JPH1064877A - Method for etching silicon nitride film and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an etching method in which etching selective ratio for a base material is large, a process at the almost same etching rate as when using heated phosphoric acid is allowed, and Si3 N4 is easily and accurately removed from a wafer. SOLUTION: A wafer 23, on the surface of which a silicon nitride film is formed, is soaked in pure water 25 in an etching vessel 11, the etching vessel 11 is sealed, and then, for example N2 gas 27 is, as inert gas, introduced into the etching vessel 11 through a gas pipe 17 by opening a gas valve 19. The gas valve 19 is closed when atmospheric pressure in the etching vessel 19 reaches 5900hPa or above, the pure water 25 is heated with a heater 21 up to 160 deg.C, and the silicon nitride film is wet-etched with the high temperature pure water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method, and more particularly to a method and apparatus for wet etching a silicon nitride film.

[0002]

2. Description of the Related Art Generally, LOCO is used for semiconductor device isolation.
The S step is used, and this step will be briefly described with reference to FIG. It should be noted that hatching (oblique lines) representing cross sections in the drawings is partially omitted for easy understanding. First, for example, an SiO ₂ film 43 is formed on a Si substrate 41, and a silicon nitride film (also referred to as a Si ₃ N ₄ film) 45, which is an oxidation-resistant film, is deposited thereon (FIG. 6).
(A)). Next, the Si in the region corresponding to the element isolation region 47 is
_The 3N ₄ film 45 and the SiO ₂ film 43 are removed (FIG. 6).
(B)). Next, the Si substrate 41 corresponding to the element isolation region 47 that is not covered with the silicon nitride film 45 is selectively oxidized thick to obtain a structure as shown in FIG. After forming the element isolation region 47, this S
Since the region covered with the i ₃ N ₄ film 45 becomes the transistor formation region 49, a silicon nitride film (Si ₃ N ₄ film)
45 is removed (etched) (FIG. 6D). In general, as the etching method, for example, dry etching using SF ₆ -based gas, and Reference 1: “Mechanism of silicon nitride film etching by hot phosphoric acid, 11th VLSI
Ultra Clean Technology Workshop, pp9
7-107 (1991) ". Wet etching with a high-temperature phosphoric acid solution has been used.

[0003]

However, in the above dry etching, a silicon nitride film and a base (generally, Si
The etching selectivity with respect to the substrate or the SiO ₂ film is small, and the base may be damaged by excessive etching. In wet etching with hot phosphoric acid, a means for shutting off the atmosphere is required to prevent environmental pollution due to phosphoric acid mist generated during etching. Further, in the process using phosphoric acid, the wafer is usually placed in a jig (carrier or the like) and processed.
Since the specific gravity value is close to i, Si in phosphoric acid solution
The wafer is lifted up, so that the position of the wafer in the carrier is changed, which may cause a transport trouble.

Accordingly, a silicon nitride film (S
i ₃ N ₄ film) In the removal of a large etching selectivity with the base, in the wet etching can be processed at the same degree of etch rate as when using hot phosphoric acid, and easily and accurately Si ₃ from wafer
N ₄ is an etching method and apparatus as removed has been desired.

[0005]

Therefore, the inventor of the present application states that although the etching rate of Document 1 is smaller than that of hot phosphoric acid, the silicon nitride film can be etched with pure water. Focusing on the description, various studies and experiments were conducted. When pure water was confined in a closed tank and the atmospheric pressure was adjusted appropriately, the temperature of the pure water was reduced to 30 ° (the conventional etching rate). 3nm) / mi
It has been discovered that it is possible to achieve temperatures that allow for a range of etch rates around n degrees.

Therefore, according to the wet etching method of the present invention, the Si ₃ N provided on the semiconductor wafer
_{(4) As} a means for removing the film, the wafer is immersed in high-temperature pure water at 130 to 170 ° C. When the temperature of pure water is 130 ° C. or higher, the etching process can be performed at a preferable etching rate. In order to perform the etching process within the withstand voltage limit of the etching apparatus, the processing is preferably performed at 170 ° C. or lower. Therefore, in high-temperature pure water at 130-170 ° C., the etching rate by conventional hot phosphoric acid is 30 ° (3 nm) / mi.
Etching can be performed in about n. Further, since pure water hardly etches the underlying Si substrate or SiO ₂ film, the etching selectivity is improved. Further, since the wafer does not float in pure water, the silicon nitride film can be accurately removed by etching, and there is no possibility of causing a transport trouble. Further, since the etching is performed only with pure water, there is no need to worry about environmental pollution.

Further, in order to keep the temperature of pure water at 130 to 170 ° C., the inside of the etching tank in which the wafer is immersed is set to a high pressure atmosphere (2600 to 6800 hPa). Considering the pressure resistance of the etching tank, the atmospheric pressure in the tank is set to 6800 hPa
It is desirable to make the following. Therefore, 2600-68
By setting the atmospheric pressure to 00 hPa, the temperature of pure water can be increased to 130 to 170 ° C., and the etching can be performed at a suitable etching rate.

The following two methods are mentioned as a method for setting the inside of the etching tank to a high-pressure atmosphere.

The inside of the etching tank is sealed, and a suitable inert gas is introduced into the tank.

[0010] The interior of the etching tank is sealed, pure water is boiled, and a high-pressure atmosphere is created by generated steam.

By using the above method, the atmospheric pressure in the tank can be easily increased. By using such a method, it is possible to simultaneously perform the process of increasing the atmospheric pressure in the tank and the process of increasing the temperature of pure water.

By setting the high-pressure atmosphere in this way, the boiling point of pure water can be easily raised to 100 ° C. or higher.

In the above etching, a non-volatile solute which does not affect the wafer and the subsequent semiconductor device manufacturing process and does not hinder the etching reaction is dissolved in pure water in advance. In addition, the boiling point of the etching solution can be easily raised without increasing the atmospheric pressure in the etching bath so much. Also, using this etching solution at the same atmospheric pressure as when etching with pure water only, it is possible to perform etching at a higher temperature than when only pure water is used.

An apparatus used for the above-mentioned etching treatment includes an etching tank for adding pure water, a water pipe for introducing pure water into the tank, a water valve for controlling the amount of water, and a valve for increasing the pressure in the tank to a high-pressure atmosphere. It is composed of a gas pipe for introducing an inert gas, a gas valve for controlling the inflow of the gas, and a heater for heating the pure water in the tank. The etching process can be performed easily and accurately by using water, and since the etching solution is pure water, there is no need to install a device for shutting off the atmosphere as a measure against environmental pollution. it can.

In the case of using steam obtained by boiling pure water to make the inside of the etching tank a high-pressure atmosphere, it is not necessary to introduce an inert gas. Therefore, the gas pipe and the gas valve are removed from the etching apparatus. It can be configured.

Further, if a drain valve and a drain pipe for draining water are provided in the above etching apparatus or an apparatus having a structure in which a gas pipe and a gas valve are removed from the etching apparatus, the drain is gradually drained after the etching is completed. As a result, the pressure inside the etching tank is reduced, and the remaining pure water starts to boil again. When drainage is completed, the tank is filled with high-temperature steam. Drying of the etched wafer can be performed using the high-temperature steam. Therefore, the etching and drying steps can be continuously performed in the same apparatus, and a drying apparatus is not required, so that the steps can be simplified.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the drawings are only schematically shown to the extent that the invention can be understood. Also, the specific materials and conditions set forth in the following description are merely preferred examples, and thus are not intended to be limiting in this description.

Further, the pure water described in this specification refers to ultrapure water usually used in a semiconductor device manufacturing process.

First Embodiment Normally, a silicon nitride film (Si ₃ N ₄ ) formed on the surface of a semiconductor wafer
The wet etching process using hot phosphoric acid used to remove the film is performed at a high temperature of 150 ° C. or more, and the etching rate is 30 ° (3 nm).
/ Min (Å / min represents the film thickness etched per minute). Therefore, in order to etch the Si ₃ N ₄ film with pure water, first, it is necessary to know the relationship between the temperature of pure water and the etching rate. FIG. 2 shows the extrapolated values of the actually measured data at a temperature of 100 ° C. or higher based on the pure water temperature dependence of the etching rate in the Si ₃ N ₄ film etching with pure water described in the above-mentioned Document 1. FIG. In FIG. 2, the horizontal axis represents temperature (1000 / T), and the vertical axis represents etching rate (Å / min), and the pure water temperature dependence of the Si ₃ N ₄ film etching rate is shown. According to FIG. 2, the etching rate of the Si ₃ N ₄ film by pure water is 30 ° (3 nm).
It can be understood that the temperature must be set to about 160 ° C. or more in order to make the temperature / min or more. Further, in order to raise the temperature of pure water to about 160 ° C. or higher, it is necessary to raise the boiling point.

Therefore, the boiling point of pure water and the external pressure (atmospheric pressure)
As a result of an experiment, the relationship as shown in FIG. 3 was obtained. In FIG. 3, the horizontal axis indicates the atmospheric pressure (external pressure) (hP
Taking a), the boiling point (° C.) of pure water is plotted on the vertical axis to show the dependency of the boiling point of pure water on the outside pressure. According to this, 160 ° C
It can be understood that in order to raise the temperature of pure water to about or more, the external pressure should be about 5900 hPa or more. The temperature range actually suitable for etching is about 130 ° C. to 170 ° C., and the optimum value is 160 ° C. The atmospheric pressure range corresponding to this temperature range is from 2600 hPa to 6
800 hPa. In addition, this 130 ° C to 170 ° C
The etching rate corresponding to FIG.
(0.8 nm) / min to 100 ° (10 nm) / min. Such a temperature range, an atmospheric pressure range, and an etching rate range are correlated with each other, and within these ranges, it is possible to shorten the etching processing time to increase the etching capability of the apparatus, and to reduce the atmospheric pressure. This is because consideration was given to keeping the pressure within the withstand pressure limit of the device.

The etching rate of the Si ₃ N ₄ film with pure water depends only on the temperature of pure water.

Next, an etching apparatus and an etching process according to the first embodiment will be described with reference to FIG.

The etching apparatus used in the present invention includes an etching tank 11 for performing an etching process, and a water pipe provided above the etching tank 11 for introducing pure water as an etching solution into the tank 11. 13 and
A water valve 15 attached to the water pipe 13 for controlling the amount of water from the water pipe 13, a gas pipe 17 provided above the etching tank 11 for introducing an inert gas into the tank 11, A gas valve 19 attached to the gas pipe 17 to control the amount of gas from the gas pipe 17
And a heater 21 mounted in the etching bath 11 for heating the pure water.

Next, the etching process will be described. An oxide film (SiO ₂ ) is formed on the surface of a silicon (Si) wafer, and a structure 23 in which a Si ₃ N ₄ film is formed on the SiO ₂ film (for example, as shown in FIG. 6C) An example of removing the Si ₃ N ₄ film by etching will be described. First, the water valve 15 is opened, and pure water 25 is introduced into the etching tank 11 through the water pipe 13. The above-mentioned structure 23 is immersed in pure water 25 of this etching tank 11. Next, the etching tank 11 is sealed, and, for example, an N ₂ gas 27 as an inert gas is opened through the gas valve 19 and introduced through the gas pipe 17. When the atmospheric pressure in the etching tank 11 becomes 5900 hPa or more, the gas valve 17 is closed. At this point, electricity is supplied to the heater 21 to heat the pure water 25. The temperature of pure water rises to 10
When the temperature reaches 0 ° C. or higher, etching of the Si ₃ N ₄ film starts. Under the atmospheric pressure of about 5900 hPa (it is considered that the atmospheric pressure is slightly increased due to water vapor volatilized by heating), the temperature of pure water 25 rises to about 160 ° C. (boiling point). If the boiling point is maintained while heating by the heater 21, the Si ₃ N ₄ film can be removed at an etching rate of about 30 ° (3 nm) / min. However, considering the pressure resistance of the apparatus, the atmospheric pressure cannot be increased so much, and the maximum pressure is preferably about 6800 hPa. Therefore, it is considered that the maximum temperature of the pure water temperature is about 170 ° C.

As a result, pure water is used as a base (Si substrate or S substrate).
Since almost no etching is performed on the (iO ₂ film), the etching selectivity is improved. Further, since only pure water is used as the etching solution, there is no concern about environmental pollution. Further, since there is a difference in specific gravity between Si and pure water, the wafer does not float in pure water. In addition, the etching with pure water can be performed at the same etching rate as the etching with hot phosphoric acid.

<Second Embodiment> Next, a second embodiment will be described with reference to FIG.

The etching apparatus has a configuration in which the gas pipe 17 and the gas valve 19 are removed from the configuration already described in the first embodiment.

In this example, after the same structure 23 as that described in the first embodiment is immersed in pure water 25, the etching tank 11 is closed, and the temperature of the pure water 25 is raised by the heater 21. To go. The atmospheric pressure in the etching tank 11 increases due to the water vapor generated when the pure water 25 boils, and accordingly, the boiling point of the pure water 25 also exceeds 100 ° C. When the atmospheric pressure in the etching tank becomes 5900 hPa or more, the temperature of the pure water 25 can be raised to 160 ° C. or more corresponding to the pressure, and if the temperature is maintained at 160 ° C. or more, the description has been given in the first embodiment. Similarly to the above, the Si ₃ N ₄ film can be etched at an etching rate of 30 ° (3 nm) / min or more according to the temperature at which the film is maintained. Even in this case, the maximum atmospheric pressure is preferably set to about 6800 hPa for the same reason as in the first embodiment.

<Third Embodiment> Further, etching is performed in high-temperature pure water, which has already been described in the first and second embodiments, without affecting a wafer or a subsequent semiconductor element manufacturing process. A non-volatile solute that does not hinder the reaction (HCl, HNO ₃ is used here) is dissolved.

This makes it possible to easily raise the boiling point of the etching solution without increasing the atmospheric pressure in the etching tank so much. Further, under the same pressure as the atmospheric pressure when etching with pure water only, etching at a higher temperature than in the case of pure water alone can be performed. Also in this case, it is desirable that the maximum atmospheric pressure be about 6800 hPa in consideration of the pressure resistance of the apparatus.

<Fourth Embodiment> Next, with reference to FIG. 5, a description will be given of a wafer drying process that can be performed continuously after etching is completed.

The apparatus is the same as the etching apparatus described in the first and second embodiments except that the apparatus for drainage and the etching tank 11 are used.
A drain pipe 29 and a drain valve 31 are newly provided below the etching tank 11 as decompression means.

After completion of the etching, the heater 21 is stopped, the drain valve 31 is opened, and the pure water 25 is gradually drained from the drain pipe 29.
The pure water 25 remaining in the tank 11 starts boiling again.
When the drainage is completed, the etching tank 11 is filled with high-temperature steam, and the high-temperature steam can be used to dry the etched wafer.

As described above, it is possible to continuously finish the wafer drying step in the same apparatus after the completion of the etching, so that the time and cost for using the drying apparatus can be reduced. If the gas pipe 17 and the gas valve 19 and the drain pipe 29 and the drain valve 31 in FIG. 5 are not used,
It is substantially equivalent to the device of FIG. If the drain pipe 29 and the drain valve 31 are not used in FIG. 5, the apparatus is substantially the same as the apparatus in FIG.

[0035]

As is clear from the above description, when the Si ₃ N ₄ film formed on the surface of the semiconductor wafer is removed, wet etching is performed in high-temperature pure water having a temperature range of 130 to 170 ° C. Since high-temperature pure water hardly etches the base made of Si or SiO ₂ , the etching selectivity of the Si ₃ N ₄ film is improved, and the Si ₃ N ₄ film is removed from the wafer surface without damaging the base. can do.

Further, since there is a difference in specific gravity between pure water and Si, the wafer does not float in the pure water, so that a transport trouble does not occur.

Further, since the etching is performed only with pure water, there is no need to worry about environmental pollution.

In addition, if a non-volatile solute that does not affect the wafer or the subsequent semiconductor device manufacturing process and does not hinder the etching reaction is dissolved in pure water used for etching in advance, the The boiling point of the etching solution can be easily raised without increasing the atmospheric pressure in the tank so much. Also, under the same pressure as the atmospheric pressure performed only with pure water, etching can be performed at a higher temperature than when only pure water is used.

In addition, the boiling point of pure water rises because the inside of the etching tank of the etching apparatus is closed and a high-pressure atmosphere is established. As a result, it is possible to perform etching at the same etching rate as wet etching with hot phosphoric acid. became.

Further, a drainage means is provided in the etching apparatus. As a result, when the drainage is performed after the etching, the pressure in the etching tank is reduced, and the pure water remaining in the tank starts to boil again. When the drainage is completed, the inside of the etching tank is filled with high-temperature steam, and the high-temperature steam can dry the etched wafer. As a result, a drying device becomes unnecessary, and time and cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an etching apparatus used for describing a first embodiment.

FIG. 2 is a characteristic curve diagram showing a relationship between a pure water temperature and a Si ₃ N ₄ etching rate.

FIG. 3 is a characteristic curve diagram showing a relationship between an external pressure and a boiling point of pure water.

FIG. 4 is a schematic sectional view of an etching apparatus used for describing a second embodiment.

FIG. 5 is a schematic sectional view of an etching apparatus used for describing a fourth embodiment;

FIG. 6 is a process diagram briefly showing an element isolation technique used for explaining a conventional technique.

[Explanation of symbols]

11: etching bath 13: water pipe 15: Water Valve 17: Gas pipe 19: gas valve 21: heater 23: structure 25: Pure water 27: Gas 29: drainage pipe 31: drainage valve 41: Si substrate 43: SiO ₂ film 45: Si ₃ N ₄ film 47: element isolation region 49: transistor formation region

Claims (8)

[Claims] 1. A structure in which a silicon nitride film is provided on a surface of a semiconductor wafer is immersed in pure water in a closed etching tank, and the pure water is heated to a temperature within a temperature range of 130 to 170 ° C. And etching the silicon nitride film by wet etching. 2. The method for etching a silicon nitride film according to claim 1, wherein the heating of the pure water is performed in a high-pressure atmosphere having a pressure in a range of 2600-6800 (hPa). Etching method. 3. The method for etching a silicon nitride film according to claim 2, wherein said high-pressure atmosphere is an atmosphere of water vapor evaporated from said pure water. 4. The method for etching a silicon nitride film according to claim 1, wherein after the etching of the silicon nitride film is completed, the wafer is continuously dried in high-temperature steam in the same etching bath. Method for etching a silicon nitride film. 5. The method for etching a silicon nitride film according to claim 1, wherein the boiling point of the pure water is increased without affecting the wafer or a subsequent semiconductor element manufacturing process. A method for etching a silicon nitride film, wherein a non-volatile solute that does not hinder the etching reaction with pure water is dissolved in pure water in advance. 6. An etching apparatus for a silicon nitride film, comprising: an etching tank for supplying an etching solution; a water pipe provided above the etching tank for introducing pure water as an etching solution into the tank; and an amount of water introduced from the water pipe. A water valve attached to the water pipe to be controlled; a gas pipe provided at the upper portion of the etching tank, for introducing an inert gas into the tank; and a gas valve attached to the gas pipe for controlling an amount of gas introduced from the gas pipe. And a heating valve mounted in the etching bath. 7. An etching apparatus for a silicon nitride film, comprising: an etching tank for supplying an etching solution; a water pipe provided above the etching tank for introducing pure water as an etching solution into the tank; and an amount of water introduced from the water pipe. A wet etching apparatus, comprising: a water valve to be controlled attached to the water pipe; and a heater for heating attached to the etching tank. 8. An etching apparatus for a silicon nitride film, comprising: an etching tank for supplying an etching solution; a water pipe provided above the etching tank for introducing pure water as an etching solution into the tank; and an amount of water introduced from the water pipe. A water valve attached to the water pipe to be controlled; a gas pipe provided at an upper part of the etching tank, for introducing an inert gas into the tank; and a gas valve attached to the gas pipe for controlling an amount of gas introduced from the gas pipe. A gas valve, a heater for heating mounted in the etching tank, a drain pipe provided at the lower part of the etching tank as a drain and a pressure reducing means, and a drain pipe for controlling an amount of drain water from the drain pipe. And a drain valve.