JPH1022272A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily remove residues of sticking photoresist by introducing gaseous nitrogen and generating gaseous nitrogen plasma containing nitrogen radicals each time a specific number of semiconductor wafers are etched completely. SOLUTION: The gaseous nitrogen is introduced into an etching device each time the etching of Si wafers 8 is completed to produce gaseous nitrogen plasma. Then next Si wafers 8 are loaded into the etching device and etched. Consequently, residues of photoresist in the etching device can be removed. The etching precision can, therefore, be improved and it take no time to remove the residues, so the throughput of the etching process can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor device. In recent years, dry etching, which is superior in terms of controllability and throughput, has been increasingly used for patterning of semiconductor elements instead of conventional wet etching, but continuous etching of a large number of semiconductor substrates using the same dry etching equipment Is performed, a phenomenon occurs in which the uniformity of the etching is impaired or the etching rate is reduced.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor device, a thin film is frequently patterned using a photoresist. For example, when forming a wiring pattern, a conductive film serving as a wiring material is deposited on a surface of a Si wafer by a sputter deposition method or the like, and then a photoresist is selectively formed, and the photoresist is used as a mask to select a conductive film. Etching. The patterning of the insulating film is performed in a similar manner. FIG. 1 is a cross-sectional view of an ECR (Electron Cyclotron Resonance) etching apparatus used for etching a thin film such as a conductive film or an insulating film. The ECR etching apparatus is separated into a plasma generation chamber 1 and an etching chamber 2,
An etching gas is introduced into the plasma generation chamber 1 through a gas introduction pipe 3. Then, the microwave guided by the waveguide 4 is applied to the etching gas in the plasma generation chamber 1 through the quartz window 5 to generate plasma. The plasma generated in the plasma generation chamber 1 generates cyclotron resonance due to the magnetic field generated by the magnetic coil 6, becomes high-density plasma, and is guided to the etching chamber 2. On an etching table 7 provided in the etching chamber 2, a silicon wafer 8 to be etched is previously loaded and placed from the outside, and is subjected to etching by being exposed to high-density plasma guided to the etching chamber 2. Will be

[0003] When mass-producing semiconductor devices, a large number of Si wafers are sequentially carried into an etching apparatus and subjected to continuous etching.

[0004]

However, when a large number of Si wafers each having a photoresist formed on the surface are sequentially loaded into the same ECR etching apparatus and subjected to continuous etching, the etching rate of the thin film gradually decreases. And the uniformity of etching is impaired.

In general, during the etching process of a Si wafer, a photoresist formed as a mask is also slightly etched and scattered in the apparatus and adheres as a residue to an inner wall or the like. During the etching process of the next Si wafer, scattered again from the inner wall of the device exposed to the plasma, re-attached to the surface of the Si wafer, and acted to prevent the etching, and as a result,
It is considered that the etching rate is reduced.

Therefore, it is necessary to perform a cleaning process inside the etching apparatus in order to prevent a decrease in the etching rate of the thin film. Normally, a wet cleaning process of disassembling the etching apparatus and immersing the apparatus parts in a chemical solution or the like for cleaning is used. However, since the processing requires a long time, there is a problem that the operation rate of the apparatus is reduced. A dry cleaning process for generating an etching gas plasma inside an apparatus to remove residues by etching does not require disassembly of the apparatus, and thus has been used conventionally without the above-mentioned disadvantages. For example, a method of generating plasma by adding oxygen gas or nitrogen gas or ammonia gas to oxygen gas to perform cleaning (Japanese Patent Laid-Open No. 63-216346), a method of generating plasma by using a fluorine-based gas and performing cleaning (Japanese Unexamined Patent Publication No.
No. 302565) has been proposed. However, when plasma containing oxygen gas is used, ashing of the photoresist is promoted during etching of the thin film, which may cause a problem such as a pattern defect. It is necessary to avoid its use as much as possible because it causes a decrease in selectivity and has problems in safety in handling and costs involved in processing.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to easily remove a photoresist residue attached to the inside of a plasma etching apparatus.

[0008]

In order to solve the above-mentioned problems, when a semiconductor substrate having a photoresist formed on its surface is sequentially carried into a plasma etching apparatus to perform etching, a predetermined number of semiconductor substrates are etched each time etching is completed. A method for manufacturing a semiconductor device, comprising: introducing a gas to generate a nitrogen gas plasma containing nitrogen radicals to remove photoresist residues attached to the inside of the device; or forming a photoresist on the surface. When a semiconductor substrate is introduced into a plasma etching apparatus to perform etching, nitrogen gas is introduced into the apparatus together with an etching gas to generate an etching gas plasma and a nitrogen gas plasma containing nitrogen radicals. The removal of the photoresist residue adhering to the surface is performed simultaneously. Method of manufacturing a semiconductor device, or be achieved by the manufacturing method of the semiconductor device is characterized in that setting the nitrogen gas flow rate to 1-10% of the etching gas flow rate.

When a semiconductor substrate having a photoresist formed on its surface is subjected to an etching treatment, the photoresist is also slightly etched at the same time and adheres to the inside of the device as a residue containing carbon. The present inventor has found that when nitrogen gas plasma is generated in the etching apparatus, nitrogen radicals excited in the nitrogen gas plasma react with carbon to become volatile substances and can be easily removed. Therefore,
Each time a predetermined number of semiconductor substrates have been etched, a nitrogen gas plasma containing nitrogen radicals is generated to remove the carbon-based residue, thereby preventing the photoresist residue from re-adhering to the semiconductor substrate and etching the thin film. It is possible to suppress the reduction in the speed and maintain the uniformity of the etching.

Further, the present inventor has introduced a nitrogen gas simultaneously with an etching gas to generate an etching gas plasma and a nitrogen gas plasma containing nitrogen radicals, thereby etching the semiconductor substrate and removing the photoresist residue adhering inside the apparatus. It has been found through experiments that the removal of the photoresist at the same time can prevent the residue of the photoresist from re-adhering to the semiconductor substrate, suppress the decrease in the etching rate of the thin film, and maintain the uniformity of the etching. In this method, the flow rate of the nitrogen gas is set to 1 to 10 times the flow rate of the etching gas.
It has been experimentally found that by setting the value to%, the decrease in the etching rate can be effectively suppressed and the uniformity of the etching can be maintained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, when patterning a semiconductor device, a photoresist is selectively formed on a thin film on a Si wafer, and the thin film is etched using the photoresist as a mask. At the time of mass production of semiconductor devices, a large number of Si wafers having a photoresist formed on the surface are sequentially loaded into a plasma etching apparatus and subjected to continuous etching. Then, when such a continuous etching process was performed, how the etching rate and the etching uniformity of the thin film were changed depending on whether or not the method according to the present invention was performed was examined by the following experiment.

First, a plurality of 8-inch diameter Si wafers having a TiN film formed on the entire surface are prepared. Further, as dummy wafers, a plurality of Si wafers each having the same diameter with a photoresist formed on the entire surface and a plurality of Si wafers having a Si oxide film formed on the entire surface are formed. Then, these Si wafers are loaded one by one into the ECR etching apparatus shown in FIG. 1 and etched for a predetermined time. When the etching is completed, each Si wafer is unloaded from the etching apparatus, and then the next Si wafer is loaded and the same etching is performed. BCl ₃ / Cl ₂ mixed gas was used as an etching gas. And gas pressure is 3 ~ 4mmTorr, microwave power is about 1K
W and microwave frequency were set to 2.45 GHz.

In the above-described continuous etching process, when the Si wafer on which the TiN film is formed is loaded on the first, fifth, and tenth sheets, and the Si wafer on which a photoresist is formed as a dummy wafer is loaded during the first wafer, The etching rates of the fifth and tenth TiN films were reduced by 16% and 20%, respectively, based on the etching rate of the TiN film of the eye. When a similar continuous etching process was performed using a Si wafer on which a Si oxide film was formed as a dummy wafer, a decrease in the etching rate as described above was hardly observed. This result indicates that the decrease in the etching rate of the TiN film is caused by the residue of the photoresist generated when the dummy wafer on which the photoresist is formed is etched.

Therefore, each time the etching of each Si wafer is completed, nitrogen gas is introduced into the etching apparatus to generate nitrogen gas plasma, and then the next Si wafer is inserted into the etching apparatus to perform the etching process.
At this time, the flow rate and supply time of nitrogen gas were set to 200
SCCM, gas pressure was set to 3 mmTorr and microwave power was set to 1 KW for 30 seconds. As in the previous experiment, the first
When the Si wafer on which the TiN film is formed is inserted on the first and tenth sheets, and the Si wafer on which the photoresist is formed is inserted between them as the dummy wafer, the fifth wafer is determined based on the etching rate of the first TiN film. The etching rates of the tenth TiN film decreased by 0% and 3%, respectively. This result indicates that a decrease in the etching rate can be significantly suppressed as compared with the case where the nitrogen gas plasma treatment is not performed. Also, the uniformity of etching within the Si wafer
Good results were obtained with little dependence on the order of insertion of the Si wafers.

Next, the following measurement was performed to examine the effect of the nitrogen gas plasma introduced in the above embodiment on the etching rate. FIG. 2 shows a mass spectrum measured by a mass spectrometer in an etching chamber in which a nitrogen gas plasma is generated. The vertical axis indicates partial pressure, and the horizontal axis indicates m.
/ e (m is the electron mass, e is the electron charge). In the figure, the beak observed at the position of m / e = 26,27 is considered to be due to CN molecules. FIG. 3 shows the result of measuring the spectrum of nitrogen gas plasma, in which the vertical axis indicates the emission intensity and the horizontal axis indicates the wavelength. As can be seen from the figure, a peak attributable to the emission of CN molecules is observed at a wavelength of 388.3 nm. From the above results, when the nitrogen plasma treatment is performed, nitrogen radicals N ^* are excited as shown below, and react with carbon C forming a photoresist residue to generate volatile CN molecules, thereby generating an etching chamber. Is interpreted as having been exhausted from.

N ₂ → N ^* C + N ^* → CN Next, another embodiment of the present invention will be described. In the previous embodiment, nitrogen gas was introduced to generate nitrogen gas plasma each time the etching of each Si wafer was completed in the continuous etching process, but in this embodiment, the apparatus was used in the etching process of each Si wafer. An etching gas plasma and a nitrogen gas plasma are simultaneously generated by introducing a nitrogen gas together with an etching gas into the inside, thereby forming each Si.
The etching of the wafer and the removal of the photoresist residue adhering to the inside of the apparatus are simultaneously performed. And
The flow rate of the nitrogen gas was set at 10 SCCM, and the other etching conditions were set the same as in the previous embodiment. As in the previous embodiment, the first, fifth, and tenth Si wafers each having the TiN film formed therein are inserted into the etching apparatus, and the Si wafers having the photoresist formed thereon as dummy wafers therebetween. As a result, the etching speed of the TiN film was measured, and the etching speed of the fifth and tenth Si wafers did not decrease as compared with the first Si wafer. Also, no deterioration in etching uniformity was observed.

In this example, it was found that if the flow rate of the nitrogen gas was too large, the etching rate of the TiN film was affected, while if it was too small, the effect of removing the photoresist residue was reduced. As a result of the experiment, the present inventors have found that when the flow rate of the nitrogen gas is within the range of 1 to 10% of the flow rate of the etching gas, the etching rate of the TiN film is not affected and the photoresist residue is sufficiently removed. Was obtained.

FIG. 4 shows a photoelectron spectrum obtained by measuring the surface of the Si wafer after the etching process using an X-ray photoelectron spectrometer (XPS). The vertical axis represents the photoelectron intensity, and the horizontal axis represents the binding energy of the photoelectrons. Is shown. The figure shows the results for the case where nitrogen gas was not added for comparison. As can be seen from the figure, a peak attributable to C1s photoelectrons is observed when nitrogen gas is not added, but is not observed when nitrogen gas is added. This is probably because nitrogen radicals generated by the nitrogen gas plasma reacted with C and were removed and did not remain on the Si wafer.

In the embodiment described above, the nitrogen gas plasma is generated by using the microwave power of the frequency 2.45 GHz. However, the present invention is not limited to this. For example, the nitrogen gas plasma is generated by the commonly used high frequency power of 13.56 MHz. Also when it is generated, nitrogen radicals are generated, and the same effect as in this embodiment can be obtained.

[0020]

As described above, according to the present invention, the photoresist residue in the etching apparatus can be removed, so that the etching accuracy can be improved and the removal of the residue requires time. This is advantageous in improving the throughput of the etching process.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an ECR etching apparatus.

FIG. 2 is a diagram showing a mass spectrum of a nitrogen gas plasma.

FIG. 3 is a diagram showing a spectrum of nitrogen gas plasma.

FIG. 4 is a diagram showing a photoelectron spectrum of a Si wafer surface.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma generation room 6 Magnetic coil 2 Etching room 7 Etching stand 3 Gas introduction tube 8 Si wafer 4 Waveguide 9 Exhaust tube 5 Quartz window

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masaaki Aoyama 2-1844-2 Kozoji-cho, Kasugai-shi, Aichi Prefecture Inside Fujitsu VSI Co., Ltd. (72) Kenichi Higuchi 2-844-2 Kozoji-cho, Kasugai-shi, Aichi Fujitsu (71) Inventor Kunihiko Nagase 4-1-1, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Fujitsu Limited

Claims (3)

[Claims] When a semiconductor substrate having a photoresist formed on its surface is sequentially carried into a plasma etching apparatus to perform etching, nitrogen gas containing nitrogen radicals is introduced each time etching of a predetermined number of semiconductor substrates is completed. A method for manufacturing a semiconductor device, comprising: generating gas plasma to remove a residue of a photoresist attached to the inside of the device. 2. When a semiconductor substrate having a photoresist formed on its surface is introduced into a plasma etching apparatus for etching, a nitrogen gas is introduced into the apparatus together with an etching gas, and an etching gas plasma and a nitrogen gas containing nitrogen radicals are introduced. A method for manufacturing a semiconductor device, comprising: generating plasma, and simultaneously performing etching of the semiconductor substrate and removal of a photoresist residue attached to the inside of the device. 3. The method according to claim 1, wherein the flow rate of the nitrogen gas is one of the flow rate of the etching gas.
3. The method for manufacturing a semiconductor device according to claim 2, wherein the setting is set to 10%.