Plasma processing device and plasma processing method

Abstract

In order to provide a plasma processing apparatus or plasma processing method for detecting the etching amount of a film to be processed with high accuracy and improving the processing yield, the plasma processing apparatus or plasma processing method includes the following steps: detecting the thickness of the film layer to be processed or the etching depth by using the results of detecting signals representing the intensity of interference light of multiple wavelengths formed by reflection from the wafer surface at multiple times from the formation of plasma to the end of etching; detecting the start time of etching processing of the film layer to be processed by using the amount of change in the intensity of the interference light of multiple wavelengths obtained in an initial period immediately after the formation of plasma in the process; and detecting the remaining film thickness or etching amount at any time based on the results of comparing actual data representing the intensity of the interference light of multiple wavelengths at any time in the process after the start time with multiple data for detecting the intensity of the interference light of multiple wavelengths corresponding to multiple values ​​of the film thickness or etching depth obtained in advance.

Description

Technical Field

[0001] The present invention relates to a plasma processing device or a plasma processing method. Background Art

[0002] In the manufacture of semiconductor devices, various components and interconnecting wiring are formed on the surface of a wafer. These components and wiring can be formed by repeatedly forming films of various materials such as conductors, semiconductors, and insulators and removing unnecessary parts.

[0003] As a process for removing unwanted parts, dry etching using plasma (hereinafter referred to as plasma etching) is widely used. In plasma etching, the gas introduced into the processing chamber of the etching device is plasmatized by a high-frequency power supply, and the wafer is exposed to the plasmatized gas to perform the etching process. In this process, anisotropic and isotropic etching are performed by sputtering based on ions in the plasma and chemical reactions based on free radicals. By using these methods separately, various components and wiring structures are formed on the wafer surface.

[0004] If the processed shape obtained by such an etching process differs from the designed shape, the manufactured semiconductor cannot exhibit desired performance. Therefore, in order to make the processed shape close to the designed shape, a process monitoring technology for monitoring and stabilizing the etching process is required.

[0005] In particular, as semiconductor devices have become increasingly miniaturized in recent years, miniaturization processes have increased, and patterning methods for semiconductor devices have become more diverse. This has led to an increasing need to monitor changes in film thickness and depth immediately after the start of etching.

[0006] In contrast, there is technology related to process monitoring, for example, which measures the thickness of films formed on wafers and the depth of trenches and holes formed on wafers by measuring reflected light from the wafer being processed. This process monitoring, known as film thickness / depth monitoring, is used for endpoint determination in etching processes, for example.

[0007] An example of etching monitoring technology is disclosed in Patent Document 1. Patent Document 1 discloses a technology that, in a process of performing plasma dry etching on a conductor film deposited on a wafer using a photoresist pattern formed on the conductor film as an etching mask, continuously monitors the waveform of light emission of a desired wavelength detected from the plasma from a change start point A to a change end point B during the dry etching process. This technology measures the uniformity of the etching rate of the film within the etched surface, and, based on this uniformity, determines the optimal etching amount of the film.

[0008] In addition, Patent Document 2 discloses a plasma processing device comprising: a detector for detecting interference light of multiple wavelengths from the surface of a sample undergoing etching processing; a pattern comparison unit for comparing actual deviation pattern data associated with the interference light obtained at any time during the processing of the sample with data on interference light of multiple wavelengths associated with the processing of other samples obtained before the processing of the sample, i.e., multiple standard deviation patterns corresponding to multiple thicknesses of the film, and calculating their deviations; a deviation comparison unit for comparing the deviations therebetween with a pre-set deviation and outputting data associated with the thickness of the film of the sample at that point in time; a remaining film thickness time series data recording unit for recording data associated with the thickness of the film as time series data; and an endpoint determiner for determining the end of a given amount of etching using the film thickness data.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 2003-243368

[0012] Patent Document 2: Japanese Patent Application Laid-Open No. 2007-234666 Summary of the Invention

[0013] Problems to be solved by the invention

[0014] In the above-mentioned prior art, the following problems arise.

[0015] First, in order to improve the reliability of the etching process, the technology of Patent Document 1 continuously measures the voltage from the change start point A to the change end point B of the waveform of light emission of a given wavelength detected from the plasma during the etching process. This allows the uniformity of the etching rate of the etched film to be measured. Furthermore, the optimal etching amount is determined based on the obtained etching rate.

[0016] However, the technology of Patent Document 1 is based on the premise that the voltage of the desired wavelength with high sensitivity increases and decreases uniformly, or so-called monotonically changes. It does not take into account the increase and decrease in the amount of light during processing, such as the amount of light emitted by plasma in actual etching, and it may be difficult to detect the film thickness with high precision.

[0017] Furthermore, in the technology of patent document 2, a database of patterns of interference light of multiple wavelengths obtained in advance is used to compare the pattern of interference light obtained from the surface of the chip at any time during the process with the pattern in the database, and the film thickness value corresponding to the data with the smallest deviation is recorded as film thickness information in a time series. The etching amount (depth, remaining film thickness, speed) at any time is calculated based on the film thickness data in these time series to determine whether the etching process has reached its end point.

[0018] However, in the technology of Patent Document 2, the etching amount is detected based on the fact that after plasma is formed and light emission starts during etching, the etching process progresses at a rate greater than a given value and the remaining film thickness decreases uniformly.

[0019] Therefore, when the etching process progresses unevenly, for example, when the process does not progress easily within a predetermined initial period from the start of plasma emission, the accuracy of film thickness detection may be significantly impaired.

[0020] As described above, during the processing period including the initial processing after the plasma light emission begins, if there are deviations in the parameters for detecting the remaining film thickness and etching amount, such as the amount of light emission, the speed at which the processing progresses, etc., the accuracy of detecting these etching amounts is impaired and the processing yield is reduced. Such problems are difficult to eliminate using the existing technology.

[0021] An object of the present invention is to provide a plasma processing apparatus or a plasma processing method that can detect the etching amount of a film to be processed with high accuracy and improve the processing yield.

[0022] Means for solving problems

[0023] In order to solve the above-mentioned problems, one of the representative plasma processing methods involved in the present invention is achieved as follows: a plasma processing method, wherein a wafer to be processed is arranged in a processing chamber inside a vacuum container, plasma is formed in the processing chamber to etch a film pre-formed on the surface of the wafer, and the method comprises the following steps: placing the wafer in the processing chamber, receiving interference light reflected from the surface of the wafer at multiple times from the formation of the plasma to the end of the etching, and generating a signal representing the intensity of the interference light; measuring the film thickness of the wafer before and after etching; determining the etching start time of the wafer based on the generated signal; and deriving the correspondence between the signal and the film thickness based on the determined etching start time.

[0024] In addition, one of the representative plasma processing devices involved in the present invention is implemented as follows: a plasma processing device, in which a wafer to be processed is arranged in a processing chamber inside a vacuum container, plasma is formed in the processing chamber to etch a film pre-formed on the surface of the wafer, and the device comprises: a detection device, which receives interference light reflected on the surface of the wafer at multiple times from the formation of the plasma to the end of the etching, and generates a signal indicating the intensity of the interference light; and a determiner, which determines the start time of etching based on the difference of the signals at multiple times.

[0025] Effects of the Invention

[0026] According to the present invention, it is possible to provide a plasma processing apparatus or a plasma processing method that can detect the etching amount of a film to be processed with high accuracy, thereby improving the processing yield.

[0027] The details of the structure, operation, and effects of the present invention will become clear from the following description of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a longitudinal sectional view schematically showing the structure of a plasma processing apparatus according to an embodiment of the present invention.

[0029] Figure 2 It is schematically represented Figure 1 FIG. 1 is a block diagram showing a configuration of a film thickness / depth determination unit of a plasma processing apparatus according to the embodiment shown.

[0030] Figure 3 This is a graph schematically showing changes in film thickness with time and changes in errors in detected film thickness in etching processing according to a comparative example.

[0031] Figure 4 This is a graph schematically showing changes in film thickness with time and changes in errors in detected film thickness in etching processing according to a comparative example.

[0032] Figure 5 It means in Figure 1 This is a graph showing an example of a spectrum of interference light obtained before and after the plasma processing apparatus according to the embodiment shown starts etching a wafer.

[0033] Figure 6 Yes Figure 1 A diagram showing correspondence between data in a database unit of a plasma processing apparatus according to the embodiment shown and the remaining film thickness detected thereafter.

[0034] Figure 7 It means in Figure 1 The flowchart is a flow of an operation of storing film thickness / spectrum data including characteristic data of a spectrum of interference light in a database unit in the plasma processing apparatus according to the embodiment shown.

[0035] Figure 8 It is schematically represented in Figure 1 Graph showing examples of the remaining film thickness and errors at each sampling time in interference light data used for detecting the remaining film thickness of the plasma processing apparatus according to the embodiment shown.

[0036] Figure 9 It is a chart, in Figure 1In the plasma processing apparatus of the embodiment, when the time when the progress start of etching is detected is slightly delayed from the actual time, the relationship between the remaining film thickness detected during the process and the actual remaining film thickness and the error therebetween is shown.

[0037] Figure 10 It is schematically represented Figure 1 A graph showing the amount of change in the spectrum detected by the plasma processing apparatus according to the embodiment shown.

[0038] Figure 11 It is schematically represented Figure 1 A graph showing the amount of change in the spectrum detected by the plasma processing apparatus according to the embodiment shown.

[0039] Figure 12 It's about Figure 1 The spectrum of the interference light 15 detected at each sampling time during wafer processing by the plasma processing apparatus according to the illustrated embodiment is a graph schematically showing changes over time in the sum of differences from the spectrum of the interference light 15 at the immediately preceding sampling time.

[0040] Figure 13 It is schematically represented Figure 1 A graph showing changes over time in the sum of spectral differences of interference light detected by a plasma processing apparatus according to a modification of the embodiment shown.

[0041] Figure 14 It is schematically represented in Figure 13 FIG. 1 is a graph showing an example of the remaining film thickness and the error at each sampling time in the interference light data used for detecting the remaining film thickness of the plasma processing apparatus according to the modification of the present invention.

[0042] Figure 15 It is schematically represented Figure 1 FIG. 1 is a block diagram showing a configuration of a signal processing unit of a plasma processing apparatus according to the embodiment shown.

[0043] Figure 16 It is schematically represented Figure 1 A schematic longitudinal sectional view showing the structure of a plasma processing apparatus according to a modified example of the embodiment shown.

[0044] Figure 17 It is schematically represented Figure 16 FIG. 1 is a timing chart showing the flow of operations of the plasma processing apparatus according to the modified example shown. DETAILED DESCRIPTION

[0045] Hereinafter, embodiments of the present invention will be described using the drawings.

[0046] Below, use Figures 1 to 15 Embodiments of the present invention will be described.

[0047] Figure 1 This is a schematic longitudinal cross-sectional view schematically illustrating the structure of a plasma processing apparatus according to an embodiment of the present invention. The plasma processing apparatus 10 shown in this figure includes: a vacuum container 11, at least a portion of which has a cylindrical shape; and a processing chamber 19 disposed within the vacuum container 11, which forms plasma 12 in the depressurized inner space.

[0048] Etching process gas is introduced into the processing chamber 19 from a gas introduction unit (not shown). A high-frequency electric field or a microwave electric field of a predetermined frequency band is generated using power supplied from a high-frequency power supply (not shown), or a magnetic field is generated using a magnetic field generator such as a solenoid coil. These electric fields, or the interaction between these electric and magnetic fields, excite atoms or molecules in the process gas, ionize them, and dissociate them, forming plasma 12.

[0049] Inside the processing chamber 19, when plasma 12 is formed, a semiconductor chip (hereinafter referred to as chip) 14 as a sample of the processing object, which is arranged on the upper surface of the sample table 13 inside the processing chamber 19 and is held, comes into contact with the reactive, highly active particles, ions and other charged particles in the plasma 12, triggering the physical and chemical action of these particles on the surface of the film layer of the processing object pre-arranged on the surface of the chip 14, and etching progresses.

[0050] In this embodiment, the operations of the various parts of the plasma processing device 10 are performed by a control unit 23 to which they can communicate data via a wired cable or wirelessly, and the operations include: the introduction of gas into the interior of the processing chamber 19; the formation of an electric field or a magnetic field and the resulting generation and disappearance of the plasma 12 and the adjustment of its intensity and distribution; the supply and stop of high-frequency power that is arranged in the sample stage 13 and supplied during the formation of the plasma 12 to form a bias potential above the chip 14, etc.

[0051] The control unit 23 of this embodiment has an input and output interface for the above-mentioned communication, an arithmetic unit such as a microprocessor based on a semiconductor device, and a RAM, ROM or a storage device such as a hard disk drive or a DVD-ROM drive that records data and software internally, and they have a structure connected in a communication manner. Through the control unit 23, the timing of the synchronous actions including the amount, start, end, etc. of the actions of each unit can be adjusted so that the film layer of the processing object on the wafer 14 in the processing chamber 19 can achieve the desired etching treatment. In addition, the control unit 23 stores the memory for executing the following Figure 7 The control program of the flowchart is executed according to the program to control the plasma processing device 10.

[0052] During the etching process, light generated in plasma 12 formed in processing chamber 19 is irradiated onto wafer 14. The irradiated light is reflected by the film structure of the semiconductor device circuit formed on the surface of wafer 14 before the process. It is reflected on multiple surfaces such as the outermost surface of the film structure, the interface between two films stacked one above the other, and the bottom surface inside the circuit pattern. These irradiated and reflected lights become interference light 15, which interferes due to the difference in the length of the paths.

[0053] Interference light 15 passes through a window member made of a light-transmitting material and facing the inside of processing chamber 19, and is received by a light receiver 16 comprising a window made of a light-transmitting material such as quartz, attached to the wall of vacuum container 11, and a lens disposed above the window. Furthermore, interference light 15 is transmitted to a detection unit 17 connected thereto via a light transmission path such as an optical fiber optically connected to light receiver 16. Detection unit 17 includes a spectrometer that splits light of a given wavelength band into light of wavelengths at predetermined wavelength intervals. At any point during processing, interference light 15 split by detection unit 17 is detected as a spectrum of interference light 15 indicating the amount of interference light of each wavelength at that point in time. Light receiver 16 and detection unit 17 constitute a detection device.

[0054] In this embodiment, the spectrum of the interference light 15 is detected at predetermined time intervals (times) during processing of each wafer 14. Signals at these sampling times are transmitted from the detection unit 17 as time-series signals representing the spectrum of the interference light 15.

[0055] The signal representing the spectrum of the interference light 15 at any given moment detected by the detection unit 17 is transmitted to the signal processing unit 20, where it is converted or processed into a signal capable of detecting the etching amount and the end point with higher accuracy. Specifically, the signal input to the signal processing unit 20 is processed to offset the light intensity and remove high-frequency noise.

[0056] The signal processed in this way is transmitted to the film thickness / depth determination unit (determinator) 21, which detects the film thickness or depth value at any time based on the transmitted signal. In this embodiment, the etching amount at each time can be detected based on the signal corresponding to that time. Furthermore, the etching amount at that time and the etching amount detected at the time before that time can be used to detect the etching amount at that time with higher accuracy.

[0057] A signal indicating the detected etching amount is sent to the display unit 22 for display or notification. Furthermore, when the film thickness / depth determination unit 21 determines that the target etching amount or remaining film thickness has been reached, the control unit 23 sends a command signal to the plasma processing apparatus 10 to stop the supply of processing gas or the formation of plasma, thereby terminating the etching process on the wafer 14.

[0058] In addition, the plasma processing device 10 is of course not limited to Figure 1 Here, the plasma processing apparatus 10 may include the signal processing unit 20, the film thickness / depth determination unit, the control unit 23, and the like as external devices.

[0059] Figure 2 It is schematically represented Figure 1 Block diagram showing the structure of the film thickness / depth determination unit of the plasma processing apparatus according to the embodiment shown. This figure schematically shows the structure of the film thickness / depth determination unit 21 in which blocks having various functions are connected.

[0060] As shown in the figure, a signal representing the spectrum of the interference light 15 at any time, processed into an appropriate signal shape by the signal processing unit 20, is sent to the film thickness / depth determination unit 21. The data of the signal is compared with previously obtained data in the comparison unit 31. The data to be compared is previously stored and stored in the storage device of the database unit 30, which is communicatively connected to the comparison unit 31.

[0061] In the storage device of the database unit 30, for example, the film thickness is stored in correspondence with the time series data of the spectra of given multiple wavelengths of the interference light 15, wherein the film thickness is obtained when a film structure having the same size and type as or similar to the film structure of the circuit for the semiconductor device manufactured by processing the wafer 14 by the plasma processing device 10 is processed under the same or similar processing conditions as the processing conditions of the wafer 14.

[0062] Such data may be data detected when another wafer (as a test wafer) having the same film structure as wafer 14 is processed in advance under the same processing conditions, or may be data obtained as a result of calculations such as simulations. In the present embodiment, based on such pre-acquired data, a plurality of etching amount values ​​such as the remaining film thickness during processing are associated with a plurality of patterns of changes in the light intensity of the spectrum of interference light 15 or its differential value relative to changes in wavelength, or with a plurality of patterns of the light intensity of interference light 15 or its differential value relative to changes in wavelength, and the data are stored in the storage device of database unit 30.

[0063] For example, the film thickness of the processing object before and after the processing of the above-mentioned test wafer is measured. Using the film thickness value and the data stored in the database unit 30, a correspondence is established between each value of the film thickness (multiple etching amounts) that changes according to the progress of etching in the same processing object and the spectrum of the interference light 15. The data of the time series pattern is stored in the database unit 30 together with the information establishing the correspondence. The data representing the correspondence between the film thickness and the characteristic data of the spectrum of the interference light is called film thickness / spectrum data. The characteristic data of the spectrum refers to information representing the spectrum, such as the waveform of the spectrum, the intensity corresponding to the wavelength, and the change of the differential value. When the differential value is used, the influence of spike noise and the like included in the original signal can be suppressed, and the signal-to-noise ratio is improved.

[0064] By comparing the film thickness / spectral data in such a database unit 30 with the spectrum of the interference light actually obtained at any time when the chip 14 is etched and processed by the signal processing unit 20, the value of the etching amount corresponding to the pattern of light amount judged to be closest to the actual data is detected as the etching amount (remaining film thickness or depth) of the chip 14 at that arbitrary time.

[0065] Furthermore, the method for determining film thickness / depth is not limited to the above-described method. For example, if the database unit 30 contains insufficient film thickness / spectral data, new spectra can be generated by interpolating the data based on multiple spectra within the film thickness / spectral data, and the film thickness can be set to a corresponding value to increase the film thickness / spectral data. Alternatively, multiple pre-measured test wafers can be prepared, and film thickness / spectral data can be set according to each of multiple conditions. Furthermore, during mass production, film thickness inspection results of wafers 14 before and after etching can be added to the database unit 30 to increase the film thickness / spectral data for comparison.

[0066] Furthermore, in the aforementioned film thickness / depth determination unit 21, the comparison unit 31 may be comprised of one or more semiconductor devices or circuits thereof, or may be a portion of a circuit within a semiconductor device. The database unit 30 may include a storage device such as RAM, ROM, or a hard disk drive or DVD-ROM drive, and an interface that enables wired or wireless communication between the storage device and the comparison unit 31 and enables data transmission and reception. The database unit 30 may be installed in the plasma processing apparatus 10 along with the comparison unit 31, or may be located remotely.

[0067] (Comparative Example)

[0068] Figure 3 、 4 This is a graph schematically showing changes in film thickness with time and changes in errors in detected film thickness in etching processing according to a comparative example.

[0069] Figure 3 (a) is a graph showing the relationship between the remaining film thickness of the film layer to be processed detected during the etching process according to the comparative example and the actual remaining film thickness. Figure 3 (b) is a graph showing the change in the difference (film thickness error) between the remaining film thickness detected during the etching process shown in (a) and the actual remaining film thickness. In these graphs, the horizontal axis represents etching time, with the start time of the etching process being 0, the end time of the etching process being Te, the remaining film thickness before the start of the process being Di, and the remaining film thickness after the end of the process being De.

[0070] Here, the following process is performed in advance: a test wafer 14 having a film structure equivalent to that of a wafer 14 used for semiconductor device manufacturing is processed under the same processing conditions as those of a wafer used for semiconductor device manufacturing, or is computationally simulated to obtain intensity (spectrum) data with the wavelength of the interference light 15 as a parameter.

[0071] In this process, the point in time when plasma 12 is formed in processing chamber 19 or high-frequency power is supplied to the bias potential-forming electrode disposed within sample stage 13 is considered the start time of processing. Interference light 15 from the surface of wafer 14 is detected at each sampling time thereafter, and the remaining film thickness at that time is calculated. Furthermore, the remaining film thickness at the calculated time is combined with the film thickness value at the sampling time during the process immediately preceding that time to ultimately calculate the remaining film thickness at that time. In this case, a recursive analysis method is used to calculate the final remaining film thickness at each sampling time, utilizing at least one remaining film thickness value from the sampling time immediately preceding that time.

[0072] Furthermore, in the comparative example, using previously acquired characteristic data of the interference light spectrum at various points in the process, the remaining film thickness in the etching process of wafer 14, which is carried out to the end of the process for semiconductor device manufacturing, is calculated by assuming that the time when etching of the target film layer begins is the time when plasma is formed or the supply of high-frequency power for generating the bias potential begins. However, in reality, at the beginning of the process after plasma 12 is formed and high-frequency power is just supplied to the electrodes within sample stage 13, the intensity and distribution of plasma 12, as well as the magnitude and distribution of the bias potential, are unstable. This results in variations in the speed (rate) of the process and the actual start of the process progress for each wafer 14. In the case of a process consisting of multiple steps, variations also occur between each step.

[0073] In other words, in the actual etching process of the wafer 14, after the plasma 12 is formed and starts to emit light, the etching and its progress do not proceed steadily. Figure 3The actual remaining film thickness value shown by the solid line 41 in (a) also requires a certain amount of time (in this example, the time from time 0 to Ti) after the plasma 12 is formed until the state stabilizes and the etching progress stabilizes, depending on the film type and processing conditions. As a result, the film thickness D value is approximately constant near the vertical axis. During this period, etching of the target film layer does not substantially progress. Therefore, the actual etching start time is shifted by Ti.

[0074] However, in the comparative example, the residual film thickness at the time point considered as the start of the process is considered to be the residual film thickness of the object being processed before the start, which is steadily and evenly reduced from the value Di to the residual film thickness De when it is determined to have reached the end point of the process, and the residual film thickness at the time point before this time point is used to recursively calculate the residual film thickness at any time point in the process. Therefore, the value of the residual film thickness D detected at each time point in the comparative example is as follows: Figure 3 The dashed line 40 in (a) schematically represents the straight line passing through the thickness De at time 0 (on the vertical axis), and the values ​​at the time before each time in the processing period from time 0 to time Te are interpolated.

[0075] As a result, in the comparative example, Figure 3 As shown in (b), a deviation (film thickness error) occurs between the detected value of the remaining film thickness and the actual value of the remaining film thickness, which is maximum at a given time (time Ti) after the formation of plasma 12 or the start of the supply of high-frequency power to the sample stage 13 for bias potential formation.

[0076] exist Figure 3 In the process, the value of the remaining film thickness at the moment when the etching process reaches the end point (end time) is determined to be consistent as De. However, in the processing of the test chip 14 for inputting and outputting the data stored in the database unit 30, since the values ​​of the structural parameters such as the film thickness, shape, size, etc. of each layer of the film structure of the data of the database unit 30 cover a wider range than the values ​​of the actual chip 14, they are usually set deeper than the actual end point of the process. Therefore, if the etching process is terminated at the moment Tt when the target remaining film thickness Dt is detected as the end point, the remaining film thickness is inconsistent with Dt, resulting in an error. As a result, as Figure 3 As shown by the solid line 42 in (b), an error occurs in the remaining film thickness detected with the etching start time Ti as the peak, and a film thickness error also occurs at the estimated time Tt at which the etching process ends. However, since the film thickness error tends to decrease as the etching time increases, the film thickness error is smaller during long etching times.

[0077] However, the shorter the time from the start to the end of the etching process, the more significant this influence becomes. Figure 4(a) is a graph showing the relationship between the estimated film thickness and the actual film thickness in a comparative example of etching time during database preparation in a short etching time. Figure 4 (b) is a graph showing the film thickness error of the comparative example in the long-term etching. Figure 3 In the case of short etching, the influence of the shift of the etching start time Ti becomes relatively large, so the error of the remaining film thickness at time Tt when the process ends with the target remaining film thickness Dt is as follows: Figure 4 The problem of increasing the size occurs as shown in (b).

[0078] Figure 5 It means in Figure 1 This is a graph showing an example of a spectrum of interference light obtained before and after the plasma processing apparatus according to the embodiment shown starts etching a wafer. Figure 5 (a) shows the result of a spectrum obtained by plotting the intensity values ​​of the interference light 15 at each sampling time from the moment when the plasma 12 is formed in the processing chamber 19 to the moment Ti when the etching of the film layer of the processing object starts, using wavelength (frequency) on the horizontal axis and overlapping each of the given multiple wavelengths (frequencies). Figure 5 (b) shows the result of superimposing the spectra of the interference light 15 obtained at each sampling time after the time Ti.

[0079] like Figure 5 As shown in (a), the spectrum of the interference light 15 hardly changes before the time Ti. Figure 5 As shown in (b), in the spectrum of the interference light 15 obtained at each sampling time after time Ti, parts with obviously different values ​​at the same wavelength are observed, and differences are generated in the vertical directions between the lines plotting the values, indicating that the spectrum changes.

[0080] The light intensity information represented by the spectrum of the interference light 15 indicates the remaining film thickness of the film layer constituting the film structure, where the film structure constitutes a circuit pattern configured on the surface of the chip 14. Therefore, it can be seen that after the time Ti, the state of the plasma 12 is stable and the etching of the film layer of the processing object progresses above a given threshold, and it can be regarded as starting the etching at the time Ti.

[0081] In this way, it is determined whether there is an amount of change greater than a given threshold between the spectrum or waveform of the interference light 15 at each sampling moment, and the sampling moment at which the change is determined to be greater than the threshold is regarded as the moment when the etching process starts, thereby determining the start time of the etching process.

[0082] Figure 6 Yes Figure 1The diagram shows the correspondence between the data in the database section of the plasma processing apparatus according to the embodiment shown and the remaining film thickness detected thereafter. Figure 6 In the embodiment, the characteristic data of the spectrum of the interference light 15 obtained at any time after the start of the processing are compared with the film thickness / spectrum data stored in the database section 30, and the result of the comparison in the comparison section 31 of the film thickness / depth determination section 21 is a comparison of the film thickness corresponding to the spectrum determined to have the smallest difference between the comparative example and the present embodiment.

[0083] exist Figure 6 , there is shown a spectrum of interference light 15 from the chip 14 obtained when a film to be processed on a test chip 14 having a structure equivalent to that of a chip 14 for performing etching processing to manufacture semiconductor devices is arranged in a processing chamber 19 and an etching process is performed, or when the etching process is calculated by simulation, etc.

[0084] exist Figure 6 In the data, the etching process is started, and the moment when plasma 12 is formed in the processing chamber 19, or high-frequency power is supplied to the electrodes in the sample stage 13 to form a bias potential that attracts charged particles such as ions in the plasma 12 to the chip 14, or the moment when the bias potential is assumed to be formed in the calculation is set as time 0 during the above process.

[0085] exist Figure 6 In the figure, the spectrum of the interference light 15 at time 0 during the process and at each sampling time thereafter is plotted and represented as a waveform in a graph, and the values ​​of the remaining film thickness detected as values ​​corresponding to each time by the plasma processing apparatus involved in the comparative example and the plasma processing apparatus 10 of the present embodiment are represented in correspondence with the time during the process adopted on the horizontal axis.

[0086] In this embodiment, the interval between sampling times (sampling interval) is set to 0.1 seconds. The thickness of the film to be processed before the start of etching is set to Di, and the target remaining film thickness at the end of etching is set to De.

[0087] like Figure 6 As shown, in the data of this embodiment, the waveform of the graph showing the spectrum obtained from the interference light 15 does not change from time 0 to Ti, and the waveform changes from the sampling time (Ti+0.1 seconds) immediately after time Ti.

[0088] Specifically, in this embodiment, if the difference (difference) between the change in the value of a predetermined wavelength (frequency) or the spectral waveform of a spectrum obtained at a sampling time after time 0 and the spectral waveform at any sampling time before that time (in this embodiment, the previous sampling time) is less than a predetermined threshold, the film is judged to be in an untreated state, where etching of the target film has not progressed. As a result, the remaining film thickness from time 0 to time Ti is detected as the same value Di as the value before etching, and the period from time 0 to Ti is considered to be an untreated period for the target film.

[0089] If a change in the spectral value or waveform exceeding the threshold value is detected at time (Ti + 0.1) [seconds], it is determined that the etching process has begun at that time (Ti + 0.1), that is, time (Ti + 0.1) is determined to be the time when the etching period begins. Furthermore, in this embodiment, if the remaining film thickness is determined to have reached the target end-point residual film thickness De at time Te, the remaining film thickness during the period from time (Ti + 0.1) to time Te (during the etching process) is calculated as Δd', which is the value obtained by dividing the change in the remaining film thickness per unit sampling time (Di - De) by the number of sampling times. For example, the calculated value of the remaining film thickness at time (Ti + 0.1) is (Di - Δd'), and the remaining film thickness at time Tt = (Ti + 0.1) × m [seconds] is (Di - Δd') × m.

[0090] On the other hand, in the comparative example, the time from the untreated period from time 0 to time Ti to time Te is regarded as the period of etching treatment, and the film thickness at time 0.1 [second] is calculated as (Di-Δd) using the change in the remaining film thickness per unit sampling interval Δd obtained by dividing the difference between the remaining film thickness values ​​Di and De by the number of sampling moments from time 0 to Te (process period ÷ sampling interval). If the number of sampling moments in the period from 0 to Ti is n, the remaining film thickness at time Ti is calculated as (Di-Δd)×n, and the film thickness at time Tt is calculated as Di-Δd×(n+m).

[0091] Thus, the data representing the spectra and intensity patterns of the plurality of interference lights 15 used in the comparative example includes periods during which etching is not performed. Consequently, errors occur in the remaining film thickness values ​​associated with such data. Furthermore, if such data is used to detect the remaining film thickness during the processing of wafers 14 for mass production of semiconductor devices, the actual remaining film thickness deviates from the desired value (film thickness error). The shorter the processing time for the target film or the actual etching progress, the greater the impact of this error, and the lower the processing yield.

[0092] Therefore, in this embodiment, as described above, after time 0 when the process is started, until the time (Ti+0.1) when it is determined that the difference between the spectral waveform (or the change in intensity corresponding to a predetermined wavelength (frequency) of the spectrum) obtained at each sampling time and the spectral waveform at any time before that time (in this case, the previous sampling time) is greater than a given threshold, the interference light 15 representing the change in such spectral waveform is determined to be in an untreated state in which the etching of the film to be processed has not progressed, and the above-mentioned data representing the spectrum of the interference light 15 during the period in which the etching process progresses from time (Ti+0.1) to time Te is used to detect the remaining film thickness.

[0093] Figure 7 It means in Figure 1 The flowchart shows the flow of operations for storing film thickness / spectral data, including characteristic data of the spectrum of interference light, in a database unit in a plasma processing apparatus according to the embodiment shown. In this embodiment, as described above, before processing of wafers 14 for mass-production semiconductor devices begins, characteristic data of the spectrum of interference light 15 at multiple wavelengths accompanying the progress of etching processing of a film layer to be processed on a test wafer 14 having a structure similar to that of the wafer 14 is stored in association with the remaining film thickness of the film layer.

[0094] exist Figure 7 2 shows the flow of operations performed in advance until such data is acquired and stored as film thickness / spectral data in the database unit 30 within the film thickness / depth determination unit 21. When this flow of operations begins, first, in step S701, the remaining film thickness Di of the film layer to be processed is measured before the start of the processing process of an equivalent test wafer 14 having the same structure (including the dimensions and structure of the film formed on the surface) as the wafer 14 used in the process of mass-producing semiconductor devices, or a structure that is similar to or can be considered to be similar to the structure (including the dimensions and structure of the film formed on the surface), and is stored in the storage device within the control unit 23.

[0095] In this step, the film thickness can be measured using any of the conventionally known measurement techniques, such as a cross-sectional SEM (Scanning Electron Microscope), an OCD (Optical Critical Dimension), or an AFM (Atomic Force Microscope). Furthermore, when data is obtained by actually performing an etching process in the processing chamber 19, it is preferable to use wafers from the same batch as those used in mass production as the test wafers 14.

[0096] Next, in step S702 , the test wafer 14 is transported into the processing chamber 19 inside the vacuum container 11 , and is placed and fixed on the sample stage 13 .

[0097] In step S703, the etching process begins under conditions that are identical or nearly identical to those used for mass-production wafers 14. Specifically, the process chamber 19 is maintained within a predetermined vacuum pressure range, plasma 12 is generated using the process gas supplied to the process chamber 19, and high-frequency power for forming a bias potential is supplied to the electrodes within the sample stage 13. In this embodiment, the process begins at time 0 during the process.

[0098] In the plasma processing device 10 of this embodiment, at the time point of starting the process of processing the film of the processing object and after the start, in the film thickness / depth determination unit 21, at each sampling moment of a given interval, the spectrum of the interference light 15 from the chip 14 received by the light receiver 16 is used to determine whether the remaining film thickness of the film layer of the processing object has reached a predetermined target value. If it has not reached it, the etching process is continued until it is determined that the predetermined target value has been reached.

[0099] That is, after the spectrum of the interference light 15 of multiple wavelengths from the chip 14 received by the light receiver 16 at each sampling moment is detected in the detection unit 17, it is processed by the signal processing unit 20 and transmitted to the film thickness / depth determination unit 21, and the characteristic data of the spectrum of the interference light 15 of multiple wavelengths at each moment is established in correspondence with the moment (including the start time point of processing) and stored in the storage device within the internal database unit 30 (step S704).

[0100] In this embodiment, whether the remaining film thickness of the target film layer has reached the target value is determined by determining whether the time assumed to reach the predetermined target film thickness has passed since the start of processing or whether the number of sampling times has been reached.

[0101] If it is determined that the time assumed to reach the desired film thickness has elapsed, the process proceeds to step S705 to terminate the etching process of the test wafer 14. Furthermore, in step S706, the test wafer 14 is unloaded from the processing chamber 19.

[0102] Then, in step S707, the remaining film thickness De of the target film layer on the test wafer 14 is measured through the same process as step S701, and the measured value is stored in the storage device within the control unit 23. Through the steps thus far, the remaining film thickness before and after etching the target film layer on the test wafer 14, and characteristic data of the spectrum of the interference light 15 at each sampling time during the etching process of the film layer are obtained.

[0103] In this embodiment, based on the characteristic data of the interference light 15 obtained, the change in the intensity of light of each wavelength of the interference light 15 from the start time of the process, or the change in the waveform of the spectrum representing the change in light intensity relative to the change in the wavelength of the interference light 15 is detected.

[0104] In step S708 , the comparison unit 31 in the film thickness / depth determination unit 21 compares the amount of change with a predetermined threshold value, and the time when the amount of change exceeds the threshold value is detected as the time when etching progress starts.

[0105] In step S709, from time 0 to the time when the etching starts ( Figure 6 At each sampling time during the unprocessed period from the time (Ti + 0.1 seconds) when etching processing has not progressed, the remaining film thickness is detected as Di and associated with the data at each time. Furthermore, the remaining film thickness value at each sampling time after the start of etching is linearly interpolated at each sampling time based on the film thickness Di at the start of etching and the film thickness De at the end point. This value is associated with the characteristic data of the spectrum at each time and stored in the database unit 30. In this way, the film thickness / spectrum data that associates the characteristic data of the spectrum of the interference light 15 with the remaining film thickness value is stored in the database unit 30, thereby constructing a database, and the process ends.

[0106] In addition, it is preferred that the film thickness / depth determination unit 21 allocates the film thickness before etching to the spectrum at the start time of etching and before, allocates the film thickness after etching to the spectrum at the end time of etching, and allocates the spectrum in between to the film thickness derived by linear interpolation relative to the etching time, thereby generating film thickness / spectrum data (the correspondence between film thickness and spectrum).

[0107] use Figure 8 , yes Figure 7 The value of the remaining film thickness at each sampling time in the data of the interference light 15 obtained in FIG. 1 and the magnitude of the error will be described. Figure 8 It is schematically represented in Figure 1 Graph showing examples of the remaining film thickness and errors at each sampling time point in interference light data used for detecting the remaining film thickness of the plasma processing apparatus according to the embodiment shown.

[0108] Figure 8 (a) shows the relationship between the remaining film thickness obtained from the film thickness / spectrum data stored in the database unit 30 and the actual remaining film thickness. Figure 8 (b) indicates Figure 8 The difference (film thickness error) between the two remaining film thickness values ​​shown in (a).

[0109] exist Figure 8 In (a), the horizontal axis represents the time after the start of the etching process of the wafer 14, and the vertical axis represents the remaining film thickness or depth of the film layer to be processed, and the magnitude of the error between the value of the remaining film thickness (depth) detected using the data and the actual value. Figure 3 The reference numerals shown are the same, and therefore description thereof will be omitted.

[0110] exist Figure 8 In (a), as shown by solid line 41, from time 0, when plasma 12 is formed and the etching process begins, an unprocessed state, or unprocessed period, occurs until time Ti, when the intensity of plasma 12 stabilizes and etching of the target film layer begins. Therefore, during this unprocessed period, the actual remaining film thickness remains approximately constant, or its variation remains within a predetermined threshold. In this embodiment, even when such an unprocessed period occurs, the start of etching is detected based on changes in the spectrum of interference light 15, and the remaining film thickness is detected using characteristic data from the spectrum at that time and thereafter.

[0111] For example, the characteristic data of the spectrum of the actual interference light 15 detected at any time during the process of processing the wafer 14 for mass production are compared with the characteristic data of the spectrum of the interference light 15 at the sampling time of the period excluding the above-mentioned unprocessed period stored in the database unit, and the value of the remaining film thickness corresponding to the characteristic data at each time whose difference with the actual data is the smallest is detected as the film thickness at that time.

[0112] Alternatively, at a sampling moment in a given initial period starting from the start (time 0) of the processing step of the mass production wafer 14, if it is determined that the change in the characteristic data of the spectrum of the interference light 15 is smaller than a predetermined threshold value, it is determined that the moment is an unprocessed period, and the remaining film thickness is deemed to be the value Di before the start of the process.

[0113] Furthermore, upon detecting that the etching process has started at a point in time when the magnitude of the change exceeds a threshold, the comparison unit 31 may compare the characteristic data of the spectrum of the interference light 15 detected at any sampling time after the start time (in the above example, time (Ti + 0.1) seconds) with the film thickness / spectrum data in the database unit 30. From the film thickness / spectrum data, the remaining film thickness at that time is used as the instantaneous film thickness to extract the film thickness corresponding to the characteristic data of the detected spectrum. A recursive analysis may be performed using this instantaneous film thickness value and the remaining film thickness detected at sampling times during the etching process at that arbitrary time in the past. The remaining film thickness at that arbitrary time is calculated from the recursive analysis as the calculated film thickness. In this case, the remaining film thickness at the past sampling times used in the recursive analysis is the calculated film thickness value detected at multiple times after time (Ti + 0.1) seconds and stored in the database unit 30 or the control unit 23.

[0114] In this way, it is possible to determine whether the etching process is in an unprocessed state or the etching process has started based on the characteristic data of the spectrum of the interference light 15. Therefore, by using the characteristic data of the spectrum of the interference light 15 after the time point when the etching process starts after the unprocessed period, the remaining film thickness is calculated at each sampling time after the start of etching. Therefore, even when the remaining film thickness is calculated by recursive analysis, the remaining film thickness expressed as Figure 8 The value of the remaining film thickness of the dotted line 43 of (a). As a result, Figure 8 As shown by the solid line 42 in (b), the film thickness error, that is, the error between the actual remaining film thicknesses is reduced.

[0115] Figure 9 is a graph that shows Figure 1 In the plasma processing apparatus of the embodiment, when the timing of detecting the start of etching progress is slightly delayed from the actual timing, the relationship between the remaining film thickness detected during processing and the actual remaining film thickness and the error therebetween is shown. Figure 9 (a) is a graph showing a change in the value of the remaining film thickness with the passage of time, wherein the horizontal axis represents time. Figure 9 (b) is a graph showing changes in error with the passage of time.

[0116] like Figure 9 As shown in (a), when etching progresses between adjacent sampling times, the film thickness / depth determination unit 21 or the control unit 23 of the plasma processing device 10 can determine that the earliest time of progress is the next sampling time, which is slightly later than the actual time.

[0117] In this case, there is a deviation between the actual change in the remaining film thickness shown by the solid line 41 and the change in the detected film thickness shown by the dotted line 43, resulting in an error. Figure 3 、 4 The difference between the solid line 40 and the dotted line 41 can be reduced. Figure 9 As shown by the solid line 42 in (b), the film thickness error can be reduced.

[0118] In addition, Figure 9 In the above description, the case where the determination of the etching start timing is delayed is described, but it goes without saying that the same effect can be obtained when the determination is advanced.

[0119] Next, a configuration for detecting changes in the spectrum of the interference light 15 in this embodiment will be described. Figure 10 as well as Figure 11 It is schematically represented Figure 1 A graph showing the amount of change in the spectrum detected by the plasma processing apparatus according to the embodiment shown.

[0120] In these Figure 10 (a) to Figure 11 In the graph (c), the horizontal axis represents the difference in spectral waveforms at two consecutive sampling times of the interference light 15 detected by the plasma processing apparatus 10, using wavelength. In each graph, the horizontal axis represents wavelength, and the vertical axis represents spectral differences (differences in light intensities) representing the differences between the intensities of the interference light 15 at multiple wavelengths detected at six sampling times (times T = 0.1, 0.3, Ti, (Ti + 0.1), (Ti + 0.2), (Ti + 0.3) seconds) after the start of the etching process for the target film layer and the intensity of the light at the immediately preceding sampling time.

[0121] As shown in these figures, 0.1 and 0.3 seconds after plasma 12 is formed and the etching process begins, the spectral differences across a predetermined range of multiple wavelengths are smaller than those observed after time Ti. This is because etching of the target film layer does not progress, and the intensity of the multiple wavelengths included in interference light 15 varies little. It is believed that the main cause of temporal changes in the intensity of interference light 15 is relatively small factors such as fluctuations in the intensity or distribution of plasma 12 and high-frequency noise flowing through the circuits used in plasma processing apparatus 10.

[0122] On the other hand, Figure 11As shown in (c), at time Ti seconds, the spectrum difference at multiple wavelengths becomes larger. This change indicates that the etching of the film layer to be processed for forming the circuit pattern on the wafer 14 by the plasma 12 has fully progressed and the etching has begun. Moreover, after time Ti, at each of (Ti+0.1), (Ti+0.2), and (Ti+0.3) [seconds], the spectrum difference is greater than the difference before Ti. Figure 10 The difference between the two spectra increases as compared to the cases (a) and (b). In particular, the amount of spectrum difference (for example, the sum of the differences between the frequencies) increases as time passes.

[0123] Furthermore, although not shown, at sampling times after time (Ti + 0.3) seconds, while there was some variation in the shape of the spectral difference, no change in its absolute value was observed, indicating that the target material was being etched steadily. Based on these results, time Ti, when the spectral difference from the spectrum immediately preceding it becomes greater than a given threshold, can be detected as the start of etching of the target film layer.

[0124] As described above, by detecting the waveform of the spectrum of the interference light 15 or the intensity change of light of multiple wavelengths using the spectrum difference between two consecutive times, the etching start time of the target film layer can be accurately detected.

[0125] The structure for detecting spectral changes is not limited to the above-described structure. For example, the spectral ratio (intensity ratio) of a specific wavelength at two consecutive moments can be calculated and compared with a given threshold to observe spectral changes. Alternatively, the difference or ratio of spectra at each moment calculated with respect to the spectrum at a given moment (e.g., immediately after plasma 12 is formed and light is generated) can be used as a reference.

[0126] Next, another method for quantitatively detecting the start time of etching processing will be described. In this method, the difference between the spectrum of interference light 15 detected at each sampling time after the plasma processing apparatus 10 starts etching the wafer 14 and the spectrum of interference light 15 at the immediately preceding sampling time is calculated. The time when the total value of the difference, summed at each sampling time, exceeds a predetermined value is detected as the start time of etching the target film layer.

[0127] Figure 12 It's about Figure 1 The spectrum of the interference light 15 detected by the plasma processing apparatus according to the illustrated embodiment at each sampling time during wafer processing is schematically shown as a graph showing the change over time of the sum of differences (hereinafter referred to as spectral differences) from the spectrum of the interference light 15 at the immediately preceding sampling time. Figure 12 The horizontal axis represents the time after the start of the etching process of the wafer 14 , and the vertical axis represents the value of the sum of the spectrum differences.

[0128] Here, regarding the spectrum of the interference light 15 obtained at any sampling time after the above process is started, the spectrum difference is the difference between the spectrum of the interference light 15 at the sampling time immediately before it. Figure 10 、 11 As shown, the intensity of each wavelength of interference light 15 obtained at two consecutive sampling times shows increases and decreases at each of the multiple wavelengths of interference light 15. The differences in these light intensities are positive and negative at each wavelength. In this embodiment, the sum of the absolute values ​​of these differences or the sum of the squares of the differences is calculated as the "sum of spectral differences." This sum of spectral differences is calculated at each sampling time after the start of the wafer 14 processing process. The sum of spectral differences can serve as characteristic data for the spectrum.

[0129] like Figure 12 As shown, the calculated sum of spectral differences is small at the sampling time immediately after the process of processing wafer 14 using plasma 12 begins. It then gradually increases over time, then rapidly increases. The rate of increase then gradually decreases, asymptotically approaching a predetermined value. In this embodiment, the moment when the sum of spectral differences increases dramatically is detected as the start of etching. The calculation of the spectral differences and the sum of spectral differences, as well as the detection of the start of etching, are performed by the film thickness / depth determination unit 21 or the comparison unit 31.

[0130] exist Figure 12 In the example shown in (a), the film thickness / depth determination unit 21 of the plasma processing apparatus 10 uses a threshold value of 50 at each sampling time and determines the sampling time when the sum of the detected spectrum differences exceeds the threshold value 50 as the time Ti for starting the etching process.

[0131] Such a threshold value varies depending on the material of the film layer to be processed and the processing conditions, and the value of the sum of the spectral differences at the moment when etching starts is appropriately selected and determined from the characteristic data of the spectrum of the interference light 15 obtained when the user of the plasma processing device 10 pre-processes the test wafer 14.

[0132] exist Figure 12 In the example shown in (b), the rate of change (slope) of the sum of the spectral differences with respect to time is calculated at each sampling moment, and the average value of the rate of change 51 during a specific period is used to determine the time Ti when the etching process starts. For example, after deriving a straight line including the average slope 51 of the measurement point to be the object, the point Ti where the straight line intersects with the horizontal axis is determined to be the time point when the etching process starts. In this way, the etching start time can be quantitatively determined. In addition, the method for determining Ti is not limited to the intersection of the average slope straight line and the horizontal axis. It can also be determined with Figure 12The threshold value combination of (a) is set as the intersection point of the threshold value and the average slope straight line.

[0133] As described above, by plotting the sum of the spectral differences between two consecutive moments at each time, and setting the time Ti under arbitrary conditions such as a threshold value or average slope, the etching start time can be quantitatively determined. Furthermore, the wavelength range for the sum can be any wavelength region, as long as it is sensitive. Furthermore, to accurately grasp the changes in the sum of the spectral differences, the vertical axis can be set to a logarithmic scale, or the plot can be smoothed.

[0134] On the other hand, if the sum of the spectral differences varies over a relatively long period, it is believed that the progress of etching of the target film layer is changing with its speed and extent gradually increasing. In such cases, simply detecting the start of etching using the configuration described in the above embodiment, while shifting the determination of the remaining film thickness and its endpoint to the unprocessed period before the start, is considered inadequate. The following describes a modified example for accurately detecting the remaining film thickness in such situations.

[0135] Figure 13 It is schematically represented Figure 1 A graph showing changes over time in the sum of spectral differences of interference light detected by a plasma processing apparatus according to a modified embodiment of the embodiment shown. In this modified embodiment, as described above, when the sum of spectral differences gradually increases over a relatively long period after the start of the process for processing wafer 14, multiple threshold values ​​are used to detect the start of etching.

[0136] That is, Figure 13 As shown, in this modification, Figure 12 Similarly, in the example shown, the sum of spectral differences calculated at the sampling point immediately after the start of the wafer 14 processing process gradually increases over time, then rapidly increases. The rate of increase then gradually decreases, gradually approaching the predetermined value. When the values ​​in the graph shown in the figure asymptotically approach the predetermined value, it is considered that stable etching has begun. This is because the sum of spectral differences begins to asymptotically approach the predetermined value at the sampling point when the threshold value 50 is reached, as the rate of change (increase) with respect to time decreases.

[0137] In this modified example, in addition to threshold 50, the value of the sum of spectral differences at the sampling point in time when the value of the sum of spectral differences begins to increase is set as a second threshold 52. These two thresholds are pre-set and stored as characteristic data of the spectrum in a storage device within control unit 23 or film thickness / depth determination unit 21. Second threshold 52 is assumed to be the value of the sum of spectral differences at which the etching rate of the target film layer increases and etching begins to progress significantly.

[0138] In this variant, the film thickness / depth determination unit 21 determines the sampling moment when the sum of the etching differences reaches the threshold value 50 as the moment Ti at which etching starts, and further determines the sampling moment when the sum of the etching differences reaches the threshold value 52 as the moment Tj at which the etching speed starts to change (starts to change), thereby detecting the change points of the two etching speeds.

[0139] In other words, we can say that we are using the curve to approximate Figure 13 There are two inflection points in the change rate of the sum of etching differences with respect to time. In this case, the time Tj of the first inflection point that precedes the etching start time is set as the etching start time, and the time Ti of the second inflection point that follows the etching start time is set as the etching start time.

[0140] Figure 14 It is schematically represented in Figure 13 FIG. 1 is a graph showing an example of the remaining film thickness and the error at each sampling time in the interference light data used for detecting the remaining film thickness of the plasma processing apparatus according to the modification of the present invention. Figure 14 (a) shows the relationship between the remaining film thickness obtained from the film thickness / spectrum data stored in the database unit 30 and the actual remaining film thickness. Figure 14 (b) means Figure 14 The difference (film thickness error) between the two remaining film thickness values ​​shown in (a).

[0141] exist Figure 14 In FIG. 1 , the horizontal axis represents the time after the start of the etching process of the wafer 14, and the vertical axis represents the remaining film thickness or depth of the film layer to be processed, and the magnitude of the error between the value of the remaining film thickness (depth) detected using the data and the actual value. Figure 3 、 Figure 13 The reference numerals shown are the same, and therefore description thereof will be omitted.

[0142] like Figure 14As shown by the solid line 41 in (a), during a given period after the etching process begins on the wafer 14, the plasma state and other processing conditions become unstable, and the detected remaining film thickness may also vary significantly. In such cases, as shown by the dotted line 43, the period from the start of the process (time 0) to the sampling time Tj is an unprocessed state in which the change in the spectrum of the interference light 15 is less than a given threshold, that is, the remaining film thickness remains constant, the same as before the start. On the other hand, after time Ti (the second interval), it becomes a stable period in which the remaining film thickness changes (decreases) at a stable rate within a range where the plasma characteristics are stable and the deviation is small. Furthermore, in this modified example, during the time from time Tj to time Ti (the first interval) between this stable period and the initial unprocessed period, etching is considered to proceed at a rate less than the rate of decrease (rate) of the remaining film thickness during the stable period, and this smaller etching rate is set. In other words, the etching rate in the second interval is greater than the etching rate in the first interval.

[0143] In this modification, during the etching condition transition period until the etching speed of the wafer 14 stabilizes after the plasma condition stabilizes from the initial state, the etching speed data is used, which is considered to be a value smaller than the etching speed in the stable state. Figure 8 Compared with the embodiment of the present invention, in the processing of the wafer 14 of the mass production semiconductor device, even if the transition period is relatively long, Figure 14 As shown by the solid line 42 in (b), the error between the detected remaining film thickness of the film layer to be processed and the actual remaining film thickness is narrowed.

[0144] In addition, in this modification, two values ​​are pre-set as the threshold values ​​used, but it is of course not limited to two. In addition, the value of the threshold value varies depending on the type of film layer to be processed by the wafer 14, the pressure in the processing chamber 19 and other processing conditions, so it is not limited to Figure 13 Alternatively, a value different from the threshold value such as the average value of the slope of the sum of spectral differences with respect to time may be used, or two or more values ​​and two or more times corresponding thereto may be detected to determine the remaining film thickness.

[0145] As described above, in this variation, after the process of processing the target film layer on wafer 14 begins, etching of the target film layer begins. As the etching rate gradually changes until it stabilizes, multiple times corresponding to predetermined etching rate thresholds are detected. Furthermore, within the data of interference light 15 used in this variation, which is pre-stored in database unit 30, a range for the detected etching rate is set for each of the multiple periods divided by these times. The change in remaining film thickness over time is also set so that the upper and lower limits of the etching rate range for these multiple periods increase evenly over time. This reduces the difference from the actual remaining film thickness value during the process of processing wafers 14 for actual mass production, enabling high-precision detection of the remaining film thickness or depth and determination of whether the target film thickness has been achieved.

[0146] use Figure 15 , the operation of the plasma processing apparatus 10 according to the above-described embodiment or modification example for processing the signal of the interfering light 15 received by the light receiver 16 will be described. Figure 15 It is schematically represented Figure 1 FIG. 1 is a block diagram showing a configuration of a signal processing unit of a plasma processing apparatus according to the embodiment shown.

[0147] exist Figure 15 In the figure, the signal representing the interference light 15 received by the light receiver 16 is transmitted to the detection unit 17 through the optical fiber, and the intensity of each wavelength of a plurality of pre-set wavelengths is detected and transmitted to the signal processing unit 20 as a signal (spectral signal) S1 representing a spectrum.

[0148] Spectral signal S1 is introduced into light intensity variation correction unit 60, where it is corrected to reduce components representing light intensity variations, such as variations in the intensity of light emitted from plasma 12 and temporal changes in optical transmittance along the light transmission path from processing chamber 19 through photoreceiver 16. Signal S2 is then smoothed by first digital filter 61, reducing fluctuations in plasma emission intensity and high-frequency noise components caused by electrical noise, resulting in signal S3.

[0149] To reduce the DC offset component, signal S3 is introduced into differentiator 62, where it becomes signal S4, which has been subjected to differentiation processing. Signal S4 is then smoothed by a second digital filter 63, resulting in signal S5 with reduced noise components generated by the processing of differentiator 62. The resulting signal S5 is transmitted to film thickness / depth determination unit 21 as a signal-processed spectrum.

[0150] Next, the filtering performed by the first digital filter 61 and the second digital filter 63 in the signal processing unit 20 and the differentiation performed by the differentiator 62 will be described. In this example, a second-order Butterworth low-pass filter is used as the first digital filter 61. Signal S2 transmitted to the first digital filter 61 is converted by the internal second-order Butterworth low-pass filter into signal S3 obtained by the following equation (1).

[0151] S3(i)=b1*S2(i)+b2*S2(i-1)+b3*S2(i-2)-[a2*S2(i-1)+a3*S2(i-2)] (1)

[0152] The low-pass filter of the first digital filter 61 in this example is characterized by processing the signal along the wavelength axis (frequency) (relative to changes in frequency) rather than along the time axis (relative to changes in time). In the above equation, Sk(i) represents the data for a given signal with wavelength i, and the coefficients bk and ak are low-pass filter coefficients derived from the signal sampling frequency (1 / sampling interval) and the cutoff frequency set for the low-pass filter.

[0153] Such filtering processing can output correct calculation results when the first two data are correct values. However, when filtering processing is performed in the time direction, there is no data at t = 0 seconds (sec), that is, just after the process of forming plasma 12 and processing the film layer of the processing object of the chip 14 begins, so the value accuracy of the signal S3 is impaired.

[0154] On the other hand, when filtering is performed in the wavelength direction, if the two points at the upper and lower limits of the range (frequency band) of the frequency (wavelength) to be detected are excluded, plasma 12 is formed at the full wavelength, and processing of the chip 14 can be performed stably with high precision right after the start of processing.

[0155] In differentiator 62, signal S3 is smoothed using a conventionally known data processing method, such as the SG (Savitzky-Golay) method. The SG method smoothes data using a polynomial curve approximating the data to be smoothed and multiple data points in the preceding, following, or vertical directions. Furthermore, the coefficients of this polynomial can be used to calculate and output a differential value. As an example, for signal S3, five values ​​are calculated using each data point and two data points before and after it, and the signal, after smoothing and differential value calculation using the SG method, is output as signal S4. Signal S4 is calculated using the following equation (2).

[0156] S4(i)=c(-2)*S3(i-2)+c(-1)*S3(i-1)+c(0)*S3(i)+c(1)*S3(i+1)+c(2)*S3(i+2) (2)

[0157] Here, the characteristic of the first-order differential is that, as described above, the differential processing is performed not in the time axis direction but in the wavelength axis direction. In the above formula, Sk(i) represents the value of a given wavelength i of the signal, and the coefficient c(k) is a weighting coefficient determined by the polynomial order and the number of windows in the arbitrary order differential. The above-mentioned differentiator 62 calculates the differential value as a result using data representing the value of an arbitrary frequency (wavelength) to be detected in the signal representing the spectrum of the interference light 15 and the values ​​of the two frequencies before and after it.

[0158] When performing differentiation along the time axis, two data points are used that are sampled after the sampling time corresponding to the target data to be smoothed. Therefore, smoothing of the target data cannot be performed until two sampling intervals have elapsed, resulting in a delay. Therefore, similar to the filtering process in the first digital filter 61, after the plasma 12 is formed and the target film layer treatment process begins (time 0), no data prior to that time exists, making smoothing or differentiation impossible.

[0159] On the other hand, when smoothing or differentiating in the wavelength axis direction, in principle, data at past sampling times is not necessary for this processing. It is possible to exclude the upper and lower limits of the range of multiple wavelengths and perform processing with high precision from the time 0 at which the above-mentioned process begins. The flow of the filtering process of the second digital filter 63 is the same as that of the first digital filter 61, and therefore its description is omitted.

[0160] Thus, in the above-described embodiment or modified example, the spectrum signal S1 of the detected interference light 15 is filtered, smoothed, or differentiated in the wavelength direction by the signal processing unit 20. This allows for stable and high-precision noise removal and differentiation from the moment plasma 12 is formed and the treatment of the target film layer on the surface of the wafer 14 begins, improving the signal-to-noise ratio. Consequently, the accuracy of the remaining film thickness detection in the film thickness / depth determination unit 21, which transmits the output signal S5, is improved.

[0161] The filtering process is not limited to the Butterworth low-pass filter described above; other low-pass filters may also be used. Furthermore, the signal processing in differentiator 62 is not limited to smoothing and calculating a first differential using the SG method using data at five points, including the target data and preceding and following data, as described above. Secondary differentials or higher-order differentials may also be used, and the number of points is not limited to five. Furthermore, techniques other than the SG method may be used as a smoothing method.

[0162] In addition, the order and number of signal processing are not limited to Figure 15 The structure shown in FIG. 1 may also change the order of processing, and the structure of the signal processing unit 20 may be different from the structure shown in FIG. 1 . Figure 15 Furthermore, in order to extract the interference component of the target spectrum to be processed, for example, the spectra of the silicon substrate and the background may be measured in advance and their relative contrast may be used.

[0163] Furthermore, the above-described example has a configuration in which signal processing is performed on the signal representing the spectrum of the obtained interference light 15 in the frequency (wavelength) direction not only after the start of the process of processing the target film layer of the wafer 14, but also during the initial period when etching has not progressed and during the process after the time (time Ti) when etching of the target film begins. In this case, the film thickness / spectral data pre-stored in the database unit 30 and compared by the comparison unit 31 of the film thickness / depth determination unit 21 for detecting the remaining film thickness and depth is data stored by associating a pattern of values ​​obtained by differentiating the intensity of the interference light 15 at multiple frequencies (wavelengths) in the frequency direction at any sampling time with multiple values ​​of the remaining film thickness of the target film.

[0164] Alternatively, the signal processing unit 20 may be configured such that the spectrum of the detected interference light 15 is processed in the frequency direction during the initial period from the start of the process for processing the wafer 14 until the progress of etching is detected, and the signal is processed in the time axis direction during the processing period after time Ti at which the etching process begins. Alternatively, the spectrum of the detected interference light 15 may be processed in parallel in both the time axis direction and the frequency (wavelength) axis direction immediately after the process begins and during the initial period, and the resulting signals are output to the film thickness / depth determination unit 21. In this case, the film thickness / spectral data previously stored in the database unit 30 and compared by the comparison unit 31 of the film thickness / depth determination unit 21 for detecting the remaining film thickness and depth is data stored by associating a pattern of values ​​(with wavelength as a parameter) obtained by differentiating the intensity of multiple wavelengths of the interference light 15 in the time axis direction at any sampling time with multiple values ​​of the remaining film thickness of the target film.

[0165] In the above embodiment and modified examples, by including the described configuration, the accuracy of establishing a correlation between the patterns of interference light 15 at multiple sampling times and the remaining film thickness in the film thickness / spectral data pre-stored and stored in the database unit 30 is improved. Therefore, the accuracy of detecting the remaining film thickness based on the spectrum obtained from interference light 15 during the processing of wafers 14 for mass production using this data is improved.

[0166] Furthermore, since the target remaining film thickness can be accurately obtained, the previously required process of correcting the difference between the remaining film thickness calculated from the detection data and the actual remaining film thickness is no longer necessary, resulting in a reduction in the cost of processing wafer 14. Furthermore, the remaining film thickness or its changes can be detected with high accuracy during the initial period immediately after the plasma 12 is formed to process wafer 14 and the process begins. This makes it possible to detect the etching amount and depth with high accuracy, compared to conventional techniques that detect the moment when the etching amount of the target film layer exceeds a predetermined threshold and begins to progress, and then assume that etching progresses during this initial period to detect the remaining film thickness.

[0167] In addition, when the initial state of the remaining film thickness of the film layer to be processed of the unprocessed wafer 14 that has been brought in can be detected, for example, when it is determined in the comparison unit 31 or the control unit 23 that the characteristic data of the spectrum of the detected interference light 15 deviates greatly from the film thickness / spectrum data in the database unit 30, a report or warning can be given to the user of the plasma processing device 10 or the management system, thereby processing the process of the wafer 14.

[0168] Furthermore, the device configuration, wafer 14 processing conditions, and interference light 15 detection conditions shown in the above-described embodiments and modifications are merely examples, and the present invention can obviously be applied to configurations and conditions other than these. Furthermore, while the above-described examples are examples of detecting the remaining film thickness of a film layer to be processed on wafer 14, the present invention can also be applied to, for example, detecting the depth of grooves or holes in line-and-space configurations of circuit structures in semiconductor devices.

[0169] In the embodiment or variation described above, the following structure is provided: a light receiver 16 arranged at the upper part of the vacuum container 11 receives interference light formed by light radiated from the plasma 12 formed inside the processing chamber 19 and reflected on multiple surfaces at different heights including the surface of a film layer of a film structure constituting the surface of the chip 14 or the boundary surface of two film layers stacked up and down, as interference light 15.

[0170] On the other hand, in recent years, as the integration density of semiconductor devices has increased, the width and aperture of the grooves in the circuit patterns have become smaller, reducing the area of ​​the film layer exposed to the processing chamber 19 or plasma 12 during etching of the wafer 14 surface. Consequently, the intensity of the light emitted by the plasma 12 generated for the process has also tended to decrease. Therefore, in these cases where plasma 12 is used as a light source, the overall intensity of the light emitted by the plasma 12 decreases. As a result, the proportion of the fluctuation and noise components of the plasma 12 included in the interference light 15 becomes relatively large. In other words, the S / N ratio of the spectrum of the interference light 15 deteriorates, increasing the possibility of adversely affecting the accuracy of the remaining film thickness and depth detection using the interference light 15.

[0171] Reference Figure 16 In order to solve the above-mentioned problems, an example of a plasma processing apparatus is described which can suppress the deterioration of the S / N ratio of the spectrum of the interference light 15 even when the intensity of the light emission of the plasma 12 is low, thereby performing stable and high-precision detection. Figure 16 It is schematically represented Figure 1 A schematic longitudinal sectional view showing the structure of a plasma processing apparatus according to a modified example of the embodiment shown.

[0172] The plasma processing device 160 of this embodiment is Figure 1 The difference of the plasma processing apparatus 10 of the embodiment shown is that it has the following structure: In the plasma processing apparatus 160, a light source unit 70 is provided on the upper part of the vacuum container 11, and light is irradiated from the outside above the processing chamber 19 to the surface of the wafer 14 arranged on the upper surface of the sample stage 13 arranged inside. Figure 1 Elements denoted by the same reference numerals as those in the illustrated embodiment have the same configuration and function as those in the embodiment, and their description will be omitted unless necessary.

[0173] The light source unit 70 of this modified example has a structure in which, as a light source, a lamp such as an LED, a xenon lamp, or a halogen lamp is used. After the remaining film thickness or depth is detected by the film thickness / depth determination unit 21, the light source is used to irradiate the surface of the wafer 14 with light of a desired wavelength and light intensity. The light emitted and radiated from the lamp of the light source unit 70 is transmitted through a light transmission path made of a light-transmitting material such as an optical fiber connected to the light source unit 70, and is then irradiated as irradiation light 72 onto a predetermined area of ​​the wafer 14 from an irradiation lens 71 mounted on the upper portion of the vacuum vessel 11, with its lower end facing the interior of the processing chamber 19.

[0174] The irradiation light 72, together with the light emitted from the plasma 12, is reflected by the multiple surfaces of the film structure on the surface of the wafer 14 to form interference light 15, which is received by the light receiver 16 and transmitted to the detection unit 17 via a light transmission path such as an optical fiber arranged above and connected thereto. The structure, function, and operation of the detection unit 17, the signal processing unit 20, the film thickness / depth determination unit 21, the display unit 22, and the control unit 23 are similar to the above. Figure 1 The embodiments shown are identical.

[0175] The intensity of the irradiation light 72 emitted from the light source unit 70 and directed toward the wafer 14 is preferably sufficiently greater than the intensity of the light emitted by the plasma 12. Depending on the processing conditions, the light emitted by the plasma 12 can become unstable immediately after its formation, sometimes resulting in significant intensity fluctuations. This is detected as a change in the spectrum of the interference light 15 at sampling times during the initial, unprocessed period before the time Ti at which etching progress begins, hindering accurate detection of the start of etching progress.

[0176] On the other hand, in this modified example, a light source unit 70 capable of emitting irradiation light 72 of sufficient intensity is used to irradiate external light with a greater intensity than that of plasma 12 during the process of processing the target film layer of wafer 14. As a result, the intensity of interference light 15 is dominated by the portion based on this irradiation light, reducing the effect of fluctuations in the emission or intensity of plasma 12 on fluctuations in the intensity of interference light 15 of multiple wavelengths, thereby suppressing any adverse effects on the detection of remaining film thickness and depth using this light.

[0177] use Figure 17 , indicating that Figure 16 The illustrated example is an operation example for suppressing the deterioration of the S / N ratio of the spectrum of the interference light 15 in the plasma processing apparatus 160 . Figure 17 It is schematically represented Figure 16 The timing diagram of the operation flow of the plasma processing device involved in the modification shown in FIG. Figure 17In FIG. 1 , the increase and decrease in the amount of light emitted by the plasma 12 , the irradiation light 72 from the light source 70 , and the interference light 15 received by the light receiver 16 over time are shown by solid lines in the graph.

[0178] In this modification, the structure of the plasma processing device 160 is similar to Figure 16 On the other hand, regarding the formation of plasma 12, the irradiation of irradiation light 72 from light source unit 70, and the reception of interference light 15 by light receiver 16, the operations of the command signal from control unit 23 that transmits and receives signals therewith are different.

[0179] In this modified example, a process of etching a target film layer is performed by switching between a predetermined ON period and a subsequent OFF period starting at time t=0 when plasma 12 is formed, repeating the formation of plasma 12 and the resulting light emission at a predetermined cycle. Furthermore, light source unit 70 begins irradiating light 72 before time 0 and continues emitting light until the film thickness / depth determination unit 21 or control unit 23 detects that the etching process has reached the end point of the target film layer.

[0180] On the other hand, the light receiver 16 is adjusted so as to receive the interference light 15 (the light receiver 16 is enabled) during the disabled period of the plasma 12, and not receive the light (the light receiver 16 is disabled) during the enabled period of the plasma 12, in contrast to the period during which the light emission of the plasma 12 is periodically repeated.

[0181] By performing such an operation, while the plasma 12 is not emitting light or the amount of light emitted is low, the interference light 15 generated by the irradiation light 72 is received by the light receiver 16. Since the amount of light from the plasma 12 received by the light receiver 16 is zero or sufficiently low, the noise component caused by the plasma 12 can be reduced, resulting in stable detection of the remaining film thickness or depth and determination of the arrival of the endpoint.

[0182] in addition, Figure 17 The timing diagram shown is merely an example, and other activation / deactivation controls can be implemented. In either case, it is preferred that the light receiver 16 be deactivated when the plasma is activated, and that the irradiation light 72 and the light receiver 16 be activated when the plasma 12 is deactivated.

[0183] Furthermore, while the above-described example describes a configuration for detecting the remaining film thickness and depth when continuously processing a film layer to be processed on the surface of a single wafer 14, the above configuration can also be applied to other processing steps. For example, in a cyclic etching process in which etching is repeated using multiple steps as one cycle, or in a multi-step process in which multiple etching processes are performed, stable film thickness tracking can be achieved through the same process.

[0184] According to the present invention, a plasma processing device that uses plasma formed in a processing chamber to etch a processing object in a processing chamber arranged inside a vacuum container can at least include: a light receiver that receives light from the processing chamber at a given plurality of times during the etching process; and a determiner that uses spectral data of a predetermined plurality of wavelengths detected based on the output of the light receiver, the film thickness before and after the etching process, the spectral data, and the film thickness to determine the etching amount of the processing object. The determiner determines the etching start time based on the spectral change of the spectral data, and derives the film thickness corresponding to the spectral data to determine the etching amount of the processing object.

[0185] Furthermore, according to the present invention, the determination device of the plasma processing apparatus can determine the etching start time based on the difference between spectra at two consecutive times in the spectrum data.

[0186] Furthermore, according to the present invention, the determination device of the plasma processing apparatus can determine the etching start time using the sum of the differences in the spectrum in a predetermined wavelength band.

[0187] Furthermore, according to the present invention, the determination device of the plasma processing apparatus can derive the change in etching rate from the temporal change in the sum of the differences in the spectra, and determine the etching rate change timing.

[0188] In addition, according to the present invention, the determiner of the plasma processing device can assign the film thickness before etching to the spectrum at the start time of etching and before, assign the film thickness after etching to the spectrum at the end time of etching, and assign the film thickness to the spectra in between by linear interpolation relative to the etching time.

[0189] Furthermore, according to the present invention, the spectrum data of the plasma processing apparatus can be subjected to predetermined signal processing in the wavelength direction after being detected by the light receiver.

[0190] The above-described embodiment is merely an example of a part of the embodiment of the present invention, and the embodiment of the present invention is not limited to the above.

[0191] The invention completed by the inventors has been specifically described above based on the embodiments, but the present invention is not limited to the above embodiments, and various changes can be made within the scope of the present invention. For example, the above embodiments are embodiments that are described in detail in order to easily explain the present invention, and are not limited to all the structures described. In addition, a part of the structure of a certain embodiment can be replaced with the structure of another embodiment, and in addition, the structure of another embodiment can be added to the structure of a certain embodiment. In addition, for a part of the structure of each embodiment, other structures can be added, deleted, or replaced.

[0192] Description of Reference Numerals

[0193] 10: Plasma treatment device

[0194] 11: Vacuum container

[0195] 12: Plasma

[0196] 13: Sample stage

[0197] 14: Chip

[0198] 15: Interference Light

[0199] 16: Light receiver

[0200] 17: Testing Department

[0201] 19: Processing Room

[0202] 20: Signal Processing Unit

[0203] 21: Film thickness / depth judgment part (judger)

[0204] 22: Display unit

[0205] 23: Control Department

[0206] 30: Database Department

[0207] 31: Comparison Department

[0208] 60: Light intensity variation correction unit

[0209] 61: First digital filter

[0210] 62: Differentiator

[0211] 63: Second digital filter.

Claims

1. A plasma processing method, wherein a wafer to be processed is arranged in a processing chamber within a vacuum container, plasma is generated in the processing chamber to etch a film previously formed on a surface of the wafer, wherein: The process is as follows: receiving, above the wafer placed in the processing chamber, interference light reflected from the surface of the wafer at a plurality of times from formation of the plasma to completion of the etching, and generating a signal indicating the intensity of the interference light; determining a start time for etching in the wafer based on the generated signal; and determining whether the etching of the film on the surface of the wafer has reached an end point based on signals indicating the intensity of the interference light at a plurality of times during the process after the determined etching start time, The signal indicating the intensity of the interference light includes a spectral waveform, the difference between the spectral waveforms at two of the plurality of times is calculated, and the time when the sum of the differences becomes greater than a given threshold is determined as the etching start time.

2. The plasma processing method according to claim 1, wherein: The difference between the waveforms of the spectrum at adjacent times is calculated, and the etching start time is determined based on the average value of the rate of change of the sum of the differences with respect to time.

3. The plasma processing method according to claim 1 or 2, wherein: The difference between the waveforms of the spectra at adjacent moments is calculated respectively. When the rate of change of the sum of the differences relative to time is approximated by a curve, the first inflection point and the second inflection point exist in a sequential time series on the curve. The moment of the first inflection point is determined as the start moment of etching, the time from the first inflection point to the second inflection point is determined as the first processing interval, and the time after the second inflection point is determined as the second processing interval where the etching speed is greater than that of the first processing interval.

4. The plasma processing method according to claim 1, wherein: The film thickness is considered to be constant until the determined etching start time.

5. A plasma processing apparatus, wherein a wafer to be processed is arranged in a processing chamber within a vacuum container, and plasma is generated in the processing chamber to etch a film previously formed on a surface of the wafer, characterized in that: have: a detection device that receives interference light reflected from the surface of the wafer at a plurality of times from the formation of the plasma to the completion of the etching, and generates a signal representing the intensity of the interference light; and a determiner that determines an etching start time based on a difference between the signals at a plurality of times, The signal representing the intensity of the interference light includes a waveform of a spectrum. The determiner calculates the difference between the waveforms of the spectrum at two of the multiple moments, determines the moment when the sum of the differences becomes greater than a given threshold value as the etching start moment, and determines whether the etching of the film on the surface of the chip has reached an end point based on the signal representing the intensity of the interference light at multiple moments in the process after the determined etching start moment.

6. The plasma processing apparatus according to claim 5, wherein: The determination unit calculates differences between waveforms of the spectrum at adjacent times, and determines the etching start time based on an average value of a rate of change of the sum of the differences with respect to time.

7. The plasma processing apparatus according to claim 5 or 6, wherein: The differences between the waveforms of the spectra at adjacent moments are calculated respectively. When the rate of change of the sum of the differences with respect to time is approximated by a curve, a first inflection point and a second inflection point exist in a sequential time series on the curve. The determiner determines the time of the first inflection point as the etching start time, the time from the first inflection point to the second inflection point as a first processing interval, and the time after the second inflection point as a second processing interval having an etching rate higher than that of the first processing interval.

8. The plasma processing apparatus according to claim 5, wherein: The determination device considers that the film thickness is constant until the determined etching start time.

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