JPH11219933A - Method of measuring particle on surface of wafer in chamber of dry etching device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent erroneous detection of particles due to a natural oxide film and to make it possible to detect the particles adhering on the surface of a wafer by a method wherein inert gas is fed in the chamber with the monitor wafer installed therein and after RF discharge is performed in the chamber, the number of the particles on the surface of the semiconductor wafer is measured. SOLUTION: A natural oxide film 2 is formed (a) on the surface of a monitor wafer 7. The wafer 1 is mounted on a prescribed position in a chamber of an etching device. Inert gas is fed in the chamber. The inert gas is gas, which does not produce reactive specifies to an etching by RF discharge, and He gas and Ar gas are suitable for the inert gas. Then, the RF discharge is performed in the chamber. At this time, a plasma is generated. After the RF discharge ends, the gas is exhausted from the chamber and the wafer 1 is taken out from the chamber 1. After that, the number of particles on the wafer is measured by a foreign particle inspection unit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring particles in a dry etching apparatus, and more particularly to a method for preventing erroneous detection due to a natural oxide film formed on the surface of a wafer and detecting particles adhering to the inner wall of a chamber. The present invention relates to a particle measurement method that enables the measurement.

[0002]

2. Description of the Related Art In recent years, progress in miniaturization and high integration of semiconductor integrated circuits has been remarkable, and patterns and patterns of about 0.25 microns have been developed.
A miniaturization process using design rules is being put to practical use. With the miniaturization of such a pattern, even a small amount of particles (dust) causes a pattern defect. Therefore, it is important to measure the number of particles adhering to the semiconductor wafer in each step and manage the number of particles to a certain number or less. Since the etching step is a step of performing pattern processing on wiring, contact holes, and the like, particularly high precision particle measurement is required in this step.

In general, particles generated by an etching apparatus include particles generated from an etching gas supply system, particles scattered and suspended in a chamber, and particles adhered to an inner wall of a chamber or a process kit. Conventionally, a semiconductor wafer for particle measurement (hereinafter, referred to as a monitor wafer) is mounted at a predetermined position in a chamber, and a reactive gas (active gas) is mounted.
Is supplied to a chamber, and then the particles deposited and adhered on the surface of the monitor wafer are counted using a foreign substance inspection device. As is well known, a foreign matter inspection device is a device that optically counts particles, adsorbs a monitor wafer on a stage of the device, rotates it, and uses an Ar laser beam (or a He-Ne laser beam). ) Is radiated onto the wafer while being moved in the radial direction of the wafer through a lens system, and scattered light from foreign matter on the surface of the wafer is detected by a light receiving unit, and the number of foreign matter is counted for each size. is there.

However, in this measuring method, particles generated from the reaction gas supply system and particles scattered or suspended in the chamber can be detected, but particles adhering to the inner wall of the chamber or the process kit can be detected. It was difficult to do.
Therefore, as with the actual process conditions of the etching equipment, HB
An RF discharge may be performed by supplying a reaction gas such as r. According to this method, the particles attached to the inner wall of the chamber are separated by being exposed to the plasma generated by the RF discharge, and can be detected by the foreign substance inspection device. However, as shown in FIG. 4A, a natural oxide film 12 is formed on the surface of the monitoring wafer 11 made of a silicon substrate. For this reason, as shown in FIG. 4B, after the RF discharge, a step caused by the natural oxide film 12 occurs in addition to the step caused by the particles 13, and the latter step is erroneously detected as a particle. Problem.

In order to solve this problem, Japanese Patent Laid-Open Publication No.
As described in JP-A-91, the monitoring wafer 11 is pre-cleaned with a mixed solution of ammonia and hydrogen peroxide,
There is a method of removing the natural oxide film 12 in advance.
However, this measurement method has problems such as an increase in man-hours, a decrease in throughput, and a deterioration in the environment due to the use of chemicals.

[0006]

The present invention has been made in view of the above-mentioned problems of the prior art. That is,
An object of the present invention is to provide a particle measurement method for a dry etching apparatus, which prevents erroneous detection due to a natural oxide film formed on the surface of a monitor wafer and enables detection of particles attached to the inner wall of a chamber. It is in.

It is another object of the present invention to provide a method for measuring particles in a dry etching apparatus, which has an improved throughput in a measurement process. Still another object of the present invention is to provide a method for measuring particles in a dry etching apparatus, which does not require the use of chemicals and has a small environmental load.

[0008]

According to a method for measuring particles in a dry etching apparatus of the present invention, a monitoring wafer made of a semiconductor substrate is mounted at a predetermined position in a chamber of a dry etching apparatus, and an inert gas is introduced into the chamber. The method includes a step of supplying and performing an RF discharge, and a step of measuring the number of particles deposited on the surface of the semiconductor wafer. (Corresponding to the first embodiment.)
According to the present invention, particles attached to the inner wall of the chamber are peeled off by the plasma generated by the RF discharge and are deposited on the surface of the semiconductor wafer, so that the particles can be measured. In addition, since no reaction gas is used, a step due to a natural oxide film can be formed, and the surface of the semiconductor wafer can be prevented from being rough, so that erroneous detection can be prevented. Further, since a cleaning step using a chemical for removing a natural oxide film can be omitted, the throughput can be improved and the environmental load can be reduced.

Further, according to the method for measuring particles of a dry etching apparatus of the present invention, a monitoring wafer having a silicon oxide film on a surface of a semiconductor substrate is mounted at a predetermined position in a chamber of a dry etching apparatus, and a reactive gas is supplied to the wafer. The method is characterized by including a step of performing RF discharge by supplying into the chamber and a step of measuring the number of particles deposited on the surface of the monitoring wafer. (Corresponding to the second embodiment.) According to the present invention, since a semiconductor substrate having a silicon oxide film is used as a monitor wafer, a natural oxide film is not originally formed.
For this reason, even if a reactive gas is used, a step due to a natural oxide film is not formed on the wafer surface, and particles can be measured under actual process conditions.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, a dry etching apparatus includes an apparatus for etching a polysilicon film or a silicon nitride film (hereinafter referred to as a polysilicon etcher) and a silicon oxide film (SiO2 film). (Hereinafter referred to as an oxide film etcher). In order to measure particles in a state close to the actual etching process, when measuring particles of polysilicon etcher, use a monitor wafer consisting of a silicon substrate, and when measuring particles of oxide film etcher, It is appropriate to use a monitor wafer in which a silicon oxide film is formed on the surface of a silicon substrate in advance by a CVD apparatus or the like.

An embodiment of the present invention will be described below for each case. (1) First Embodiment In a polysilicon etcher, a silicon substrate itself is used as a monitoring wafer. As shown in FIG. 1A, a natural oxide film 2 is formed on the surface of a monitor wafer 1. The monitoring wafer 1 is mounted at a predetermined position in a chamber of an etching apparatus. Generally, a dry etching apparatus includes a chamber 4, an upper electrode 5a, a lower electrode 5b, a wafer table 6,
It is composed of a gas supply port 7, an exhaust port 8, and a high frequency power supply 9,
A high frequency power supply 9 is connected to the upper electrode 5a. The monitoring wafer 1 is mounted on the wafer table 6.

Then, the inert gas 10 is supplied from the gas supply port 7.
Is supplied into the chamber 4. The inert gas is a gas that does not generate reactive species for etching by RF discharge, and He gas and Ar gas are appropriate. As a supply condition of He gas, a flow rate of 30 sccm and a pressure of about 200 mTorr are appropriate. Similar conditions may be used for Ar gas.

Next, RF discharge is performed in the chamber 4 for 30 seconds to 120 seconds. At this time, the RF power was set to 300 W, and 1
A plasma is generated by supplying an electromagnetic wave of 3.56 MHz. After the end of the RF discharge, the gas is exhausted from the exhaust port 8, the monitor wafer 1 is taken out of the chamber 4, and then the number of particles on the monitor wafer 1 is measured by a foreign matter inspection device.

It is to be noted that O2 gas may be added to the inert gas 10 to form a mixed gas. In this case, the upper electrode 5
Particles may be generated due to abrasion or deterioration of a, but this problem can be solved by appropriately setting the gas flow ratio, pressure, and RF power. For example, O2 gas, He
Gas flow ratio is 50sccm, 30sccm, pressure 200mT, R
In the case of the F power of 300 W, the above problem occurred, but the flow ratios of the O2 gas and the He gas were set to 40 sccm, 200 sccm, and
The problem was solved by setting 00mT and RF power 200W.

According to the present embodiment, particles adhered to the inner wall of the chamber and the process kit are peeled off by the plasma and deposited on the surface of the monitor wafer 1 as shown in FIG. Can be measured. Also, this plasma has no reactivity with the silicon substrate. Therefore, the natural oxide film 2
Does not act as a micromask and a step is not formed on the surface of the monitoring wafer 11, so that erroneous detection of particles can be prevented. By setting the size of the foreign matter to be detected in the foreign matter inspection apparatus to a certain size or less, it is possible to prevent the natural oxide film 2 from being erroneously detected as a particle.

The inventor of the present application conducted a comparative experiment on the same etching apparatus on the same day to confirm the effect of the measuring method of the present invention. According to an experiment in which He gas was used as an inert gas and an RF discharge was performed, the number of particles was about 2000 particles / wafer. On the other hand, the number of particles in an experiment using a reactive gas and not performing RF discharge was about 40
Pieces / wafer. Assuming that the particle standard is 50 / wafer, the apparatus is conventionally erroneously determined to have no abnormality, whereas according to the present invention, the apparatus is determined to be abnormal.

As described above, according to the measuring method of the present invention, the abnormality of the etching apparatus can be found at an early stage, whereas the conventional method cannot catch the abnormality of the etching apparatus. Thus, the abnormality of the device can be appropriately and promptly recovered. (2) Second Embodiment In the oxide film etcher, as shown in FIG. 3A, a monitor wafer 1 in which an SiO2 film 1a is previously formed on the surface of a silicon substrate 1b by a CVD apparatus is used. It is. Further, the second embodiment differs from the first embodiment in that a reactive gas is used as a gas supplied into the chamber 4.
The conditions for the RF discharge are the same as in the first embodiment.

It is necessary to consider the material of the upper electrode 5a as the reactive gas. (It is not necessary to consider the upper electrode 5b because it is not exposed when the monitor wafer 1 is mounted.) When the material of the upper electrode 5a is amorphous carbon, the consumption of the electrode is accelerated when O2 gas is used. As a result, there was a concern that the life would be shortened and particles would be generated. However, as a result of the experiment, it was found that there was no problem even if the O2 gas was introduced. Therefore, the O2 gas may or may not be introduced, and may be supplied as needed according to the actual process conditions.

According to an experiment, O2 gas, CF4 gas and Ar gas were supplied at a flow rate of 40 sccm, 60 sccm and 800 sccm, respectively, at a flow rate of 2000 m
Suitably, it is supplied to the chamber 4 under a pressure of rr. When O2 gas is not used, CHF3 gas, CH4
Gas, using a mixed gas of Ar gas, 30sccm, 50sc respectively
It is appropriate to supply at a pressure of 1600 mTorr at a flow rate of 1000 sccm at a flow rate of 1000 sccm.

Thereafter, an RF discharge is performed to take out the monitor wafer 1 from the chamber 4, and then the number of particles 3 on the monitor wafer 1 is measured by a foreign matter inspection device. At this time, particles 3a attached before the RF discharge or at the initial stage thereof (shown in FIG. 3B)
In the portion of the above, the SiO2 film 1a is composed of the particles 3b.
Is used as a mask, a step occurs as shown in FIG. However, according to the foreign matter inspection device, the number of both particles 3a and 3b can be measured.

As described above, in this embodiment, the semiconductor substrate 1b having the SiO2 film 1a on the surface of the monitor wafer 1 is used.
Is used as a monitor wafer, so a natural oxide film is not originally formed. For this reason, even if a reactive gas is used, a step due to a natural oxide film is not formed on the wafer surface, and particles can be measured with high accuracy under actual process conditions.

[0022]

As described above, according to the first to third aspects of the present invention, the particles attached to the inner wall of the chamber are peeled off by the plasma generated by the RF discharge and are deposited on the surface of the semiconductor wafer. Therefore, the particles can be measured. As a result, an abnormality in the etching apparatus can be found at an early stage, which can contribute to an improvement in production efficiency.

Further, since a step due to a natural oxide film is formed and the surface of the semiconductor wafer is prevented from being rough, erroneous detection of particles can be prevented.
Further, since a cleaning step using a chemical for removing a natural oxide film can be omitted, the throughput can be improved and the environmental load can be reduced. Further, according to the invention described in claims 4 to 6, since a semiconductor substrate having a silicon film on the surface of the monitor wafer is used as the monitor wafer, a natural oxide film is originally formed. Absent. For this reason, even if a reactive gas is used, a step due to a natural oxide film is not formed on the wafer surface,
Particles can be measured with high accuracy under actual process conditions.

[Brief description of the drawings]

FIG. 1 is a process sectional view for explaining a particle measuring method of a dry etching apparatus of the present invention.

FIG. 2 is a process sectional view for explaining a particle measuring method of the dry etching apparatus of the present invention.

FIG. 3 is a schematic diagram of a dry etching apparatus.

FIG. 4 is a process sectional view for explaining a particle measuring method of a conventional dry etching apparatus.

Claims (6)

[Claims] A step of mounting a monitor wafer made of a semiconductor substrate at a predetermined position in a chamber of a dry etching apparatus, supplying an inert gas into the chamber, and performing RF discharge; Measuring the number of particles deposited on the substrate. 2. A step of mounting a monitor wafer comprising a semiconductor substrate at a predetermined position in a chamber of a dry etching apparatus, supplying a mixed gas of an inert gas and O2 gas into the chamber, and performing RF discharge. Measuring the number of particles deposited on the surface of the monitor wafer. 3. The method according to claim 1, wherein the inert gas is He gas or Ar gas. 4. A step of mounting a monitor wafer having a silicon oxide film on a surface of a semiconductor substrate at a predetermined position in a chamber of a dry etching apparatus, supplying a reactive gas into the chamber, and performing RF discharge. And a step of measuring the number of particles deposited on the surface of the monitor wafer. 5. The method according to claim 4, wherein the reactive gas is a mixed gas of O2 gas and CF4 gas. 6. The method according to claim 4, wherein the reactive gas is a mixed gas of a CHF3 gas and a CF4 gas.