JPH1098032A - Formation of thin film and thin film forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deposition rate of a silicon nitride film or a silicon dioxide film from being reduced and to enable forming a thin film of highly even film thickness on a large-area substrate by a method, wherein an optical pumping of gas molecules, which do not generate a deposition of the thin film by a decomposition of the gas molecules themselves, is conducted in a gas-introducing device which is different from a reaction tank and the silicon nitride film or the silicon dioxide film is deposited, without putting directly light in the substrate and the reaction tank. SOLUTION: A GaAs substrate 3 is charged on a sample stage 2 in a reaction chamber 1, the substrate 3 is heated by a heater, a valve 4 is opened, NH3 gas is introduced into a gas cell 6, an AsF excimer laser beam is focused and introduced in the gas cell 6 by a lens 9 via an optical window 8, in such a way as to have the focal point of the laser beam in the cell 6 and the excited HN3 gas is put in the chamber 1 from the cell 6 through an orifice 7. A valve 10 is opened, SiH4 gas is put in the chamber 1 through a nozzle 11, and a deposition of a silicon nitride film is started. As a result, the growth rate of the silicon nitride film is held stably, extending over a long period of time, and the formation of a thin film, which has a high uniformity in film thickness, is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for forming a thin film based on a chemical vapor deposition method using photoexcitation, and more particularly to a method for forming a thin film having a high throughput and a uniform film thickness at a low substrate temperature. The present invention relates to a forming method and a forming apparatus.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor device, a process of forming a dielectric thin film (silicon nitride, silicon dioxide, etc.)
Conventionally, a chemical vapor deposition (CVD) method has been mainly used.
In the CVD method, gas molecules supplied as a raw material are decomposed or excited by heat or plasma and used for thin film deposition. When a dielectric thin film is formed by thermal decomposition, the film is formed at a substrate temperature of 400 ° C. or higher. In the method using plasma excitation, the film is formed at a substrate temperature of 300 ° C. or higher.

Recently, a photo-excited CVD method has been used as an alternative to the above-mentioned heat or plasma excitation. The raw material gas molecules (ammonia, nitrous oxide, etc.) introduced into the reaction tank are excited by light (wavelength of 300 nm or less) and supplied to a film forming reaction, so that a thin film can be deposited at a substrate temperature of 300 ° C. or more.

[0004]

Among the above-mentioned prior arts, the CVD method using thermal decomposition requires a high substrate temperature of 400 ° C. or more, so that a dielectric thin film is formed after the electrode metal forming step of a semiconductor device. In addition, electrical characteristics are significantly deteriorated due to a thermal reaction between the electrode metal and the semiconductor substrate. In the case of the plasma-excited CVD method, which can form a film at a low temperature, it is possible to suppress the deterioration of the electrodes. Deteriorates.

[0005] The photo-excited CVD method allows a film to be formed at a low temperature without ion bombardment, and does not deteriorate the electrical characteristics of the device. However, in the case of optical excitation, there are the following problems.

1) When a thin film is deposited on an optical window through which light is introduced to cause a reaction between source gases (for example, silane and ammonia) in a reaction tank, the effective light intensity applied to the substrate surface decreases. Resulting in a reduced deposition rate.

2) The in-plane distribution of the growth rate of the thin film in the plane of the substrate strongly depends on the in-plane distribution of the light applied to the substrate, and it is difficult to form a thin film having a uniform thickness on a large-area substrate.

[0008]

The photoexcitation is performed in a gas cell separated from the reaction tank.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, photoexcitation of gas molecules (for example, ammonia and nitrous oxide), which do not form a thin film due to decomposition of the raw material gas molecules, in a gas introduction device separated from a reaction tank. Do with. Thereafter, the excited gas molecules are introduced into the reaction tank through the nozzle, and separately from the second raw material gas (for example,
Silane) and deposit silicon nitride or silicon dioxide without introducing light directly into the substrate and the reaction tank.

In this method, the in-plane distribution of the growth rate of the thin film is determined by the intensity distribution of the excited molecular beam emitted from the nozzle, and is not related to the intensity distribution of light.

Further, according to the present invention, the light introduced into the gas introducing device can be focused in the introducing device by using an optical system installed outside the device, so that the excitation efficiency for the introduced gas can be improved. Is extremely high. That is, since high-density excited molecules can be supplied, the deposition rate of the thin film can be increased.

Embodiment 1 Embodiment 1 will be described with reference to FIG. In this embodiment, monosilane (SiH ₄ ) and ammonia (NH ₃ ) are used to form Ga.
A method and an apparatus for forming a silicon nitride film on an As (001) substrate will be described. First, a GaAs substrate 3 is loaded on a sample stage 2 installed in a reaction tank 1. The sample stage 2 is provided with a substrate heating heater. Substrate 3
The rotation was performed 10 times per minute by a rotation mechanism. The reaction tank 1 is evacuated by a turbo molecular pump (TMP) to a degree of vacuum of 3 × 10 to ¹⁰
It has been exhausted to Torr. Next, the substrate 3 is heated at 300 ° C. by a heater. Subsequently, the valve 4 is opened, and NH ₃ gas (flow rate 50 sccm) is introduced. At this time, the degree of vacuum in the gas cell 6 was adjusted to 10 T by adjusting the valve 5.
Keep at orr. The NH ₃ gas in the gas cell 6 (a cube having a side of 5 cm) enters the reaction tank 1 through the orifice 7. At this time, the degree of vacuum in the reaction tank 1 was 0.5 Torr. Subsequently, an ArF excimer laser (wavelength 193 nm,
(Intensity 100 mJ, frequency 100 Hz) is introduced into the gas cell 6 through the optical window 8. At this time, the excimer laser light is focused by the lens 9 so as to have a focal point in the gas cell. The excimer laser is irradiated for 10 minutes. Thereafter, the excimer laser irradiation is interrupted, the valve 10 is opened, and SiH ₄ (flow rate 5 sccm) is introduced from the nozzle 11. After waiting for the degree of vacuum in the reactor 1 to stabilize at 1 Torr, the NH ₃ gas is excited by irradiating the gas cell 6 with an excimer laser, and the deposition of the silicon nitride film is started. After deposition, the film thickness was measured with an ellipsometer.
A 150 nm silicon nitride film was deposited by the laser irradiation for 5 minutes. 2% film thickness distribution on 4 inch diameter substrate
It was below. Similarly, the refractive index distribution was 3% or less.

In ordinary laser CVD or optical CVD, if the deposition of a thin film is continued, the optical window gradually becomes cloudy and the deposition rate is reduced.
In the range up to mm, a decrease in deposition rate of 5% or more was not observed.

In this embodiment, a silicon nitride film has been described. However, when nitrous oxide gas is introduced instead of NH ₃ gas, a silicon dioxide film having a film thickness distribution equivalent to that of silicon nitride is formed. Was completed.

[0015] In addition, phosphine instead of SiH ₄ (P
By introducing H ₃ ), a phosphorus nitride film could be formed.

Embodiment 2 Embodiment 2 will be described with reference to FIG. In this embodiment,
A method and an apparatus for forming a silicon nitride film on a GaAs (001) substrate using monosilane (SiH ₄ ) and ammonia (NH ₃ ) will be described. The same method as in Example 1 was used for the substrate loading method before gas introduction and the evacuation of the reaction tank. In this embodiment, only the method of introducing NH ₃ gas is different.

First, NH ₃ gas (flow rate 50 sccm) is introduced by opening the valve 12 into a gas cell 13 having a square section of 5 cm on a side and a length of 15 cm in the gas introduction direction. The NH 3 gas passes through the orifice 14 and reacts in the reaction tank 1.
to go into. The degree of vacuum at this time is 10 To
rr was 0.5 Torr in the reaction tank 1. continue,
The valve 10 is opened and SiH ₄ (flow rate 5 sccm) is introduced from the nozzle 11. At this time, the reaction vacuum was 1 Torr
It became.

Subsequently, excimer laser light (wavelength 193n)
m, intensity 100 mJ, frequency 100 Hz)
(5 × 110 mm rectangle) and introduced into the gas cell 13 to excite NH ₃ gas to start the deposition of the silicon nitride film. The excimer laser light was directly introduced without focusing a rectangular parallel beam of 2 × 100 mm.

After the deposition, the film thickness was measured by an ellipsometer. As a result, a 300-nm silicon nitride film was deposited by laser irradiation for 10 minutes. The film thickness distribution on a substrate having a diameter of 4 inches was 1.5% or less. Similarly, the refractive index distribution is 2
% Or less.

In this embodiment, no decrease in the deposition rate of 5% or more was observed in the range up to the cumulative film thickness of 100 mm.

Embodiment 3 Embodiment 3 will be described with reference to FIG. In this embodiment,
A method and an apparatus for forming a phosphorus nitride and silicon nitride film on a GaAs (001) substrate using phosphine (PH ₃ ), monosilane (SiH ₄ ), and ammonia (NH ₃ ) will be described. The same method as in Example 1 was used for the substrate loading method before gas introduction and the evacuation of the reaction tank.

First, the valve 4 is opened and the PH ₃ gas (flow rate 5
0 sccm). At this time, the degree of vacuum in the gas cell 6 is maintained at 5 Torr by adjusting the valve 5. Gas cell 6
PH ₃ gas enters the reaction tank 1 through the orifice 7. At this time, the degree of vacuum in the reaction tank 1 was 0.25 Torr. Subsequently, an ArF excimer laser (wavelength 193n)
m, intensity 100 mJ, frequency 100 Hz) is introduced into the gas cell 6 through the optical window 8. At this time, the excimer laser light is focused by the lens 9 so as to have a focal point in the gas cell. The excimer laser is irradiated for 10 minutes. Thereafter, the excimer laser irradiation is interrupted, and the valve 12 is opened in the gas cell 13 so that the NH ₃ gas (flow rate 50 sc
cm). NH ₃ gas enters the reactor 1 through the orifice 14. At this time, the degree of vacuum is
10 Torr in the reactor and 0.75 Torr in the reactor 1. Subsequently, excimer laser light is introduced into the gas cells 6 and 13 through the optical windows 8 and 15, and PH ₃ gas and N
The H ₃ gas is excited to start the deposition of the phosphorus nitride film. The growth rate of the phosphorus nitride film thus deposited was 20 nm per minute. When PH ₃ gas was introduced without being excited by excimer laser light, the growth rate was 10 nm / min. In the case of SiH ₄ , since dissociation does not occur due to excimer laser light,
Irradiation of SiH ₄ with a laser does not increase the growth rate, but PH ₃ gas is dissociated by the laser irradiation, so that the reaction with NH ₃ gas is accelerated and the growth rate is increased.

[0023]

According to the present invention, when a nitride film or an oxide film is formed by photoexcited CVD, deposition of a thin film on an optical window for introducing light is suppressed, so that the growth rate is extended over a long period of time. And is kept stable. Further, since the in-plane distribution of the film thickness of the thin film deposited on the substrate is not affected by the distribution of incident light, a thin film having high film thickness uniformity can be formed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a thin film forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a thin film forming apparatus according to a second embodiment of the present invention.

FIG. 3 is a sectional view of a thin film forming apparatus according to a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reaction tank, 2 ... Sample stand, 3 ... Substrate, 4 ... Valve, 5 ...
Valve, 6 gas cell, 7 orifice, 8 optical window,
9: lens, 10: valve, 11: nozzle, 12: valve, 13: gas cell, 14: orifice, 15: optical window.

Claims (4)

[Claims] 1. A thin film forming method for photo-exciting at least one kind of gas molecules and depositing a thin film using said gas molecules as a raw material on the surface of a substrate loaded in a reaction tank, wherein said gas molecules are formed outside said reaction tank. A method for forming a thin film, comprising: individually exciting light, and then introducing the photoexcited molecules into the reaction tank to deposit the thin film. 2. A thin film forming apparatus comprising: a reaction vessel having a substrate heating section; and at least one gas cell connected to the reaction vessel and having a light introducing optical window. 3. The thin film forming apparatus according to claim 2, wherein the connection between the reaction tank and the gas cell is made by an orifice provided in the connection portion of the gas cell with the reaction tank. 4. The thin film forming apparatus according to claim 2, wherein said thin film forming apparatus further comprises an optical lens for focusing on said optical window for light introduction.