JPS6323324A - Dry etching apparatus - Google Patents

Abstract

PURPOSE:To improve the controllability of etching and increase the accuracy of an object to be etched by controlling the progress of etching on the basis of optical path difference information. CONSTITUTION:Multiwavelength light from a light source 1 is led to an etching chamber 3 via a first optical fiber bundle included in a coaxial type optical fiber bundle 2 and emitted to a substrate 10. Reflected light is detected by a second optical fiber bundle included in the coaxial type optical fiber bundle and led to a spectroscope 5 provided outside the etching chamber 3. Optical path difference information is formed from spectral signals obtained in the spectroscope 5. Then, the arithmetically processed optical path difference information is fed to a control system 7. The control system 7 supplies a high-frequency power source 13, a gas source 14, an evacuation equipment 15 and the like constituting the driving units of an etching apparatus with control signals to control an etching operation.

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 in particular, an etching apparatus equipped with a monitor function in dry etching using plasma, , relating to a ching device.

<Prior Art> Regarding the etching time during the semiconductor device manufacturing process, dry etching is widely used because of its 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. 0 <Problems to be solved by the invention> Since the emission spectroscopy method that detects the end point of etching only detects the point at which the film to be etched has completely disappeared, it is difficult to finish etching by leaving a part of the film to be etched, for example. It cannot be used in a process where the substrate itself is etched by a specified amount, such as when forming a trench 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 was made to solve the above-mentioned problems, and it uses reflected light obtained by irradiating an object to be etched with light of multiple wavelengths to a multi-channel light receiving element. After receiving the light, it is separated into
The present invention provides a dry etching apparatus in which the etching conditions are digitized, the digital signal is then controlled by a microprocessor based on a high-speed calculation section, and the end point of etching is detected.

Function: By using multiple wavelengths of light to irradiate the object to be etched and measuring the amount of etching on the object in real time, it is possible to improve the controllability of etching and improve the precision of the object to be etched. .

<Embodiment> FIG. 1 shows a block diagram of a dry etching apparatus according to this embodiment.

The dry etching apparatus, like the conventional apparatus, has a substrate 10, which is an object to be etched, mounted in an etching chamber 3, and a support base 11, which serves as one electrode of the plasma generation chamber.
A counter electrode 4 serving as the other electrode is installed opposite the support base 11.

Further, the dry etching apparatus is connected to a high frequency power source 13 for generating plasma, and a gas supply device 14. A vacuum evacuation device 15 and the like are connected.

Multi-wavelength 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 1o. 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 an 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 transmitted to the second optical fiber included in the coaxial optical fiber.
The light is detected by an optical fiber and guided to a spectrometer 5 installed outside the etching chamber 3. Here, by guiding the incident light and the reflected light through a coaxial optical fiber 2, we aim to improve the collection efficiency of the reflected light.The spectroscopy of the reflected light is performed by mechanical scanning using a multi-channel light receiving element. Do it all at once without. Compared to conventional methods, (1) the spectroscopic time is short (within 3 seconds including calculation); (2)
It has the advantage of being highly efficient (bright) in the use of information. In this example, a region of 400 nm to 11100 nm is separated by a linear multi-channel light receiving element with approximately 400 channels. 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 spectroscope 5, as will be described later. Next, the optical path difference information obtained through calculation processing is sent to the control system 7. control system 7
is a high frequency power supply 13. Etching devices such as a gas supply device 14 and a vacuum exhaust device 15 are configured. A control signal is supplied to the drive section to control the enching 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. , and send the signal to the control system 7 and subtract 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 5tO2 (4000A) formed on the surface, and Figure 3 is a reflection of the sample shown in Figure 2. This is a plot of spectral intensity versus wave number.

In FIG. 3, signals with two or more types of periods are observed.

As shown in Figure 2, this reflects the reflected light from the SiO□ surface.
The reflected light from the interface between i02 and Si (■) and the reflected light from the groove bottom (■) are caused by the existence of three optical path differences corresponding to the SiO2 film thickness and Si etching depth. Therefore, it is difficult to obtain information on the etching depth.

Therefore, the spectral signal is subjected to arithmetic processing and separated to determine the 2-soching 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. Numerical operations for fast Fourier transform were performed using an object program programmed using the Pascal language and compiled for an 8086 series CPU. Using this program, the time required to convert 512 points on the wavenumber axis is less than about 6 seconds. 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 spectroscopic 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. The three peaks observed in Figure 4 are still labeled A, A, and A, respectively.
Named B and C, beak A shows the optical path difference between the lights ■ and ■ in Figure 2, beak B shows the optical path difference between the lights ■ and ■ in Figure 2, and beak C shows the optical path difference between the lights ■ and ■ in Figure 2. The optical path difference between the lights ① and ② in Fig. 2 is shown. As the etching progresses and the silicon level difference becomes larger, the beak B and the beak 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 1゜□'' The optical path difference obtained in this example matches the optical path difference expected from the structure of the sample within the range of Fourier transform resolution. Here, the resolution of Fourier transform is
A quantity given by the theory of discrete Fourier transform, which corresponds to the reciprocal of the signal bandwidth before transformation.

Using this example, by repeating reflection spectroscopy and Fourier transformation of the object to be etched during etching, it is possible to monitor the amount of etching of the object to be etched during etching, and to control the etching conditions. Become.

In this example, the case of trenching on a silicon substrate was described, but
It is clear that the present invention is also applicable to the etching of general multilayer films.

<Effects of the Invention> The present invention improves the reproducibility of the etching process, especially when it is desired to terminate the etching in the middle of the material, such as in the groove etching 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 is shown in which the spectral intensity is plotted against the wave number, and FIG. 4 is a diagram showing the result of fast Fourier transformation of the reflection spectral signal in FIG. 3. 1 Light source, 2 Coaxial optical fiber, 3 Enching 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, Patent attorney Takeshi Sugiyama (and 1 other person) Figure 1 Figure 2

Claims (1)

[Claims] A multi-wavelength light source that irradiates light onto a surface to be etched, a light receiving element that receives reflected light from the surface to be etched, and optical path difference information is formed from a spectral signal output from the light receiving element. and a control means for controlling the progress of etching based on the optical path difference information.