaxial wafers) that had been subjected to cleaning treatment under the same cleaning conditions were prepared as experimental wafers.

[0045] <LPD measurement before film formation on experimental wafers> LPD measurement was performed on the entire in-plane area of ​​one surface of each of the four experimental wafers using a defect inspection device, and the LPD detection size (scattered light intensity) and coordinate data were obtained for all detected LPDs.

[0046] <Deposition Process of Experimental Wafers> After the pre-deposition LPD measurement, nitride films (silicon nitride films) with different film thicknesses (20 nm, 70 nm, 120 nm, 140 nm) were formed using the same film-forming material on the surfaces of the four experimental wafers after the LPD measurement in the same LP-CVD deposition apparatus.

[0047] <LPD measurement after film formation on experimental wafers> LPD measurement was performed on the entire surface of the coating (nitride film) formed on the surface of each of the four experimental wafers using a defect inspection device, and the LPD detection size (scattered light intensity) and coordinate data were obtained for all detected LPDs.

[0048] <LPD Classification Process for Experimental Wafers> All LPDs detected throughout the entire surface of the coating formed on each of the four experimental wafers were observed using an SEM. Specifically, the coordinate data obtained by the post-deposition LPD measurement was used to observe the protrusions and obtain secondary electron images. Based on the shapes of the secondary electron images, the coating surface was classified into coating protrusions and post-deposition particles. Figure 2 shows specific examples of SEM images of coating protrusions and post-deposition particles.

[0049] <Calculation of Size Expansion Ratio> The LPD size expansion ratio before and after film formation was calculated using the LPD measurement results obtained for all LPDs that were determined to be film protrusions by SEM observation and were also detected in the pre-film formation LPD measurement at the same positions. Specifically, for the four experimental wafers, the pre-film formation LPD detection size was plotted on the X axis and the post-film formation LPD detection size was plotted on the Y axis. The graph obtained in this way is shown in Figure 3. For each experimental wafer, a line Y = aX was fitted using the least squares method. The value "a" thus obtained was taken as the size expansion ratio.

[0050] <Determination of Film Thickness Range> As described above, the lower measurement limit of SP7 was set to 15 nm for the pre-deposition LPD measurement and 24 nm for the post-deposition LPD measurement. Therefore, if the value "1.6" calculated as "24 nm / 15 nm = 1.6" is used as the threshold value for the size expansion ratio, the film thickness of 20 nm was below the threshold, and the film thickness of 70 nm, 120 nm, and 140 nm was above the threshold. Based on these results, the range of "70 nm to 140 nm" was determined as the "film thickness range in which the scattered light intensity obtained by the defect inspection device is equal to or greater than a predetermined intensity." The film thickness of 120 nm, which was the film thickness formed on the surface of the experimental wafer with the largest size expansion ratio among the four experimental wafers, was used as the film thickness to be formed on the surface of the wafer to be evaluated (described later).

[0051] From the slope a of each line Y = aX shown in Figure 3, it is possible to estimate the size of the LPDs on the wafer surface before film deposition that represent the LPDs of the LPD detection size determined by the LPD measurement after film deposition. For example, when a 120 nm thick film was formed, the size enlargement factor was 2.9 (see Figure 3). Therefore, the LPDs for the 24 nm LPD detection size set as the lower limit of measurement in the LPD measurement after film deposition can be calculated as "24 nm / 2.9 = 8.3 nm." From these calculation results, it can be confirmed that defects of sizes below the lower limit of detection in the LPD measurement before film deposition can be detected as LPDs by the LPD measurement after film deposition.

[0052] [Measurements and Evaluations of Evaluation Target Wafers] <Preparation of Evaluation Target Wafers> Five levels of silicon single crystal wafers (epitaxial wafers) (levels A, B, C, D, and E) with different cleaning conditions were prepared as evaluation target semiconductor wafers.

[0053] <Formation of a coating on the surface of the wafer to be evaluated> A nitride film (silicon nitride film) having a thickness of 120 nm was formed on the surface of the epitaxial layer of each of the five wafers described above. The same film forming apparatus and film forming material as those used for the film forming process on the experimental wafers were used in the film forming process.

[0054] <LPD measurement after film formation on evaluation wafer> LPD measurement was performed on the entire surface of the coating formed on the surface of each of the five levels of evaluation wafers using a defect inspection device, and the LPD detection size (scattered light intensity) and coordinate data were obtained for all detected LPDs.

[0055] <LPD Classification for Evaluation Wafers> All LPDs detected throughout the entire surface of the coating formed on each of the five evaluation wafers were observed using an SEM. Specifically, the coordinate data obtained by the post-deposition LPD measurement was used to observe the protrusions and obtain secondary electron images. Based on the shape of the secondary electron images, the coating protrusions on the coating surface and post-deposition particles were classified.

[0056] <Evaluation of Coating Protrusions> Figure 4 shows the number of coating protrusions found for the wafers evaluated at the five levels. As shown in Figure 4, level D had the most coating protrusions, and level E had the fewest. From these results, for example, the cleaning conditions for level E can be determined as cleaning conditions that can clean and remove even minute particles, and can be used as actual manufacturing conditions. Furthermore, for example, it can be determined that the cleaning conditions for level D should be modified in order to be used as actual manufacturing conditions.

[0057] According to one aspect of the present invention, it is possible to provide a high-quality semiconductor wafer with few microparticles. For example, a high-quality semiconductor wafer with few microparticles can be used as a semiconductor substrate in cutting-edge logic devices. Cutting-edge logic devices can be installed in, for example, smartphones, enabling the smartphone to achieve multifunctionality and high performance. For example, cutting-edge logic devices can run multiple applications simultaneously and improve graphics processing capabilities to smoothly process high-resolution images and / or videos. As described above, one aspect of the present invention enables the manufacture of high-performance logic semiconductors, thereby enriching people's lives.

[0058] One aspect of the present invention is useful in the field of manufacturing various semiconductor wafers such as silicon wafers.

Claims

1. A method for evaluating a semiconductor wafer, comprising: determining a range of film thicknesses for which the scattered light intensity obtained by a defect inspection device is equal to or greater than a predetermined intensity; forming a film on the surface of a semiconductor wafer to be evaluated, the film having a film thickness within the range, which expands defects present on the surface; inspecting the surface of the film using a defect inspection device and performing LPD measurement; identifying the position of the LPD to be observed based on coordinate data acquired by the LPD measurement, and observing the position using a scanning electron microscope to determine whether the LPD to be observed is a film protrusion caused by the film being raised; and performing an evaluation of the film protrusion.

2. The method of evaluating semiconductor wafers according to claim 1, wherein determining the film thickness range of the coating comprises: preparing a plurality of wafers as experimental wafers; inspecting the surfaces of the plurality of experimental wafers with a defect inspection device and performing LPD measurement; forming coatings of different film thicknesses on the surfaces of the plurality of experimental wafers; inspecting the surfaces of the coatings of the plurality of experimental wafers with a defect inspection device and performing LPD measurement; identifying the position of an LPD to be observed for each of the plurality of experimental wafers based on coordinate data obtained by LPD measurement after the coating has been formed, and observing the position with a scanning electron microscope to determine whether the LPD to be observed is a coating protrusion caused by a rise in the coating; calculating, for LPDs determined to be coating protrusions for each of the plurality of experimental wafers, a ratio between an LPD detection size obtained by LPD measurement before the coating has been formed and an LPD detection size obtained by LPD measurement after the coating has been formed; and determining the film thickness range based on the calculated ratio.

3. The semiconductor wafer evaluation method according to claim 1, wherein the coating is a nitride film.

4. The semiconductor wafer evaluation method according to claim 1, wherein the defect is a particle.

5. The semiconductor wafer evaluation method according to claim 2, wherein the coating is a nitride film, and the defects are particles.

6. A method for evaluating semiconductor wafers, comprising: forming a coating on the surface of a semiconductor wafer to be evaluated, with a thickness in the range of 70 nm to 140 nm, which expands defects present on the surface; inspecting the surface of the coating using a defect inspection device and performing LPD measurement; identifying the position of the LPD to be observed based on coordinate data acquired by the LPD measurement, and observing the position using a scanning electron microscope to determine whether the LPD to be observed is a coating protrusion caused by the coating being raised; and evaluating the coating protrusion.

7. The semiconductor wafer evaluation method according to claim 6, wherein the coating is a nitride film.

8. The semiconductor wafer evaluation method according to claim 6, wherein the defect is a particle.

9. The semiconductor wafer evaluation method according to claim 7, wherein the defect is a particle.

10. The semiconductor wafer evaluation method according to any one of claims 1 to 9, further comprising: determining whether the semiconductor wafer being evaluated is good or bad based on the results of the evaluation regarding the coating protrusions.

11. A method for manufacturing semiconductor wafers, comprising: manufacturing semiconductor wafers under manufacturing conditions to be evaluated; evaluating the manufactured semiconductor wafers using the evaluation method described in claim 10; determining, based on the results of the evaluation, manufacturing conditions that have been modified from the manufacturing conditions to be evaluated as subsequent manufacturing conditions, or determining the manufacturing conditions to be evaluated as the manufacturing conditions to be continued; and manufacturing semiconductor wafers under the determined manufacturing conditions.

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