JP2009194356A - Etching amount calculating method, storage medium, and etching amount calculating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an etching amount calculating method which can stably and accurately calculate the amount of etching even if a disturbance is added. <P>SOLUTION: In the etching of a wafer W which forms a trench 132 using a mask film 131, laser beam L1 is irradiated on the wafer W. Superposed interference wave is calculated by receiving the superposed interference light resulting from superposition of mask film interference light and trench interference light. A waveform of a window which defines the present timing T as the endpoint is extracted. Max entropy method is used for the waveform of the window, and the trench interference light is detected from frequency distribution obtained by performing frequency analysis. While shifting the endpoint of the window by only Δt, the calculation of the superposed interference wave, the extraction of the waveform of the window, the frequency analysis of the wave form of the window, and the detection of the trench interference period are repeated, and the detected trench interference periods are integrated and averaged at each repetition. The etching amount of the trench 132 is calculated based on the integrated and averaged trench interference periods. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an etching amount calculation method, a storage medium, and an etching amount calculation device, and more particularly, to an etching amount calculation method when a recess such as a trench or a hole is formed on a wafer using a mask film.

  In the manufacturing process of a semiconductor device, etching for forming a trench or a hole in a layer to be etched is performed using a mask film on a wafer. In etching, a portion of the layer to be etched that is not covered with the mask film is physically and chemically removed by plasma. However, in forming a trench, it is necessary to control the depth of the trench. Therefore, it is necessary to calculate the depth of the trench, that is, the etching amount during etching, but conventionally, a method using light interference has been widely used as a method for calculating the etching amount.

  FIG. 22 is a diagram for explaining light interference during etching.

In FIG. 22, a trench 132 is formed by etching on a wafer W having a mask film 131 formed on the etching target layer 130. When the wafer W is irradiated with laser light L 1, the surface of the mask film 131 is exposed. Reflected light L ₂ , reflected light L ₃ from the interface between the mask film 131 and the etching target layer 130, and reflected light L ₄ from the bottom of the trench 132 are generated.

When the reflected lights L _{2 to} L ₄ are received by the detector, the optical path length of each reflected light differs by the thickness of the mask film 131 and the depth of the trench 132 as shown in FIG. Then, the phase of each reflected light is different, and interference light (for example, interference light of reflected light L ₂ and reflected light L ₄ (hereinafter referred to as “trench interference light”) or interference light of reflected light L ₂ and reflected light L ₃ ( Hereinafter, it is referred to as “mask film interference light”)).

Since the depth of the trench 132 changes every moment during the etching, the optical path length difference between the reflected light L ₂ and the reflected light L ₄ also changes every moment and the intensity of the interference light changes, that is, the reflected light. Interference waves (hereinafter referred to as “trench interference waves”) are generated from L ₂ and reflected light L ₄ . Since the period of the interference wave is determined by the change rate (etching rate) of the depth of the trench 132, the etching rate is calculated from the period of the interference wave, and further, the etching amount (trench) is calculated from the calculated etching rate and etching time. 132 depth) can be calculated.

By the way, during etching, the mask film 131 is also etched by a small amount to change its thickness, so that interference waves (hereinafter referred to as “mask film interference waves”) are also generated from the reflected light L ₂ and the reflected light L ₃ . Since each interference wave is detected by the same detector, the interference wave detected by the detector is a superposition of a plurality of interference waves having different periods (hereinafter, referred to as “superimposed interference wave”) ( (See FIG. 23).

  In order to calculate the depth of the trench 132 (the etching amount of the etching target layer 130) from the superimposed interference wave as shown in FIG. 23, it is necessary to separate the trench interference wave from the superimposed interference wave.

  In the superimposed interference wave of FIG. 23, the short-cycle interference wave and the long-cycle interference wave can be separated relatively clearly. Here, since the rate of change of the depth of the trench 132 during etching is larger than the rate of change of the thickness of the mask film 131, the trench interference wave has a shorter period than the mask film interference wave. Therefore, the short-period interference wave in the superimposed interference wave in FIG. 23 is a trench interference wave, and the period of the trench interference wave is easily calculated from the time between the extreme values in the short-cycle interference wave (“Δt” in the figure). can do.

  In the method of reading the time between extreme values from the superimposed interference wave, it is necessary that the short-period interference wave and the long-period interference wave are relatively clearly separable in the superimposed interference wave. With a superimposed interference wave in which it is difficult to separate the interference wave of the period, the period of the trench interference wave cannot be calculated. Further, since the period of the trench interference wave is assumed to be constant between the extreme values in the short-period interference wave, the calculated period of the trench interference wave (etching rate of the etching target layer 130) is as shown in FIG. , Step by step. That is, the method of reading the time between extreme values from the superimposed interference wave has low resolution.

Therefore, in recent years, a method of calculating the period of the trench interference wave by frequency analysis without reading the time between extreme values from the superimposed interference wave has been developed. In this method, the frequency distribution (see FIG. 26A) is obtained from the superimposed interference wave by frequency analysis (for example, fast Fourier transform method), and the period of the trench interference wave is detected from the frequency distribution (for example, patents). Reference 1).
Japanese Patent Laid-Open No. 2-71517

  However, as shown in FIG. 25, an apparent period change (“II” in the figure) due to an abnormality in the laser light source or detector (“I” in the figure) or interference between the mask film interference wave and the trench interference wave in the superimposed interference wave. Such disturbances may be added to the superimposed interference wave. In the method using the frequency analysis described above, the period of the trench interference wave is only detected from the frequency distribution obtained by analyzing the superimposed interference wave over the entire time during the etching. The frequency distribution becomes inaccurate because a peak occurs in a non-existing interference cycle (see FIG. 26B), and as a result, the etching amount cannot be calculated stably and accurately.

  An object of the present invention is to provide an etching amount calculation method, a storage medium, and an etching amount calculation apparatus capable of stably and accurately calculating an etching amount even when a disturbance is applied.

  In order to achieve the above object, the etching amount calculation method according to claim 1 is an etching amount calculation method for calculating the etching amount of the recess in etching of the substrate in which the recess is formed using a mask film, An irradiation step for irradiating light, a light receiving step for receiving superimposed interference light in which interference light of at least reflected light from the mask film and reflected light from the bottom of the recess is superimposed on other interference light, and the light receiving An interference wave calculation step of calculating a superimposed interference wave from the superimposed interference light, a waveform extraction step of extracting a waveform of a predetermined period from the superimposed interference wave, a frequency analysis step of performing frequency analysis on the extracted waveform, An interference period for detecting the period of the interference wave of the reflected light from the mask film and the reflected light from the bottom of the recess from the frequency distribution obtained by the frequency analysis And repeating the step of calculating the interference wave, the step of extracting the waveform, the step of analyzing the frequency, and the step of detecting the interference period while shifting the predetermined period by a predetermined time, and the period of the detected interference wave is repeated each time it is repeated. An integration averaging step for integrating and averaging, and an etching amount calculating step for calculating the etching amount of the concave portion based on the period of the integrated and averaged interference wave are provided.

  The etching amount calculation method according to claim 2 is the etching amount calculation method according to claim 1, wherein the predetermined period has a period longer than an interference wave of reflected light from the mask film and reflected light from the bottom of the recess. It is characterized by being longer than one period of the long waveform of the other interference light.

  The etching amount calculation method according to claim 3 is the etching amount calculation method according to claim 1 or 2, wherein the waveform period of the other interference light is reflected light from the mask film and reflected light from the bottom of the recess. Pre-analysis processing for removing most of the portion occupied by the waveform of the other interference light from the waveform of the predetermined period extracted from the superimposed interference wave prior to the frequency analysis step when the period of the interference wave is longer than The frequency analysis step further includes performing frequency analysis on the waveform from which most of the portion occupied by the waveform of the other interference light has been removed.

  The etching amount calculation method according to claim 4 is the etching amount calculation method according to claim 3, wherein, in the pre-analysis processing step, a waveform obtained by approximating the extracted waveform with a second-order polynomial is extracted from the extracted waveform. It is characterized by removing.

  The etching amount calculation method according to claim 5 is the etching amount calculation method according to claim 3 or 4, wherein the predetermined period is equal to or less than ¼ period of the waveform of the other interference light.

  The etching amount calculation method according to claim 6 is the etching amount calculation method according to any one of claims 3 to 5, wherein the aperture ratio of the recesses on the surface of the substrate is 0.5% or less. Alternatively, the concave portion is a deep trench.

  The etching amount calculation method according to claim 7 is the etching amount calculation method according to any one of claims 1 to 6, wherein the frequency analysis uses a maximum entropy method.

  The etching amount calculation method according to claim 8 is the etching amount calculation method according to any one of claims 1 to 7, wherein a period of the interference wave detected from the frequency distribution corresponds to an abnormal value. Further includes an interference period correcting step for removing the period of the interference wave.

  The etching amount calculation method according to claim 9 is the etching amount calculation method according to claim 8, wherein, in the interference period correction step, a period before the predetermined period in which the period of the interference wave corresponding to the abnormal value is obtained. The period of the interference wave obtained from the predetermined period or the subsequent predetermined period is regarded as the period of the interference wave of the predetermined period in which the period of the interference wave corresponding to the abnormal value is obtained.

  The etching amount calculation method according to claim 10 is the etching amount calculation method according to any one of claims 1 to 9, wherein interference waves of reflected light from the mask film and reflected light from the bottom of the recess are reduced. In the interference period detection step, in the frequency distribution obtained by the frequency analysis, an interference wave of reflected light from the mask film and reflected light from the bottom of the recess in the frequency distribution obtained by the frequency analysis is predicted. The period is detected.

  The etching amount calculation method according to claim 11 is the etching amount calculation method according to any one of claims 1 to 10, wherein the other interference light includes reflected light from the surface of the mask film, and the mask. The interference light is reflected light from the boundary surface between the film and the surface of the substrate.

  In order to achieve the above object, a storage medium according to claim 12 stores a program for causing a computer to execute an etching amount calculation method for calculating an etching amount of the recess in etching a substrate on which the recess is formed using a mask film. The etching amount calculation method includes: an irradiation step of irradiating the substrate with light; and interference light of at least reflected light from the mask film and reflected light from the bottom of the recess Receiving a superimposed interference light superimposed on another interference light, an interference wave calculating step calculating a superimposed interference wave from the received superimposed interference light, and extracting a waveform of a predetermined period from the superimposed interference wave A waveform extracting step, a frequency analyzing step for performing frequency analysis on the extracted waveform, and a frequency analysis step obtained by the frequency analysis. An interference period detecting step for detecting a period of interference waves of reflected light from the mask film and reflected light from the bottom of the recess from a frequency distribution; the interference wave calculating step while shifting the predetermined period by a predetermined time; and the waveform The extraction step, the frequency analysis step, and the interference cycle detection step are repeated, and the integration average step of integrating and averaging the detected interference wave cycle each time it is repeated, and based on the integration averaged interference wave cycle And an etching amount calculating step for calculating the etching amount of the recess.

  In order to achieve the above object, an etching amount calculation apparatus according to claim 13 is an etching amount calculation apparatus that calculates an etching amount of the recess in etching of the substrate on which the recess is formed using a mask film. An irradiating unit that irradiates the interference light of at least the reflected light from the mask film and the reflected light from the bottom of the recess, and the light receiving unit that receives the superimposed interference light superimposed on the other interference light; and An interference wave calculation unit that calculates a superimposed interference wave from the superimposed interference light, a waveform extraction unit that extracts a waveform of a predetermined period from the superimposed interference wave, a frequency analysis unit that performs frequency analysis on the extracted waveform, and the frequency An interference period detection unit for detecting a period of interference waves of reflected light from the mask film and reflected light from the bottom of the recess from a frequency distribution obtained by analysis; and the predetermined period is predetermined. Accumulation that repeats calculation of the superimposed interference wave, extraction of the waveform during the predetermined period, frequency analysis, and detection of the period of the interference wave while shifting the interval, and integrating and averaging the period of the detected interference wave at each repetition An average portion and an etching amount calculation unit that calculates an etching amount of the concave portion based on the cycle of the integrated and averaged interference wave are provided.

  According to the etching amount calculation method according to claim 1, the storage medium according to claim 12, and the etching amount calculation device according to claim 13, the superimposed interference wave is calculated while the predetermined period is shifted by a predetermined time, and the waveform of the predetermined period is calculated. Extraction, frequency analysis, and detection of the period of the interference wave of the reflected light from the mask film and the reflected light from the bottom of the recess were repeated, and the period of the interference wave detected at each repetition was integrated and averaged. The etching amount of the recess is calculated based on the period of the interference wave. Therefore, even if a disturbance is applied to the extracted waveform of a certain predetermined period, the period of the interference wave detected based on the waveform of the certain predetermined period is based on the waveform of another predetermined period. Therefore, the influence of the period of the interference wave detected based on the waveform of the predetermined period with the disturbance on the period of the interference wave to be averaged is reduced. Therefore, the etching amount can be calculated stably and accurately even when a disturbance is applied.

  According to the etching amount calculation method according to claim 2, the predetermined period is longer than one period of the waveform of the other interference light having a longer period than the interference wave of the reflected light from the mask film and the reflected light from the bottom of the recess. Therefore, the reliability of the frequency analysis of the waveform during the predetermined period can be improved, and the etching amount can be calculated more accurately.

  According to the etching amount calculation method according to claim 3, when the period of the waveform of the other interference light is longer than the period of the interference wave of the reflected light from the mask film and the reflected light from the bottom of the recess, the frequency analysis is performed. First, since most of the portion occupied by the waveform of the other interference light is removed from the waveform of the predetermined period extracted from the superimposed interference wave, the amount of reflected light from the bottom of the recess is small, Even when the waveform of the interference light occupies most of the superimposed interference wave, the ratio of the portion occupied by the interference wave of the reflected light from the mask film and the reflected light from the bottom of the recess in the waveform after removal may be increased. Therefore, the period of the interference wave of the reflected light from the mask film and the reflected light from the bottom of the recess can be accurately calculated in the frequency analysis.

  According to the etching amount calculation method of the fourth aspect, a waveform obtained by approximating the extracted waveform with a second order polynomial is removed from the waveform extracted prior to the frequency analysis. When the amount of reflected light from the bottom of the recess is small, and the waveform of the other interference light occupies most of the superimposed interference wave, the waveform of the superimposed interference wave is almost equal to the waveform of the other interference light, A waveform obtained by approximating the extracted superimposed interference wave with a second-order polynomial is also substantially equal to the waveform of the other interference light. Therefore, most of the portion occupied by the waveform of the other interference light can be reliably removed from the extracted waveform.

  According to the etching amount calculation method of the fifth aspect, the predetermined period is equal to or shorter than a quarter cycle of the waveform of the other interference light. Since the other interfering light waveform that occupies most of the superimposed interference wave is close to a sine wave, if the portion of the other interfering light waveform that is less than ¼ period is extracted, the extracted waveform is accurately expressed by a second order polynomial. Can be approximated. Thereby, most of the portion occupied by the waveform of the other interference light can be accurately removed from the extracted waveform.

  According to the etching amount calculation method of claim 7, since the maximum entropy method is used in the frequency analysis, the reliability of the frequency analysis can be improved even if the number of waveforms in the predetermined period is small. Calculation can be performed more accurately.

  According to the etching amount calculation method according to claim 8, when the period of the interference wave detected from the frequency distribution corresponds to an abnormal value, the period of the interference wave is removed. Thus, the influence of the period of the interference wave detected based on the interference wave period on the integrated average can be removed, and the etching amount can be calculated more stably and accurately even when disturbance is applied. .

  According to the etching amount calculation method according to claim 9, the period of the interference wave obtained from the predetermined period before or after the predetermined period from which the period of the interference wave corresponding to the abnormal value is obtained is set to the abnormal value. Since the period of the corresponding interference wave is regarded as the period of the interference wave obtained for the predetermined period, the influence of the interference light detected based on the waveform of the predetermined period to which the disturbance is added can be reliably removed.

  According to the etching amount calculation method according to claim 10, the frequency distribution obtained by predicting in advance the period of the interference wave of the reflected light from the mask film and the reflected light from the bottom of the concave portion, and analyzing the waveform in a predetermined period. Therefore, since the period of the interference wave is detected from the vicinity of the predicted period, it is possible to quickly detect the period of the interference wave and to suppress the detection of the abnormal value.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, the etching amount calculation method and the substrate processing apparatus to which the etching amount calculation method according to the first embodiment of the present invention is applied will be described. This substrate processing apparatus is configured to perform etching using plasma on a semiconductor wafer (hereinafter simply referred to as “wafer”) W as a substrate. Note that the wafer W includes the etching target layer 130 and the mask film 131 formed in a predetermined pattern on the etching target layer 130 as shown in FIG.

  FIG. 1 is a cross-sectional view schematically showing a configuration of a substrate processing apparatus to which the etching amount calculation method according to the present embodiment is applied.

  In FIG. 1, a substrate processing apparatus 10 includes, for example, a processing chamber 11 made of a conductive material such as aluminum, a lower electrode 12 disposed on a bottom surface in the processing chamber 11 as a mounting table on which a wafer W is mounted, And a shower head 13 disposed above the lower electrode 12 at a predetermined interval.

  An exhaust unit 14 connected to a vacuum exhaust device (not shown) is connected to the lower part of the processing chamber 11, and a high frequency power supply 16 is connected to the lower electrode 12 via a matching unit 15, and a buffer inside the shower head 13. A processing gas introduction pipe 18 is connected to the chamber 17, and a processing gas supply device 19 is connected to the processing gas introduction pipe 18. The shower head 13 has a plurality of gas holes 20 in the lower portion for communicating the buffer chamber 17 with the processing space S that is a space between the shower head 13 and the lower electrode 12. The shower head 13 supplies the processing gas introduced into the buffer chamber 17 from the processing gas introduction pipe 18 into the processing space S through the plurality of gas holes 20.

  In the substrate processing apparatus 10, after the processing chamber 11 is depressurized to a predetermined degree of vacuum by the exhaust unit 14, the processing is performed from the shower head 13 to the processing space S in a state where a high frequency voltage is applied from the lower electrode 12 to the processing space S. Gas is supplied, and plasma is generated from the processing gas in the processing space S. The generated plasma collides and contacts the etching target layer 130 not covered with the mask film 131 on the wafer W to etch the etching target layer 130, thereby forming a trench 132 (recess) in the etching target layer 130. .

  The shower head 13 in the processing chamber 11 is provided with a monitor device 21 for observing the wafer W placed on the lower electrode 12 from above. The monitor device 21 is made of a cylindrical member and penetrates the shower head 13. A window member 22 made of a transparent material such as quartz glass is provided at the upper end of the monitor device 21. In addition, an optical fiber 24 is disposed above the processing chamber 11 so as to face the upper end of the monitor device 21 via a condenser lens 23.

  The optical fiber 24 is connected to an etching amount calculation device 25 that calculates the etching amount of the etching target layer 130. The etching amount calculation device 25 includes a laser light source 26 (irradiation unit) and a detector 27 (light receiving unit) connected to the optical fiber 24, and a calculation unit 28 (interference wave calculation unit, waveform extraction) connected to the detector 27. Unit, frequency analysis unit, interference period detection unit, integration average unit, etching amount calculation unit) and operate under the control of the controller 29 of the substrate processing apparatus 10. As the laser light source 26, for example, a semiconductor laser is used. As the detector 27, for example, a photomultiplier or a photodiode is used. The controller 29 is connected not only to the computing unit 28 but also to each component of the substrate processing apparatus 10, for example, the high-frequency power supply 16, and controls the operation of each component.

  The etching amount calculation device 25 irradiates the laser light from the laser light source 26 toward the wafer W on the lower electrode 12 via the optical fiber 24, the condenser lens 23, and the monitor device 21, and also reflects the reflected light from the wafer W. That is, trench interference light (interference light of reflected light from the mask film and reflected light from the bottom of the recess) and superposed interference light on which mask film interference light (other interference light) is superimposed are transmitted through the optical fiber 24 and the like. The light is received by the detector 27. The superimposed interference light received by the detector 27 is converted into an electrical signal and transmitted to the calculation unit 28.

  The calculation unit 28 calculates a superimposed interference wave from the superimposed interference light based on the received electrical signal. Further, the calculation unit 28 calculates the etching amount of the trench 132 by executing an etching amount calculation method of FIG. 6 described later based on the calculated superimposed interference wave.

  By the way, in etching, the etching rate is not constant, and varies depending on various factors (change in pressure in the processing space S and disturbance of high-frequency voltage). In particular, when a trench having a large aspect ratio (for example, a deep trench) is formed by etching, when the etching amount (etching depth) of the trench 132 is increased, deposits are attached to the entrance of the trench 132 and the trench 132 is filled. Since the entry of plasma into the substrate is suppressed, the etching rate is reduced (see FIG. 2). Further, as shown in FIG. 2, since the etching rate repeats minute changes, it is necessary to calculate the etching rate in small increments in order to accurately calculate the etching amount of the trench 132.

  In order to calculate the etching rate in small increments in etching, it is usually sufficient to differentiate the waveform of the reflected light from the wafer W at each timing. However, as described above, the reflected light from the wafer W is reflected by the trench interference light or the mask film. Since the interference light is superimposed interference light, the etching rate of the trench 132 cannot be obtained accurately even if the waveform of the reflected light is simply differentiated at each timing.

  Therefore, in the present embodiment, frequency analysis is performed, and the period of the trench interference wave (hereinafter referred to as “trench interference period”) is calculated from the superimposed interference wave. In addition, in the frequency analysis, using a data length of a certain value or more, specifically, using a data length of one cycle or more of the waveform to be analyzed contributes to improving the reliability of the frequency analysis. Therefore, an etching rate at a certain timing is obtained. Therefore, in this embodiment, a waveform for a predetermined period is extracted from the superimposed interference wave, and the extracted waveform is subjected to frequency analysis. As described above, since the etching rate is related to the trench interference period, in this embodiment, first, the trench interference period is obtained from the extracted waveform, and the etching rate is calculated from the trench interference wave.

  FIG. 3 is a diagram for explaining extraction of a waveform for a predetermined period from the superimposed interference wave in the etching amount calculation method according to the present embodiment.

  In FIG. 3, since the superimposed interference wave 30 vibrates at a cycle of about 30 seconds, the predetermined period is set to 30 seconds. Here, in order to obtain the trench interference period at the timing A, the waveform of the superimposed interference wave 30 in the period 31 from the timing A to 30 seconds before (the waveform of the portion surrounded by a square in the drawing) is extracted. In the present embodiment, the predetermined period is hereinafter referred to as “window”. The window 31 has a start point 32 and an end point 33. The start point 32 corresponds to 30 seconds before the timing A, and the end point 33 corresponds to the timing A.

  In this embodiment, frequency analysis is performed on the extracted waveform of the window 31. Here, since the extracted waveform is at most one cycle, the maximum entropy method is used as an analysis method. The maximum entropy method is a method of calculating the frequency distribution of observation phenomena from the measurement results of extremely short measurement time with high resolution ("Waveform data processing for scientific calculation" (CQ Publishing Co., Ltd., April 30, 1986, first edition) Since the number of waveforms to be analyzed is not so large, it is more suitable for the etching amount calculation method according to the present embodiment than the fast Fourier transform method that requires many cycles of waveforms.

  FIG. 4 is a diagram showing a frequency distribution obtained by frequency analysis using the maximum entropy method from the waveform of the window in FIG.

  Since the superimposed interference wave 30 mainly includes two of the trench interference wave and the mask film interference wave, the frequency distribution obtained from the waveform of the window 31 has a peak frequency (interference wave) as shown in FIG. There are mainly two periods (about 0.012 Hz and about 0.037 Hz in FIG. 4). Here, as described above, since the trench interference wave has a shorter cycle (higher frequency) than the mask film interference wave, a frequency of about 0.037 Hz corresponds to the trench interference cycle. Therefore, a frequency of about 0.037 Hz is detected as the trench interference period. Thus, in this embodiment, since it is predicted that there are two peaks in the frequency distribution obtained by the frequency analysis, the trench interference period is predicted in advance prior to the frequency analysis, and the obtained frequency is obtained. It is preferable to detect the trench interference period from the vicinity of the trench interference period predicted in the distribution.

  Since the window 31 includes the waveform of the superimposed interference wave 30 30 seconds before the timing A, the frequency distribution shown in FIG. 4 is the frequency distribution in the superimposed interference wave 30 30 seconds before the timing A. Therefore, the trench interference period detected from the frequency distribution shown in FIG. 4 is the average period of the trench interference light in the superimposed interference wave 30 from the timing A to 30 seconds before, but in this embodiment, it is shown in FIG. The trench interference period detected from the frequency distribution is regarded as a trench interference period at timing A for convenience. In the present embodiment, as will be described later, a plurality of windows are set for the superimposed interference wave 30, and the trench interference period obtained from the frequency distribution of the waveform of each window is integrated and averaged to obtain the entire trench interference period. Since the average value is calculated, the adverse effect of considering the average period of the trench interference light in the window 31 as the trench interference period at the timing A is eliminated.

  In addition, in the etching amount calculation method according to the present embodiment, the etching is performed from the time when the first predetermined period (the start point 32 corresponds to the start of etching and the end point 33 corresponds to the corresponding window 31 30 seconds after the start of etching) has elapsed. The average value of the etching rate over the entire period until the timing for calculating the amount is calculated, and the etching amount is calculated from the average value of the etching rate.

  FIG. 5 is a diagram for explaining a method for calculating an average value of etching rates in the etching amount calculating method according to the present embodiment, and shows a case where 80 seconds have elapsed after the start of etching.

In FIG. 5, n windows W _k (k = 1 to n, where n is a natural number) shifted by Δt (predetermined time) with respect to the superimposed interference wave 50 are set, and the frequency distribution is obtained in each window W _k . N trench interference periods f _k (k = 1 to n, n is a natural number) are detected from each frequency distribution.

Next, n trench interference periods f _k are averaged based on the following formula (1).

The trench interference period f _ave is calculated as the average value of the trench interference wave up to 80 seconds after the start of etching. Further, if the measurement wavelength (the wavelength of the laser beam from the laser light source 26) is λ, the average value of the etching rate up to 80 seconds after the start of etching is calculated from the following equation (2). Average value of etching rate = f _ave × λ / 2 (2)
Next, the etching amount up to 80 seconds after the start of etching is calculated from the following formula (3). Etching amount = Average value of etching rate x Etching time (3)
In the etching amount calculating method according to the present embodiment, when _(the t one of natural numbers 1 to n) one window W _t disturbance is applied to the superposed interference wave 50 in the trench interference obtained from the window W _t Although the period ft is an abnormal value, the trench interference period ft is an integrated average of the trench interference period f _u obtained from another window W _u (where u is any one of 1 to n and is a natural number other than t). _Therefore , the influence of the trench interference period ft on the integrated and averaged trench interference period f _ave is small.

  Next, an etching amount calculation method according to the present embodiment will be described.

  FIG. 6 is a flowchart showing an etching amount calculation method according to the present embodiment.

  In FIG. 6, first, after the substrate processing apparatus 10 starts etching the etching target layer 130 of the wafer W, the laser light source 26 transmits the laser light L <b> 1 through the optical fiber 24, the condenser lens 23, and the monitor device 21. (Step S61) (irradiation step), and the detector 27 receives superimposed interference light, which is reflected light from the wafer W, via the optical fiber 24 or the like (step S62) (light reception step).

  Next, in step S63, the calculation unit 28 determines whether or not the current timing T has passed a preset etching end time, and if the etching end time has passed (YES in step S63). When this process is finished and the etching end time has not passed (NO in step S63), the calculation unit 28 determines from the etching start to the current timing T based on the superimposed interference light received by the detector 27. The superimposed interference wave is calculated (updated) (step S64) (interference wave calculation step).

  Next, the computing unit 28 extracts the waveform of the window whose end point is the current timing T (step S65) (waveform extraction step), and performs frequency analysis using the maximum entropy method on the extracted waveform of the window (step S65). S66) (frequency analysis step). Here, the time from the start point to the end point of the window is set longer than one period of the mask film interference wave.

  Thereafter, the calculation unit 28 detects, as a trench interference period at the current timing T, a frequency indicating a peak near the trench interference period predicted in advance in the frequency distribution obtained by the frequency analysis (step S67) (interference period detection). Step).

  Next, the calculation unit 28 calculates the trench interference period at the current timing T detected this time and the trench interference period at each timing detected between the elapse of the first predetermined period and the current timing T by the above equation (1). (Step S68) (integration average step), and the integrated and averaged trench interference period is measured from the etching start time to the current timing T and the etching time (from the etching start time to the current timing T). Is converted into the etching amount of the trench 132 using the above formulas (2) and (3) (step S69) (etching amount calculating step).

  Thereafter, the calculation unit 28 adds Δt to the current timing T to update the current timing T, that is, shifts the window end point by Δt (step S70), and returns to step S63.

  According to the etching amount calculation method according to the present embodiment, the superimposed interference wave is calculated while the end point of the window is shifted by Δt, the window waveform is extracted from the superimposed interference wave, the frequency analysis, and the trench interference period at the current timing T. The detection is repeated, and the trench interference period at the current timing T detected at each repetition and the trench interference period at each timing detected between the elapse of the first predetermined period and the current timing T are integrated and averaged, The averaged trench interference period is converted into the etching amount of the trench 132. Therefore, even if a disturbance is added to the waveform of a certain window extracted, the trench interference period which is an abnormal value obtained from the certain window is the same as the trench interference period obtained from the other window. Since the integrated averaging is performed, the influence of the trench interference period, which is an abnormal value, on the integrated averaged trench interference period can be reduced, so that the calculation of the etching amount of the trench 132 can be performed stably and accurately even when a disturbance is applied. Can be done.

  In the etching amount calculation method according to the present embodiment, the time from the start point to the end point of the window is longer than one period of the superimposed interference wave calculated in step S64. Reliability can be improved.

  Furthermore, since the maximum entropy method is used in the frequency analysis in the etching amount calculation method according to the present embodiment, the reliability of the frequency analysis can be improved even if the number of window waveforms is small.

  In the etching amount calculation method according to the present embodiment, the trench interference period is predicted in advance, and the trench interference period at the current timing T is detected from the vicinity of the predicted trench interference period in the frequency distribution obtained by frequency analysis. Therefore, the detection of the trench interference period can be performed quickly, and the detection of an abnormal value as the trench interference period can be suppressed.

  Next, an etching amount calculation method according to the second embodiment of the present invention will be described.

  Since the configuration and operation of this embodiment are basically the same as those of the first embodiment described above, the description of the overlapping configuration and operation will be omitted, and the description of the different configuration and operation will be described below. Do.

  FIG. 7 is a flowchart showing an etching amount calculation method according to the present embodiment.

  In FIG. 7, first, steps S61 to S67 are executed, and then, in step S71, the calculation unit 28 detects the trench interference period detected as the trench interference period at the current timing T in step S67 (for example, step S66). It is discriminated whether it corresponds to the maximum frequency or the minimum frequency in the frequency distribution obtained in (1).

  As a result of the determination in step S71, if the trench interference period detected as the trench interference period at the current timing T does not correspond to the abnormal value (NO in step S71), the process proceeds to step S68 as it is, and the detected interference period is abnormal. If the value corresponds to the value (YES in step S), the trench interference period detected as the trench interference period at the current timing T is removed, and it is detected from the window corresponding to the timing immediately before the current timing T. By setting the trench interference period as the trench interference period at the current timing T, the trench interference period is corrected (step S72) (interference period correcting step).

  Next, the calculation unit 28 executes Steps S68 to S70.

  According to the etching amount calculation method according to the present embodiment, when the trench interference period detected as the trench interference period at the current timing T corresponds to an abnormal value, the detected trench interference period is removed and the current Since the trench interference period detected from the window corresponding to the timing before the timing T is set as the trench interference period at the current timing T, the trench interference period corresponding to the abnormal value is integrated with respect to the averaged trench interference period. The influence can be removed, so that the amount of etching of the trench 132 can be calculated more stably and accurately even when a disturbance is applied.

  In the etching amount calculation method according to the present embodiment described above, when the detected trench interference period corresponds to an abnormal value, the trench interference period detected from the window corresponding to the timing immediately before the current timing T. Is set as the trench interference period at the current timing T. However, the trench interference period detected from the window corresponding to the timing immediately after the current timing T may be set as the trench interference period at the current timing T.

  Next, an etching amount calculation method according to the third embodiment of the present invention will be described.

  This embodiment is basically the same in configuration and operation as the first embodiment described above, and pre-processes the extracted waveform of the window before performing frequency analysis on the extracted waveform. Since only the points are different, the description of the duplicated configuration and action will be omitted, and the different configuration and action will be described below.

When the percentage of the ratio of the opening of the trench 132 to the surface of the wafer W (hereinafter referred to as “opening ratio”) is small, for example, below 0.5%, the reflected light L ₄ from the bottom of the trench 132 is reduced. Since the absolute light amount is reduced, the ratio of the portion occupied by the trench interference light in the superimposed interference light received by the detector 27 is reduced.

  FIG. 9 is a diagram illustrating a change in part of the superimposed interference wave when the aperture ratio changes.

As shown in FIG. 9, when the aperture ratio is 5%, it is clear that two types of interference waves (mask film interference wave and trench interference wave) are superimposed on the superimposed interference wave. If 0.5%, the absolute amount of the reflected light L ₄ is reduced, almost no waveform of the trench interference wave to the superposition interference wave. Such a phenomenon occurs even when the ratio of the hole openings on the surface of the wafer W is small or when the aspect ratio of the trench (or hole) is large (for example, when the trench 132 is a deep trench). This can happen because the absolute amount of reflected light from the bottom of the hole is reduced.

  When the waveform of the trench interference wave hardly appears in the superimposed interference wave (when the aperture ratio is 0.5%), the waveform of the window 31 is extracted from the superimposed interference wave, and the extracted waveform is directly subjected to frequency analysis. In the frequency distribution obtained, the peak of the period of the trench interference wave (trench interference period) becomes small.

  FIG. 10 is a diagram illustrating a change in the frequency distribution of the waveform of the window when the aperture ratio changes.

  As shown in FIG. 10, when the aperture ratio is 5%, two peaks in the frequency distribution (the period of the trench interference wave (about 0.8 Hz) and the period of the mask film interference wave (about 0.1 Hz)) are clear. However, when the aperture ratio is 0.5%, only one peak (period of the mask film interference wave) clearly appears in the frequency distribution, and the period of the trench interference wave hardly appears. As a result, the trench interference period cannot be accurately detected, and the etch rate cannot be accurately calculated.

  Therefore, in this embodiment, most of the portion occupied by the mask film interference wave is removed from the superimposed interference wave before frequency analysis of the waveform extracted from the superimposed interference wave by the window 31.

  FIG. 11 is a diagram showing a superimposed interference wave when the aperture ratio is 0.5%.

  As shown in FIG. 11, when the aperture ratio is 0.5%, as shown in FIG. 11, since the trench interference wave having a short period does not appear in the superimposed interference wave, the superimposed interference wave is almost the mask film interference wave. Is occupied by. Therefore, the waveform approximating the superimposed interference wave is substantially equal to the waveform of the mask film interference wave. Therefore, in this embodiment, a waveform approximating the superimposed interference wave is removed from the superimposed interference wave. Thereby, most of the portion occupied by the mask film interference wave can be removed from the superimposed interference wave.

  Further, as shown in FIG. 11, the superimposed interference wave that is substantially occupied by the mask film interference wave is close to a sine wave, and the portion of the sine wave having a quarter period or less can be accurately approximated by a quadratic polynomial. Therefore, in the present embodiment, when extracting the waveform of the window 31 from the superimposed interference wave, a portion having a quarter period or less of the mask film interference wave is extracted.

That is, in this embodiment, as shown in FIG. 12, n windows W _k (k = 1 to n, n is a natural number) corresponding to a quarter period or less of the mask film interference wave are shifted by Δt. set Te, extracting a waveform of each window W _k, extracted extract out waveform from a waveform to remove the waveform approximated by quadratic polynomial, to obtain a waveform most is removed portion where the mask film interference wave occupies (FIG. 13) The frequency of the waveform after removal is analyzed. Thereby, as shown in FIG. 14, a frequency distribution in which the peak of the trench interference period (about 0.8 Hz) clearly appears can be obtained. Incidentally, no peak appears the cycle (approximately 0.1 Hz) of the mask film interference wave in the frequency distribution of FIG. 14, because the most from the waveform of the window W _k of the portion occupied by the mask film interference wave is removed.

  FIG. 15 is a flowchart showing an etching amount calculation method according to the present embodiment. Note that the etching amount calculation method according to the present embodiment is executed when the aperture ratio is small, for example, when the aperture ratio is less than 0.5%.

  In FIG. 15, first, steps S61 to S64 are executed, and then the calculation unit 28 extracts, as a window waveform, a portion of the superimposed interference wave that is ¼ period or less with the current timing T as the end point (step S65). ) (Waveform extraction step).

  Next, the calculation unit 28 calculates a waveform (hereinafter simply referred to as “approximate waveform”) obtained by approximating the extracted window waveform by a second-order polynomial (step S151), and the calculation is performed from the extracted window waveform. The approximate waveform is removed (step S152) (pre-analysis processing step), a waveform from which most of the portion occupied by the mask film interference wave is removed is obtained, and the waveform after the approximate waveform is removed is subjected to frequency analysis (step S153).

  Next, the calculation unit 28 executes Steps S67 to S70.

  According to the etching amount calculation method according to the present embodiment, most of the portion occupied by the mask film interference wave is removed from the waveform of the window extracted prior to the frequency analysis. Even when the rate is less than 0.5%, it is possible to increase the proportion of the portion of the trench interference wave occupied in the waveform after the approximate waveform removal, and thus the peak of the trench interference period becomes clear by frequency analysis. Can be obtained. As a result, the period of the trench interference wave can be accurately calculated. Note that the etching amount calculation method according to the present embodiment described above can be used only when the period of the waveform of the mask film interference light is longer than the period of the interference wave of the trench interference light.

  In the etching amount calculation method according to the present embodiment, a waveform (approximate waveform) obtained by approximating the extracted window waveform with a quadratic polynomial is removed from the extracted window waveform prior to the frequency analysis. When the aperture ratio is small, the waveform of the superimposed interference wave is substantially equal to the mask film interference wave, and therefore the approximate waveform is also substantially equal to the mask film interference wave. Therefore, most of the portion occupied by the mask film interference wave can be reliably removed from the extracted waveform of the window.

  Further, in the etching amount calculation method according to the present embodiment, a portion having a quarter period or less of the mask film interference wave is extracted as a window waveform. Since the mask film interference wave that occupies most of the superimposed interference wave is close to a sine wave, if the portion of the mask film interference wave that is less than ¼ period is extracted, the extracted waveform of the window can be accurately approximated by a quadratic polynomial. can do. Thereby, most of the portion occupied by the mask film interference wave can be accurately removed from the extracted waveform of the window.

  Note that when the aperture ratio in the present embodiment is small, not only the ratio of the openings of the trenches 132 on the surface of the wafer W is small but also the ratio of the openings of the holes on the surface of the wafer W is small. This is also the case when the aspect ratio of the trench (or hole) is large.

  In each of the above-described embodiments, the maximum entropy method is used in frequency analysis. However, when the number of interference waveforms in each window is large, a fast Fourier transform method may be used. Since the fast Fourier transform method requires fewer calculations than the maximum entropy method, the etching amount of the trench 132 can be calculated earlier.

Further, when the etching amount (etching depth) of a certain trench is calculated using the etching amount calculation method according to each of the above-described embodiments, when the mask film 131 is a film that transmits laser light, As shown in FIG. 8, an error may occur between the calculated etching amount (“monitor depth” in the figure) and the actually measured etching amount (“etching depth” in the figure). This is because the superimposed interference light mainly includes the interference light of the reflected light L ₃ and the reflected light L ₄ , not the interference light of the reflected light L ₂ and the reflected light L ₄ , and the mask film 131 is affected by the change in the optical path length of the reflected light L _3. This is probably because not only the thickness change but also the refractive index of the mask film 131 affects.

  When an error occurs between the calculated etching amount and the actually measured etching amount, the etching amount (etching rate) of the trench 132 is measured using the test wafer W prior to the etching amount calculation, and It is preferable to calculate the etching amount of the trench 132 by the etching amount calculation method according to each of the above-described embodiments, and obtain a regression equation between the actually measured etching amount and the calculated etching amount. In the subsequent etching, after the etching amount of the trench 132 is calculated by the etching amount calculation method according to each of the embodiments described above, the calculated etching amount may be corrected by a regression equation.

  In each of the above-described embodiments, the etching amount of the trench 132 is calculated. However, the etching amount of holes may be calculated by executing the etching amount calculation method shown in FIGS.

  Another object of the present invention is to supply a computer (for example, the controller 29) with a storage medium storing software program codes for realizing the functions of the above-described embodiments, and the CPU of the computer is stored in the storage medium. It is also achieved by reading and executing the program code.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code and the storage medium storing the program code constitute the present invention.

  Examples of the storage medium for supplying the program code include RAM, NV-RAM, floppy (registered trademark) disk, hard disk, magneto-optical disk, CD-ROM, CD-R, CD-RW, DVD (DVD). -ROM, DVD-RAM, DVD-RW, DVD + RW) and other optical disks, magnetic tapes, non-volatile memory cards, other ROMs, etc., as long as they can store the program code. Alternatively, the program code may be supplied to the computer by downloading from another computer or database (not shown) connected to the Internet, a commercial network, a local area network, or the like.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) running on the CPU based on the instruction of the program code. Includes a case where part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.

  Further, after the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. This includes a case where the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  The form of the program code may include an object code, a program code executed by an interpreter, script data supplied to the OS, and the like.

  Next, examples of the present invention will be described.

Example 1
First, a wafer W on which a mask film 131 that transmits a laser beam L1 made of an oxide film is formed on a layer to be etched 130 made of silicon is prepared, and a deep trench 132 is formed in the layer to be etched 130 by etching with the substrate processing apparatus 10. Formed. The etching conditions at this time were as follows.
Actual etching rate: 1200 nm / min Selection ratio: 10 to 1 (etched layer 130 to mask film 131)
Aperture ratio: 0.05
Measurement wavelength (wavelength of laser light L1): 300 nm
Sampling rate: 10Hz
In the etching of the deep trench 132, the time from the start point to the end point of the window is set to 30 seconds, and the etching amount calculation method of FIG. 6 is executed to obtain the integrated and averaged trench interference period at each timing. The etching rate of the deep trench 132 at each timing was obtained from the trench interference period. Then, the obtained etching rate is shown in a graph (see FIG. 16).

Comparative Example 1
Further, in the above-described etching of the deep trench 132, a superposition interference wave from the wafer W is observed by the detector 27, a short period interference wave in the superposition interference wave is read, and between each extreme value in the short period interference wave. From this time, the trench interference period was obtained, and the etching rate of the deep trench 132 between each extreme value was obtained from the trench interference period. Then, the obtained etching rate is shown in a graph (see FIG. 16).

  From the graph of FIG. 16, it was found that the etching rate of Example 1 was smaller and more stable than the etching rate of Comparative Example 1.

  Further, the error in the etching amount of Example 1 and the error in the etching amount of Comparative Example 1 are shown in a graph in time series (see FIG. 17).

  From the graph of FIG. 17, it was found that the etching amount of Example 1 had a smaller error than the etching amount of Comparative Example 1. Accordingly, it was found that the etching amount calculation method of FIG. 6 can accurately calculate the etching amount.

Example 2
Next, a wafer W having a mask film 131 made of an oxide film formed on the layer to be etched 130 made of silicon was prepared, and the shallow trench 132 was formed in the layer to be etched 130 by etching with the substrate processing apparatus 10. The etching conditions at this time were as follows.
Actual etching rate: 360 nm / min Selection ratio: 10 to 1 (etched layer 130 to mask film 131)
Aperture ratio: 0.2
Measurement wavelength (wavelength of laser light L1): 300 nm
Sampling rate: 10Hz
In the etching of the shallow trench 132, the time from the start point to the end point of the window was set to 25 seconds, and the etching amount calculation method of FIG. 6 was executed to calculate the etching amount (etching depth) of the shallow trench 132 at each timing. . Then, the calculated etching amount is shown in a graph (see FIG. 18).

Comparative Example 2
Further, in the above-described etching of the shallow trench 132, the superimposed interference wave from the wafer W is observed by the detector 27, the frequency distribution is obtained by frequency analysis from all the superimposed interference waves from the start of etching to each timing, Based on the frequency distribution, the trench interference period between the start of etching and each timing was obtained, and the etching amount (etching depth) of the shallow trench 132 at each timing was calculated from the trench interference period. That is, the etching amount was calculated from the superimposed interference wave without using the window shown in FIG. Then, the calculated etching amount is shown in a graph (see FIG. 18).

  In the graph of FIG. 18, the etching amount data of Comparative Example 2 is disturbed. This is considered to be because a disturbance is added to the superimposed interference wave. On the other hand, the etching amount data of Example 2 was not disturbed. Since Example 2 and Comparative Example 2 are etching amounts obtained from the same superimposed interference wave to which disturbance is added, the etching amount calculation method in FIG. 6 calculates the etching amount even when disturbance is added to the superimposed interference wave. Has been found to be stable and accurate.

Example 3
In the etching of the trench 132 on the other wafer W from the first and second embodiments described above, the etching amount calculation method of FIG. 6 was executed to obtain the etching rate of the trench 132 at each timing. Then, the obtained etching rate is shown in a graph (see FIG. 19).

Comparative Example 3
Further, in the same etching as in the third embodiment, the etching amount calculation method under the same conditions as the etching amount calculation method in FIG. 6 is executed except that the fast entropy method is used instead of the maximum entropy method, and the trench 132 is etched at each timing. I asked for the rate. Then, the obtained etching rate is shown in a graph (see FIG. 19).

  From the graph of FIG. 19, it was found that the etching rate of Example 3 was smaller and more stable than the etching rate of Comparative Example 3. Thus, it was found that the etching amount can be calculated stably when the maximum entropy method is used.

Example 4
First, a wafer W with an aperture ratio of 5% and a wafer W with an aperture ratio of 0.5% are prepared, and the etching amount calculation method shown in FIG. Each etching rate was determined. The obtained etching rates are shown in a graph (see FIG. 20).

Comparative Example 4
Similar to the fourth embodiment, when the wafer W having an aperture ratio of 5% and the wafer W having an aperture ratio of 0.5% are prepared and the etching target layer 130 of each wafer W is etched, the etching amount calculation of FIG. The method was carried out to determine each etching rate. The obtained etching rates are shown in a graph (see FIG. 21).

  Comparing the graphs of FIGS. 20 and 21, when the etching amount calculation method of FIG. 6 is executed, the etching rate is stable when the aperture ratio is 5%, but the etching rate is stable when the aperture ratio is 0.5%. On the other hand, when the etching amount calculation method of FIG. 15 was executed, it was found that both the etching rate at an aperture ratio of 5% and the etching rate at an aperture ratio of 0.5% were stable. . Thus, when the approximate waveform of the window waveform is removed from the extracted window waveform before frequency analysis of the extracted window waveform, the etching rate can be accurately obtained even when the aperture ratio is small. I understood.

1 is a cross-sectional view schematically showing a configuration of a substrate processing apparatus to which an etching amount calculation method according to a first embodiment of the present invention is applied. It is a figure for demonstrating the fall of the etching rate in the etching of a trench. It is a figure for demonstrating extraction of the waveform of the predetermined period from the superimposed interference wave in the etching amount calculation method which concerns on this Embodiment. It is a figure which shows the frequency distribution obtained by the frequency analysis using the maximum entropy method from the waveform of the window in FIG. It is a figure for demonstrating the calculation method of the average value of the etching rate in the etching amount calculation method which concerns on this Embodiment. It is a flowchart which shows the etching amount calculation method which concerns on this Embodiment. It is a flowchart which shows the etching amount calculation method which concerns on the 2nd Embodiment of this invention. It is a figure which shows the difference | error between the calculated etching amount and the measured etching amount. It is a figure which shows a part change of the superposition interference wave when an aperture ratio changes. It is a figure which shows the change of the frequency distribution of the waveform of the window when an aperture ratio changes. It is a figure which shows the superimposed interference wave in case an aperture ratio is 0.5%. It is a figure for demonstrating extraction of the waveform of the window in the etching amount calculation method which concerns on the 3rd Embodiment of this invention. It is a figure which shows the waveform from which most of the part which a mask film | membrane interference wave occupies was removed from the superimposition interference wave. It is a figure which shows the frequency distribution obtained by the frequency analysis from the waveform from which most of the part which a mask film | membrane interference wave occupies was removed from the superimposition interference wave. It is a flowchart which shows the etching amount calculation method which concerns on this Embodiment. FIG. 7 is a comparison diagram of the etching rate calculated by the etching amount calculation method of FIG. 6 and the etching rate obtained from the time between each extreme value in the interference wave. FIG. 7 is a comparison diagram of an error between an etching amount and an actual etching amount calculated by the etching amount calculating method in FIG. 6, and an etching amount and an actual etching amount error obtained from the time between each extreme value in an interference wave . FIG. 7 is a comparison diagram between an etching amount calculated by the etching amount calculation method of FIG. 6 and an etching amount obtained by frequency analysis of a superimposed interference wave from the start of etching to each timing. It is a comparison figure of the etching rate computed using the maximum entropy method, and the etching rate computed using the fast Fourier transform method. It is a figure which shows the etching rate of each wafer from which the aperture ratios obtained using the etching amount calculation method of FIG. 15 differ. It is a figure which shows the etching rate of each wafer from which the aperture ratios obtained using the etching amount calculation method of FIG. 6 differ. It is a figure for demonstrating the interference of the light during an etching. It is a figure which shows a superimposed interference wave. It is a figure which shows the etching rate calculated | required from the time between each extreme value in an interference wave. It is a figure which shows the superimposed interference wave to which the disturbance was added. FIG. 26A shows a frequency distribution obtained by frequency analysis of the superimposed interference wave. FIG. 26A shows a case where no disturbance is added to the superimposed interference wave, and FIG. 26B shows a case where disturbance is added to the superimposed interference wave. is there.

Explanation of symbols

L1 Laser light L ₂ , L ₃ , L ₄ reflected light W Wafer 10 Substrate processing device 25 Etching amount calculation device 26 Laser light source 27 Detector 28 Calculation unit 30, 50 Superimposed interference wave 31 Window 130 Etched layer 131 Mask film 132 Trench

Claims (13)

An etching amount calculation method for calculating an etching amount of the recess in etching of a substrate that forms a recess using a mask film,
An irradiation step of irradiating the substrate with light;
A light receiving step of receiving a superimposed interference light in which interference light of at least reflected light from the mask film and reflected light from the bottom of the recess is superimposed on other interference light;
An interference wave calculating step of calculating a superimposed interference wave from the received superimposed interference light;
A waveform extraction step of extracting a waveform of a predetermined period from the superimposed interference wave;
A frequency analysis step of performing frequency analysis on the extracted waveform;
An interference period detection step of detecting a period of interference waves of reflected light from the mask film and reflected light from the bottom of the recess from the frequency distribution obtained by the frequency analysis;
An integration in which the interference wave calculation step, the waveform extraction step, the frequency analysis step, and the interference cycle detection step are repeated while shifting the predetermined period by a predetermined time, and the cycle of the detected interference wave is integrated and averaged each time it is repeated. Average step and
An etching amount calculating method, comprising: an etching amount calculating step of calculating an etching amount of the concave portion based on a cycle of the integrated and averaged interference wave.   2. The predetermined period is longer than one period of a waveform of the other interference light having a longer period than an interference wave of reflected light from the mask film and reflected light from the bottom of the recess. The etching amount calculation method described. When the period of the waveform of the other interference light is longer than the period of the interference wave of the reflected light from the mask film and the reflected light from the bottom of the recess, prior to the frequency analysis step, from the superimposed interference wave An analysis pre-processing step for removing most of the portion occupied by the waveform of the other interference light from the extracted waveform of a predetermined period;
3. The etching amount calculation method according to claim 1, wherein in the frequency analysis step, frequency analysis is performed on a waveform from which most of the portion occupied by the waveform of the other interference light is removed.   4. The etching amount calculation method according to claim 3, wherein, in the pre-analysis processing step, a waveform obtained by approximating the extracted waveform with a second-order polynomial is removed from the extracted waveform.   The etching amount calculation method according to claim 3 or 4, wherein the predetermined period is equal to or less than ¼ period of the waveform of the other interference light.   6. The etching amount calculation method according to claim 3, wherein an opening ratio of the recesses on the surface of the substrate is 0.5% or less, or the recesses are deep trenches. .   The etching amount calculation method according to claim 1, wherein a maximum entropy method is used in the frequency analysis.   8. The method according to claim 1, further comprising an interference period correcting step of removing the period of the interference wave when the period of the interference wave detected from the frequency distribution corresponds to an abnormal value. The etching amount calculation method according to item.   In the interference period correcting step, the period of the interference wave obtained from the predetermined period before or after the predetermined period from which the period of the interference wave corresponding to the abnormal value is obtained is set to the abnormal value. The etching amount calculation method according to claim 8, wherein the period of the interference wave corresponding to is considered as the period of the interference wave in the predetermined period obtained. Predicting the period of the interference wave of the reflected light from the mask film and the reflected light from the bottom of the recess,
In the interference period detection step, in the frequency distribution obtained by the frequency analysis, a period of interference waves of reflected light from the mask film and reflected light from the bottom of the recess is detected from the vicinity of the predicted period. The etching amount calculation method according to claim 1, wherein:   11. The other interference light is reflected light from a surface of the mask film and interference light of reflected light from a boundary surface between the mask film and the surface of the substrate. The etching amount calculation method according to claim 1. A computer-readable storage medium storing a program for causing a computer to execute an etching amount calculation method for calculating an etching amount of the recess in etching a substrate on which a recess is formed using a mask film, the etching amount calculating method Is
An irradiation step of irradiating the substrate with light;
A light receiving step of receiving a superimposed interference light in which interference light of at least reflected light from the mask film and reflected light from the bottom of the recess is superimposed on other interference light;
An interference wave calculating step of calculating a superimposed interference wave from the received superimposed interference light;
A waveform extraction step of extracting a waveform of a predetermined period from the superimposed interference wave;
A frequency analysis step of performing frequency analysis on the extracted waveform;
An interference period detection step of detecting a period of interference waves of reflected light from the mask film and reflected light from the bottom of the recess from the frequency distribution obtained by the frequency analysis;
An integration in which the interference wave calculation step, the waveform extraction step, the frequency analysis step, and the interference cycle detection step are repeated while shifting the predetermined period by a predetermined time, and the cycle of the detected interference wave is integrated and averaged each time it is repeated. Average step and
An etching amount calculating step of calculating an etching amount of the concave portion based on the cycle of the integrated averaged interference wave. In an etching amount calculation apparatus for calculating an etching amount of the recess in etching of a substrate that forms a recess using a mask film,
An irradiation unit for irradiating the substrate with light;
A light receiving unit that receives at least the interference light of the reflected light from the mask film and the reflected light of the reflected light from the bottom of the concave portion superimposed on the other interference light;
An interference wave calculator for calculating a superimposed interference wave from the received superimposed interference light;
A waveform extraction unit that extracts a waveform of a predetermined period from the superimposed interference wave;
A frequency analysis unit for performing frequency analysis on the extracted waveform;
An interference period detection unit that detects the period of the interference wave of the reflected light from the mask film and the reflected light from the bottom of the recess from the frequency distribution obtained by the frequency analysis;
The calculation of the superimposed interference wave, the extraction of the waveform during the predetermined period, the frequency analysis, and the detection of the period of the interference wave are repeated while shifting the predetermined period by a predetermined time, and the period of the detected interference wave is repeated each time it is repeated. A cumulative average part for cumulative average;
An etching amount calculation apparatus comprising: an etching amount calculation unit that calculates an etching amount of the concave portion based on a cycle of the integrated and averaged interference wave.

Images