JPS6410090B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a nitride film on the surface of a semiconductor substrate.

Conventionally, the so-called CVD method has been mainly used as a method for forming a nitride film on a semiconductor surface.
However, according to this method, it is extremely difficult to obtain a particularly thin nitride film, for example, one with a thickness of several tens to 200 angstroms, with good uniformity.

On the other hand, progress in large-scale integrated circuits has been remarkable in recent years, and in this field there is a strong need for a nitride film with a thickness of 100 to 200 Å and uniformity. I couldn't find a method for forming a nitride film.

The present invention has been made to eliminate these conventional drawbacks, and its purpose is to:
It is an object of the present invention to provide a method for forming a nitride film that can stably, precisely, and uniformly obtain a thin nitride film.

In order to achieve such an objective, the present invention
Nitrogen ions are implanted from the surface of a silicon semiconductor substrate, and then laser light is irradiated to dissolve the surface of the semiconductor substrate, forming a silicon nitride film in which the atomic weight of silicon is 3 and the atomic weight of nitrogen is 4. At the same time, the amount of the nitrogen ion atoms implanted at this time is approximately 4/3 times the amount of silicon atoms contained in the silicon semiconductor substrate up to the depth where the nitrogen ions are implanted. That is.

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 is an explanatory diagram showing the state of the ion implantation step of the nitride film forming method according to the present invention. N ₂ ⁺ ions 2 are implanted into the surface of a silicon wafer 1 to form an ion implantation layer. The ions to be implanted are most preferably N ²⁺ ions, but various nitrogen ions such as N ⁺ , multivalent ions, or molecular ions can be used.

FIG. 2 is an explanatory diagram showing the state of the laser beam irradiation process. A silicon wafer 1 having an ion-implanted layer formed thereon is attached to a part of the inner wall of a vacuum container 3 by a supporting method such as a vacuum chuck. This vacuum container 3 is provided with an inlet 4 through which dry N ₂ gas is supplied and an outlet 5 through which it is discharged.
By adjusting the flow rate of these inlets 4 or outlets 5, the nitrogen partial pressure of the nitriding atmosphere within the vacuum vessel 3 can be freely controlled. In addition,
6 is a pressure gauge. When closing the outlet 5, the nitrogen pressure can be monitored with a pressure gauge 6, and when closing the inlet 4, a flow meter can be provided in front of the inlet 4 to control the nitrogen pressure while flowing _N2 gas. In this way, the nitrogen pressure in the vacuum vessel 3 is maintained at a desired value. This nitrogen pressure may be 1 atm or less, or may be increased to 1 atm or more when increasing the growth rate.

On the other hand, the inner wall of the vacuum container 3 opposite to the inner wall to which the silicon wafer 1 is attached is made of a material that is transparent to the wavelength of the laser beam. For example, when using an argon laser, glass, transparent reinforced resin, etc. are used. The light emitted from the laser 7 is narrowed down to a narrow beam diameter by a lens 8, and then passed through a Y-axis mirror sweeper 9 and an X-axis mirror sweeper 10.
, and the entire surface of the silicon wafer 1 is swept and irradiated. The diameter of the laser beam spot is usually about 10 to 200 μm, but the overlap of the sweeping beams is well adjusted so that uniform irradiation can be obtained over the entire surface. As a result, if a silicon wafer with a diameter of 3 inches is used, for example, sweeping of the entire surface can be completed in about 2 minutes. Note that the laser 7 may be of any type as long as it can be used, but a continuous wave argon ion laser is preferred in order to obtain irradiation light of uniform intensity over the entire surface of the wafer. be.

Generally, the composition of silicon nitride film is Si:N=
The ratio is 3:4. In order to satisfy such conditions, the following settings were made in this embodiment.
For example, if the thickness of a silicon nitride film (Si ₃ N ₄ ) to be formed is 200 Å, and the amount of silicon atoms is approximately 5 × 10 ²² /cm ³ , the amount of nitrogen necessary to form this film thickness is 200 Å. The amount of atoms is as follows.

5 × 10 ²² × 4/3 × 200 × 10 ^-8 = 1.3 × 10 ¹⁷ /cm ³ Here, when N ₂ ⁺ ions are implanted as nitrogen ions onto the surface of the silicon wafer, the amount of N ₂ ⁺ ions to be implanted is becomes as follows.

1.3×10 ¹⁷ ÷2=6.5×10 ¹⁶ /cm ³ The thickness at which silicon on the surface of the silicon wafer is consumed is approximately 150 Å (=200×3/4). Therefore, N ₂ ⁺ ions are present on the silicon wafer surface at approximately 150
The energy is implanted to a depth of Å. In this example, an ion-implanted layer with a desired thickness could be formed by implanting with an energy of 5 KeV.

FIG. 3 is a graph showing the relationship between the depth of the silicon wafer and the nitrogen concentration when ions are implanted. 0 on the horizontal axis indicates the surface of the silicon wafer. Nitrogen is ion-implanted to a depth of about 150 Å from the surface with a concentration of Gaussian distribution. Therefore, an ion-implanted layer (shaded area) is formed to a depth of about 150 Å from the surface, and a silicon layer is formed deeper than this. However, in this state, the ion implantation layer is a silicon nitride film (Si ₃ N ₄ ).
The composition has not changed. Next, when this ion-implanted layer is irradiated with laser light and heated, silicon is dissolved and a silicon nitride film having a composition of Si ₃ N ₄ is formed. The output power of the laser beam at this time is set at a level that melts the silicon to a depth of approximately 150 Å. In this example, the output power is
Set to 14.8W, the diameter of the laser light beam is
Irradiation was carried out at 150 μm. Nitrogen diffuses extremely quickly in the molten silicon, and even with short-term heat treatment such as laser, the distribution of nitrogen remains almost constant in the molten layer, resulting in a nitride film with a thickness of about 200 Å.

FIG. 4 is a graph showing the relationship between the depth of a silicon wafer and the nitrogen concentration when heat treated with laser light. The negative sign on the horizontal axis indicates the height protruding from the surface of the silicon wafer. Approximately from the protruding surface
A silicon nitride film (shaded area) having a uniform nitrogen concentration distribution over a depth of 200 Å is formed, and the area deeper than 150 Å becomes a silicon layer as described above.

In this case, as explained with reference to FIG. 2, the heat treatment using laser light is carried out in a nitrogen atmosphere at an appropriate nitrogen pressure, so outward diffusion of nitrogen, etc. is suppressed and a high quality nitride film is formed.

Additionally, it is generally believed that setting the output power of a laser for melting silicon is difficult, but in this example, the ion-implanted layer of N ₂ ⁺ ions has an absorption coefficient that is lower than that of a single crystal due to damage from the implanted ions. Since it is sufficiently larger than silicon, it is not very difficult to dissolve it at the interface between the ion-implanted layer and single-crystal silicon. This increase in absorption coefficient is particularly noticeable near the wavelength of the Nd:YAG laser (1.06 μm), making it easier to control melting by laser light in this case, but even the wavelength of argon laser or ruby laser is sufficient. Needless to say, control is possible.

This example shows an example of forming a nitride film with a thickness of 200 Å, but as the film thickness increases, the nitride film with the desired thickness can be obtained by changing the ion implantation amount, implantation energy, and laser output power accordingly. It will be done.

FIG. 5 is a cross-sectional view of each process of a semiconductor device showing an application example of the present invention. As shown in FIG. 1A, a resist pattern 11 is formed on the surface of the silicon wafer 1, leaving a region where a nitride film will be formed. Next, figure b
As shown in FIG. 2, N ₂ ⁺ ions 2 are implanted into the surface of the silicon wafer 1 using the resist pattern 11 as a mask to form an ion implantation layer 12. Next, after removing the resist pattern 11, a heat treatment using a laser beam is performed to form a nitride film 13 in a desired region as shown in FIG.

FIG. 6 is a cross-sectional view of each process of a semiconductor device showing another application example. As shown in Figure a, an oxide film 14 is formed on the surface of the silicon wafer 1, leaving a region where a nitride film will be formed. Then, as shown in figure b,
Using the oxide film 14 as a mask, N ₂ ⁺ ions 2 are implanted to form an ion implantation layer 12. Next, a heat treatment using laser light is performed to form the nitride film 13 as shown in Figure c.
form. Note that in addition to the oxide film, a nitride film can also be used as a mask.

In this way, it is possible not only to nitride the entire silicon wafer, but also to partially nitride it.

The present invention is applicable to the formation of thin nitride films used in nonvolatile memory elements, oxidation masks for partial oxidation processes, etc.
It can be applied to a wide variety of semiconductor manufacturing processes.

As described above, the method for forming a nitride film according to the present invention has the effect of easily forming a stable, uniform, and thin nitride film.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the state of the ion implantation step in the nitride film forming method according to the present invention, FIG. 2 is an explanatory diagram showing the state of the laser beam irradiation step, and FIG. 3 is the depth of the silicon wafer when ions are implanted. Figure 4 is a graph showing the relationship between the depth of a silicon wafer and nitrogen concentration when subjected to laser photothermal treatment, and Figures 5 and 6 are graphs of semiconductor devices showing application examples. It is a sectional view of each process. The same reference numerals in the drawings indicate the same or corresponding parts. 1...Silicon wafer, 2... _N2 ⁺ ions, 3
...Vacuum container, 4...Inlet, 5...Outlet, 7...
Laser, 8...Lens, 9...Y-axis direction mirror sweeper, 10...X-axis direction mirror sweeper.

Claims (1)

[Claims] 1 Nitrogen ions are implanted from the surface of a silicon semiconductor substrate, and then laser light is irradiated to melt the surface of the semiconductor substrate to form a silicon nitride film in which the atomic weight of silicon is 3 and the atomic weight of nitrogen is 4. In the nitride film forming method, the amount of nitrogen ion atoms implanted is approximately 4/3 times the amount of silicon atoms contained in the silicon semiconductor substrate up to the depth where nitrogen ions are implanted. A method for forming a nitride film, characterized in that the amount is set to .