JPH0541367A - Selective removal method of silicon nitride film with reference to silicon oxide film - Google Patents

Abstract

PURPOSE:To selectively remove a silicon nitride film from the surface of a silicon wafer in a sufficient selective ratio which is practically suitable for a silicon oxide film. CONSTITUTION:The vapor of nitric acid 40 is added to the vapor of hydrofluoric acid 32; their mixed gas is supplied to the surface of a silicon wafer W on which a silicon oxide film and a silicon nitride film have been formed. At this time, the surface temperature of the wafer is kept higher than the temperature of the mixed gas by within a prescribed range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface of a silicon wafer, a surface of a polysilicon film, a surface of an amorphous silicon film (hereinafter, these surfaces are collectively referred to as "silicon layer surface").
The present invention relates to a method for selectively removing an insulating film formed on a silicon oxide film, particularly to a method for selectively removing a silicon nitride film (SiNx film) from a silicon layer surface with respect to a silicon oxide film. Is, for example, LOCOS (Localized Oxidation of Silico) of dynamic memory.
n) Used in the manufacturing process of semiconductor devices, such as the removal of the silicon nitride film, which is the final step in the process.

[0002]

2. Description of the Related Art A silicon nitride film is formed on a silicon wafer in a dynamic memory LOCOS process. Here, the LOCOS process is a process of forming a boron diffusion layer for a channel stopper and a thick silicon oxide film in an element isolation region by selective oxidation using a silicon nitride film. In this LOCOS process,
First, after forming a thin silicon oxide film on the surface of a silicon wafer, a silicon nitride film is grown on the surface. A thermal decomposition reaction of ammonia (NH ₃ ) and monosilane (SiH ₄ ) is used for growing the silicon nitride film. next,
A photoresist film pattern is formed by lithography so as to cover a portion of the nitride film where the nitride film should be left, and a carbon tetrafluoride (CF ₄ ) gas is used to etch the nitride film by a plasma etching apparatus. Perform etching. Then, boron of the channel stopper is ion-implanted into the element isolation region using the resist film and the nitride film as a mask. After that, after removing the resist film from the nitride film, a silicon thermal oxide film is selectively formed (LOCOS oxidation) using the nitride film as a mask. Then, after the thin oxide film formed into a nitride film during the LOCOS oxidation is removed by wet etching, the silicon nitride film is selectively removed from the silicon wafer with respect to the field oxide film, and a series of LOCOS processes is performed. finish.

In the above LOCOS process, the selective removal of the silicon nitride film, which is performed as the final step, is conventionally disclosed in, for example, JP-A-2-96334 and JP-A-61-168925. To
A high-concentration (about 85%) phosphoric acid aqueous solution is used as an etching solution, and the phosphoric acid aqueous solution stored in the etching tank is heated to a high temperature of 140 to 180 ° C. It was carried out in a batch process by a wet etching method of immersing the.

[0004]

In the conventional method of selectively removing a silicon nitride film by wet etching, an etching solution obtained by heating a high-concentration phosphoric acid aqueous solution to a high temperature near the boiling point as described above is used. It is extremely dangerous to handle, and requires a circulation filtration system, etc., which complicates the configuration of the equipment.Furthermore, components such as pumps and filters, and piping are resistant to corrosion and durability such as fluororesin and polypropylene. Even if a material excellent in heat resistance is used, the pump and the like will deteriorate in a relatively short time due to the high concentration and high temperature acid. In addition, since the etching process is performed while maintaining the temperature of the phosphoric acid aqueous solution near the boiling point, the water content of the phosphoric acid aqueous solution evaporates and its concentration increases with the passage of time. It is necessary to replenish the amount of pure water according to the amount of evaporated water. However, if pure water is dropped into a high-concentration aqueous solution of phosphoric acid, the water will locally boil and it is dangerous, so it is necessary to devise various methods for supplying pure water. It is troublesome. Further, it is difficult to control the amount of replenishing water, and there is a problem in controllability of the etching process. Furthermore, the wet etching method also consumes a large amount of etching liquid.

The present invention has been made in view of the various problems described above when the selective removal of the silicon nitride film is performed by the conventional wet etching method. It is a technical object to newly provide a dry etching method capable of selectively removing a nitride film from a silicon layer surface with a sufficient selection ratio suitable for practical use with respect to a silicon oxide film.

[0006]

According to the present invention, vapor or gas of an oxidant substance is added to a gas containing hydrogen fluoride,
The mixed gas to which the vapor or gas of the oxidant substance is added is supplied to the surface of the substrate on which the two kinds of insulating films of the silicon oxide film and the silicon nitride film are formed, and at that time, the mixed gas. The gist of the configuration is that the surface temperature of the substrate is kept relatively higher than the above temperature in a predetermined range.

As the oxidant substance, nitric acid (HN
O ₃ ), ozone (O ₃ ), hydrogen peroxide (H ₂ O ₂ ), hypochlorous acid (HClO), chloric acid (HClO ₃ ), nitrous acid (H
NO ₂ ), oxygen (O ₂ ), sulfuric acid (H ₂ SO ₄ ), chlorine (Cl
₂ ), at least one selected from the group consisting of bromine (Br ₂ ) and the like is used. For example, when the silicon oxide film is a thermal oxide film and nitric acid is used among the above-mentioned oxidizer substances, the above-mentioned predetermined range may be set to a range of 12 ° C or higher and 120 ° C or lower. Further, the treatment may be performed while irradiating the surface of the substrate with ultraviolet rays.

When the silicon nitride film is selectively removed from the silicon layer surface with respect to the silicon oxide film by the method of the present invention configured as described above, the surface temperature of the substrate is a gas containing hydrogen fluoride. Since the silicon nitride film is kept at a temperature higher than a predetermined temperature in a predetermined range, the etching rate of the silicon nitride film becomes higher than that of the silicon oxide film, and the silicon nitride film is selective to the silicon oxide film from the surface of the silicon layer. Will be removed.
Further, in the method of the present invention, the etching selectivity of the silicon nitride film with respect to the silicon oxide film is improved by adding an oxidizer substance such as nitric acid, ozone and hydrogen peroxide to the gas. This is because when an oxidizer substance is added to the gas, the silicon oxide film is originally an oxide and is hardly affected by the addition of the oxidizer, and the silicon oxide film is simply etched according to the temperature difference between the gas and the substrate surface. It is considered that, while the rate only changes, in the silicon nitride film, the oxidation is promoted by the addition of the oxidizing agent, and is easily decomposed (etched) by hydrogen fluoride.

Here, for example, when the silicon oxide film is a thermal oxide film and nitric acid is used as the oxidant substance, if the difference between the mixed gas and the surface temperature of the substrate is less than 12 ° C. Although the etching rate of the oxide film is higher than that of the silicon nitride film, the magnitude relationship between the etching rates of both films is reversed when the temperature difference becomes 12 ° C. or more. When the temperature difference is further increased and the temperature difference becomes larger than 120 ° C., the magnitude relationship of the etching rates of both films is reversed again, and the etching rate of the silicon thermal oxide film becomes larger than the etching rate of the silicon nitride film. .. Therefore, if the surface temperature of the substrate is kept high within the range of 12 ° C. or higher and 120 ° C. or lower, the silicon nitride film is selected from the silicon layer surface with respect to the silicon thermal oxide film. Will be removed. The phenomenon of reversal and re-reversal of the etching rate relationship is thought to be closely related to the adsorption of vapor on the substrate surface, but the clear reason for this is unknown.

Further, when the surface of the substrate is irradiated with ultraviolet rays during the etching process, the selectivity in etching is further improved.

[0011]

The preferred embodiments of the present invention will be described below.

FIG. 1 is a schematic block diagram showing an example of an apparatus for carrying out the method according to the present invention. In FIG. 1, the silicon wafer W to be etched is held on the upper surface of the hot plate 10 by vacuum suction means or the like. The hot plate 10 is internally provided with a heater (not shown), is rotatably arranged around the vertical axis, and is integrally connected to the spindle 12.
It is configured to be rotationally driven in the horizontal plane by the electric motor 14 via the. The heater installed in the hot plate 10 is controlled by a temperature control means (not shown),
The temperature of the silicon wafer W held on the hot plate 10 is kept at a predetermined temperature.

A vapor supply section 16 constituting a mixed gas supply means having a diffusion plate 18 is provided directly above the hot plate 10 so as to face the silicon wafer W held by the hot plate 10. In the vapor supply unit 16, a plurality of ultraviolet irradiation lamps 20 for irradiating the surface of the silicon wafer W with ultraviolet rays are arranged in parallel with the silicon wafer W. As will be described later, when the hydrofluoric acid vapor is supplied from the mixed vapor supply unit 16 to the surface of the ultraviolet irradiation lamp 20, sapphire glass is used to prevent corrosion. The ultraviolet irradiation lamp 20 does not necessarily have to be provided.

The vapor supply unit 16 is connected to a hydrofluoric acid (an aqueous solution of liquid hydrogen fluoride, hereinafter referred to as "hydrofluoric acid") vapor supply pipe 22 and a nitric acid vapor supply pipe 24, respectively. The steam supply pipes 22 and 24 join together to form a single mixed steam pipe 26, which is connected to the steam supply unit 16. A valve 28 is provided in the hydrofluoric acid vapor supply pipeline 22, and the proximal end side of the hydrofluoric acid vapor supply pipeline 22 communicates with the hydrofluoric acid tank 30. Hydrofluoric acid is appropriately supplied into the hydrofluoric acid tank 30 from a hydrofluoric acid supply source (not shown) through a supply pipe, and a predetermined amount of hydrofluoric acid 32 is constantly stored in the hydrofluoric acid tank 30. The hydrofluoric acid tank 30 is provided with a supply pipe 34 which is connected to a nitrogen (N ₂ ) gas supply source (not shown) so as to be connected to the N ₂
By supplying N ₂ gas into the hydrofluoric acid tank 30 from the gas supply source through the supply pipeline 34 and opening the valve 28, the hydrofluoric acid vapor is supplied through the hydrofluoric acid vapor supply pipeline 22 to the vapor supply unit 16
It is configured to be supplied to. Further, a valve 36 is provided in the nitric acid vapor supply pipeline 24, and the nitric acid vapor supply pipeline is provided.
The proximal end side of 24 communicates with the nitric acid tank 38. Nitric acid tank
A predetermined amount of nitric acid 40 is stored in the 38, and nitric acid is appropriately replenished into the nitric acid tank 38 from a nitric acid supply source (not shown) through a supply pipe. Also nitric acid tank
A supply pipe 42, which is connected to an N ₂ gas supply source (not shown), is arranged in the 38, and N ₂ gas is supplied from the N ₂ gas supply source into the nitric acid tank 38 through the supply pipe 42. By opening the valve 36, nitric acid vapor is supplied to the vapor supply unit 16 through the nitric acid vapor supply conduit 24.

The above gas supply unit 44 surrounded by a broken line
Is adjusted to a predetermined temperature by a temperature controller and heating means (not shown), and the silicon wafer W is supplied from the vapor supply unit 16.
The temperature of the mixed vapor containing hydrofluoric acid and nitric acid supplied toward the surface of the is maintained at a predetermined temperature.

Using a device having a structure as shown in FIG.
The temperature of the silicon wafer W is 12 higher than the temperature of the mixed vapor supplied from the vapor supply unit 16 to the surface of the silicon wafer W.
The temperature is adjusted so that the temperature is maintained at a high temperature of 120 ° C. to 120 ° C., preferably 20 ° C. to 100 ° C., and while the silicon wafer W is rotated, a mixed vapor containing hydrofluoric acid and nitric acid is supplied to the surface of the silicon wafer W to perform etching treatment. ..

Further, instead of adding nitric acid vapor in hydrofluoric acid vapor as oxidizing agent, blowing O ₃ gas is hydrofluoric acid to the storage hydrofluoric acid tank, O ₃ from hydrofluoric acid tank to the steam supply unit The hydrofluoric acid vapor mixed with gas may be supplied. Further, nitrogen gas is blown into the mixed liquid tank in which hydrofluoric acid and H ₂ O ₂ are mixed and stored, and the mixed vapor of HF and H ₂ O ₂ is supplied from the mixed liquid tank to the vapor supply section. Good. Other oxidant substances added to the hydrofluoric acid vapor include HClO, HClO ₃ , and HN.
O ₂ , O ₂ , H ₂ SO ₄ , Cl ₂ , Br ₂ or the like can be used.

Next, examples of experiments conducted in connection with the method of the present invention will be described.

First, the schematic construction of the experimental apparatus used in this experiment will be described with reference to FIG. This experimental device
An air heater 58, a wafer heating cover 60, and a mixed liquid serving as a vapor source are provided in a draft chamber 50 having a work opening 54 provided with an opening / closing shutter 52 and an exhaust port 56 connected to a forced exhaust fan (not shown). A cylindrical container 62 accommodating 64 is internally provided. Then, the silicon wafer W supported horizontally by the wafer support member 66 is arranged so as to face the upper end opening surface of the cylindrical container 62 and directly above it. On the surface of the silicon wafer W, C
An A (chromel-alumel) thermocouple 68 is attached in a contact state, the thermocouple 68 monitors the surface temperature of the silicon wafer W, and the temperature controller 70 controls the air heater 58 on the basis of the detected value. By applying hot air to the surface of the wafer W, the surface temperature of the silicon wafer W is maintained at a predetermined value. Further, the inside of the draft chamber 50 is kept at room temperature (22 ° C.), so that the temperatures of the mixed liquid 64 and the mixed vapor V in the cylindrical container 62 are also kept at room temperature.

In the experiment, a silicon thermal oxide film having a film thickness of 5,000 Å was deposited on a silicon wafer having a diameter of 6 inches, and a film having a thickness of 1,500 Å was formed on a silicon wafer having a diameter of 5 inches. Each of the samples coated with a thick silicon nitride film was used as a sample body. Then, the silicon wafer W was horizontally installed right above the cylindrical container 62 with the side on which the silicon thermal oxide film or the silicon nitride film was formed facing downward. As the vapor source, a commercially available hydrofluoric acid 50% liquid (manufactured by Daikin Industries, Ltd.), the hydrofluoric acid being HF (50%): H ₂ O
16.7% hydrofluoric acid diluted at a ratio of 1: 2, and hydrofluoric acid (50%) and nitric acid (60%) 2: 1,
Mixtures with a volume ratio of 1: 2 and 1: 5 were used. In addition, the film thickness of the insulating film after the etching treatment is
Lambda Ace (optical interference type film thickness meter using a microspectroscope; manufactured by Dainippon Screen Mfg. Co., Ltd.) is used for etching amount of 50 Å or more, and ellipsometer ( A film thickness measuring device based on ellipsometry; manufactured by Gardner) was used.

Prior to the explanation of the experimental results by the method according to the present invention, the silicon nitride film (SiNx) and the silicon thermal oxide film (th-SiO ₂ ) were each etched by hydrofluoric acid vapor to which nitric acid was not added. Etching rate and temperature of mixed vapor (t ₁ )
A temperature difference between the temperature (t ₂₎ of the silicon wafer surface (t ₁ <
t ₂ ) (hereinafter, simply referred to as “temperature difference”) is shown in FIG.
It was shown to. In this experiment, hydrofluoric acid having an azeotropic composition (39.6%) was used as a vapor source. As shown in FIG. 3, when the temperature difference is small, the etching rate of the silicon nitride film is significantly smaller than that of the silicon thermal oxide film, but when the temperature difference is about 12 ° C. or more, the silicon nitride film and the silicon thermal oxide film are separated from each other. The etching rate reverses at, and the etching rate of the silicon nitride film becomes higher than that of the silicon thermal oxide film. From this result, the possibility of selective etching of the silicon nitride film with respect to the silicon thermal oxide film was found, and the selective etching of the silicon nitride film was put into practice by taking appropriate measures to increase the etching rate difference between the two insulating films. It can be seen that it can be suitable for.

FIGS. 4 and 5 show the relationship between the temperature difference and various etching rates of the silicon nitride film (Si ₃ N ₄ ) and the silicon thermal oxide film (th-SiO ₂ ) when the vapor source is variously changed. It is a diagram showing. From the experimental results shown in FIGS. 4 and 5, the etching rate of the silicon nitride film sharply decreases as the temperature difference increases unless nitric acid (oxidizer) is added to hydrofluoric acid (see FIG. 5). It is understood that, when nitric acid is added to hydrofluoric acid, the etching rate of the silicon nitride film does not decrease so rapidly even if the temperature difference increases (see FIG. 4). On the other hand, it can be seen that the etching rate of the silicon thermal oxide film sharply decreases with increasing temperature difference regardless of whether nitric acid is added to hydrofluoric acid (see FIGS. 4 and 5). Considering these results together, it is understood that the addition of nitric acid to hydrofluoric acid improves the etching selectivity of the silicon nitride film with respect to the silicon thermal oxide film. Further, the selectivity increases as the temperature difference increases, and when the temperature difference is 30 ° C., the selection ratio (Si ₃ N ₄ : th-SiO ₂ ) is 6.5 to 7.3, but the temperature difference is 40. Selectivity of 20.0-37.0 at ℃
When the temperature difference becomes 45 ° C., the selectivity becomes further 47.
It becomes as large as 5 to 68.0 (see FIG. 4). Further, the selection ratio also changes depending on the mixing ratio of the hydrofluoric acid (HF / H ₂ O) vapor and the nitric acid (HNO ₃ / H ₂ O) vapor (see FIG. 4). In the conventional wet selective etching method, for example, a 4-inch wafer on which an oxide film having a film thickness of 6,076 Å and a nitride film having a film thickness of 1,400 Å are formed is used as a sample, and is heated to 180 ° C. When an acid (H ₃ PO ₄ ) is used, a silicon nitride film (SiNx) and an oxide film (Si
The etching rates of O ₂ ) were about 93 Å / min and about 4 Å / min, respectively, and the selection ratio thereof was about 23: 1. As described above, when the experimental apparatus shown in FIG. 2 is used, it is recognized that in the present invention, a considerably large selection ratio can be obtained according to the set temperature difference as compared with the conventional wet selective etching method. .. When the vapor source is a 50% hydrofluoric acid liquid, the selectivity ratio at a temperature difference of 30 ° C. is 2.0, the selectivity ratio at a temperature difference of 40 ° C. is 5.8, and the hydrofluoric acid 16% When the 0.7% liquid is used as the vapor source, there is almost no selectivity (see FIG. 5).

Further, the same experiment as the above-mentioned experiment conducted by using the experimental apparatus shown in FIG. 2 was conducted by using a prototype apparatus having the same constitution as the apparatus whose schematic constitution is shown in FIG. Will be described.

In this experiment, hydrofluoric acid having an azeotropic composition (39.6%), hydrofluoric acid (50%) and nitric acid (6%) were used as vapor sources.
0%) and a mixture of 1: 1 by volume, and a mixture of hydrofluoric acid (50%) and nitric acid (69%) by a volume of 2: 1. Use 90 each
0 cc of liquid was supplied and stored in the steam generation tank. In the apparatus shown in FIG. 1, in order to generate mixed vapor of hydrofluoric acid and nitric acid, hydrofluoric acid vapor and nitric acid vapor are separately generated and then both vapors are mixed. , In this experiment, a mixed solution of hydrofluoric acid and nitric acid was stored in a tank, and a carrier gas (N ₂ gas) was supplied into the tank to directly generate a mixed vapor of hydrofluoric acid and nitric acid. I have to. The temperature of each liquid is kept constant at 40 ° C., and N as carrier gas or purging gas is used.
The temperature of the _two gases was also fixed at 40 ° C. On the other hand, the temperature of the hot plate was changed in the range of room temperature to 150 ° C. The supply flow rate of the carrier gas (N ₂ gas) was 20 LM, and the exhaust pressure was -40 mmH ₂ O.
A lambda ace and an ellipsometer were used to measure the thickness of the insulating film after the etching process, as in the above experiment. The measurement points were 17 points on the surface of a silicon wafer having a diameter of 5 inches when using Lambda Ace and 21 points when using an ellipsometer.

The results of the experiment are shown in FIGS. Figure 6
Shows the case where hydrofluoric acid having an azeotropic composition is used as a vapor source.
When using a 1: 1 mixture of hydrofluoric acid and nitric acid,
Shows the respective results when a 2: 1 mixed solution of hydrofluoric acid and nitric acid was used. Each of these figures shows a silicon nitride film (S
FIG. 6 is a diagram showing a relationship between the hot plate temperature when the i ₃ N ₄ ) and the silicon thermal oxide film (th-SiO ₂ ) are vapor-phase etched, that is, the temperature of the silicon wafer and the etching rate.

From the experimental results shown in FIGS. 6 to 8, the magnitude relation between the etching rate of the silicon nitride film and the etching rate of the silicon thermal oxide film is that the temperature of the silicon wafer is near the temperature of the steam (40 ° C.). It turns out that the magnitude relationship of the etching rates is again reversed between 90 ° C. and 150 ° C. although it varies depending on the vapor source. Therefore, if the temperature range of the silicon wafer is almost equal to that of the vapor to the re-inversion point existing at 90 ° C. to 150 ° C., which is determined by the composition of the vapor source, the silicon thermal oxidation is performed. It has been found that selective etching of the silicon nitride film with respect to the film is possible. In that case, the selection ratio (Si ₃ N ₄ / SiO ₂ )
Was about 20 at maximum.

Next, using a prototype device having the same structure as the device shown in FIG. 1, the hydrofluoric acid vapor and the nitric acid vapor were separately generated, and then both vapors were mixed, and the mixed vapor was converted into silicon. The experimental results when the method of etching by supplying to the surface of the wafer is used will be described.

In this experiment, hydrofluoric acid having an azeotropic composition (39.6%) was used as a hydrofluoric acid vapor source, and the hydrofluoric acid was placed in a tank and the temperature was adjusted to 40 ° C. Separately from the hydrofluoric acid vapor source, nitric acid with an azeotropic composition (69%) was placed in a Teflon tank, and the tank was immersed in a constant temperature bath and the temperature was adjusted to 40 ° C. And
Then, each vapor generated separately from each vapor source is converted into a carrier gas (N ₂
Gas), and both vapors were mixed and fed into the reaction chamber. The supply flow rate of the carrier gas (N ₂ gas) at that time is 10 LM, respectively.
And the exhaust flow rate of the reaction chamber was 0.35 m ³ / min. Then, the temperature of the hot plate is changed in the range of room temperature to 150 ° C., and the silicon nitride film (Si ₃ N ₄ ) and the silicon thermal oxide film (th-Si) at the respective temperatures are changed.
Each etching rate of O ₂ ) was measured. Lambda Ace was used to measure the thickness of each insulating film. The results of this experiment are shown in FIG.

Comparing the experimental result shown in FIG. 9 with the experimental result shown in FIG. 7 or FIG. 8, when the hydrofluoric acid vapor and the nitric acid vapor are separately generated and controlled, Although the etching rate was slightly lower than that when a mixed solution of hydrofluoric acid and nitric acid was used as the source, the characteristics of the change in etching rate with respect to the temperature change of the silicon wafer were not changed.

It should be noted that, in comparison with the experimental result of the present invention conducted using the experimental apparatus shown in FIG. 2, the selection of the silicon nitride film with respect to the silicon thermal oxide film in the experimental result conducted using the prototype shown in FIG. The etching ratio is considerably small. (1) In the former case, the mixed vapor V is directly supplied to the silicon wafer W from the cylindrical container 62, whereas in the latter case,
Since the mixed vapor is diluted by using N ₂ gas as the carrier gas, (2) in the former, the silicon wafer W is processed in a stationary state, whereas in the latter, the silicon wafer W is rotated. Is processed,
(3) In the former case, the mixed vapor V generated from the mixed liquid 64 contained in the cylindrical container 62 comes into contact with the silicon wafer positioned directly above with the surface to be treated facing downward, whereas in the latter case, it is generated. Since the mixed vapor is brought into contact with the silicon wafer W located directly under the vapor supply section 16 with the surface to be processed facing upward through the vapor supply section 16, it is possible to consider such as, but the clear cause is unknown. ..

[0031] Alternatively, it is acceptable to fix the temperature of the hot plate to 80 ° C., and a carrier gas (N ₂ gas) flow rate of the carrier gas (N ₂ gas) flow rate and the hydrofluoric acid vapor of nitric acid vapor, and the sum is 20LM The etching rate changes when the ratio of nitric acid vapor in the mixed vapor supplied to the surface of the silicon wafer is changed, and the selection ratio of the silicon nitride film to the silicon thermal oxide film (S
The change in iNx / SiO ₂ ) was investigated. The results are shown in FIGS. 10 and 11.

From the experimental results shown in FIGS. 10 and 11,
It is understood that the etching rate and the selection ratio change depending on the mixing ratio of nitric acid vapor in the mixed vapor of hydrofluoric acid vapor and nitric acid vapor. Then, the etching rate becomes maximum when the ratio of nitric acid vapor is 50%, and the selection ratio is maximum when the ratio of nitric acid vapor is approximately 75%.
The selection ratio at that time was 20.6.

From the above, nitric acid was added to the hydrofluoric acid vapor source, and the temperature difference between the mixed vapor and the silicon wafer surface was reduced to 1
It was concluded that the temperature of 2 ° C. or higher, preferably 20 ° C. or higher, and 120 ° C. or lower, preferably 100 ° C. or lower enables selective etching of the silicon nitride film with respect to the silicon thermal oxide film.

In the above embodiment, the case where the hydrofluoric acid vapor (HF, H ₂ O) and the vapor or gas of the oxidant substance are used as the mixed gas used for the selective removal has been described.
The present invention is not limited to this, and a mixed gas of anhydrous hydrogen fluoride (HF) gas and a vapor or gas of an oxidant substance may be used.

Furthermore, in the above embodiment, the LOCO is mainly used.
Silicon nitride film (SiN
Although the selective removal of x) for the thermal oxide film (th-SiO ₂ ) has been described, it goes without saying that the application during this process is not limited. The film that is not selectively removed is not limited to the thermal oxide film (th-SiO ₂ ), but may be an oxide film such as a native oxide film (Native Oxide) or a non-doped CVD oxide film (CVD-SiO ₂ ). ..

Further, in the above example, the case where the temperature of the treatment mixed gas is kept constant and the surface temperature of the substrate is kept high in a predetermined range has been described, but the present invention is not limited to this. In short, the latter temperature may be kept relatively higher than the former temperature in a predetermined range. Therefore, the surface temperature of the substrate may be kept constant and the temperature of the mixed gas may be kept low in the predetermined range.

[0037]

Since the present invention is constructed and operates as described above, when the method of the present invention is used to selectively remove the silicon nitride film with respect to the silicon oxide film, the conventional wet etching is performed. Various problems in the case of using the law can be solved. That is, (1) since a high-concentration and high-temperature phosphoric acid aqueous solution is not used, work safety is improved, a circulation filtration system or the like is unnecessary, and pure water is added to the high-concentration phosphoric acid aqueous solution. Since it is not necessary to devise a means for replenishing, the structure of the apparatus for carrying out the method of the present invention is relatively simple. (2) The life of the apparatus is longer than that of the wet etching method in which a high concentration and high temperature phosphoric acid aqueous solution is pumped or circulated, and only the temperature difference between the mixed gas and the substrate surface is appropriate. Therefore, the controllability is improved as compared with the wet etching method. Further, (3) the chemical solution consumption for etching is smaller than that of the wet etching method. The above-mentioned various advantages associated with the dry etching process can be greatly utilized in the method according to the present invention, for example, for removing the silicon nitride film as the final step of the LOCOS process of the dynamic memory. Is.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a schematic configuration of an apparatus used for carrying out a method for selectively removing a silicon nitride film from a silicon thermal oxide film according to the present invention.

FIG. 2 is a vertical cross-sectional view showing a schematic configuration of an experimental apparatus used in an experiment conducted on the method according to the present invention.

FIG. 3 is a diagram showing a relationship between a temperature difference between a mixed vapor containing hydrofluoric acid and a surface of a silicon wafer and respective etching rates of a silicon nitride film and a silicon thermal oxide film.

[Fig. 4]

5A and 5B are diagrams showing the results of an experiment performed using the experimental apparatus shown in FIG. 2, respectively.

[Figure 6]

8A and 8B are diagrams showing the results of an experiment conducted using the prototype device whose schematic configuration is shown in FIG.

[Fig. 9]

FIG. 11 is a diagram showing the results of an experiment conducted using the prototype device whose schematic configuration is shown in FIG. 1.

[Explanation of symbols]

 W Silicon wafer 10 Hot plate 16 Steam supply section 20 Ultraviolet irradiation lamp 22 Hydrofluoric acid vapor supply line 24 Nitric acid vapor supply line 30 Hydrofluoric acid tank 32 Hydrofluoric acid 38 Nitric acid tank 40 Nitric acid

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H01L 27/108

Claims (4)

[Claims] 1. A silicon oxide film and a silicon nitride film
A silicon oxide film, in which a mixed gas containing at least hydrogen fluoride is supplied to the surface of a substrate on which various types of insulating films are formed so that the silicon nitride film is selectively removed from the substrate surface with respect to the silicon oxide film. In the method for selectively removing a silicon nitride film with respect to, the vapor or gas of an oxidant substance is added to the gas, and the surface temperature of the substrate is higher than the temperature of the mixed gas to which the vapor or gas of the oxidant substance is added. A method for selectively removing a silicon nitride film with respect to a silicon oxide film, characterized in that it is kept relatively high in a predetermined range. 2. The nitric acid, ozone, hydrogen peroxide, hypochlorous acid, chloric acid, nitrous acid, oxygen, sulfuric acid as the oxidizer substance,
2. The method for selectively removing a silicon nitride film from a silicon oxide film according to claim 1, wherein at least one selected from the group consisting of chlorine and bromine is selected. 3. The silicon oxide film is a thermal oxide film,
Nitric acid is used as the oxidizer substance, and the predetermined range is 12
The method for selectively removing a silicon nitride film with respect to a silicon oxide film according to claim 1, wherein the temperature is in the range of ℃ to 120 ℃. 4. The mixed gas is supplied while irradiating the surface of the substrate with ultraviolet rays.
5. The method for selectively removing a silicon nitride film with respect to a silicon oxide film according to any one of 1.