JP2010034582A - Etching-depth detecting method, etching-monitor apparatus, and etching apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an etching-depth detecting method which can detect an etching depth accurately by suppressing an effect of the distortion of a particular phase of an interference wave shape even if the distortion exists in the interference wave shape. <P>SOLUTION: In a method for irradiating light on a semiconductor wafer W and detecting an etching depth by using the reflecting light thereof, the etching-depth detecting method includes a process for irradiating the light on the semiconductor wafer W, a process for detecting interference light which varies periodically by the reflected light from the top surface of the etched light E of the wafer and from the front surface of an etched portion E' of the wafer, a frequency analyzing process for searching a frequency ω(t) by performing frequency analysis to the detected data at each time extended from a time t to a time (t+Δt) of an interference light wave shape, an etching-speed calculating process for calculating an etching speed E(t) by using the frequency ω(t), and a process for searching the etching depth by time-integrating the etching speed E(t). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an etching depth detection method capable of detecting an etching depth in real time, an etching monitor device, and an etching device.

  An etching method using plasma has been widely applied to a semiconductor manufacturing process or an LCD substrate manufacturing process. The etching apparatus includes, for example, an upper electrode and a lower electrode arranged in parallel with each other in a processing chamber, and plasma is generated from an etching gas by discharge between the upper electrode and the lower electrode while a semiconductor wafer is placed on the lower electrode. And an object to be processed such as a semiconductor wafer is etched according to a predetermined pattern. Emission spectroscopic analysis has been proposed as a method for monitoring etching. This is a method for detecting the time when a specific wavelength of the emission spectrum of a gas generated by etching is changed as the end point of etching. I can't know.

  An etching apparatus capable of detecting the etching depth is proposed in, for example, Japanese Patent No. 2545948. In the case of this etching apparatus, an observation window is provided in the upper electrode, light is irradiated to the surface of the semiconductor wafer from the outside of the processing chamber through this window, and reflected light that has interfered with the surface of the semiconductor wafer is detected by a detector. The signal that is detected and photoelectrically converted by this detector is subjected to frequency analysis of the interference waveform using the maximum entropy method in the waveform analysis means, and the etching depth is calculated in real time by calculating the etching depth based on the frequency distribution of the interference wave. To detect.

  However, the conventional etching depth detection method obtains an interference waveform using monochromatic light such as a laser beam and detects the etching depth by frequency analysis or the like. In this interference waveform, the period at a specific phase is detected. Therefore, there is a problem that it is difficult to avoid a general distortion, and the etching rate of the distortion portion is periodically greatly shifted, so that the etching depth cannot be accurately measured and monitored.

  The present invention has been made in order to solve the above-described problems. Even when a specific phase of an interference waveform is distorted, the etching depth can be accurately detected by suppressing the influence of the distortion. It is an object to provide a method, an etching monitor device, and an etching device.

  According to a first aspect of the present invention, there is provided a method for detecting an etching depth, wherein the object to be processed is irradiated with light, and the reflected light is used to detect the etching depth. Frequency analysis of the process, the step of detecting interference light that varies periodically due to the reflected light from the upper surface of the layer to be etched and the surface of the part to be etched, and the detection data for each time from time t to (t + Δt) of the interference waveform Performing a frequency analysis step for obtaining the frequency ω (t), an etching rate calculating step for calculating the etching rate E (t) using the frequency ω (t), and time integration of the etching rate E (t). And a step of obtaining the etching depth.

  According to a second aspect of the present invention, there is provided an etching depth detection method according to the first aspect of the present invention, wherein the interference light and the interference waveform are both plural.

  According to a third aspect of the present invention, there is provided an etching depth detection method according to the second aspect of the invention, wherein the etching rate calculation step calculates the etching rate using the frequency of each of the interference waveforms. In addition, an etching rate supplementing step for calculating the average etching rate by complementing the plurality of calculated etching rates with each other is provided, and in the etching rate supplementing step, the distortion of each interference waveform is large. The calculated etching rates are weighted and averaged according to the above, and the calculated etching rate deviation based on any one of the interference waveform distortions is supplemented by the calculated etching rate based on the interference waveform having no other distortions. In the step of obtaining the etching rate and obtaining the etching depth, the average etching rate is integrated over time. The one in which the features.

  According to a fourth aspect of the present invention, there is provided an etching depth detection method according to the third aspect of the present invention, wherein the phase of each interference waveform is also obtained in the frequency analysis step, and these steps are performed in the etching rate complementation step. The calculated etching rates are weighted and averaged according to the phase of the interference waveform.

  An etching depth detection method according to claim 5 of the present invention is the invention according to any one of claims 1 to 4, wherein, in the frequency analysis step, the time from the time t of the interference waveform is obtained. The detection data for each time of (t + Δt) is data of a certain time width Δt.

  Moreover, the etching depth detection method according to claim 6 of the present invention is the invention according to any one of claims 1 to 5, wherein the maximum entropy method is used as frequency analysis in the frequency analysis step. It is characterized by using.

  According to a seventh aspect of the present invention, there is provided an etching depth detection method according to any one of the first to fifth aspects, wherein in the frequency analysis step, fast Fourier transform is performed as frequency analysis. It is characterized by using.

According to an eighth aspect of the present invention, there is provided an etching monitor apparatus for irradiating a target object with light and monitoring an etching depth using the reflected light. A light source that emits light, a photodetector that detects interference light that periodically varies due to reflected light from the top surface of the etched layer and the surface of the etched portion, and the interference light is analyzed based on a signal from the photodetector Analyzing / calculating means for obtaining the etching depth, and a control device linked to the analyzing / calculating means, wherein the analyzing / calculating means converts the detected data from the time t of the interference waveform to detection data every (t + Δt). Frequency analysis means for determining the frequency ω (t) by performing frequency analysis on the
Etching rate calculating means for calculating the etching rate E (t) using the frequency ω (t), and depth calculating means for obtaining the etching depth by integrating the etching rate E (t) with time. It is characterized by this.

  The etching monitor apparatus according to claim 9 of the present invention is the etching monitor apparatus according to claim 8, wherein the frequency analyzing means has a predetermined time width Δt as detection data every (t + Δt) from time t of the interference waveform. It is characterized by using the following data.

  An etching monitor apparatus according to claim 10 of the present invention is characterized in that, in the invention according to claim 8 or claim 9, the frequency analysis means uses a maximum entropy method as frequency analysis. is there.

  According to an eleventh aspect of the present invention, in the invention according to the eighth or ninth aspect, the frequency analysis means uses a fast Fourier transform as a frequency analysis. is there.

  An etching monitor apparatus according to a twelfth aspect of the present invention is the invention according to any one of the eighth to eleventh aspects, wherein there are a plurality of the interference light and the interference waveform. It is what.

  According to a thirteenth aspect of the present invention, in the invention according to the twelfth aspect, the etching rate calculation means calculates the etching rate based on the frequency of each interference waveform, and calculates each of them. An etching rate complementing means for obtaining an etching rate and further calculating the average etching rate by complementing the plurality of calculated etching rates with each other is provided, and the etching rate complementing means is provided according to the magnitude of distortion of each interference waveform. Each of the calculated etching rates is weighted averaged, and the calculated etching rate based on any one of the interference waveform distortions is supplemented by the calculated etching rate based on the interference waveform having no other distortion to obtain the average etching rate. The depth calculation means integrates the average etching rate over time.

  According to a fourteenth aspect of the present invention, in the invention according to the thirteenth aspect, the frequency analysis means also obtains the phase of each interference waveform, and the etching rate complementing means Each of the calculated etching rates is weighted and averaged according to the phase of the interference waveform.

  An etching apparatus according to a fifteenth aspect of the present invention includes the etching monitor apparatus according to any one of the eighth to fourteenth aspects.

  According to the present invention, there is provided an etching depth detection method, an etching monitor device, and an etching device capable of accurately detecting an etching depth by suppressing the influence of the distortion even if the specific phase of the interference waveform is distorted. can do.

It is a block diagram which shows one Embodiment of the etching apparatus to which the detection method of the etching depth of this invention is applied. It is explanatory drawing for demonstrating the interference light at the time of etching a semiconductor wafer. It is a figure which shows the spectrum of the emitted light from the light source of the etching apparatus shown in FIG. It is a flowchart which shows the procedure of the detection method of the etching depth of this invention using the etching apparatus shown in FIG. FIG. 2 is an actual measurement waveform diagram showing interference signals of three types of interference waveforms obtained by reflected light from the etched portion and the top surface of the etched layer when the etching apparatus of FIG. 1 is used. It is a graph which shows the etching rate (nm / sec) calculated | required separately from the interference waveform of single wavelength 350nm, 450nm, and 550nm shown in FIG. It is a graph which shows the etching rate calculated | required by mutually complementing the etching rate of each interference waveform of single wavelength 350nm, 450nm, and 550nm shown in FIG. 6, and weighting. FIG. 7 is a graph showing the etching depth obtained using a single wavelength of 450 nm at each time shown in FIG. 7, and the etching depth shown by the alternate long and short dash line is obtained from the etching rate shown in FIG. The etching depth is obtained from the etching rate shown in FIG. It is a block diagram which shows a form other than an etching apparatus. It is a prediction figure of the time change of the amplitude of an interference waveform using the etching apparatus shown in FIG. It is the graph which calculated | required the etching depth based on the prediction figure shown in FIG.

Hereinafter, the present invention will be described based on the embodiment shown in FIGS.
First, an embodiment of an etching apparatus of the present invention capable of realizing the etching depth detection method of the present invention will be described with reference to FIG. An etching apparatus 10 shown in FIG. 1 includes a processing chamber 11 made of a conductive material such as aluminum, and a mounting table that is disposed on the bottom surface of the processing chamber 11 and mounts a semiconductor wafer W as an object to be processed. The lower electrode 12 is also provided, and the upper electrode 13 disposed above the lower electrode 12 with a predetermined interval. A gas supply unit 11A to which a gas supply source (not shown) is connected is formed at the upper part of the peripheral surface of the processing chamber 11, and a vacuum exhaust device (not shown) is connected to the lower part of the peripheral surface of the processing chamber 11. A gas discharge part 11B is formed. Further, a high frequency power source 15 is connected to the lower electrode 12 via a matching box 14, and a high frequency power source 17 having a higher frequency is connected to the upper electrode 13 via a matching box 16 to etch the semiconductor wafer W.

  After evacuating the gas exhaust unit 11B through a vacuum exhaust device and reducing the pressure in the processing chamber 11 to a predetermined degree of vacuum, the high frequency power is applied to both the upper and lower electrodes 12, 13 from the gas supply unit 11A. When an etching gas is supplied into the processing chamber 11, an etching gas plasma is generated between the electrodes 12 and 13. For example, as shown in FIG. 2, the opening of the resist layer R on the surface of the semiconductor wafer W on the lower electrode 12. The etched portion E ′ of the etched layer E is etched from the portion O to form a groove T having a predetermined depth.

Thus, a cylindrical monitor window member 18 is mounted in the processing chamber 11, and a monitor window 18 A made of a transparent material such as quartz glass is attached to the upper end of the window member 18. The lower end portion of the window member 18 passes through the through hole of the upper electrode 13 and faces the surface of the semiconductor wafer W. Then, the etching state of the semiconductor wafer W in the processing chamber 11 is monitored via an etching monitor device 20 connected to the window member 18. As shown in FIG. 1, the etching monitor device 20 includes a light source 21, an optical fiber 22, a lens 23, a polychromator 24, a photodetector 25, an analysis / calculation unit 26, and a memory 27, and the emitted light L from the light source 21. irradiating on the surface of the semiconductor wafer W in the processing chamber 11, to detect the reflected light L ₀ from the semiconductor wafer W surface, the etching conditions in real time based on the three types of interference light L _1, L _2, L ₃ When the etching depth reaches a predetermined depth, the high frequency power supplies 15 and 17 are turned off via the control device 28 to terminate the etching.

For example, when light having a spectrum in the wavelength region shown in FIG. 3 is emitted from the light source 21, the emitted light L is incident on the etched portion E and the resist layer R of the semiconductor wafer W in the processing chamber 11 through the optical fiber 22. As shown in FIG. 2, the light is reflected at each portion (the interface between the resist layer and the semiconductor wafer (the upper surface of the etched layer E) and the etched portion E ′), and the reflected lights interfere with each other to generate interference light. . That is, the reflected light _{L 0} as shown in FIG. 1 is spectrally through the polychromator 24 via the optical fiber 22, of which a wavelength lambda = 350 nm, 450 nm, the interference light _L 1 having a 550 _{nm, L} 2, L ₃ is detected by the first, second, and third photodetectors 25A, 25B, and 25C, respectively. These photodetectors 25A, 25B, 25C photoelectrically convert the interference light of each wavelength and output it as analog signals S ₁ , S ₂ , S ₃ . These analog signals are amplified via an amplifier (not shown) and then converted into digital signals via an A / D converter (not shown) and input to the analysis / calculation means 26. The analysis / calculation means 26 determines the etching depth based on these digital signals as will be described later. For example, a xenon lamp is used as the light source 21.

By the way, since the etched portion E ′ is deepened by being etched, the intensity of each interference light periodically changes in accordance with this depth to form each interference waveform. These interference waveforms are theoretically expressed as sine waves expressed by the following equation (1) and change with time. The relationship between the frequency ω and the etching depth in the equation (1) is theoretically expressed by the following equation (2). In equations (1) and (2), I _dc is the direct current component of the interference waveform, I _pp is the amplitude of the alternating current component of the interference waveform, ω is the angular frequency of the interference waveform (hereinafter referred to as “frequency”), and n. Is the refractive index, δ is the etching depth, and λ is the wavelength of the light used for the measurement.
I = I _dc + I _pp sin (ωt) (1)
ω = 2πd (nδ / λ) / dt (2)

  As shown in FIG. 1, the analysis / calculation means 26 includes a frequency analysis means 26A for analyzing the frequency of interference light using a maximum entropy method or a fast Fourier transform, and a frequency ω obtained by the frequency analysis means 26A. An etching rate calculating unit 26B that calculates the etching rate of each interference waveform based on the etching rate complementing unit 26C that calculates the etching rate more realistic by complementing the etching rates obtained by the etching rate calculating unit 26B. And an etching depth calculating means 26D for calculating the etching depth based on the etching speed obtained by the etching speed complementing means 26C, and a judging means 26E for determining the etching depth obtained by the etching depth calculating means 26D. And. The memory 27 stores a program for maximum entropy method and fast Fourier transform, a program used for calculating an etching rate and an etching depth, interference waveform data, and the like.

  The frequency analysis unit 26A of the analysis / calculation unit 26 analyzes the frequency of the three types of interference light described above using a maximum entropy method or a fast Fourier transform (in this embodiment, the maximum entropy method). The frequency ω (t) and the phase p (t) at time t are obtained for each interference waveform from t−Δt). The frequency is obtained every time t.

Since the relationship between the etching rate E (t) and the frequency ω (t) is expressed by the following equation (3), the etching rate calculating means 26B follows the program from time (t−Δt) to time t. When the frequency ω (t) is obtained for each interference waveform, from the relationship between the frequency ω (t) and the etching rate, the etching rate E (t) corresponding to each interference waveform at that time is expressed by the following equation (3). Is calculated at each time t based on the above.
E (t) = dδ (t) / dt = ω (t) λ / (2πn) (3)

  The actually observed interference waveform is distorted by various factors. However, when the time width Δt used for frequency analysis is a certain time (one period or more, Δt> 2π / ω), the influence of this distortion is averaged and does not have a great influence. However, Δt needs to be made as small as possible in order to improve the ability to follow the etching rate over time (referred to herein as “time response”). Both the maximum entropy method and the fast Fourier method can be analyzed if Δt is greater than or equal to a half period of the observed interference waveform (Δt> π / ω). However, when Δt is short as described above, the etching rate is affected by the distortion of the interference waveform, and the etching rate is reduced by, for example, about 20% when it hits the phase p = π / 2 in the sine wave, and corresponds to p = 3π / 2. By the way, the etching rate has a large value of about 20%, for example.

As described above, each interference waveform is distorted at specific phases (π / 2, 3π / 2,..., Mπ / 2: m is an odd number), and the etching rate at these phases deviates from the original rate. The time with distortion varies depending on the interference waveform if the wavelength is different. Therefore, for the interference waveforms having different wavelengths (three types in the present embodiment), the respective etching speeds are obtained at the same time, and the respective phases p are obtained. Since the wavelengths of the interference waveforms are selected so that there is no distortion in the two interference waveforms, the etching rate obtained from the former interference waveform is complemented by the etching rate obtained from the latter waveform. In the etching rate complementing means 26C, in the program, the calculated etching rate E _i (t) obtained at time t for the i-th wavelength λ _{i is} set to cos ² (p) with respect to the phase p _i (t) at that time. _i (t)) is weighted, and an average value of the weighted etching rates is obtained as an average etching rate E _ave (t) by the following equation (4). Phase (p = π / 2,3π / 2 , ···) distorted the waveform by this process approach the _{^{cos 2 (p i (t)}} ) is zero in the vicinity, the weight data of the waveform is not distorted is relatively large Thus, it is possible to automatically compensate for the difference in etching rate due to mutual distortion and obtain the average etching rate E _ave (t) as a value close to the original etching rate. However, always within the etching time (4) of Shigumacos 2 is a denominator ^(p _i (t)) must select ≠ 0 and becomes wavelength.
E _ave (t) = ^{_{[ΣE i (t) cos 2 (}} p i (t)) ] _{^{/ Σcos 2 (p i (t}} )) ·· (4)

The etching depth calculating means 26D calculates the etching depth δ (t) every time t by integrating the average etching rate E _ave (t) with time as shown in the following equation (5). Then, the determination unit 26E determines whether or not the etching depth δ (t) has reached the target etching depth. If the etching depth δ (t) has not reached the target etching depth, the series of operations described above is performed until the target etching depth is reached. repeat.
_{δ (t) = ∫E ave (} t) dt ··· (5)

Next, the etching depth detection method of this embodiment will be described with reference to FIG. When the etching of the semiconductor wafer W is started in the processing chamber 11 of the etching apparatus, the etching monitor apparatus 20 is automatically operated, and radiates perpendicularly to the surface of the wafer W from the light source 21 made of, for example, a xenon lamp via the optical fiber 22. When the light L is irradiated (step S1), the emitted light L is reflected from the etched portion and other portions. The reflected light L ₀ reaches the polychromator 24 through the optical fiber 22 while interfering, and is split into interference light L ₁ , L ₂ and L ₃ having wavelengths of 350 nm, 450 nm and 550 nm (step S 2). Next, after each interference light is detected by the first, second, and third photodetectors 25A, 25B, and 25C, and each interference light is photoelectrically converted by each of the photodetectors 25A, 25B, and 25C (step S3), The interference intensity signals S ₁ , S ₂ , S ₃ corresponding to the interference lights L ₁ , L ₂ , L ₃ are output to the frequency analysis means 26 A of the analysis / calculation unit 25 via the amplifier and the A / D converter. .

Frequency analysis means interference intensity signals _S 1 at _26A, S 2, _S the interference intensity signals _S 1 using the maximum entropy method or Fourier transform based on the _3, S 2, _{S 3} and the frequency analysis, the time (t-Delta] t ) from the frequency omega ₁ up to the time _{t (t), ω 2 (} t), ω 3 (t) and _{p 1 (t), p 2} (t), p 3 Request (t) (step S4). The time width Δt is set to be a half cycle of each interference waveform. When the frequency analysis means 26A outputs the frequency signals ω ₁ , ω ₂ , ω ₃ of each interference waveform to the etching speed calculation means 26B, the etching speed calculation means 26B uses the respective frequency signals to etch the etching speed corresponding to each interference waveform. E ₁ (t), E ₂ (t), and E ₃ (t) are calculated based on the above equation (3) (step S5). When the etching rate calculating unit 26B outputs the calculated etching rate signals E ₁ , E ₂ , E ₃ of each interference waveform to the etching rate supplementing unit 26C, the etching rate supplementing unit 26C uses these calculated etching rate signals to perform these etchings. The average speed value E _ave (t) is calculated based on the above equation (4) (step S6). When the etching rate complementing unit 26C outputs the average etching rate signal E _ave to the etching depth calculating unit 26D, the etching depth calculating unit 26D uses the average etching rate signal to set the etching depth δ (t) to the above (5). Calculation is performed based on the formula (step S7). When the etching depth δ (t) is calculated, the determination means 26E determines whether or not the etching depth δ (t) has reached the target etching depth (step S8), and has reached the target etching depth. If not, the operations from step S2 to step S8 are repeated, and when the target etching depth is reached, the high-frequency power sources 15 and 17 are turned off via the control device 28, and the etching is terminated.

  The following was found from FIGS. 5 to 8 showing the results obtained by this series of operations. FIG. 5 shows interference waveforms of 350 nm, 450 nm, and 550 nm, the horizontal axis indicates the elapsed time (unit: seconds), and the vertical axis indicates the intensity of the interference wave. In FIG. 5, the interference waveform does not appear to be distorted at the phases π / 2 and 3π / 2, but it can be seen that the waveform analysis is distorted. FIG. 6 shows the etching rate (nm / second) obtained individually from interference waves having a single wavelength of 350 nm, 450 nm, and 550 nm using the equation (3). FIG. 7 shows the etching rate obtained by weighting the interference waves with single wavelengths of 350 nm, 450 nm, and 550 nm using the equation (4) and weighting each other. FIG. 8 shows the relationship between time and etching depth, the one-dot chain line shows the etching depth of a single wavelength of 450 nm at each time obtained based on the equation (3), and the solid line is obtained based on the equation (4). The etching depth at each time is shown.

According to the results shown in FIG. 6, when the etching rate of the soot that is essentially constant is calculated etching rates E ₁ (t), E ₂ (t), and E ₃ (t) obtained from the three types of interference waveforms. In each case, it was found that about ± 200 nm was changed around 800 nm / second. However, according to the results shown in FIG. 7, three kinds of calculation etch rate average etching rate E _ave obtained by interpolating the respective calculated etching rate from each other by performing weighting (t) is the error of the etching rate of about It was suppressed to about ± 80 nm, and it was found that the etching rate error was remarkably improved as compared with the case where a single wavelength was used. Further, according to the result shown in FIG. 8, the etching depth δ obtained based on the average etching rate E _ave (t) complementing each other using three kinds of wavelengths changes linearly with time. Although the inclination is drawn, it was found that the inclination is wavy due to the error of the etching rate in the case of a single wavelength.

As described above, according to this embodiment, the semiconductor wafer W is irradiated with three types of light having different wavelengths, and the interface between the resist layer R and the etching target layer E (the upper surface of the etching target layer E) and the etching target. When the reflected light L ₀ from the surface of the part E 'enters the analyzing and calculating means 20, the analyzing and calculating means 20, the reflected light L 3 kinds of interference light L _1, having different wavelengths to periodic variation of ₀ L ₂ , L ₃ are detected by the first, second, and third photodetectors 25 A, 25 B, and 25 C, and then the frequency analysis of these interference lights L ₁ , L ₂ , and L ₃ is performed to obtain respective interference waveforms. The frequencies ω ₁ (t), ω ₂ (t), and ω ₃ (t) are obtained, and the etching rates corresponding to the respective interference waveforms are calculated based on these frequencies. Etching rates E ₁ (t) and E ₂ (t), E ₃ (t), and these calculated etching A weighted average based on the phases p ₁ (t), p ₂ (t), and p ₃ (t) of each interference waveform is performed on the velocity to obtain an average etching rate E _ave (t) of the three types of interference waveforms. Then, the average etching rate E _ave (t) is integrated to calculate the etching depth δ (t), so that one interference waveform has a specific phase (for example, π / 2) at a certain time. Even if there is distortion, other interference waveforms do not correspond to the phase of π / 2, so the latter two calculated etching rates complement the former one etching rate, and the influence of distortion at the former π / 2. And the etching depth can be accurately detected.

In the present embodiment, when calculating the etch rates, three of the interference waveform frequency _{ω 1 (t), ω 2} (t), ω 3 (t) calculated etching rate of each of the etching rate based on the E ₁ Average etching in which (t), E ₂ (t), and E ₃ (t) are obtained, and the deviation of the calculated etching rate based on the distortion of one of the interference waveforms is complemented by the calculated etching rate based on the interference waveform having no other distortion Since the speed E _ave (t) is obtained as the etching speed, even if any interference waveform has distortion, the etching speed in which the influence of the distortion is suppressed can be obtained. As a method of complementing the deviation of the calculated etching rate based on the distortion of one of the interference waveforms with the calculated etching rate based on the interference waveform having no other distortion, the phase p ₁ ( t), p ₂ (t), and p ₃ (t) are also obtained, and the calculated etching rates E ₁ (t), E ₂ (t), and E ₃ (t) are cos according to the phases of these interference waveforms. ^Since the average etching rate E _ave (t) weighted averaged by ² (p _i (t)) is obtained as an etching rate, π / 2π, 3/2,... (N + 1 / 2) With π, the influence of each distortion can be reliably suppressed. Since the interference waveform in which the wavelengths of the three types of interference waveforms are not (n + 1/2) π at the same time was selected during the weighted average, the calculated etching rate shift based on the distortion of one of the interference waveforms is used as the interference waveform having no other distortion. The calculated etching rate based on can be reliably complemented.

FIG. 9 is a configuration diagram showing an example of an etching apparatus according to another embodiment capable of realizing an etching depth detection method different from that of the above embodiment.
As shown in FIG. 9, the etching apparatus 10 </ b> A of this embodiment includes a processing chamber 11 for a semiconductor wafer W and an etching monitor device 30 for monitoring the etching status of the semiconductor wafer W in the processing chamber 11. Except the apparatus 30, it is comprised according to the etching apparatus 10 of the said embodiment. Therefore, the following description will focus on the etching monitor device 30.

As shown in FIG. 9, the etching monitor device 30 applied to the etching device 10 </ b> A of this embodiment includes a light source 31, an optical fiber 32, a lens 33, a monochromator 34, a photodetector 35, an analysis / calculation means 36, and a memory 37. the provided, irradiating radiation L from the light source 31 on the surface of the semiconductor wafer W in the processing chamber 11, to detect the reflected light L ₀ reflected from the semiconductor wafer W surface, based on a single interference light L ₁ The etching status is monitored in real time, and when the etching depth reaches a predetermined depth, the etching is terminated via the control device 38.

The analysis and calculation means 36, as shown in FIG. 9, the extreme detection unit 36A for detecting the maximum and minimum values successive interference waveform of the interference light L _1, detected through the extreme detection unit 36A Amplitude predicting means 36B for predicting the amplitude of the subsequent interference waveform based on the maximum and minimum values of the interference waveform, and calculating the phase of the interference waveform based on the ratio of the intensity of the interference waveform and the predicted amplitude at a certain time. The phase calculation means 36C, the etching depth calculation means 36D for calculating the etching depth based on the phase obtained via the phase calculation means 36C, and the etching depth obtained by the etching depth calculation means 36D Determination means 36E for determination.

That is, as described above, the interference waveform changes periodically as expressed by the equation (1). However, the interference light is affected by the plasma emission, and the reflectance and transmittance depend on the etching depth, so that the amplitude gradually attenuates as shown in FIG. Therefore, here, the interference waveform in consideration of the attenuation factor exp (γt) is approximated by the following equation (6). In the approximate expression (6), I _dc , I _pp , and γ are constants.
I = I _dc + I _pp exp (γt) sin (ωt) (6)

In the extreme value detection means 36A, when the phase p = ωt of the actual interference waveform is π / 2, 3π / 2, 5π / 2,... Mπ / 2 (m is an odd number), the interference waveform intensity I The maximum value and the minimum value of are detected. Strictly speaking, these are not extreme values, but in the observed interference waveform, the frequency ω is empirically far larger than γ, and can be regarded as an extreme value. However, the constants I _dc , I _pp , and γ also change with time, although slowly compared to ω. Therefore, _three extreme values I ₁ , I ₂ , and I ₃ are detected in succession at each of the times t ₁ , t ₂ , and t ₃ , and the amplitudes of these extreme values I ₁ , I ₂ , and I ₃ are predicted. Output to means 36B. These extreme values are indicated by x in FIG.

In the amplitude estimating means 36B, the envelope through three extrema using dichotomy is numerical solutions of extreme detection unit value of the extreme values of successive three interference intensity from _{36A I 1, I 2, I} 3 The line is determined from the approximate expression (6). Next, constants I _dc , I _pp, and γ of approximate expression (6) are determined based on the _three extreme values I ₁ , I ₂ , and I ₃ of this envelope, and the constant of approximate expression (6) is determined. The approximate expression (6) for which the constant is determined is determined and output to the phase calculating means 36C.

If the phase calculation means 36C detects the intensity I (t) of the interference waveform at a certain time (t) using the constants I _dc , I _pp , and γ determined by the amplitude prediction means 26B, the equation (6) is obtained. The phase p (t) at a certain time (t) can be obtained from the following equation (7) obtained by deformation, and the phase signal is output to the etching depth calculation means 36D.
p (t) = Arcsin [(I (t) −I _dc ) / (I _pp exp (γt))] (7)

In the etching depth calculation unit 36D, the etching depth δ (t) obtained by the phase calculation unit 36C at a certain time (t) is between the phase p (t) and the etching depth δ (t). It can be obtained using the following equation (8) representing the relationship. FIG. 11 is a graph showing the relationship between the etching depth δ (t) thus determined and time. As is apparent from FIG. 11, the etching depth does not swell, and it can be seen that the etching rate is constant.
δ (t) = p (t) λ / (2πn) (8)

The constants I _dc , I _pp , γ can be obtained by the least squares method using more points, but in the case of the approximate expression (6) obtained in this way, the interference waveform (I = I _dc + I _pp exp (γt) sin (ωt)) does not pass through all the extreme values, and the value of the phase p (t) in the vicinity of the extreme value becomes extremely inaccurate. However, when the constants I _dc , I _pp , and γ are obtained from the three extreme values as in this embodiment, the interference waveform always passes through all the extreme values, so that the accuracy of the interference waveform can be ensured.

Next, an etching depth detection method according to this embodiment will be described with reference to FIGS. When the interference light signal is input to the calculation / analysis means 36 via the monochromator 34 and the light detector 35, the extreme value of the interference intensity is detected with time by the extreme value detection means 36A. For example, as shown in FIG. 10, the extreme value detection means 36A sequentially detects the extreme values I ₁ , I ₂ , and I ₃ of the interference intensity at times t ₁ , t ₂ , and t ₃ . Based on these interference intensities, the amplitude predicting means 36B uses a bisection method, which is a numerical analysis method, to determine an envelope that passes through three consecutive points from the approximate expression (6), and then the constant I _{dc of} this envelope, I _pp and γ are obtained, these constants are determined as constants of the approximate expression (6), and the approximate expression (6) is determined. Between the next time t ₃ and time t ₄ , the approximate expression in which the constant is determined and the interference intensity at that time are used to calculate the interval between the time t ₃ and time t ₄ (between time t ₃ and time t ₄ ). The etching depth can be obtained sequentially. At time t ₄ the next extreme value, when the value of the extreme values I _2, I _3, I ₄ consecutive three, including extreme values I ₄ of interference intensity at this time described above using a dichotomy and The constant and approximate expression (6) at this time are determined in the same procedure. Then, the etching depth between time t ₄ and time t ₅ can be obtained from the newly determined approximate expression and extreme values of the interference intensity therebetween. The same procedure is repeated until the etching is completed. Finally, when the predetermined etching depth is reached, the high frequency power sources 15 and 17 are turned off via the control device 28 to complete the etching.

As described above, according to the present embodiment, the step of irradiating the semiconductor wafer with the light L, and the interference light L whose period fluctuates due to the reflected light L ₀ from the upper surface of the etched layer E and the surface of the etched portion E ′. ₁ , an approximate expression determining process for determining the approximate expression (6) of the interference light L ₁ , and an approximate expression constant for determining the constants I _dc , I _pp , and γ of the approximate expression (6) from the interference light intensity Etching depth for calculating the etching depth δ (t) based on the determining step, the approximate expression (6) determined for the constants I _dc , I _pp , γ and the extreme values I ₁ , I ₂ , I _{3 of the} interference light intensity Therefore, if at least three extreme values are detected, the etching depth can be calculated in a short time with a small amount of calculation, and the time response is excellent.

When determining the approximate expression constant, the envelope of the approximate expression (6) is determined from the approximate expression (6), and the envelope constants I _dc , I _pp , γ are determined from the interference light intensities I ₁ , I ₂ , I _3. Since these constants are determined as the constants I _dc , I _pp , and γ of the approximate expression (6), a highly accurate interference waveform can be obtained as compared with a method such as the least square method. In addition, since the envelope constants I _dc , I _pp , and γ are obtained from the _three extreme values I ₁ , I ₂ , and I _{3 of} the interference light intensity, the envelope can be determined with very little data. The etching depth can be obtained with time, and the time response is excellent. Furthermore, when calculating the etching depth, interference is performed based on the approximate expression (6) determined by the constants I _dc , I _pp , and γ using the expression (8) and the interference light intensities I ₁ , I ₂ , and I _3. Since the phase p (t) of the waveform is obtained and the etching depth is calculated based on this phase, the etching depth can be obtained in a short time from extremely small data.

Accordingly, in the present embodiment, extreme values I ₁ three maximum and minimum values successive interference waveform of the interference light L _1, detected by the extreme value detection section 36A as I _2, I _3, these extreme values I The amplitude of the subsequent interference waveform is predicted from the approximate expression (6) based on ₁ , I ₂ , and I ₃ , and the ratio of the interference intensity I to the amplitude [(I (t) −I _dc ) / (I _pp exp (γt))] is calculated from the phase p (t), and the etching depth δ (t) is calculated based on the phase p (t). If at least three extreme values are detected, The etching depth can be obtained by calculating the subsequent etching rate in a short time with a small amount of calculation.

The phase p in the latter embodiment (t) is, p (t) = Arcsin ( f (t)), f (t) = (I (t) -I dc) / (I pp exp (γt)) The error Δp of the phase p (t) is expressed by the following equation (9), and an error occurs in the phase p = mπ / 2 (m is a positive odd number). Therefore, similarly to the former embodiment, light having a plurality of wavelengths is used, and in the phase p (t) in which one interference waveform has distortion, the above error is reliably suppressed by using the phase of another interference waveform. The etching depth can be obtained with high accuracy. In the program, the average value is obtained by weighting the etching depth δ _i obtained by the equation (8) with respect to each wavelength λ by cos ² (p) as in the case of the former embodiment as in the equation (10). In this case, the etching apparatus uses a polychromator and a plurality of photodetectors instead of the monochromator and photodetector shown in FIG.
Δp = dp / df * Δf = 1 / cos (p) * Δf (9)
δ (t) = Σδ (t) cos ² (p (t)) / Σcos ² (p (t)) (10)

  In each of the above embodiments, the method of detecting the etching depth using the maximum entropy method or the fast Fourier transform method, and the method of detecting the etching depth by predicting the time change of the amplitude of the interference waveform have been described. The former method is not easily affected by the distortion of the interference waveform, and has characteristics that allow easy programming, while the latter method has characteristics that are excellent in time response and calculation speed. Therefore, these methods may be properly used depending on the contents of etching, or both may be used in combination as appropriate as explained at the end. The present invention is not limited to the above embodiments, and is encompassed by the present invention without departing from the gist of the present invention.

  The present invention can be suitably used for an etching technique.

10, 10A Etching device 11 Processing chamber 12 Lower electrode 13 Upper electrode 20, 30 Etching monitor device 21, 31 Light source 22, 32 Optical fiber (light guiding means)
26, 36 Analysis / calculation means 26A Frequency analysis means 26B Etch rate calculation means 26C Etch rate complement means 26D Etch depth calculation means 36A Extreme value detection means 36B Amplitude prediction means 36C Phase calculation means 36D Etch depth calculation means E Etched portion E 'Etched Layer Db, Da Control Device

Claims (15)

In the method of irradiating the object to be processed and detecting the etching depth using the reflected light,
Irradiating the object with light;
Detecting interference light periodically changing due to reflected light from the upper surface of the etched layer and the surface of the etched portion;
A frequency analysis step of obtaining a frequency ω (t) by performing a frequency analysis on detection data every time from the time t of the interference waveform to (t + Δt);
An etching rate calculating step of calculating an etching rate E (t) using the frequency ω (t);
And a step of obtaining the etching depth by integrating the etching rate E (t) with time, and a method of detecting the etching depth.   2. The etching depth detection method according to claim 1, wherein there are a plurality of the interference light and the interference waveform. In the etching rate calculation step, the etching rate is calculated using the frequency of each interference waveform to obtain the calculated etching rate,
An etching rate complementing step for calculating an average etching rate by complementing the plurality of calculated etching rates with each other is provided,
In the etching rate complementing step, the calculated etching rates are weighted and averaged according to the magnitude of the distortion of each interference waveform, and the deviation of the calculated etching rate based on any of the distortions of the interference waveform is calculated as another distortion. The above average etching rate is obtained by complementing the calculated etching rate based on the interference waveform without
The method for detecting an etching depth according to claim 2, wherein in the step of obtaining the etching depth, the average etching rate is integrated over time.   The phase of each said interference waveform is also calculated | required by the said frequency analysis process, and each calculation etching rate is weighted-averaged according to the phase of these interference waveforms at the said etching rate complementation process, The said Claim 3 characterized by the above-mentioned. Etching depth detection method.   5. The detection method according to claim 1, wherein in the frequency analysis step, detection data for each time from time t to (t + Δt) of the interference waveform is data of a certain time width Δt. Method for detecting the etching depth.   6. The etching depth detection method according to claim 1, wherein a maximum entropy method is used as the frequency analysis in the frequency analysis step.   6. The etching depth detection method according to claim 1, wherein in the frequency analysis step, fast Fourier transform is used as frequency analysis. An etching monitor device that irradiates a target object with light and monitors the etching depth using the reflected light,
A light source for irradiating the object with light;
A photodetector that detects interference light that fluctuates periodically due to reflected light from the top surface of the etched layer and the surface of the etched portion;
Analyzing / calculating means for analyzing the interference light based on a signal from the photodetector and obtaining the etching depth;
A control device cooperating with the analysis / calculation means,
The analysis / calculation means is
A frequency analysis means for obtaining a frequency ω (t) by performing frequency analysis on detection data every (t + Δt) from time t of the interference waveform;
Etching rate calculating means for calculating an etching rate E (t) using the frequency ω (t);
An etching monitor apparatus comprising: depth calculation means for obtaining an etching depth by integrating the etching rate E (t) with time.   9. The etching monitor apparatus according to claim 8, wherein the frequency analysis means uses data of a certain time width Δt as detection data every (t + Δt) from the time t of the interference waveform.   The etching monitor apparatus according to claim 8 or 9, wherein the frequency analysis means uses a maximum entropy method as frequency analysis.   10. The etching monitor apparatus according to claim 8, wherein the frequency analysis means uses fast Fourier transform as frequency analysis.   The etching monitor apparatus according to claim 8, wherein there are a plurality of the interference light and the interference waveform. The etching rate calculation means calculates the etching rate based on the frequency of each interference waveform to obtain the calculated etching rate,
An etching rate complementing means for calculating an average etching rate by complementing the plurality of calculated etching rates with each other is provided,
The etching rate complementing means weights and averages the calculated etching rates in accordance with the magnitude of the distortion of each interference waveform, and shifts the calculated etching rate based on any of the interference waveform distortions to other distortions. The above average etching rate is obtained by complementing the calculated etching rate based on the interference waveform without
The etching monitoring apparatus according to claim 12, wherein the depth calculation means integrates the average etching rate over time.   The frequency analysis means also obtains the phase of each of the interference waveforms, and the etching rate complementing means weights and averages the calculated etching rates according to the phases of the interference waveforms. The etching monitor apparatus as described. An etching apparatus comprising the etching monitor apparatus according to claim 8.

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