Plasma treatment method and plasma treatment device

Abstract

Provided is an etching treatment method or an etching treatment device which improves the accuracy of detecting the remaining film thickness or the etched amount of a film to be treated on a sample. This plasma treatment device comprises: a spectrometer 108 that detects interference light of a plurality of wavelengths from the surface of a sample which is being treated; a pattern comparison means 113 that compares interference light intensity information of a plurality of wavelengths obtained at a discretionary time during the treatment of the sample and from a discretionary number of sampling points at that time, a plurality of standard deviation patterns respectively corresponding to a plurality of thicknesses of the film, and a plurality of interference light beams which serve as interference light data of a plurality of wavelengths pertaining to a treatment of a different sample obtained before treatment of the current sample and which respectively corresponding to the plurality of thicknesses of the film, and as a result of such comparison, the pattern comparison means calculates the deviation of the foregoing; a film thickness determination unit 114 that compares the deviation among the foregoing with a preset deviation to determine the thickness of the sample at such time; and an endpoint determination unit 115 for determining that a predetermined amount of etching has been completed.

Description

Plasma processing method and plasma processing apparatus

[0001] The present disclosure relates to a plasma processing method or apparatus.

[0002] In semiconductor wafer manufacturing, dry etching is widely used to remove or pattern layers of various materials, especially dielectric materials, formed on the surface of the wafer. The most important control of process parameters is the accurate determination of the etch endpoint to stop etching at a desired film thickness and etch depth during processing of such layers.

[0003] During the dry etching process of a semiconductor wafer, the emission intensity of a specific wavelength in plasma light changes as the etching of a specific film progresses (for example, the emission intensity of a specific wavelength decreases during etching). Therefore, one conventional method for detecting the etching endpoint of a semiconductor wafer is to detect the change in the emission intensity of a specific wavelength from the plasma during the dry etching process and to detect the etching endpoint of a specific film based on this detection result. For example, a method is known in which the endpoint is determined based on the change in the amount of light reflected from the wafer during etching.

[0004] One such technique is disclosed in Japanese Patent Laid-Open Publication No. 2007-234666 (Patent Document 1). In this technique, a sample wafer for acquiring data is etched under conditions equivalent to those for processing the product wafer. The sample wafer has the same or substantially similar configuration as the wafer used to manufacture the product semiconductor device. During this etching, interference light from the surface of the sample wafer is detected, and data indicating the intensity of the interference light or its time change, using wavelength as a parameter, is acquired as a database. The interference light data detected during processing of the product wafer (actual wafer) is compared with database data acquired using the sample wafer to determine the amount of etching or remaining film thickness corresponding to the closest data. The end of processing is determined based on the detected amount of etching or remaining film thickness. The database is disclosed as being created by correlating a pattern indicating the intensity of interference light or its time change, using wavelength as a parameter, obtained during etching of a sample such as a semiconductor wafer with the amount of etching or remaining film thickness of the sample wafer, or the elapsed time since the start of processing.

[0005] Japanese Patent Application Laid-Open No. 2007-234666

[0006] However, the above-mentioned conventional techniques have the following problems.

[0007] That is, when the aperture ratio of a sample, such as a wafer, to be plasma etched is small or the etching rate (ER) is small, the intensity and time variation of the interference light from the sample surface change little as the etching progresses. As a result, the difference between the interference light pattern data at a specific sampling time during wafer processing and the interference light pattern data at the sampling times before and after that becomes small. At multiple consecutive sampling times during the etching process, including the specific sampling time during such actual wafer processing, the same interference light pattern data and the corresponding remaining film thickness (remaining film amount) or etching amount (etching depth) are extracted as a result of comparing the detected interference light data with the database. As a result, the accuracy of detecting these amounts is degraded.

[0008] For this reason, the above-mentioned conventional techniques do not take into consideration the problem that the variation in the processed shape as a result of processing a sample such as a wafer becomes large, which reduces the yield of the process for manufacturing semiconductor devices.

[0009] The present disclosure aims to provide a plasma processing method and a plasma processing apparatus that improve the accuracy of detecting the remaining film thickness of a film to be processed on a sample and the etching amount of the film to be processed. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

[0010] A brief summary of representative aspects of this disclosure is as follows.

[0011] A plasma processing method according to one aspect of the present disclosure is a plasma processing method for processing a film to be processed, which is pre-positioned on a surface of a wafer placed in a processing chamber inside a vacuum vessel, using plasma formed in the processing chamber, the method comprising: a step of comparing a set of actual data indicating the intensities of light at multiple wavelengths from the surface of the wafer, which is obtained at an arbitrary time during processing using the plasma and a predetermined number of times prior to the arbitrary time and separated by a predetermined interval, with a detection pattern in which pattern data of the intensities of light at multiple wavelengths obtained in advance is associated with the time of the processing and the remaining thickness of the film, the comparison being performed with the detection pattern data for each processing time of the detection pattern and the set of detection pattern data for times separated by the predetermined interval from the detection pattern data; and a step of determining, as the remaining film thickness at the arbitrary time during the processing, the value of the remaining film thickness corresponding to the detection pattern data compared with the arbitrary time among the set of detection pattern data with the smallest deviation obtained as a result of the comparison; and adjusting the processing conditions based on the result of the determination.

[0012] Furthermore, a plasma processing apparatus according to one aspect of the present disclosure is a plasma processing apparatus that processes a film to be processed, which is placed in advance on the surface of a sample placed in a processing chamber inside a vacuum vessel, using plasma formed in the processing chamber, and includes: a spectrometer that detects interference light of multiple wavelengths from the surface of the sample during processing; a pattern comparison means that compares intensity information of the interference light of multiple wavelengths obtained at any time during processing of the film on the surface of the sample and for any number of arbitrary sampling points at the any time, multiple standard deviation patterns corresponding to multiple thicknesses of the film, and data of interference light of multiple wavelengths related to processing of another sample obtained before processing of the sample, which corresponds to multiple thicknesses of the film, and calculates the deviation; a film thickness determiner that compares the deviation between these with a preset deviation to determine the thickness of the film on the sample at that time; and an end point determiner that determines when etching of a predetermined amount of the film has been completed.

[0013] According to the present disclosure, it is possible to provide a plasma processing method and a plasma processing apparatus that improve the accuracy of detecting the remaining film thickness of a film to be processed on a sample and the etching amount of the film to be processed.

[0014] 1 is a block diagram illustrating the overall configuration of a semiconductor wafer plasma processing apparatus equipped with an etching depth measurement device according to a first embodiment of the present disclosure.

[0023] FIG. 1 is a flowchart illustrating a procedure for determining the remaining film thickness of a processing target film when performing an etching process using an etching depth measurement device according to a conventional technique.

[0024] FIG. 1 is a flowchart illustrating a procedure for determining the remaining film thickness of a processing target film when performing an etching process using the etching depth measurement device of FIG. 1.

[0025] FIG. 1 is a diagram illustrating interference light pattern data. (a) is interference light pattern data set as a DB (database 116), in which the time-differentiated values ​​of interference light intensity changes at multiple wavelengths are represented by color intensity from the start to the end of processing. (b) is pattern data having interference light pattern data for one sampling using a pattern matching method according to the conventional technique. (c) is interference light pattern data for an arbitrary number of samplings (for several arbitrary sampling points) according to the present disclosure.

[0026] FIG. 1 is a graph illustrating the change in the remaining film thickness value over time after the start of etching processing, detected by the plasma processing apparatus according to the embodiment shown in FIG. 4(a) is a graph illustrating the change over time in the detected remaining film thickness value when the remaining film thickness is detected using the actual waveform pattern Dij according to the conventional technique shown in (b) of FIG. 4B is a graph showing the change over time of the remaining film thickness detected when the remaining film thickness is detected using the actual pattern set DSij according to the present embodiment shown in FIG. 4C.

[0015] Hereinafter, embodiments and examples will be described with reference to the drawings. However, in the following description, the same components will be assigned the same reference numerals, and repeated description may be omitted. Note that the drawings may be more schematic than the actual embodiment to clarify the description, but they are merely examples and do not limit the interpretation of the present invention.

[0016] (Embodiments) More specific embodiments of the present disclosure will be described below.

[0017] The present disclosure relates to a plasma processing method or plasma processing apparatus for etching or other processing a film to be processed that has been previously formed on the surface of a substrate-like sample, such as a semiconductor wafer, as a processing object placed in a processing chamber inside a vacuum vessel used in the manufacture of semiconductor integrated circuits, using plasma generated in the processing chamber. In particular, the present disclosure relates to a plasma processing method or plasma processing apparatus for detecting the end point of processing or the remaining thickness of a film to be processed using light obtained from the surface of the sample, such as a semiconductor wafer, during processing.

[0018] The above object is achieved by performing the following algorithm when estimating the current film thickness by calculating the time differential waveform of the interference waveform for each of a plurality of wavelengths, setting the waveform pattern in a database of waveform data previously acquired under the same processing conditions, and comparing the waveform pattern in the database with the waveform pattern calculated by the time differential, thereby processing and monitoring the film thickness and etching depth with high precision.

[0019] In the present disclosure, the reason for using a pattern showing the wavelength dependence of the time differential value of the interference waveform is that the measurement is based on in-situ measurement (measurement performed on the spot in real time) during etching, and the film thickness of the film being processed changes from moment to moment. Therefore, time differential processing of the interference waveform is possible, and the effects of contamination of the measurement window, scraping of the measurement window, and other problems that arise in interference intensity measurement can be reduced. However, time differential processing of the interference waveform is not necessarily required.

[0020] In order to solve the problems of the conventional techniques and to achieve the object of the present disclosure, the present inventors have developed the following algorithms (methods) 1) to 3). Note that this method relates to plasma processing for etching a layer (film) to be processed formed on the main surface (upper surface) of a workpiece (wafer).

[0021] 1) time-differentiating intensity information of interference light of multiple wavelengths observed from a workpiece (actual wafer) at a predetermined time during plasma etching processing and the intensity changes of the interference light of multiple wavelengths for several arbitrary sampling points prior to that time; 2) comparing the time-series pattern information with a time-series pattern of differential values ​​obtained by differentiating the intensity changes of interference light of multiple wavelengths related to the processing of another workpiece (test wafer) obtained before the processing of the workpiece; 3) estimating the film thickness (remaining film thickness) and etching depth of the workpiece when the standard differential waveform patterns corresponding to the respective thicknesses of the workpiece are most similar. This allows the actual remaining film thickness and etching depth of the workpiece to be accurately measured in real time (online). Therefore, a plasma processing method and plasma processing apparatus can be provided that improve the accuracy of detecting the remaining film thickness and etching depth of the workpiece.

[0022] Hereinafter, an embodiment of the present disclosure will be described with reference to FIGS. 1 to 5. FIG.

[0023] An overview of the configuration of a plasma processing apparatus according to the present disclosure will be described using FIG. 1 . FIG. 1 is a diagram schematically illustrating the configuration of a plasma processing apparatus according to a first embodiment of the present disclosure. In FIG. 1 , the plasma processing apparatus 100 of the first embodiment is a semiconductor device manufacturing apparatus capable of performing a plasma processing method in which plasma is generated in a processing chamber 101 disposed inside a vacuum vessel and a target film formed on a substrate-like sample 104, such as a semiconductor wafer, disposed in the processing chamber 101 is etched. Here, a film structure including a target film layer as the target film and a mask layer used as an etching mask when etching the target film is formed on the surface of the semiconductor wafer (hereinafter, referred to as wafer) 104 in advance. The plasma processing apparatus 100 is a semiconductor device manufacturing apparatus capable of relatively accurately detecting the amount of etching or the remaining film thickness (remaining film thickness) of the target film layer during etching at multiple times during the etching process of the target film layer.

[0024] The plasma processing apparatus 100 of this embodiment includes a vacuum vessel, a processing chamber 101 provided inside the vacuum vessel and configured to be depressurized, and a sample stage 102 located at the bottom of the processing chamber 101. A wafer 104 is placed on the upper surface of the sample stage 102 and undergoes processing such as etching. Although not shown, a vacuum pump such as a turbomolecular pump is connected to the bottom of the vacuum vessel. The vacuum pump is provided in communication with the interior of the processing chamber 101 and is configured to be able to evacuate gases inside the connected processing chamber 101 and reduce the pressure.

[0025] The plasma processing apparatus 100 further includes an etching amount detection device 107. The etching amount detection device 107 is connected to the top of the vacuum chamber above the wafer 104, receives light from the surface of the wafer 104 during processing, detects the light intensity of multiple wavelengths and its change over time, and forms at least a part of an apparatus or system that uses the time-series data to detect the etching amount or remaining film thickness of the film layer being processed.

[0026] In this embodiment, a wafer 104 placed inside the processing chamber 1 has a film structure to be etched pre-positioned on its surface. This film structure has multiple layers of film in the vertical direction, including a resist film layer as a mask layer above and a film layer to be processed placed below it. Figure 6 is a cross-sectional view schematically showing the film structure of the wafer 104. A film layer 1041 to be processed is formed on the surface of the wafer 104, and a mask layer 1042 with a pattern formed thereon is formed on the film layer 1041.

[0027] In this embodiment, plasma processing of a wafer 104 begins by placing the wafer 104 on the upper surface of a sample stage 102 disposed inside a processing chamber 101, and then supplying a processing gas into the processing chamber 101 to generate plasma 105. Grooves and holes are formed in the processing target film 1041 by etching in a shape that conforms to the pattern of a mask layer 1042 when viewed from above. The process of manufacturing a semiconductor device includes multiple steps for forming a circuit pattern on the wafer 104, and by performing these multiple steps, a semiconductor device can be manufactured on the wafer 104. The plasma processing method relating to the etching process of this embodiment constitutes part of the process of manufacturing a semiconductor device.

[0028] 1, during a plasma etching process of a wafer 104, light from the plasma formed in the process chamber 101 or light irradiated onto the surface of the wafer 104 from above the wafer 104 by an etching amount detection device 107 or the like is reflected by a plurality of film layers of different heights in the film structure on the surface of the wafer 104 to form interference light 103. It is known that attenuation of light of wavelengths in the ultraviolet region of the interference light 103 is relatively large.

[0029] That is, the interference light 103 includes components whose intensity increases or decreases depending on the wavelength due to interference of light containing multiple wavelengths reflected by the end face of the target film 1041, whose film thickness changes as etching progresses, or by the end face of another film layer (e.g., the mask layer 1042). The intensity of the interference light 103 for each specific wavelength, or the pattern of the time-varying values ​​of the interference light 103 (or the intensity for each specific wavelength), is considered to uniquely correspond to the remaining film thickness (remaining film thickness) of the target film 1041. Therefore, a database (116) is created in advance by acquiring multiple data patterns with wavelength as a parameter, corresponding to the remaining film thickness (remaining film thickness) of the target film 1041 or the etching amount of the target film 1041. The database (116) is then searched based on the data patterns (actual patterns) obtained from the interference light from the surface of the actual wafer at times during the processing of the actual wafer. Then, by detecting a data pattern that is closest to the data pattern (actual pattern) from the patterns stored in the database (116), it becomes possible to relatively accurately detect the remaining film thickness (remaining film thickness) of the film to be processed 1041 and the etching amount of the film to be processed 1041. In this embodiment, the interference light 103 and the light that is not reflected from the surface of the wafer 104 are received by a photodetector 1081 disposed above the processing chamber 101, and transmitted to the etching amount detecting device 107 through an optical fiber 106 that connects the photodetector 1081 and the etching amount detecting device 107.

[0030] The etching depth detecting device 107 receives the interference light 103 from the surface of the wafer 104, received by the photodetector 1081, through the spectrometer 108 at predetermined intervals (sampling intervals) during the processing of the wafer 104. The etching depth detecting device 107 then calculates the light intensity or the time change data of the light intensity, with the wavelength of the interference light 103 as a parameter, using signals indicating the intensity of each interference light 103 for each of a plurality of wavelengths. The etching depth detecting device 107 further compares the light intensity or the time change pattern of the light intensity, with the wavelength as a parameter, with the pattern data of the intensity of the interference light 103 or the time change of the light intensity, which is associated with the film thickness and stored in advance in the differential waveform pattern database 116. The etching depth detecting device 107 uses the results of this comparison to calculate the remaining film thickness and the etching depth of the film 1041 to be processed.

[0031] The etching depth detection device 107 includes a spectrometer 108, a first digital filter 109, a differentiator 110, a second digital filter 111, a waveform information storage unit 112, a differential waveform comparator 113, a differential waveform pattern database 116, an end point determiner 114 that determines the end point of etching based on the result of the comparator 113, an end point determiner 115 that determines the end point, and a display 117 that displays the determination result.

[0032] The actual configuration of the etching depth detection device 107, excluding the display 117 and the spectrometer 108, can be made up of a CPU, a storage device, a data input / output device, and a communication control device. The storage device includes a ROM that stores various data such as an etching depth and film thickness detection processing program and a database of differential waveform patterns of the interference light 103, a RAM for storing detection data, an external storage device, etc. This is the same as in Figures 2 and 3.

[0033] At any sampling time during the processing of the wafer 104, the interference light 103 received by the photodetector 1081 is transmitted to the spectrometer 108 through the optical fiber 106. The spectrometer 108 separates the transmitted interference light 103 into a plurality of predetermined wavelengths, and detects the light intensity of each wavelength. The detected light intensity of each wavelength is converted into a digital signal indicating the light intensity of the interference light 103 at each wavelength.

[0034] The interfering light 103 from the film structure on the top surface of the wafer 104 captured by the spectroscope 108 during processing includes light of multiple wavelengths. The interfering light 103 is converted into a current detection signal corresponding to the light intensity for each wavelength, and further converted into a voltage signal. For example, the interfering light 103 of multiple wavelengths received at an arbitrary sampling time i and sent to the spectroscope 108 is output as a sampling signal indicating the intensity of each of the multiple wavelengths at time i, and is stored as time-series data yij in a storage device such as a RAM (not shown).

[0035] Next, the time series data yij from the spectrometer 108 is transmitted to a first digital filter 109, where data above a predetermined frequency contained in the time series data yij is removed and smoothed, and the processed data is stored in a storage device such as a RAM as smoothed time series data Yij. This smoothed time series data Yij is transmitted to a differentiator 110, where time series data dij of the time change rate of the time series data yij of the interference light 103 at a predetermined sampling time, i.e., the derivative value (first derivative value or second derivative value), is calculated and stored in a storage device such as a RAM. The derivative value time series data dij is transmitted to a second digital filter 111, where it is smoothed again and stored in a waveform information storage unit 112 as smoothed derivative time series data Dij.

[0036] Here, the calculation of the smoothed differential coefficient time series data Dij will be described. In the following description, the symbol j will be omitted as it describes the interference light 103 of an arbitrary wavelength. As the first digital filter 109, for example, a second-order Butterworth low-pass filter is used, and the smoothed time series data Yi is obtained by the low-pass filter (109) using equation (1).

[0037] Yi = b1 yi + b2 (yi-1) + b3 (yi-2) - [a2 (Yi-1) + a3 (Yi-2)] (1) where the coefficients a and b vary depending on the sampling time (sampling interval or sampling frequency) and the cutoff frequency. For example, in the case of a sampling frequency of 10 Hz and a cutoff frequency of 1 Hz, the coefficient values ​​are a2 = -1.143, a3 = 0.4128, b1 = 0.067455, b2 = -0.013491, and b3 = 0.067455.

[0038] The time series data di of the second derivative value is calculated by the differentiator 110 from the five points of time series data Yi using the polynomial adaptive smoothing differentiation method according to equation (2) as follows:

[0039] k=2 di=Σwk·Yi+k (2) k=-2 Here, k=-2 is the first value of the variable k of Sigma Σ, and k=2 is the last value of the variable k of Sigma Σ (k=-2, -1, 0, 1, 2). Here, examples of values ​​of the weighting coefficient wk are w-2=2, w-1=-1, w0=-2, w1=-1, and w2=2.

[0040] Using the time series data di of the differential coefficient values, the smoothed differential coefficient time series data Di is calculated from equation (3) as follows, using, for example, a second-order Butterworth low-pass filter as the second digital filter 12. Di=b1·di+b2·(di−1)+b3·(di−2)−[a2·(Di−1)+a3·(Di−2)] (3) In this embodiment, the waveform information storage unit 112 stores the smoothed differential coefficient time series data Dij of the interference light 103 obtained at each sampling time from a time that is a predetermined number of sampling intervals before a predetermined time obtained when etching a wafer 104 (actual wafer) in real time to the current time (current sampling time), as information indicating the interference light intensity or pattern (actual pattern) data of its time change obtained from the actual wafer.

[0041] Meanwhile, data Psj of the pattern of the interference light 103T is stored in advance in the differential waveform pattern database 116. The data Psj is data of the pattern of the interference light 103T, with the wavelength of the interference light 103T including a plurality of wavelengths obtained when a test wafer 104T, which has the same material, shape, and configuration as a wafer 104 for manufacturing semiconductor devices and its film structure, is etched under the same conditions as the wafer 104. The data Psj of the pattern of the interference light 103T is data on the interference light 103 from the film to be processed 1041 corresponding to different remaining film thicknesses (remaining film thickness) of the film to be processed 1041, or data values ​​indicating the remaining film thickness of the film to be processed 1041, and includes patterns with the wavelength of the intensity of the interference light 103 or the value of the change in intensity over time as a parameter. In this embodiment, the pattern data Psj of the interference light 103T is stored as a differential waveform pattern database 116 used when detecting the remaining film thickness of the target film 1041 and the etching amount of the target film 1041 in a memory device such as a RAM or ROM (not shown) included in the etching amount detection device 107, or in a storage device such as a hard disk or DVD disk. The pattern data Psj can be considered as a plurality of standard deviation patterns, detection patterns, or detection pattern data corresponding to a plurality of film thicknesses. The pattern data Psj is data on interference light of a plurality of wavelengths related to the processing of another sample (a test wafer 104T) obtained before the processing of the actual wafer, and includes interference light of a plurality of wavelengths corresponding to a plurality of thicknesses of the target film 1041.

[0042] The differential waveform comparator 113, which serves as pattern comparison means, compares the data (pattern data Psj) stored in the differential waveform pattern database 116 with an actual pattern set DSij, which is a set (plurality of actual data) of actual pattern data Dij of the interference light 103 corresponding to each of the current sampling time and a predetermined number (M in this example) of sampling times (plurality of past times) before the current sampling time (plurality of past times) stored in the waveform information storage unit 112. That is, a comparison is made between the actual pattern data set DSij, which is a set (set) of actual patterns Dij, and a plurality (sets) of pattern data Psj representing the intensity of interference light or the temporal change in the intensity of interference light, each of which is data indicating a pattern stored in the differential waveform pattern database 116 and which has as a parameter a wavelength associated with a different etching amount, remaining film thickness, or time after the start of etching. The differential waveform comparator 113 then calculates the difference (also called deviation) between these (between a plurality (sets) of pattern data Psj and the actual pattern data set DSij (set)), and detects the etching amount of the target film 1041, the remaining film thickness of the target film 1041, or the etching time of the target film 1041 corresponding to the pattern data with the smallest difference value. From these detected values ​​(etching amount, remaining film thickness, etching time), for example, the remaining film thickness is detected as the instantaneous film thickness value Zi at the current sampling time, and the value of the instantaneous film thickness value Zi is stored in the memory device of the etching amount detection device 107 as time-series data.

[0043] A film thickness and depth determiner (film thickness determiner) 114 receives the output from the differential waveform comparator 113 or reads out data on the instantaneous film thickness value Zi at sampling time i stored in a storage device, and also reads out instantaneous film thickness values ​​Zi-n (i-n are sampling times before i) from the storage device, performs regression analysis using these, and calculates the film thickness value at time i from the results of a regression line approximation. That is, the film thickness and depth determiner 114 determines a linear regression line Y=Xa·t+Xb (Y: remaining film thickness, t: etching time, Xa: absolute value of etching rate, Xb: initial film thickness), and calculates and determines the film thickness Yi (calculated film thickness) at sampling time i from this regression line.

[0044] Next, data indicating the calculated film thickness Yi is sent to the end-point determiner 115, which compares the film thickness Yi with the target film thickness (target film thickness) of the etching process. That is, the end-point determiner 115 determines that etching has ended when the etching amount of the target film 1041 reaches a predetermined amount (target etching amount). If the comparison results in the film thickness Yi being equal to or greater than the target film thickness, the etching process continues. On the other hand, if the comparison results in the film thickness Yi being equal to or less than the target film thickness, the etching amount of the target film 1041 on the wafer 104 has reached the target, and this result is displayed on the display 117. If it is determined that etching has ended, the generation of the electric field or magnetic field in the plasma generating section is stopped, the plasma 105 is extinguished, and the etching process for the wafer 104 is terminated. If it is determined that etching has not ended, the processing conditions, such as the etching gas and pressure, are changed, and the processing of the target film 1041 is continued.

[0045] In this embodiment, the number n of multiple pattern data Psj (standard deviation patterns) stored in the differential waveform pattern database 116 and associated with different etching amounts, remaining film thicknesses, or times after the start of etching is set to be greater than the number of the current sampling time and a predetermined number of past sampling times to which each pattern data in the actual pattern data set DSij corresponds. That is, the number n of multiple pattern data Psj stored in the differential waveform pattern database 116 is greater than or equal to the number M of pattern data in the actual pattern data set DSij. The differential waveform comparator 113 compares each of M pieces (sets) of pattern data Psj selected from the n pieces of pattern data Psj in order of the corresponding etching amount, remaining film thickness, or etching time with each piece of data Dij (sets) in the actual pattern data set DSij in order of sampling time, and calculates the magnitude of the difference between them.

[0046] For example, each of the first, second, ..., Mth actual pattern data Dij in the actual pattern data set DSij in ascending order of sampling time is compared with the first and second pieces of M pattern data Psj selected from n pattern data Psj in ascending order of etching time, and the magnitude of the difference between them is calculated. In this case, the intervals between the corresponding etching times of the M pattern data Psj selected from n are set to be the same as the intervals between the corresponding sampling times of the M actual pattern data Dij.

[0047] In this case, if the M pieces of actual pattern data Dij are from the i-th current sampling time to the i-(M-1)-th past sampling time, M pieces of pattern data Psj corresponding to the etching times at intervals of M-1 sampling times from the i-(M-1)-th sampling time to the i-th sampling time in the actual pattern data Dij are selected in order from the n pieces of pattern data Psj corresponding to the shortest etching time. Then, each of the selected M pieces of pattern data Psj is compared with each of the M pieces of actual pattern data Dij, and the sum of their differences is calculated.

[0048] Next, starting from the pattern data corresponding to the next smallest etching time among the n pattern data Psj, each of the M pattern data Psj is compared with each of the M actual data Dij at each sampling interval, and the sum of the mutual differences is calculated.

[0049] The selection of M pieces of pattern data Psj, comparison with the set of actual data Dij, and calculation of the sum of the differences constitute one cycle, and this cycle is performed (n-M-1) times by sequentially selecting the n pieces of pattern data Psj from the set of actual data Dij. From the results of the sum of the differences calculated in the multiple cycles, the M pieces of pattern data Psj in the cycle that produces the smallest sum of the differences are selected. Then, of the selected M pieces of pattern data Psj, the pattern data Psj with the longest etching time is detected as the pattern data Psj at the current sampling time. Then, the etching amount or remaining film thickness corresponding to the etching time of the selected pattern data Psj is detected as the etching amount or remaining film thickness (instantaneous film thickness Zi) at the current sampling time.

[0050] In this embodiment, such a comparison cycle begins with a comparison using at least the first to Mth sets of pattern data Psj among n sets of pattern data Psj arranged in ascending order of etching time, including time 0, and is performed until the Mth pattern data Psj in each cycle becomes the pattern data corresponding to the longest etching time among the n pattern data Psj. In this example, the interval between each set of data Dij in the real pattern data set DSij is set equal to the sampling interval at which the etching amount detection device 107 detects the interference light 103 via the photodetector 1081 during processing of the real wafer 104. However, the sampling interval between the M sets of real pattern data Dij used to detect the instantaneous film thickness does not need to be fixed to a predetermined value, and it does not need to be equal to the sampling interval. It may be appropriately selected depending on the required film thickness detection accuracy, the time required for detection, etc.

[0051] In the differential waveform pattern database 116, different etching times corresponding to the pattern data Psj are associated with different remaining film thicknesses or etching amounts, and therefore, the remaining film thickness corresponding to the maximum etching time of the pattern data Psj in the comparison cycle in which the sum of the detected differences is minimized is calculated. In the above example, the case where each piece of pattern data Psj is associated with a different time after the start of etching has been described. If the pattern data Psj is associated with different etching amounts or remaining film thickness values ​​of the processing target film 1041, the multiple pattern data Psj may be converted, before processing the wafer 104, into data representing the corresponding etching amounts or remaining film thicknesses using well-known techniques such as regression analysis or interpolation, such that the intervals between these values ​​match the intervals between the sampling times of the actual pattern data Dij.

[0052] As described above, in this embodiment, the intervals between adjacent pieces of pattern data Psj used to detect the instantaneous film thickness are selected or set in advance to match the intervals between the current sampling time and each of the adjacent sampling times for a predetermined number of previous times corresponding to each piece of pattern data Dij in one or more comparison cycles. This increases the number of samples of the calculated sum of differences in each comparison cycle, thereby improving the accuracy of detecting and selecting the instantaneous film thickness corresponding to the smallest sum of differences. Furthermore, in this embodiment, the intervals between adjacent pieces of pattern data Psj used to detect the instantaneous film thickness are set equal to the sampling interval at which the interference light 103 is detected during processing of the actual wafer 104, or a natural number multiple of the sampling interval of the interference light 103.

[0053] Next, a procedure for calculating the etching amount of a film to be processed when performing etching processing using the etching amount detection device 107 of Fig. 1 will be described in order of each step using the flowchart of Fig. 3. Fig. 3 is a flowchart showing the flow of operations for detecting the etching amount of the plasma processing apparatus according to the embodiment shown in Fig. 1. The flowchart mainly shows the flow of operations of the etching amount detection device 107.

[0054] (Step 301) In this embodiment, prior to processing wafers (actual wafers) 104 to be etched in a mass production process for semiconductor devices, the etching amount detection device 107, based on a command signal from a controller (not shown) of the plasma processing device 100, sets the target remaining film thickness of the film to be processed and pattern data selected from the differential waveform pattern database 116 to be used for detecting or determining the target remaining film thickness. The differential waveform pattern database 116 pre-stores data (data Psj) indicating the intensity of interference light or its time change obtained when the actual wafers 104, which are the target wafers to be processed for manufacturing semiconductor devices, and test (sample or test) wafers having the same material, shape, and configuration as the actual wafers 104 in terms of the film structure on their surfaces, are etched under conditions equivalent to those of the actual wafers 104. The data Psj is data on patterns (standard patterns) of the intensity of interference light or its time change, using wavelengths associated with different etching amounts or remaining film thicknesses of the film to be processed or etching times after the start of etching as parameters. In this step 301, the pattern data Psj of the interference light is set in correspondence with different etching amounts or remaining film thicknesses of the film to be processed and the processing time (etching time) after the start of etching, along with the target etching amount or remaining film thickness value for etching the actual wafer 104 and the tolerance or threshold value for determining the target value performed by the differential waveform comparator 113.

[0055] (Step 302) Next, plasma 105 is formed in processing chamber 101 to start processing wafer 104, and interference light obtained from actual wafer 104 including a film to be processed during the etching process is detected at predetermined sampling intervals (e.g., 0.1 to 0.5 seconds). At this time, high-frequency power is supplied to an electrode disposed inside sample stage 102 after plasma 105 is formed, and as the etching process begins, a sampling start command is issued. During the process, the intensity of the multi-wavelength interference light, which changes as the etching progresses, is transmitted to spectrometer 108 of etching amount detection device 107, and the photodetector detects and outputs a photodetection signal of a voltage corresponding to the light intensity for each predetermined frequency.

[0056] (Step 303) The photodetection signal of the spectrometer 108 is converted into a digital signal, and a sampling signal yij is obtained as a data signal associated with an arbitrary time. Next, the multi-wavelength output signal yij from the spectrometer 108 is smoothed by a first digital filter 109 in the first stage, and time-series data Yij at the arbitrary time is calculated.

[0057] (Step 304) Next, the time series data Yij is transmitted to the differentiator 110, and the differential coefficient dij of the time series is calculated by the SG method (Savitzky-Golay method). That is, the coefficient (first or second order) dij of the signal waveform is detected by the differentiation process (SG method).

[0058] (Step 305) The differential coefficient dij is transmitted to the second digital filter 111 in the second stage, and smoothed differential coefficient time series data Dij is calculated.

[0059] (Step 306) The obtained smoothed differential coefficient time series data Dij is transmitted to and held (stored) in the waveform information storage unit 112.

[0060] (Step 307) In the differential waveform comparator 113, a comparison cycle is performed a number of times that allows M to be selected from n pieces of pattern data Psj, in which a set DSij of waveform patterns Dij obtained from the actual wafer 104 corresponding to a predetermined number (M) of sampling times stored in the waveform information storage unit 112 is compared with M pieces of pattern data Psj selected from a plurality (n pieces, n≧M) of pattern data Psj stored in the differential waveform pattern database 116. In each comparison cycle that is performed a plurality of times, a value of σs(t)=√(ΣΣ(Dij-Psj)2 / j) is calculated as the sum of the differences in values ​​at each wavelength for each of the M sampling times between the selected M pieces of pattern data Psj and the actual pattern Dij, and the value of σs(t) obtained during the comparison cycle is calculated to be the smallest.

[0061] (Step 308) The remaining film thickness corresponding to the calculated minimum value of σs(t) is calculated as the instantaneous film thickness data Zi at the arbitrary sampling time (current time) i, and the remaining film thickness at the current time i (calculated film thickness) calculated by regression analysis using the instantaneous film thickness values ​​at one or more previous sampling times before the current time and the instantaneous film thickness data Zi is determined to be the remaining film thickness at the current time i.

[0062] The remaining film thickness corresponding to the minimum value of σs(t) is determined by detecting the longest etching time associated with the M pieces of pattern data Psj in the comparison cycle in which σs(t) was minimized, calculating the etching amount or remaining film thickness corresponding to the etching time, and detecting it as the etching amount or remaining film thickness at the current sampling time. The detected remaining film thickness is stored in a memory device within the etching amount detection device 107 as instantaneous film thickness data Zi at the current sampling time i. The correlation between the etching amount or remaining film thickness corresponding to the plurality of pattern data Psj and the etching time is performed in the differential waveform pattern database 116 or differential waveform comparator 113 of the etching amount detection device 107 before the start of the etching process, based on a command signal from a controller (not shown).

[0063] (Step 309) In the end point determiner 115, the calculated film thickness of the film being processed at the current time i is compared with the predetermined target remaining film thickness value (set in step 301) to determine whether the end point has been reached. If it is determined that the calculated film thickness is equal to or less than the target remaining film thickness value (309: YES), it is determined that the target has been reached, and the etching amount, such as the etching depth, is determined. If it is determined that this is sufficient, a signal to terminate the etching process is sent to the plasma processing apparatus 100, and sampling is set to end (step 310). On the other hand, if it is determined that the target has not been reached (309: NO), the process returns to step 303, and the subsequent steps (303-308) are performed again. At this time, the etching process conditions can be adjusted in the plasma processing apparatus 100 based on the results of the determination. Then, the process proceeds to step 309 again. If it is determined that the calculated film thickness is equal to or less than the target remaining film thickness (309: YES), the etching amount, such as the etching depth, is determined. If it is determined that this is sufficient, a signal to terminate the etching process is sent to the plasma processing apparatus 100, and the end of sampling is set (step 310).

[0064] Next, as a comparative example, a procedure for determining the remaining film thickness of a film to be processed will be described using the flowchart of Fig. 2. Fig. 2 is a flowchart showing the procedure for determining the remaining film thickness of a film to be processed when performing an etching process using an etching depth measuring device according to a conventional technique.

[0065] (Step 201) to (Step 205) are the same as (Step 301) to (Step 305) in FIG. 3, so the explanation will be omitted.

[0066] (Step 206) The obtained smoothed differential coefficient time series data Dij is compared with the differential waveform pattern database 116, and the similarity is quantified.

[0067] (Step 207) Based on the quantified similarity, the etching amount corresponding to the closest data is detected and calculated.

[0068] (Step 208) The calculated etching amount is compared with the target film thickness to determine whether the etching amount has reached the target film thickness. If it is determined that the etching amount has not reached the target film thickness (208: NO), the process proceeds to step 203 and continues. If it is determined that the etching amount has reached the target film thickness (208: YES), the process ends.

[0069] As such, it can be seen that the operations of steps 307-309 of the flowchart of FIG. 3 according to the present disclosure are different from the operations of steps 207-209 of the flowchart of FIG.

[0070] 4 will be used to explain examples of pattern data Psj of the intensity of interference light or its time change value, which are stored in the differential waveform pattern database 116 and which are used in this embodiment, and which have wavelengths associated with different etching amounts, remaining film thicknesses, or etching times as parameters, and pattern data Dij of actual waveforms obtained during processing of the actual wafers 104. Figures 4(a), (b), and (c) are graphs showing configuration examples of patterns of the intensity of interference light or its time change value, which are stored in the differential waveform pattern database 116 of the plasma processing apparatus 100 according to the embodiment shown in Figure 1.

[0071] 4A shows pattern data Psj as a standard waveform pattern (standard deviation pattern) in which the magnitude of the differential value of the intensity of interference light is represented by color shading, with different etching amounts, remaining film thicknesses, or etching times on the horizontal axis and wavelengths on the vertical axis. FIG. 4B shows actual pattern data Dij, which corresponds to the prior art, in which the magnitude of the differential value of the intensity of interference light is represented by color shading, with wavelengths obtained at only one arbitrary sampling time represented by the vertical axis. FIG. 4C shows a set DSij of actual waveform pattern data Dij, which is used in this embodiment and shows the magnitude of the differential value of the intensity of interference light by color shading, with wavelengths at multiple sampling times (25 in this figure) consisting of the current sampling time and past times. The set DSij can be considered as intensity information of interference light at multiple wavelengths obtained at any number of sampling points.

[0072] The actual waveform pattern data Dij of the interference light intensities of N wavelengths or their time variations based on the interference light data obtained at any time during the etching process after the start of the etching process shown in Figure 4(b) or (c) is compared with the waveform pattern data Psj. In this comparison, the change with time after the start of the process (etching time) in the etching time or remaining film thickness value corresponding to the pattern having the smallest total sum of the differences between the two among the waveform pattern data Psj corresponding to each value of the parameter on the horizontal axis shown in Figure 4(a) will be described with reference to Figure 5.

[0073] 5A and 5B are graphs illustrating the change in the remaining film thickness value over time after the start of the etching process detected by the plasma processing apparatus according to the embodiment shown in FIG. 5A. In the graphs of FIGS. 5A and 5B, the horizontal axis represents the etching time, and the vertical axis represents the remaining film thickness value. FIG. 5A is a graph showing the change in the remaining film thickness value over time when the remaining film thickness is detected using the actual waveform pattern Dij according to the conventional technology shown in FIG. 4B. FIG. 5B is a graph showing the change in the remaining film thickness value over time when the remaining film thickness is detected using the 25 actual pattern sets DSij obtained at the current sampling time and 24 different sampling times in the past from the actual wafer according to the embodiment shown in FIG. 4C.

[0074] As shown in FIG. 5A, in the process of the differential waveform comparator 113 shown in step 308 of FIG. 3, the comparison of the waveform pattern data Psj with the actual waveform pattern data Dij of the interference light 103 obtained at multiple sampling times during the etching period shows the same remaining film thickness value at multiple consecutive values ​​of the etching time (sampling time) plotted on the horizontal axis. In other words, no change in the etching amount or film thickness associated with the progress of etching is detected during these time periods. This indicates that, at these times, the change in the actual waveform pattern data Dij associated with changes in etching time is very small, so that a pattern corresponding to the same etching time is selected from the same waveform pattern data Psj. Possible reasons for such small change in the actual waveform pattern data Dij at multiple consecutive times include a small percentage of the area of ​​the wafer 104 surface not covered by the mask layer 1042 (as viewed from above) or a small etching rate. In such cases, the accuracy of the detection of the remaining film thickness and etching amount is impaired, resulting in a problem of reduced yield in the etching process.

[0075] On the other hand, in Figure 5(b), even at a plurality of consecutive times where the remaining film thickness shown in Figure 5(a) is the same, the detected remaining film thickness changes, indicating that the deterioration of the accuracy of detecting the remaining film thickness is suppressed even during these time periods. In this example, the actual waveform pattern data of the interference light 103 from the actual wafer 104 obtained at an arbitrary sampling time i, as well as the actual waveform pattern data obtained at 24 consecutive sampling times before the arbitrary sampling time i, are used as a single set of actual waveform pattern data DSij. Then, a comparison cycle is performed in which this set of actual waveform pattern data DSij is compared with 25 pattern data corresponding to 25 consecutive etching times in the waveform pattern data Psj, each corresponding to a plurality of different etching times. Then, a set of pattern data corresponding to 25 consecutive etching times that has the smallest sum of the values ​​for each wavelength with the actual pattern data DSij is detected from the plurality of waveform pattern data Psj. As a result, changes in the pattern of the interference light 103 obtained from the actual wafer 104 over time can be detected, and the accuracy of detecting the amount of etching or remaining film thickness, and ultimately the accuracy of the processed shape of the wafer 104 surface obtained as a result of the etching process, can be improved.

[0076] The disclosure made by the present inventor has been specifically described above based on examples, but it goes without saying that the present disclosure is not limited to the above examples and can be modified in various ways.

[0077] 101: Vacuum processing chamber, 102: Sample stage, 103: Interference light, 104: Material to be processed (wafer), 1041: Film to be processed, 1042: Mask film, 105: Plasma, 106: Optical fiber, 107: Film thickness measuring device, 1081: Light receiver, 108: Spectrometer, 109: First digital filter, 110: Differentiator, 111: Second digital filter, 112: Waveform information storage unit, 113: Differential waveform comparator, 114: Film thickness / depth determiner, 115: End point determiner, 116: Differential waveform pattern database, 117: Display.

Claims

1. A plasma processing method for processing a film to be processed, which is placed in advance on the surface of a wafer placed in a processing chamber inside a vacuum vessel, using plasma formed in the processing chamber, the method comprising: a step of comparing a set of actual data indicating the intensity of light at multiple wavelengths from the surface of the wafer, obtained at an arbitrary time during processing using the plasma and at a predetermined number of times before the arbitrary time and separated by a predetermined interval, with a detection pattern in which the previously obtained pattern data of the intensity of light at multiple wavelengths is associated with the time of the processing and the remaining thickness of the film, the step of comparing the detection pattern data for each processing time of the detection pattern with the set of detection pattern data for times separated by the predetermined interval from the detection pattern data; and a step of determining, as the remaining film thickness at the arbitrary time during the processing, the value of the detection pattern data corresponding to the detection pattern data compared with the arbitrary time, among the set of detection pattern data with the smallest deviation obtained as a result of the comparison, 2. A plasma processing method according to claim 1, wherein the remaining film thickness is determined using the actual data set with the smallest sum of deviations between the data in the set of actual data and the set of detection patterns as a result of the comparison.

3. A plasma processing method according to claim 1 or 2, wherein the comparing step compares a plurality of sets of actual data indicating differential values ​​of the light intensity of the plurality of wavelengths from the surface of the wafer obtained at the arbitrary time during the processing and at a plurality of past times spaced apart from the arbitrary time by the predetermined interval, with the detection pattern in which pattern data of differential values ​​of the light intensity of the plurality of wavelengths obtained in advance is associated with the time of the processing and the remaining thickness of the film.

4. A plasma processing method according to claim 1 or 2, wherein the actual data indicating the intensities of light of the plurality of wavelengths is detected at a plurality of times at predetermined sampling intervals during the processing, and the comparison step uses a set of the actual data obtained at the arbitrary time and at past times at the predetermined number of sampling intervals therefrom.

5. A plasma processing apparatus that processes a film to be processed, which is placed in advance on the surface of a sample placed in a processing chamber inside a vacuum vessel, using plasma formed in the processing chamber, comprising: a spectrometer that detects interference light of multiple wavelengths from the surface of the sample during processing; a pattern comparison means that compares intensity information of the interference light of multiple wavelengths obtained at any time during processing of the film on the surface of the sample and for any number of arbitrary sampling points at the any time, multiple standard deviation patterns corresponding to multiple thicknesses of the film, and data on interference light of multiple wavelengths related to the processing of another sample obtained before the processing of the sample, which corresponds to multiple thicknesses of the film, and calculates the deviation; a film thickness determiner that compares the deviation between these with a preset deviation to determine the thickness of the film on the sample at that time; and an end point determiner that determines when etching of the film by a predetermined amount has been completed.

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