JPH0456215A - Plasma etching device and cleaning method - Google Patents

Abstract

PURPOSE:To remove in a short time the reaction product generated by etching and adhered to the substrate, and to make it possible to conduct a stable etching while a reaction chamber is being maintained in a stationary state at all times by a method wherein a third electrode, which is almost vertical to first and second electrodes, is provided in the space located between the first electrode and the second electrode. CONSTITUTION:A substrate 3 to be etched, a first electrode 1 whereon the substrate 3 to be etched is placed, a second electrode 2 opposing to the first electrode 1, and a third electrode 12, which is formed almost vertical to the first and the second electrodes 1 and 2 on the position where the electrode 12 is not brought into contact with the first and the second electrodes 1 and 2 at least in the space located between the first electrode 1 and the second electrode 2, are provided. Also, high-frequency waves are applied to the first electrode 1, plasma is generated between the first electrode 1 and the second electrode 2, and an etching treatment is conducted on the substrate 3 to be etched. After the above-mentioned etching treatment has been finished, plasma is generated by applying the second high-frequency waves on the third electrode 12, and at least the first and second electrodes 1 and 2 are cleaned by etching.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a plasma etching apparatus and cleaning method using a reactive gas.

BACKGROUND OF THE INVENTION In recent years, the mainstream etching technology has been plasma etching using parallel plate type high frequency discharge in order to improve microfabrication performance. Conventional plasma etching equipment
It consists of a cathode, an anode, an etching substrate, and a ceramic ring for determining the positions of the etching substrate. Gas is introduced from the gas inlet and exhausted from the gas exhaust port. Further, the high frequency is supplied from a high frequency power supply, and the discharge impedance is controlled by a matching box.

A general aspect of the discharge method of such a device is that one electrode (hereinafter referred to as cathode) arranged parallel to each other has a 13.5
By applying a high frequency such as 6 MHz, a glow discharge is generated between the cathode and the anode, and due to the difference in mobility between electrons and ions, a few cycles after applying high frequency power, a glow discharge is generated on the cathode electrode surface. A large negative potential is generated and a steady state is reached. Positive ions in the plasma are exposed to the negative potential (
This method is called reactive ion etching (hereinafter referred to as RIE), in which ions are accelerated by a cathode drop voltage) and perpendicularly collide with the etching substrate, and etching is effected by the assist effect of the ions and a chemical reaction.

Further, in order to suppress the amount of change in dimension due to etching to a small value, a reactive gas is used which has a low vapor pressure of a reaction product produced by etching and can relatively easily form a sidewall protective film of a pattern. Therefore, the reaction products generated by etching must be desorbed in the gas phase, but if the surface temperature is low, such as on the side wall of the electrode 1 reaction chamber, some of them will adhere and accumulate on the side wall of the electrode 1 reaction chamber. . The attached and deposited reaction products contaminate the inside of the reaction chamber as particles.

As a method for removing this deposit, wet cleaning using alcohol, acetone, water, etc. has generally been performed.

Problems to be Solved by the Invention This conventional method has the problem that it is necessary to bring the inside of the reaction chamber, which is kept in a vacuum state, into an atmospheric state, and that the processing time is extremely long.

Means for Solving the Problem In order to solve this problem, the present invention uses a cylindrical third electrode whose surface temperature is controlled to be lower than that of the cathode and anode when performing reactive ion etching as the cathode in the reaction chamber. The reaction product dissociated during substrate etching is attached to the third electrode, and after the substrate etching is completed, low frequency power is applied to the third electrode to generate plasma between it and the reaction chamber, and the substrate etching is performed. The purpose is to remove the reaction products generated and attached.

Function: With this configuration, while maintaining the reaction chamber in a vacuum state, reaction products generated and attached by etching the substrate can be removed in a short period of time, and stable etching can be performed by constantly maintaining the reaction chamber in a steady state.

Example The present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view of a plasma etching apparatus according to an embodiment of the present invention.

In FIG. 1, 1 is a cathode, 2 is an anode, and the cathode diameter is 200 mm. Further, 3 is a semiconductor substrate, 4 is a ceramic ring for determining the position of the semiconductor substrate, and further includes a reaction chamber 5, a gas inlet 6, a gas exhaust lower, constant temperature water pipes 8 and 9, a high frequency power source 10, and a matching box 11. It is. Furthermore, the third electrode 12. Low frequency power supply 13. It is composed of a matching box 14.

The device of this embodiment is of a type generally called cathode coupling, in which a substrate 3 for etching is placed on a cathode 1, and matching boxes 11 and 13.
It is grounded via a 56 MHz high frequency power source 10.

The reaction chamber 5 has a cubic shape, and the cathode 1 is placed on the bottom of the reaction chamber 5.
An anode 2 is grounded on the upper surface facing the cathode 1. The third electrode 12 has a cylindrical shape and is provided around the outer periphery of the cathode 1 inside the reaction chamber. Further, the third electrode is grounded via a matching box 14 constituted by a capacitor and a low frequency power source 13 of 400 kHz. Anode 2. The cathode 1 and the third electrode 12 are electrically insulated, and the anode 2
is connected to the peripheral wall of the reaction chamber 5 and grounded.

Cathode of this example 1. The anode 2 and the third electrode 12° reaction chamber 5 are made of aluminum alloy, and since the plasma generated during etching has an energy of several eV to several hundred eV, the surfaces of the cathode 1 and anode 2 are in direct contact with each other. The temperature of the area increases.

Etching turns gas into high-energy plasma and uses that energy to cause physical and chemical reactions on the substrate surface to process the substrate surface. As the temperature of the substrate surface rises, each reaction speeds up. Etching cannot be controlled due to etching time. In addition, the reaction products generated by etching are removed from the third electrode 1.
In order to concentrate and adhere to the cathode 1. It is necessary to control the surface temperature of the anode 2 to be higher than that of the third electrode 12. For this reason, in the apparatus of this embodiment, constant temperature water at a temperature of 30° C. is circulated within the cathode 1 so that the cathode 1 can always be kept at a constant temperature. For the same reason, the temperature inside the cathode 2 is also 50°C.
The device is designed to circulate constant-temperature water at a temperature of about 100 mL to ensure highly stable etching. This allows the temperature of the third electrode to be set lower than that of the cathode and anode. Here, the constant temperature water pipes 8 and 9 are designed to circulate through a part of the inside of the cathode 1 and anode 2, but it is more effective to circulate the entire inside of the cathode 1 and anode 2, and for this reason, the spiral shape It is also possible to use a pipe.

A gas inlet 6 is provided on the side wall of the reaction chamber 5, and the reactive gas introduced from the gas inlet 6 is delivered to the cathode 1 and the anode 2.
The high-frequency voltage applied during this period causes a discharge, and the reactive gas dissociates to generate active particles and charged particles. Each particle then reacts with the substrate 3 and contributes to the processing of the substrate 3, but some of the products obtained by the reaction and the remaining reactive gas that does not contribute to the reaction are pumped through the gas exhaust lower. (not shown). In this way, the gas pressure within the reaction chamber 5 is kept constant and etching is performed. Gas pressure is strongly related to etching speed and etching uniformity. For this reason, the gas introduction port 6 may be formed into a circular shape surrounding the cathode 1 and the anode 2 so that the reaction gas is uniformly introduced from a predetermined position of the circle.

Furthermore, this apparatus is a single-layer etching apparatus that processes one substrate in one etching process.

A case where etching is performed using plasma generated by this etching device will be described.

FIG. 2 shows the voltage distribution of the plasma generated between the cathode 1 and the anode 2. The horizontal axis indicates the distance from the cathode 1 to the anode 2 with the surface of the cathode 1 as the origin, and the vertical axis indicates the voltage. This distribution can also be divided into three regions, region 20
is a region called the sheath that occurs in contact with the cathode 1,
The region 21 is the plasma body, and the region 22 is the sheath generated directly below the anode 2.

Etching is performed with the substrate 3 in contact with the sheath.
Active particles that are not charged in the plasma body of region 21,
Charged particles such as ions are generated, uncharged active particles reach the substrate 3 by diffusion, and the charged particles are accelerated by the sheath and reach the substrate 3, thereby etching the substrate 3.

In etching using uncharged active particles, isotropic etching is predominant, whereas charged particles are accelerated by the sheath and reach the substrate 3, resulting in strongly anisotropic etching. As described above, highly anisotropic etching using RIE is an indispensable technique for increasing the density of devices and forming patterns at predetermined positions with high precision. However, in order to form a pattern whose dimensions do not change at all even when using RIE, it is necessary to utilize the effect that reaction products produced by etching adhere to the pattern sidewalls and protect them from etching.

FIG. 3 shows the reaction products generated by etching, their boiling points, and the amount of change in pattern dimensions due to etching using various reactive gases commonly used for etching polysilicon films. To completely limit pattern dimensional changes, very high boiling reaction products must be used to protect the pattern sidewalls. As a result, reaction products are likely to adhere to the inside of the reaction chamber.

A case where a polysilicon film is etched using this etching apparatus will be described.

HBr=60sccm as reactive gas, 0202-1
sc, pressure = 100-500 mTorr.

The polysilicon film is etched under the condition of high frequency power = 500W. Although HBr is used here as the reactive gas, it may also be a gas containing at least one of the following gases, such as C12°5iC1,<, HCl, etc. In addition, the flow rate of the reactive gas HBr was 60 s.
e cm was used, but it varies depending on the volume of the reaction chamber,
Usually used in the range of 10 to 100 seconds. Furthermore, although 500 W of high frequency power was used, high frequency power affects the etching time and in-plane uniformity of etching, but in the apparatus of this example, good results can be obtained within the range of 50 W to 1 kW. Ta.

When 50 sheets were etched under the above conditions, reaction products such as 5iBr+ were attached to the third electrode 12 to the extent that it was visible to the naked eye. As a result, the atmosphere in the reaction chamber changes, causing fluctuations in the etching rate, amount of change in pattern dimensions, etc.

Therefore, at the same time that 50 sheets have been processed under the above conditions,
Continuously enters the cleaning process using the third electrode. Here, a cleaning step was performed after processing 50 sheets, but the etching conditions vary from 50 to 500 sheets.

The cleaning conditions were CF4=50s as a reactive gas.
ecm, Oz=500sec, pressure 500mTor
r to ITo r r, and the low frequency power is 1 kW.

The reason why low-frequency power is used here is that it can have a higher specific ion energy than high-frequency power and has a high cleaning effect.

By carrying out the treatment for 10 minutes under the above conditions, the inside of the reaction chamber can be returned to the atmosphere before etching.

Effects of the Invention As described above, according to the present invention, reaction products attached by etching in the reaction chamber can be quickly removed. A gas can be used, and a pattern with no dimensional change can be formed.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a plasma etching apparatus according to an embodiment;
FIG. 2 is a diagram showing the plasma voltage distribution, and FIG. 3 is a diagram showing the reaction products generated by etching, their boiling points, and the amount of change in pattern dimensions due to etching. 1... cathode, 2... anode, 3...
...Semiconductor 5-piece substrate, 4...Ceramic ring,
5...Reaction chamber, 6...Gas inlet, 7
...Gas exhaust port, 8,9... Constant temperature water pipe, 10... High frequency power supply, 11.14...
... Matching box, 12... Third electrode, 13...
...Low frequency power supply.

Claims (3)

[Claims] (1) A substrate to be etched, a first electrode on which the substrate to be etched is placed, a second electrode placed opposite to the first electrode, and at least the first electrode and the second electrode. A plasma etching apparatus comprising: a third electrode formed substantially perpendicularly to the first and second electrodes at a position that does not contact the first and second electrodes in the space between the electrodes. (2) a step of applying a first high frequency to a first electrode to generate plasma between the first electrode and the second electrode to etch the substrate to be etched; A cleaning method comprising etching at least the first and second electrodes by applying a second high frequency to the electrodes to generate plasma. (3) The frequency of the second high frequency is from 50kHz to 400kHz
The cleaning method according to claim 2, characterized in that the cleaning frequency is Hz.