JPH11214360A - Plasma optical spectrophotometer and dry etching final point detection device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an input level to be increased by miniaturizing an optical filter in a detection device which spectralizes plasma light and detects the final point of etching. SOLUTION: Plasma light is dispersed for a specific wavelength by a dichroic mirror 3 and reflected light and transmitted light are received by first and second photosensitive elements, 4, 5, respectively. At least one of the first and second photosensitive elements 4, 5 is provided with optical filters 6, 7. Since light is thereby dispersed in advance by the dichroic mirror 3 per wavelength, a photosensitive level is not reduced by half and a constitution of the optical filters 6, 7 can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma optical spectroscope for monitoring the state of plasma and a dry etching end point detecting apparatus using the same.

[0002]

2. Description of the Related Art A low-pressure reactive gas or an inert gas is introduced into a vacuum vessel, a plasma of the gas is generated by DC or high-frequency discharge, and the plasma is used to etch the surface of a substrate installed in the vessel. The plasma etching apparatus is used in a process of manufacturing a semiconductor integrated circuit. In addition, a cathode sputtering device, a plasma CDV device, a plasma polymerization device, a surface treatment device, and the like, which generate a thin film on the surface of a substrate placed in a container by utilizing discharge in a gas, are also used in the process of manufacturing a semiconductor integrated circuit. . When using such an apparatus, it is important to monitor the processing steps using plasma light. 2. Description of the Related Art In order to monitor plasma, it has been practiced to disperse plasma light and determine the state of the plasma from its wavelength.

[0003] For example, in a conventional plasma spectroscopic monitoring apparatus disclosed in Japanese Patent Application Laid-Open No. 60-58793 or the like, a half mirror or a branch fiber is used to split incident plasma light, and a filter is provided on the transmission side of the half mirror. A configuration is shown in which a light having a predetermined wavelength is detected by using a monochromator that receives only light having a predetermined wavelength on the reflection side, and the light receiving level is detected. There has been proposed a plasma spectroscopic monitoring apparatus that detects the light intensity levels of different spectral regions obtained in this way and determines the state of the plasma based on the difference or ratio.

Further, Japanese Patent Publication No. 5-46971 proposes a method for detecting the end of dry etching based on a change in the emission spectrum of glow discharge plasma in order to detect the end of dry etching. In this application, the change over time of the value obtained by subtracting the emission spectrum intensity of carbon monoxide and the emission spectrum of helium is monitored, and the end of dry etching is detected based on this change over time.

[0005]

All of these methods use a half mirror or a branch fiber to separate the plasma light, and the light receiving level at each wavelength is reduced to about 1/2, so that a small signal change is caused. There is a drawback that it becomes difficult to capture An interference filter is used to extract a spectrum of a predetermined wavelength. The interference filter generates a side lobe in a wavelength region other than a wavelength having sharp selectivity as shown in FIG. Therefore, it is necessary to use a color filter in combination to transmit only light of a specific wavelength, and to transmit only a predetermined wavelength as a whole as shown in FIG. The use of an optical filter using a lamination of an interference light filter and a color filter or the like has the disadvantage that it is expensive and the thickness is too large to handle. In addition, the use of a color filter also has a problem that the transmittance of the entire filter is reduced.

The present invention has been made in view of such a conventional problem, and has been made to reduce the cost of an optical filter and to receive light of a specific wavelength without lowering the light receiving level. Aim.

[0007]

According to a first aspect of the present invention, there is provided a dichroic mirror for guiding plasma light and transmitting a part of the emission wavelength thereof, and a first dichroic mirror for receiving light reflected by the dichroic mirror. A light receiving element, a second light receiving element for receiving light transmitted through the dichroic mirror, and an optical filter provided on at least one of the front surfaces of the first and second light receiving elements and transmitting light of a predetermined wavelength. , Are provided.

The optical filter used here is one of the light obtained by reflecting or transmitting the dichroic mirror.
An optical filter for extracting light having a wavelength of a spectrum with a large change that can be identified by a plasma optical spectrometer. This spectrum may be a line spectrum or a spectrum having a certain width. By separating the plasma light at a specific wavelength by the dichroic mirror in this way, the wavelengths that can be received by the first and second light receiving elements are defined in advance, and a change in the spectrum of the plasma light can be detected with high sensitivity. .

According to a second aspect of the present invention, there is provided a dichroic mirror for guiding plasma light and transmitting a part of the emission wavelength thereof, a first light receiving element for receiving light reflected by the dichroic mirror, and the dichroic mirror. A second light receiving element for receiving light transmitted through the mirror, an optical filter provided on at least one of the front surfaces of the first and second light receiving elements, and transmitting light of a predetermined wavelength; Signal processing means for detecting a change in the emission spectrum accompanying the end of the etching based on the output of the second light receiving element.

According to the second aspect of the present invention, the at least one optical filter is an optical filter for extracting light having a wavelength of a spectrum having a large change before and after etching, out of light obtained by transmitting or reflecting through the dichroic mirror. .
The spectrum having a large change may be a line spectrum or a spectrum having a certain width. Using such an optical system, the end of etching is detected by signal processing means.

According to a third aspect of the present invention, in the dry etching end point detecting apparatus according to the second aspect, the signal processing means includes an averaging means for averaging levels of the first and second light receiving elements; Adding means for calculating an added value of the first and second outputs; subtracting means for subtracting the outputs of the first and second light receiving elements; and calculating an output ratio of the first and second light receiving elements. Calculating means for calculating a difference with respect to the sum of outputs of the first and second light receiving elements or one of the outputs, and adding means, subtracting means, ratio calculating means and dividing means. And comparing means for comparing any one of the selected outputs with a predetermined threshold level, and detecting an end point of the etching based on the output of the comparing means.

According to the third aspect of the present invention, the end of the etching can be reliably detected by selecting an arithmetic expression in accordance with the type of the etching substance or the gas atmosphere.

[0013]

FIG. 1 is a diagram showing a configuration of an optical system portion of an etching end point detecting device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a configuration of a signal processing unit. As shown in FIG. 1, in the etching end point detecting apparatus according to the present embodiment, plasma light in the peripheral portion of the substrate is guided from an unillustrated vacuum layer to the optical system of the etching end point detecting apparatus via an optical fiber 1. A lens 2 is provided on the end surface of the optical fiber 1, and a first light receiving element 4 is disposed at a focal position of the lens 2 at a position where the light is reflected by the dichroic mirror 3. Further, a second light receiving element 5 is disposed at a focal position of light transmitted through the dichroic mirror 3. Light receiving elements 4 and 5
Are provided with optical filters 6 and 7, respectively. The dichroic mirror 3 separates light in a wavelength range to be detected according to the wavelength. For example, as shown in FIG. 3, the dichroic mirror 3 reflects light having a wavelength of 580 nm or more and transmits light having a shorter wavelength. Is to be separated.

In this embodiment, Si is formed on a silicon substrate.
It is assumed that a polysilicon layer is formed on the O ₂ layer and an upper portion thereof, and an etching end point when the polysilicon layer is etched is detected. The plasma light generated by the plasma discharge has light emission characteristics as shown in FIG. 4A during the etching of the polysilicon, and when the etching of the polysilicon layer is completed and the etching of the SiO ₂ layer is started, the figure is obtained. It is assumed that a spectrum as shown in FIG. From this spectrum, a predetermined wavelength, for example, 704n
The change before and after the end of the etching is large at the wavelength of m and the wavelength of 780 nm. Also, it can be seen that the entire light amount of 400 to 600 nm is larger when the polysilicon layer is etched than when the SiO ₂ layer is etched. For this reason, for example, as shown in FIG.
An interference light filter having a sharp characteristic at 04 nm is used. Although the optical filter 6 transmits light at a wavelength of 610 nm or less, the optical filter 6 has a wavelength of 610 nm due to the dichroic mirror 3.
Light below m is not reflected. Therefore, it is sufficient to dispose only the interference filter in front of the light receiving element 4 without using a color filter for blocking light of 610 nm or less in addition to the interference filter of FIG. A filter having such characteristics can be realized by using, for example, an interference filter in which about 10 dielectric thin films are deposited on a glass substrate. In this case, the thickness of the optical filter 6 is substantially equal to the glass substrate, and can be realized, for example, at about 1 mm. Further, it is not necessary to use another color filter on the optical filter in a superimposed manner. Since light transmitted only through the interference filter can be received by the light receiving element, the transmittance can be kept high. In this case, the optical filter 7 becomes unnecessary. When the optical filter 6 is replaced with a filter for detecting the presence or absence of a peak at 780 nm as shown in FIGS. 4A and 4B, for example, as shown in FIG.
It can be configured using a cut filter that transmits the above light. In this embodiment, there is no need to consider the level of wavelengths higher than this, because it is low.

In the block diagram shown in FIG. 2, light from the light receiving elements 4 and 5 is amplified by preamplifiers 11 and 12, respectively, and guided to analog switches 13 and 14.
The outputs of the preamplifiers 11 and 12 are analog switches 13 and
One of the outputs is selected by 14 and guided to the main amplifier 15. The main amplifier 15 amplifies the selected output, and the output is supplied to a peak hold circuit (P / H circuit) 16. The peak hold circuit 16 is held / reset by a pulse from the CPU 17. This peak value is given to the CPU 17. The CPU 17 has an A / D conversion unit 17a, an average value processing unit 17b, D / A conversion units 17c and 17d, and an oscillation / frequency division unit 17e, and the peak value is temporarily converted to a digital value by the A / D conversion unit 17a. And the average value processing unit 17b performs the average value processing. Then, the average level of each of the light receiving elements 4 and 5 after the average value processing is output to the analog output circuits 18 and 19 via the D / A converters 17c and 17d.
Given to. The oscillating / frequency dividing unit 17e alternately supplies a timing signal to the analog switches 13 and 14 and outputs a hold / reset pulse to the peak hold circuit 16 at a predetermined cycle. Analog output circuit 18,
The analog signals output from 19 are S1 and S2, respectively. The analog signals S1 and S2 are input to an adder 21, a subtractor 22, a ratio calculator 23, and a divider 24 of the signal processing unit 20. The adder 21 is S1 + S2, and the subtractor 22 is S1-
S2 is calculated, and the ratio calculator 23 calculates S1 / S2
Is calculated. The divider 24 divides the sum and the difference,
For example, an operation of (S1−S2) / (S1 + S2) or a sum and one of the divisions, that is, an operation of S1 / (S1 + S2) or an operation of S2 / (S1 + S2) is performed. These outputs are connected to a multiplexer (MPX) 25
, One of the outputs is selected and given to the comparator 26. The comparator 26 outputs an etching end point detection signal by comparing the signal selected by the multiplexer 25 with a threshold value. The signal processing section 20 is provided with an arithmetic expression selecting section 27 for selecting any one of the inputs of the multiplexer 25.

When detecting the end of etching using such an etching end point detecting device, the light from the optical fiber 1 is split by the dichroic mirror 3 and
And 5 are incident. As shown in FIG. 4 SiO ₂
In order to detect the end of the etching of the polysilicon on the layer, since the etching has been advanced from the polysilicon to the SiO ₂ layer, the interference having the peak of 704 nm as the optical filter 6 as described above is used as the optical filter 6. An optical filter is used. The other light receiving element 5 has an optical filter 7 for detecting the light receiving amount of all shorter wavelengths.
Is not used. Then, the light receiving signals are alternately selected by the analog switches 13 and 14, the output thereof is amplified by the main amplifier 15, the peak value is held, and the average value calculation process is performed to obtain the respective analog output signals S1 and S2. In this case, the end of the etching can be easily determined by the ratio or the division of the output signals S1 and S2.

[0017] In this embodiment, an etching end point detecting device that detects the end of etching of polysilicon on a SiO ₂ layer is described. However, characteristics such as a unique peak wavelength determined by an etching substance and a gas atmosphere are described. By grasping the points and detecting them, it is possible to detect the end of the etching even in an atmosphere of another substance or another gas. For example, when etching a SiO ₂ film with F radicals,
What is necessary is just to detect 451 nm, 482 nm, and 520 nm. In the case of aluminum, 306 nm, 394 nm,
396 nm, and 362n in the case of Si ₃ N ₄
The end of the etching can be detected by detecting the level of the peak at m, 674 nm, 388 nm or the like. In this case, a dichroic mirror and an optical filter for separating the respective wavelengths are used. It goes without saying that this optical filter uses the wavelength of the spectrum of the light obtained through the dichroic mirror, which has a large change before and after the etching, and also uses the arithmetic expression of the signal processing unit that changes greatly before and after the etching.

Further, when detecting the end of etching of another substance to be etched, the end of etching of various substances can be detected by selecting a filter and its arithmetic expression based on the plasma emission spectrum. Can be.

In this embodiment, an apparatus for detecting the end of etching is shown. However, not only the end of etching but also the start / stop of plasma can be similarly determined based on the plasma emission spectrum. Becomes In addition, a cathode sputtering device, a plasma CDV device, a plasma polymerization device, a surface treatment device, and the like, which generate a thin film on the surface of a substrate placed in a container by utilizing discharge in a gas, are also used in the process of manufacturing a semiconductor integrated circuit. . By monitoring the state of the plasma also in such an apparatus, the apparatus can be used for knowing the progress of a thin film when forming a thin film on a semiconductor.

[0020]

As described above in detail, according to the first aspect of the present invention, since the dichroic mirror is used in the optical system, the light transmitted or reflected by the dichroic mirror is received by the light receiving element. Thus, the wavelength for detecting the plasma state can be defined by receiving light with each light receiving element. Therefore, the plasma state can be monitored without the light being attenuated by the half mirror or the like. According to the second aspect of the present invention, the end of dry etching can be detected based on a change in the level of light having a predetermined wavelength using this optical system. Further, in the invention according to claim 3, by comparing with a predetermined threshold value based on any one of the sum and difference of the average value of the outputs of the first and second light receiving elements, the ratio and the division value of the sum and difference. The end of etching is detected. Therefore, by selecting an appropriate arithmetic expression according to the substance to be etched or the surrounding gas, the effect of detecting the end of various types of etching can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an optical system portion of an etching end point detecting device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an etching end point detecting device according to the embodiment.

FIG. 3 is a diagram showing characteristics of a dichroic mirror according to the embodiment.

4A is an emission spectrum of plasma light at the time of etching polysilicon, and FIG. 4B is an emission spectrum of plasma at the time of etching SiO ₂ .

FIG. 5 is a diagram showing an example of characteristics of the optical filter according to the embodiment.

FIG. 6 is a diagram illustrating an example of characteristics of an optical filter according to another embodiment of the present invention.

FIG. 7 is a diagram showing an example of an optical filter used in a conventional dry etching end point detecting device.

[Description of Signs] 1 Optical fiber 2 Lens 3 Dichroic mirror 4 First optical element 5 Second optical element 6,7 Optical filter 11,12 Preamplifier 13,14 Analog switch 15 Main amplifier 16 Peak hold circuit 17 CPU 17a A / D converter 17b Average value processor 17c, 17d D / A converter 17e Oscillator / divider 18, 19 Analog output circuit 20 Signal processor 21 Adder 22 Subtractor 23 Ratio calculator 24 Divider 25 Multiplexer 26 Comparator 27 Operation expression selection section

Claims (3)

[Claims] 1. A dichroic mirror for guiding plasma light and transmitting a part of an emission wavelength thereof, a first light receiving element for receiving light reflected by the dichroic mirror, and receiving light transmitted through the dichroic mirror. Second
And a light filter provided on at least one of the front surfaces of the first and second light receiving elements and transmitting light of a predetermined wavelength. 2. A dichroic mirror for guiding plasma light and transmitting a part of the emission wavelength thereof, a first light receiving element for receiving light reflected by the dichroic mirror, and receiving light transmitted through the dichroic mirror. Second
A light-receiving element, an optical filter provided on at least one of the front surfaces of the first and second light-receiving elements, and transmitting light of a predetermined wavelength, and etching based on an output of the first and second light-receiving elements. And a signal processing means for detecting a change in the emission spectrum accompanying the end of the dry etching. 3. An averaging means for averaging levels of the first and second light receiving elements; an adding means for calculating an added value of the first and second outputs; Subtracting means for subtracting the output of the first and second light receiving elements; ratio calculating means for calculating the output ratio of the first and second light receiving elements; and calculating the output of the first and second light receiving elements. Dividing means for calculating a difference with respect to the sum or any one of the outputs; and comparing one of the outputs selected from the adding means, the subtracting means, the ratio calculating means and the dividing means with a predetermined threshold level. 3. The dry etching end point detecting device according to claim 2, further comprising a comparing unit, wherein an end point of the etching is detected based on an output of the comparing unit.