JPH09306894A - Optimum emission spectrum automatic detecting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically set an optimum wavelength for detecting the end point prior to the execution of a plasma treatment. SOLUTION: A monochromator 2 is capable of separating a light 18 emitted during trial of a preliminary plasma treatment to select desired wavelength. A servo motor 6 drives the monochromator 2 to automatically sweep wavelengths to be selected in a desired range. A photomultiplier 3 converts the emission received by the wavelengths selected by the sweep into electric signals according to the intensity of the emission by the wavelengths. An intensity difference detection circuit 7 processes the electric signals to detect the change quantity of the emission intensity by the wavelengths before and after the end point of the tried plasma treatment. An optimum w setting circuit 8 determines an optimum wavelength for the end point detection, based on the change quantity detected by the wavelengths and controls the servo motor 6 to lock the wavelength selected by the monochromator 2 to the determined optimum wavelength. At the plasma treatment thereafter, the circuit 5 detects the end point, based on the time change of the emission intensity at the optimum wavelength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for automatically detecting an optimum emission spectrum for detecting an end point of processing performed in a plasma device.

[0002]

2. Description of the Related Art An example of a conventional plasma processing system will be briefly described with reference to FIG. This system includes a plasma device 1 and performs desired plasma processing such as etching. The plasma device is a chamber 11 that can be evacuated.
Parallel plate electrodes 12 and 13 which are arranged to face each other are mounted therein. Upper electrode 1
2 is grounded in the chamber 11, while the lower electrode 1
A high frequency power supply 14 is connected to 3 via a capacitor. A substrate 15 to be processed is provided on the lower electrode 13.
Is placed. A plasma 16 is generated by introducing a process gas into the chamber 11 and supplying high-frequency power between the pair of electrodes 12 and 13. By irradiating the surface of the substrate 15 with this plasma 16, a desired plasma treatment such as etching is performed. A window 17 made of quartz glass or the like is attached to the chamber 11 and guides light emission 18 generated from the plasma 16 to the outside. The plasma 16 contains various particles, and the spectrum unique to these is included in the emission 18. Since the concentration distribution of particles contained in the plasma 16 changes as the plasma processing on the substrate 15 progresses, the intensity of each spectrum contained in the light emission 18 changes with time accordingly. In this spectrum, the end point of plasma processing (end point)
There is a particular spectrum where the intensity changes abruptly. The monochromator 2 is arranged so as to face a window 17 provided in the chamber 11. The monochromator 2 disperses the light emission 18 generated from the plasma 16 and wavelength-selects only the above-mentioned specific spectrum. In order to perform this wavelength selection, a manual dial 21 is attached to the monochromator 2. A photomultiplier tube (photomultiplier) 3 is arranged at the output portion of the monochromator 2, receives a specific emission spectrum 19 selected by the monochromator 2, and outputs an electric signal corresponding to its intensity. An end point detection circuit 5 is connected to the photomultiplier 3 via an amplifier 4. The end point detection circuit 5 is composed of a personal computer (personal computer) or the like, processes the electric signal voltage-amplified by the amplifier 4, analyzes the temporal change of the intensity of a specific emission spectrum, and based on the analysis result, the end point of the plasma processing. To detect. High-frequency power supply 1 according to this detection result
4 is turned off and the plasma processing is terminated. For example, when etching is performed by plasma processing, it is possible to optimally control the etching amount by executing this end point detection.

[0003]

As can be understood from the above description, in order to execute the plasma treatment and detect the end point, the emission spectrum whose intensity changes rapidly before and after the end point is specified in advance. It is necessary to set the wavelength in the monochromator 2. For example, when etching is performed with a plasma device, a plurality of materials may be included in plasma emission depending on the material to be processed, the underlying film exposed after the etching, and other materials such as an intermediate film and a material forming a process gas. The spectrum of the species is included. The emission spectrum unique to each substance is selected by operating the dial 21 of the monochromator 2 one by one. Record the change in emission intensity for each spectrum on a recorder. The change in recorded emission intensity is calculated to determine the optimal emission spectrum for endpoint detection. Based on this determination, the monochromator wavelength is finally fixed to a particular emission spectrum. However, in this conventional method, some emission spectra are theoretically selected based only on the basic data of substances constituting various films, and these intensity changes are detected one by one to specify the optimum emission spectra. ing. However, in the case of actually etching a semiconductor device, etc., the film to be etched, the base film, other intermediate films, the material of the mask used for etching, the masked area, the film structure due to the step of the base, etc. Since various factors are intertwined with each other, the spectral distribution of the plasma emission 18 cannot always be theoretically predicted. Even if some of the theoretically obtained emission spectra are investigated and the optimum one for the end point detection is specified, it cannot be said that this is actually the optimum wavelength. In particular, when a plurality of emission spectra are overlapped in a relatively narrow wavelength range, there is a problem such as resolution of a monochromator, and the theoretical emission spectrum wavelength is not always the optimum one for end point detection. Absent.
Conventionally, the end point is detected by using the emission spectrum peculiar to a specific substance, although the wavelength is not the true optimum wavelength. However, this causes an error between the actual end point and the detected end point, so various algorithms have been developed to perform the correction calculation. Even in this case, when performing plasma processing for a large number of small quantities, a large amount of end point detection deviation occurs, which is a cause of defects.

[0004]

Means for Solving the Problems In order to solve the above-mentioned problems of the prior art, the following measures have been taken. That is, the optimum emission spectrum automatic detection system according to the present invention analyzes the emission generated by the plasma processing performed using the plasma device, and determines the end point of the plasma processing based on the temporal change of the emission intensity at a specific wavelength. In the case of automatically detecting, the optimum wavelength for detecting the end point is automatically set in advance prior to the execution of the plasma processing. The present system includes a selection unit, a drive unit, a conversion unit, a detection unit, and a setting unit. The selection unit can select an arbitrary wavelength by spectrally separating the light emission generated during the preliminary plasma processing trial. The driving means drives the selecting means during the trial of the plasma treatment to automatically sweep the wavelength to be selected in a desired range. The conversion means receives the light emission for each wavelength selected by the sweep and converts it into an electric signal according to the emission intensity for each wavelength. The detecting means processes the electric signal and detects the amount of change in the emission intensity before and after the end point of the plasma processing attempted for each wavelength. The setting means determines the optimum wavelength for end point detection based on the variation detected for each wavelength, controls the driving means, and fixes the wavelength selected by the selecting means to the determined optimum wavelength. With such a configuration, when the plasma processing is executed thereafter, the end point can be detected based on the temporal change of the emission intensity at the optimum wavelength.

Preferably, the detecting means detects the difference between the level of emission intensity before the end point of the plasma processing and the level of emission intensity after the end point for each wavelength to obtain the change amount. For example, the detection means detects a difference between the maximum level of emission intensity before the end point of the plasma etching process and the minimum level of emission intensity after the end point. Further preferably, the setting means determines the wavelength having the maximum detected difference as the optimum wavelength.

According to the present invention, the selection means such as a monochromator or the like capable of spectrally separating the light emission generated during the preliminary plasma processing trial and selecting an arbitrary wavelength is provided with the driving means such as a servo motor. It is installed and the wavelength is automatically swept and selected. After sweeping the wavelength, the emission intensity for each wavelength is converted into a corresponding electric signal by a conversion means such as a photomultiplier. A detection means is connected to this photomultiplier through an amplifier to detect the amount of change in emission intensity for each wavelength. A setting means such as a personal computer is interposed between the detection means and the servo motor to interlock the servo motor and the detection means. The personal computer collects data of the emission intensity difference of innumerable wavelengths in a short time according to the material of the article to be plasma-treated, and selects the wavelength with the largest intensity difference among them as the optimum wavelength for the monochromator. It is set. As a result, it becomes possible to set the optimum wavelength of the light emission for detecting the end point based on the actual measurement result rather than theoretically, according to the material of the article to be plasma-processed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing the basic configuration of an optimum emission spectrum automatic detection system according to the present invention. As shown in the figure, the present system analyzes the light emission 18 generated by the plasma processing performed using the plasma device, and automatically determines the end point of the plasma processing based on the temporal change of the emission intensity at a specific wavelength. At the time of detection, the optimum wavelength for detecting the end point is automatically set in advance prior to the execution of the plasma processing. As shown in the figure, this system is equipped with a monochromator 2 and emits light 1 generated during the preliminary plasma treatment trial.
8 is dispersed and an arbitrary wavelength is selected. In this embodiment, the potentiometer 22 is used as a dial for selecting this wavelength. This potentiometer 2
A servo motor 6 is connected to 2 and drives the monochromator 2 during the trial of plasma processing to automatically sweep the wavelength to be selected within a desired range. Further, a photomultiplier 3 is arranged at the output part of the monochromator 2, receives the light emission 20 for each wavelength selected by the sweep, and converts it into an electric signal according to the emission intensity for each wavelength. An intensity difference detection circuit 7 is connected to the photomultiplier 3 via an amplifier 4.
The intensity difference detection circuit processes the electric signal amplified by the amplifier 4 and detects the amount of change in emission intensity before and after the trial end point of the plasma processing for each wavelength. For example, the difference between the level of the emission intensity before the end point of the plasma processing and the level of the emission intensity after the end point is detected for each wavelength and set as the above-described change amount. More specifically, the difference between the maximum level of emission intensity before the end point of the plasma etching process and the minimum level of emission intensity after the end point is detected. An optimum wavelength setting circuit 8 composed of a personal computer or the like is connected to the intensity difference detection circuit 7, and the optimum wavelength for end point detection is determined based on the amount of change detected for each wavelength. Specifically, the wavelength having the maximum difference detected by the intensity difference detection circuit 7 is determined as the optimum wavelength. The optimum wavelength setting circuit 8 further controls the servomotor 6 via a control circuit 9 composed of a microcomputer or the like, and fixes the wavelength selected by the monochromator 2 at the optimum wavelength. After that, when the plasma processing is executed, the end point is detected based on the change with time of the emission intensity at the optimum wavelength. Specifically, an end point detection circuit 5 composed of a personal computer or the like is connected to the photomultiplier 3 via an amplifier 4, and the plasma is generated based on the temporal change of the emission intensity at the optimum wavelength set in the monochromator 2. Automatically detect the end point of processing.
A detection algorithm for this purpose is programmed in the personal computer forming the end point detection circuit 5. Each component (servo motor 6, intensity difference detection circuit 7, optimum wavelength setting circuit 8, control circuit 9) included in a portion 10 surrounded by a dotted line in FIG. 1 is an optimum emission spectrum automatic detection system according to the present invention. It is added to configure the.

Next, the operation of the optimum emission spectrum automatic detection system according to the present invention will be described in detail with reference to FIG. The servomotor 6 for driving is connected to the potentiometer 22 used as a wavelength selection dial of the monochromator 2 to automate the wavelength sweep of the monochromator 2. The servomotor 6 is controlled by a control circuit 9 composed of a microcomputer or the like to improve the wavelength selection accuracy of the monochromator 2. While driving the monochromator 2, an electric signal is taken out through the amplifier 4 connected to the photomultiplier 3. The intensity difference detection circuit 7 processes the voltage of this electric signal to detect the voltage difference before and after the end point. This voltage difference corresponds to the emission intensity difference. Specifically, the difference between the high voltage in the area before the end point and the low voltage in the area after the end point, which is stable after the light emission starts, is detected. The end time is
You can make a rough estimate by conducting a sample test. In this sample test, a substrate or the like to be actually processed is put into a chamber of a plasma apparatus and plasma processing is performed to check the light emission condition. In this way, the voltage for a certain period of time before and after the roughly predicted end point is detected by the intensity difference detection circuit 7, and the difference is calculated, whereby the change amount before and after the end point can be easily obtained. The optimum wavelength setting circuit 8 sequentially captures the value of the wavelength during the sweep and the data of the emission intensity difference corresponding thereto, and automatically detects the emission intensity difference for each wavelength included in the sweep range by a program. The wavelength with the largest emission intensity difference is determined as the optimum wavelength, and this is set in the monochromator 2 via the control circuit 9 and the servomotor 6. As described above, in the present invention, the driving servomotor 6 is attached to the monochromator 2 for selecting the wavelength of the plasma emission 18, and the wavelength can be automatically swept and set by using the personal computer. During the wavelength sweep, the intensity difference detection circuit 7 is connected to the photomultiplier 3 for converting the emission intensity into an electric signal via the amplifier 4 to detect the variation amount of the emission intensity (difference between the maximum value and the minimum value). . Further, the servo motor 6 is driven by the optimum wavelength setting circuit 8 including a personal computer.
And the intensity difference detection circuit 7 are interlocked with each other, and data of emission intensity difference of innumerable wavelengths is taken in a short time every time the article to be plasma-processed is changed, and the wavelength having the largest intensity difference among them is acquired. Monochromator 2 as the optimum
Set to.

FIG. 2 shows intensity changes of various spectra included in plasma emission. In this example, the polycrystalline silicon film formed on the insulating substrate is etched. When etching a polycrystalline silicon film with a plasma device, a fluorine-based gas is used as a process gas. In this case, SiF, F, O,
Molecules and atoms such as N ₂ exist, and an emission spectrum peculiar to these exists. (A) shows the change in the emission intensity of the emission spectrum (wavelength 777.0 nm) corresponding to SiF. In this spectrum, the emission intensity sharply decreases at the end point of the etching process. The intensity difference predicted before and after the end point is shown on the graph. (B) represents the intensity change of the emission spectrum (wavelength 775.5 nm) corresponding to F. The intensity of the emission spectrum of F increases at the end point of the etching process. (C) represents the intensity change of the emission spectrum (wavelength 777.2 nm) corresponding to O. The emission spectrum intensity of O slightly increases at the end point. (D) represents the intensity change of the emission spectrum (wavelength 775.3 nm) corresponding to N ₂ . The emission spectrum of N ₂ shows almost no change in intensity at the end point. As is clear from the graph of FIG. 2, the emission spectrum of SiF changes most remarkably at the end point. Therefore, conventionally, the selection wavelength of the monochromator is set to 777.0 nm, and the end point is detected based on the emission spectrum of SiF.

However, as shown in the graph of FIG. 2, the wavelength 777.0 of the emission spectrum corresponding to SiF.
There are emission spectra corresponding to other particles near nm. There is no problem if the monochromator has sufficient wavelength resolution, but it is difficult for the monochromator currently used to completely separate a plurality of emission spectra in the vicinity of 777.0 nm. Actually, as shown in FIG.
The emission spectra corresponding to iF, F, O, N _2, etc. are observed in an overlapping state. Here, the overlapping spectra will be referred to as a synthetic spectrum. FIG. 3A shows the intensity change of the combined spectrum at a certain wavelength λa. The intensity of this synthetic spectrum decreases considerably at the end point. This is represented as an actual intensity difference on the graph. There is a deviation between the “predicted intensity difference” shown in FIG. 2A and the “actual intensity difference” shown in FIG. 3A. The “actual intensity difference” is smaller than the “predicted intensity difference”. Therefore, S
When the end point is detected based on the emission spectrum corresponding to iF, an error may occur, which makes it difficult to detect the end point accurately. Therefore, in the present invention, the optimum wavelength λa for detecting the end point is detected in advance, and this is set in the monochromator. Here, the optimum wavelength is set to a wavelength that maximizes the "actual intensity difference". The “actual intensity difference” is maximum at the wavelength λa shown in (A). On the other hand, at another wavelength λb shown in (B), the “actual intensity difference” is smaller than in the case of λa. In the present invention, the plasma treatment is tried in advance and the amount of change in the emission intensity before and after the end point is detected for each wavelength. The optimum wavelength λa for end point detection is determined based on the amount of change detected for each wavelength. Further, the servo motor is controlled to fix the wavelength selected by the monochromator to the determined optimum wavelength. In this way, by automatically detecting the difference in intensity for each wavelength without spending man-hours, when various spectra emitted from particles contained in the actual object to be processed or process gas, etc. overlap. But
The optimum wavelength for end point detection can be easily detected.

The above-described embodiment is a case where the plasma device is applied to the etching process of polycrystalline silicon, but the present invention is not limited to this. The present invention can be applied to any plasma device that uses plasma to perform a desired process and is a system that uses plasma emission to detect an end point. For example, in a plasma apparatus that performs chemical vapor deposition (CVD), if there is any change in intensity in the synthetic spectrum at the time when the deposition of a predetermined film thickness is completed, the chemical vapor deposition is performed using the present invention. It is also possible to detect the end point of. Furthermore, by combining the optimum wavelength setting program of this system and the end point detection program, the optimum wavelength for end point detection can be set according to the processing target and processing conditions, and the end point detection program can be set based on this set optimum wavelength. It becomes possible to execute.

[0012]

As described above, according to the present invention, when the end point of plasma processing is automatically detected by the change in the intensity of plasma emission in the plasma device, it is most suitable for the end point detection according to the processing target and processing conditions. It can automatically detect various wavelengths in a short time. In the present invention, the plasma emission generated under the actual processing target and processing conditions is analyzed to determine the optimum wavelength, so that the accuracy of end point detection is improved and defects due to end point shift are reduced. Further, in the present invention, since the wavelength sweep is performed to determine the optimum wavelength, it is possible to analyze the wavelength of the plasma emission in a wide range, and for example, the plasma CV which has been difficult to date
It becomes possible to determine the optimum wavelength suitable for the detection of the deposition end point of the D device. In addition, in the present invention, since the wavelength selection dial of the monochromator and the electric signal representing the intensity difference for each wavelength are linked by the personal computer, even if the settings of the dial or the like are accidentally deviated, the monochromator is automatically operated. It is possible to fine-tune the setting wavelength of to the optimum one.

[Brief description of drawings]

FIG. 1 is a block diagram showing an optimum emission spectrum automatic detection system according to the present invention.

FIG. 2 is a graph showing intensity changes of various emission spectra included in plasma emission.

FIG. 3 is a graph showing a change in plasma emission intensity at a specific wavelength.

FIG. 4 is a block diagram showing an example of a conventional plasma processing system.

[Explanation of symbols]

1 ... Plasma device, 2 ... Monochromator, 3 ... Photomul, 4 ... Amplifier, 5 ... End point detection circuit, 6 ... Servo motor, 7 ... Intensity difference detection circuit, 8 ... Optimal wavelength setting circuit, 9
... Control circuit

Claims (4)

[Claims] 1. A plasma when an end point of plasma processing is automatically detected based on a change with time of emission intensity at a specific wavelength by analyzing light emission generated by plasma processing performed by using a plasma device. This is a system that automatically sets the optimum wavelength for detecting the end point in advance prior to the execution of processing, and it is possible to select any wavelength by spectrally analyzing the light emitted during the preliminary plasma processing trial. Means, driving means for automatically sweeping the wavelength to be selected in a desired range by driving the selecting means during the trial of the plasma treatment, and receiving light emission for each wavelength selected by the sweep and emitting light for each wavelength Conversion means for converting into an electric signal according to the intensity, detection means for detecting the amount of change in emission intensity before and after the trial end point of the plasma processing by processing the electric signal by wavelength, and detecting by wavelength And a setting means for controlling the driving means to fix the wavelength of the selecting means to the determined optimum means, based on the amount of change thus determined. An optimum emission spectrum automatic detection system characterized by enabling end point detection based on a change with time of emission intensity at the optimum wavelength when executing processing. 2. The detecting means detects the difference between the emission intensity level at a time point before the plasma processing end point and the emission intensity level at a time point after the end point for each wavelength to obtain the variation amount. The optimum emission spectrum automatic detection system according to claim 1. 3. The optimum emission spectrum automatic detection system according to claim 2, wherein the setting means determines the wavelength having the maximum value of the detected differences as the optimum wavelength. 4. The detection means detects a difference between a maximum level of emission intensity at a wavelength before the end point of the plasma etching process and a minimum level of emission intensity at a time point after the end point. Item 2. The optimum emission spectrum automatic detection system according to Item 2.