JPH0374843A - Device and method for dry etching - Google Patents

Abstract

PURPOSE:To improve working accuracy for dry etching by measuring the potential produced on a sample during the etching through contacting a metal terminal directly with the rear surface of the sample and detecting the end point of the etching from the change of the potential. CONSTITUTION:A wafer 1 is fixed on a stage 1 provided in a reaction chamber. A metal terminal 3 is brought into sure contact with the wafer by the spring force of a coiled spring 5. The metal terminal 3 is received in a holder 4 and is not exposed to plasma space. The coiled spring 5 is also incorporated in the holder 4. The holder 4 is made of metal, and the inner and outer surfaces thereof are covered with an insulator. Measured potential is led out to the atmosphere side via a wiring 6 made of a coaxial cable and a feed through 7. A chamber 8 is grounded and is used as the potential reference. A voltage is measured by a monitoring device 9. When the end point is detected, a signal processing circuit 10 supplies a signal to a shutter driving circuit 11 to close a shutter, which was opened during the etching, to prevent the wafer 1 from being irradiated with plasma.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dry etching apparatus and method,
More specifically, the present invention relates to a dry etching apparatus and method capable of sensitively and accurately detecting the end point of etching.

[Prior Art] Conventionally, a reactive ion etching apparatus (RIE), for example, has been used as a dry etching apparatus in the manufacturing process of semiconductor devices. On the other hand, in recent years, as devices have become more densely integrated, there have been strict requirements for finer patterns, higher selectivity, lower damage, and no heavy metal contamination. One dry etching technique that meets these demands is ECR dry etching that utilizes electron cyclotron resonance.

Now, including RIE and ECR dry etching equipment,
In etching apparatuses that generally use reactive gases, detection of the etching end point is extremely important in order to guarantee processing accuracy and achieve uniformity between samples. In particular, in micro devices, the dimensional accuracy of pattern width and film thickness are subject to strict conditions, so side etching after etching and overetching of the underlying film layer are likely to be problems.Accurate endpoint detection is therefore This will become increasingly necessary in the future.

Optical measurement methods, mass spectrometry, probe methods, emission spectroscopy, etc. have been proposed as methods for detecting the etching endpoint in conventional dry etching equipment, but these methods have a proven track record as endpoint monitors for actual equipment. is emission spectroscopy. Emission spectroscopy is a method of detecting differences in emission spectra from plasma space caused by differences in the materials of the material to be etched and the underlying material. For example, Si3 with CF4 and 02 gas as etching gas.
When etching the N4 film, a nitrogen spectrum (357 nm) appears while the 5isN4 film is being etched, but when the Si3N film is completely etched and the underlying surface is exposed, this spectrum disappears and a spectrum unique to the underlying material appears. Occur. This change in spectrum was used as the etching endpoint signal.

On the other hand, JP-A-63-128718 discloses a method of detecting changes in the potential of a high-frequency applying electrode on which a sample is placed before and after the end point of etching, and using this as an end point signal.

[Problem to be solved by the invention] However, this spectroscopy and Japanese Patent Application Laid-Open No. 1287-1987
The inventor of the present invention has found that the detection of an endpoint signal by changing the high-frequency applied electrode potential of Publication No. 18 has the following problems.

First, spectroscopy has the following issues.

(1) As a problem in the principle of spectroscopy, even if the materials are different, it is not possible to distinguish between materials that have spectra at the same wavelength. Therefore, it is impossible to use this method in such cases.

(2) Problems in handling the sensor include the fact that installing the sensor inside the device to increase the S/N ratio requires changing the structure of the device, or installing the sensor outside the quartz window of the device. When installing, it is necessary to carefully determine the orientation of the sensor and to keep the quartz window clean at all times.

(3) Highly sensitive sensors and their signal processing devices are generally expensive, and maintenance costs are high if they are used while maintaining sensitivity.

On the other hand, the method of detecting an endpoint signal based on a change in the potential of a high-frequency application electrode has the following problems.

(4) The potential of the high frequency application electrode is unstable due to large noise and drift.

(5) If the area of the sample to be etched is small compared to the area of the electrode, the change in electrode potential will be extremely small, making it difficult to measure with high sensitivity and difficult to accurately detect the end point.

(6) To prevent heavy metal contamination of the sample, the high frequency application electrode is usually coated with an insulating material such as quartz.

Therefore, it is difficult to sensitively measure plasma potential and self-bias, which slightly change before and after the end point, as changes in electrode potential.

[Means for Solving the Problems] The dry etching apparatus of the present invention has a metal terminal arranged so as to be able to directly contact any position on the back surface of a sample installed in a reaction chamber; and means for measuring the potential of the etching via the metal terminal, so that the end point of etching can be measured from the change in the potential.

Furthermore, the dry etching method of the present invention is characterized in that the potential generated in the sample during etching is measured by directly contacting the back surface of the sample with a metal terminal, and the end point of etching is detected from the change in the potential. [Function] The function and detailed structure of the present invention will be explained below together with the findings obtained in making the present invention.

The present invention focuses on changes in the potential of the sample itself, measures the potential of the sample itself, and detects the end point from the change. This method is completely different from spectroscopy, and is also clearly different from the method of measuring the potential of a high-frequency applying electrode described in JP-A-63-128718.

The inventor of the present invention, after conducting extensive research to solve the above-mentioned problems of the conventional technology, came up with the idea that it would be possible to detect the end point by the potential of the sample (explained using Kueh as an example). Therefore, when we investigated the behavior of the wafer, we obtained the following knowledge.

That is, when the wafer is in a floating state, a potential is generated in the wafer that acts to make the sum of the ion current and electron current incident on the wafer O. Furthermore, when a high frequency wave is applied to the wafer, a potential is generated that acts to make the net current of one cycle of the high frequency wave O. These potentials generated on the surface of the wafer differ depending on the layer structure formed on the surface of the wafer. When the material to be etched is etched and the underlying material is exposed, the potential changes. That is, the potential applied to the quench changes at the end point of etching. The inventors have discovered that by bringing a metal terminal into direct contact with the wafer, the wafer potential itself can be sensitively and accurately measured and used as an endpoint signal, leading to the present invention.

According to the above detection method, it is possible to detect the true end point of etching with high sensitivity and accuracy using a simple potential measurement system.

[Example] Hereinafter, the present invention will be explained in more detail based on Examples.

In the embodiment, an ECRC writing device will be described as an example.

FIG. 1 is a diagram showing a typical method for detecting wafer potential. Before explaining the method of detecting the wafer potential, a brief outline of the ECRC lasma apparatus will be described here. Microwaves of 2.45 GH2 generated by the microwave oscillation circuit 13 are guided to the plasma generation chamber by a waveguide. Gas for plasma generation is also introduced into the plasma generation chamber. The magnet creates a resonant magnetic field and a pulsating magnetic field of 875 Gauss. The resonantly heated electrons repeatedly collide with introduced gas molecules within the plasma generation chamber, effectively generating active species and ions that contribute to the reaction. The electrons drift toward the reaction chamber, and as a result, ions are guided into the reaction chamber so as to satisfy plasma neutralization conditions, and the active species and ions perform a predetermined processing on the wafer.

Now, using FIG. 1, a method for detecting the potential of the wafer will be described below. The wafer 1 is fixed to a stage 2 provided within the reaction chamber on which the wafer is placed. The metal terminal 3 is brought into reliable contact with the wafer by the spring force of a coil spring 5, for example.

In this example, the metal terminal 3 is housed in a holder 4 and is not exposed to the plasma space. A coil spring 5 is also incorporated into the holder 4 as shown in the figure. Further, in this example, the holder 4 is made of metal, and its inner and outer surfaces are coated with an insulating material so that it is insulated from the metal terminals 3 and the wafer. Since the holder 4 is made of metal, the metal terminal 3 is less likely to pick up noise. The measured potential is taken out to the atmosphere through a coaxial cable wiring 6 and a field through 7.

In this example, the chamber 8 is grounded to the ground, and this is used as the reference potential. The voltage is measured by a monitor device 9 such as an XT recorder or a digital voltmeter.

The outer conductors of the coaxial cables of the holder 4 and the wiring 6 are grounded to the same ground. In either case, this is to prevent noise from being introduced. A capacitor with a capacity of C is connected to the input terminal of the XT recorder and digital voltmeter. This is to short-circuit the introduced high-frequency noise components. When the end point is detected, the signal processing circuit 10 sends a signal to the shutter drive circuit 11 to close the shutter 12, which was kept in an oven during etching, so that the wafer 1 is not irradiated with plasma. In FIG. 1, the shutter 12
indicates a closed case.

At the same time, necessary predetermined operations such as introducing another gas or controlling the microwave oscillation circuit 13 to stop the microwave are automatically performed.

FIG. 2 is a diagram illustrating a method of detecting the potential on the wafer when an electrostatic adsorption method is used to fix and hold the wafer. The chamber etc. are not shown, but the surface is made of Al2O5, for example.
T-pole 14 coated with a thin insulating film such as or AJ2N
A DC voltage is applied between the floating output DC high-voltage power supply 15 and the wafer 1 is attracted by electrostatic force between the metal terminal 3 and the metal terminal 3. It can be measured in the same way as the metal terminal 3.
In this way, the electrode can play two roles: as one electrode of the power source 15, and as a contact for measuring the potential of the wafer. It is extremely useful in terms of the device configuration that the electrode for electrostatic adsorption of the wafer can be used as it is to automatically measure the potential of the wafer without configuring a special element for measuring the potential of the wafer. However, the capacitor capacity expected from the metal terminal of the high-voltage power supply 15 used in this case needs to be selected to be sufficiently small.

Although ohmic contact between the back surface of the wafer 1 and the metal terminal 3 is desirable, there is no problem even if the back surface of the wafer has a natural oxide film or a thin insulating film. This is because it is only necessary to measure the potential of the wafer 1, and there is no need to extract the current. Therefore, the input impedance (input resistance R) of the XT recorder or digital voltmeter is required to be sufficiently high. The equivalent circuit of the detection section is shown in FIG. ■A is the wafer potential. C,,R, is the capacitor capacitance and contact resistance between the wafer and the gold R terminal 3, and C is,
The capacitor L connected to remove high frequency noise is
Similarly, the inductance R for removing high frequency noise is
This is the human resistance of the detector. If the time constants RC, Rs, and Cs are shorter than the potential change of the wafer to be measured,
The detected voltage vM is as follows: VM=R-vw/(Rs+R). On the other hand, if RC, Rg, and Cs are longer than the potential change to Que, the detected voltage is Vw = Cs - V
w / ((, t + C) 0 Usually, the former method is used to measure the wafer potential. In that case, it is necessary to remove the oxide film on the back surface of the wafer.

Next, Figures 4 and 5 show an example of etching end point detection when the ECR dry etching apparatus shown in Figure 1 holds the wafer in the manner shown in Figure 2 and measures the potential. shows.

FIG. 4 shows the change in wafer potential that occurs when poly-5i is etched using C12 gas while the wafer is floating.

The pressure in the reaction chamber during etching was 4 mTorr, and the pressure in the reaction chamber was 4 mTorr.
The etching rate of ly-5t is 90 nm per minute. In region a, poly-5t is etched at a constant rate. Base material (SiO2) in b
The exposure of C begins, and the underlying material is completely exposed at C. That is, C is the end point. The wafer potential has increased by 0.4V in the positive direction. The slope between b and c varies depending on the etching conditions and the uniformity of the poly-Si film thickness. The faster the etching rate, the more
The more uniform the poly-St film thickness is, the more the slope between b and c becomes vertical.

FIG. 5 shows finely patterned 5i on a Si wafer in a floating state using C12 gas.
It shows the change in wafer potential when etching is performed using Ozfli as a mask. The point at which the S i O of the mask is etched away is clearly visible. a is Si and S
in, is the region etched at a constant speed, b is 5
When in2 begins to disappear, C is the potential when SiO□ is completely etched and the Si surface is exposed. a and c
There is a potential difference of about 2V, and it clearly appears that C is the end point. In this example, the pressure in the reaction chamber during etching was 0.6 mTorr, and the pressure of the mask was 50 mTorr.
The etching rate of i02 was 4 nm/min.

In both of the embodiments shown in FIGS. 4 and 345, the end point can be easily subjected to signal processing by taking the differential value of the potential change to the que.

[Effects of the Invention] As described above, in the present invention, the end point can be detected sensitively and accurately by directly measuring the potential of the sample by bringing a metal terminal into contact with the back surface of the sample.
Enables true endpoint detection. by this,
The processing accuracy of dry etching is improved. It can also be applied to dry etching processes where endpoint signals cannot be detected using spectroscopy. The apparatus of the present invention has an extremely simple configuration and is inexpensive, and can reduce the cost of the manufacturing apparatus.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of an etching apparatus showing an embodiment of the present invention. FIG. 2 is a conceptual diagram showing another embodiment of the present invention in which an electrostatic adsorption method is used to fix and hold a sample. FIG. 3 is an equivalent circuit diagram of the detection section in FIG. 2. FIG. 4 is a graph showing changes in the potential of a sample when poly-3i is etched. FIG. 5 is a graph showing changes in the potential of the sample when etching a Si sample using a Si film as a mask. (Explanation of symbols) 1... Sample (wafer), 2... Stage, 3...
Metal terminal, 4... Holder 5... Coil spring, 6
...Wiring, 7...Field through, 8...Chamber, 9...Monitor device, 10...Signal processing circuit, 11...Shutter drive circuit, 12...Shutter,
13... Microwave oscillation circuit, 14... Electrostatic adsorption electrode, 15... DC high voltage power supply, 16... Inductance, 17... Capacitor. Figure 1 Figure 4 Figure 5

Claims (4)

[Claims] (1) A metal terminal arranged so as to be able to directly contact any position on the back surface of the sample installed in the reaction chamber; a metal terminal for measuring the potential generated in the sample during etching via the metal terminal. 1. A dry etching apparatus comprising means for determining the end point of etching from the change in potential. (2) The dry etching apparatus according to claim 1, wherein the metal terminal is housed in a holder so that the metal terminal is not exposed to the plasma space. (3) The dry etching apparatus according to claim 1 or 2, wherein the metal terminal is configured to also serve as one electrode of a holding mechanism that attracts the sample by electrostatic force. (4) A dry etching method characterized in that the potential generated in the sample during etching is measured by directly contacting a metal terminal with the back surface of the sample, and the end point of etching is detected from the change in the potential.