JPH0518454B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to an etching apparatus used for etching, which is a process of semiconductor manufacturing, and particularly to a dry etching apparatus equipped with a monitoring function in dry etching using plasma. <Prior Art> In the etching step in the semiconductor device manufacturing process, dry etching is widely used because it has higher processing accuracy than wet etching. Among dry etching methods, dry etching using plasma is currently becoming mainstream for use in microfabrication technology because it allows control of selection ratio and anisotropic etching. Incidentally, in order to perform dry etching with good controllability, it is essential to control etching conditions such as etching time while monitoring the progress of etching. There are various methods for monitoring the progress of etching, but as mentioned above, in dry etching using plasma, emission spectroscopy is used to monitor the appearance or attenuation of specific wavelengths in the plasma emission spectrum. . <Problems to be Solved by the Invention> Since the emission spectroscopy method for detecting the end point of etching only detects the point at which the film to be etched has completely disappeared, etching may be completed while leaving a part of the film to be etched, for example. It cannot be used in processes where the substrate itself is etched by a specified amount, such as when forming trenches in a silicon substrate. In order to deal with such cases, we irradiate the object to be etched with a laser beam, measure the intensity of the reflected light that changes due to interference from the remaining etching film on the object, and perform etching based on the time change in the intensity of the reflected light. A method has been developed to calculate the total amount of film loss from the starting point. The above method can also be applied to a process in which etching is stopped midway. However, since the signal obtained by measurement contains an interference signal due to the mask material in addition to an interference signal due to the etching residual film, there is a problem in that etching cannot be properly monitored. <Means for Solving the Problems> The present invention has been made to solve the above-mentioned problems, and includes a multi-channel light-receiving element that receives reflected light obtained by irradiating an object to be etched with continuous light. Then, the digital signal is subjected to high-speed calculation processing using a microprocessor to obtain optical path difference information, and based on the obtained optical path difference information, the etching amount is monitored and the etching conditions are controlled. The present invention provides a dry etching device for etching. <Function> By irradiating the object to be etched with continuous light and measuring the amount of etching of the object in real time, it is possible to improve the controllability of etching and improve the accuracy of the etching object. <Example> FIG. 1 shows a block diagram of a dry etching apparatus according to this example. The dry etching apparatus, like the conventional apparatus, has a substrate 10 as an object to be etched mounted in an etching chamber 3, a support table 11 serving as one electrode for plasma generation, and a support table 11 opposite to the support table 11 on the other side. A counter electrode 4 serving as an electrode is installed. Further, the dry etching apparatus is connected to a high frequency power source 13 for generating plasma, and is also connected to a gas supply device 14, a vacuum evacuation device 15, and the like. Continuous light emitted from the light source 1 is guided into the etching chamber 3 through a first optical fiber included in the coaxial optical fiber 2, and is irradiated onto the substrate 10. An optical system using a lens is attached to the tip of the first optical fiber to focus light onto the substrate, and is separated from the vacuum vessel by an optical window. The optical window is purged with inert gas to prevent fogging from reaction products during etching. The optical system integrated with the tip of the first optical fiber is embedded in the counter electrode 4 of the etching device. The light reflected on the substrate is detected by a second optical fiber included in the coaxial optical fiber and guided to a spectrometer 5 installed outside the etching chamber 3. Here, by guiding incident light and reflected light through a coaxial optical fiber 2, the collection efficiency of reflected light is improved. Spectroscopy of reflected light is performed at once without mechanical scanning using a multichannel light receiving element. Compared to conventional methods, this method has the following advantages: (1) shorter spectroscopic time (within 3 seconds including calculation), (2) higher information utilization efficiency (brighter),
It has the advantage of In this example, 400n
A linear multi-channel photodetector with approximately 400 channels is used to separate light in the region from 1,100 nm to 1,100 nm. The signal obtained by the light receiving element is digitized and then sent to the microprocessor 6 for arithmetic processing. The microprocessor 6 forms optical path difference information from the spectral signal obtained by the spectrometer 5, as will be described later. Next, the optical path difference information obtained through calculation processing is sent to the control system 7. The control system 7 includes a high frequency power source 13 and a gas supply device 1.
A control signal is supplied to drive units constituting the etching apparatus, such as the etching device 4 and the vacuum evacuation device 15, to control the etching operation. In dry etching using plasma, plasma emission sometimes interferes with measurement.
This can be prevented by making the incident light intensity sufficiently stronger than the plasma emission intensity, but as another means, the plasma emission intensity can be monitored with a second spectrometer 8 as shown in FIG. It is more effective to prevent this by sending the signal to the control system 7 and subtracting it from the signal of the reflected light. Figure 2 is a cross-sectional view of a sample in which the monitor function of this example is applied to trench etching of a silicon substrate with SiO ₂ (≒4000 Å) formed on the surface, and Figure 3 is a cross-sectional view of the sample shown in Figure 2. This is a plot of the reflection spectrum intensity versus wavenumber. In FIG. 3, signals with two or more types of periods are observed. As shown in Figure 2, if we consider the reflected light from the SiO ₂ surface, the SiO ₂ and Si interface, and the groove bottom, this will depend on the SiO ₂ film thickness and Si etching depth. This is caused by the existence of three optical path differences, and it is difficult to obtain information on the etching depth in this state. Therefore, the spectral signal is subjected to arithmetic processing and separated to determine the etching depth. In this embodiment, fast Fourier transform was adopted as the arithmetic processing of the spectral signal, and the processing was performed by the microprocessor 6. The numerical calculation of fast Fourier transform is
The 8086 series is programmed using the Pascal language.
This was done using an object program compiled for the CPU. Using this program, the time required to convert 512 points on the wavenumber axis is approximately 6
It takes less than a second. This is fast enough to measure the extent of etching progress in situ. FIG. 4 shows the result of fast Fourier transformation after digitizing the reflection spectrum signal of FIG. 3. Here, the horizontal axis in FIG. 4 corresponds to optical path difference information, and the vertical axis represents spectral intensity in logarithm. Spectral intensities that are symmetrical about the optical path difference of 0 are obtained. Also, if the three peaks observed in Figure 4 are named A, B, and C, respectively, peak A indicates the optical path difference between the light in Figure 2 and peak B in Figure 2. The peak C shows the optical path difference between the light in FIG. 2 and the light in FIG. As the etching progresses and the silicon level difference becomes larger, peak B and peak C move toward the side where the optical path difference is larger. Therefore, by setting the optical path difference of the desired etching depth in advance in the control system 7, the etching end point can be automatically detected. Table 1 compares the optical path difference obtained using this example with the optical path difference predicted from step measurement. A stylus-type surface roughness measuring device was used to measure the thickness of the silicon oxide film and the silicon level difference.

[Table] The optical path difference obtained in this example matches the optical path difference expected from the structure of the sample within the resolution of Fourier transform. Here, the resolution of Fourier transform is a quantity given by the theory of discrete Fourier transform, and corresponds to the reciprocal of the bandwidth of the signal before transform. Using this example, by repeating reflection spectroscopy and Fourier transformation of the object to be etched during etching, it is possible to monitor the etching amount of the object to be etched during etching, and to control the etching conditions. It becomes possible. Although this embodiment describes the case of trenching a silicon substrate, it is clear that the present invention is also applicable to etching a general multilayer film. <Effects of the Invention> By using the multi-channel light receiving element of the present invention that receives interference light between the reflected light from the surface to be etched and the reflected light from other surfaces and separates it into spectra, the spectroscopic time can be shortened, and , information utilization efficiency can be increased, and the collection rate of reflected light can be improved by using a coaxial optical fiber that guides incident light and reflected light. It has the above configuration, a light source that irradiates continuous light, a calculation means for forming optical path difference information from a spectral signal by fast Fourier transformation, and a means for controlling the progress of etching based on the optical path difference information. By using a dry etching device that is characterized by This improves reproducibility when you want to terminate the process. Therefore, it is possible to improve the yield and reliability of semiconductor devices such as highly integrated memories.

[Brief explanation of the drawing]

FIG. 1 shows a configuration diagram of a dry etching apparatus according to this embodiment, FIG. 2 shows a cross-sectional view of a sample of trench etching of a silicon substrate according to this embodiment, and FIG. 3 shows a reflection diagram of the sample of FIG. 2. A diagram showing the spectrum intensity plotted against the wavenumber is shown.
FIG. 4 is a diagram showing the results of fast Fourier transform of the reflection spectroscopic spectrum signal of FIG. 3. 1...Light source, 2...Coaxial optical fiber, 3...
Etching chamber, 4... Counter electrode, 5... Multi-channel spectrometer for reflection spectrum spectroscopy, 6...
...Microprocessor, 7.Control system, 8.Multi-channel spectrometer for plasma emission spectroscopy.

Claims (1)

[Scope of Claims] 1. A light source that irradiates continuous light onto a surface that has a surface to be etched, and a multi-channel that receives and separates interference light between the light reflected from the surface to be etched and the light reflected from other surfaces. a coaxial optical fiber that guides incident light and reflected light; a calculation means for forming optical path difference information by fast Fourier transform from a spectral signal output from the light receiving element; 1. A dry etching apparatus comprising means for controlling the progress of etching based on the etching process.