JPS6232616B2 - - Google Patents

Description

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

Conventional methods for forming an oxide film on the surface of a semiconductor have mainly been carried out using an oxygen atmosphere or a steam atmosphere using a thermal furnace. Furthermore, a so-called CVD method has been used to obtain an oxide film at a lower temperature than in a thermal furnace. However, these methods
For example, it has been extremely difficult to form a thin oxide film having a thickness of several tens of angstroms to 200 angstroms with good uniformity.

On the other hand, advances in highly integrated LSIs have been rapid in recent years, and as a result, 100~
A gate oxide film with a thickness of 200 Å is required, and prototype research is being widely conducted. Furthermore, devices such as nonvolatile memories called MNOS that utilize tunneling phenomena require thin, uniform oxide films with a thickness of several tens of angstroms. However, as described above, it has been difficult to satisfactorily meet these requirements using conventional oxide film forming methods.

The present invention was made to solve these conventional problems, and its purpose is to form an oxide film that can stably form a thin oxide film with excellent precision and uniformity. The purpose is to provide a method.

In order to achieve such an objective, the present invention
An ion-implanted layer is formed by implanting oxygen ions into the main surface of the semiconductor substrate to a depth of about half the thickness of the oxide film to be formed, and then this ion-implanted layer is The laser beam is irradiated with a power level that melts the semiconductor substrate to approximately half the depth.

Hereinafter, the present invention will be described in detail with reference to examples.

FIG. 1 is an explanatory diagram of the oxide film forming method according to the present invention. FIG. 1a shows a state in which oxygen ions 2 are implanted into a silicon wafer 1. As shown in FIG. The oxygen ions to be implanted may be O ⁺ , O ⁺ ₂ , multivalent ions, or even molecular ions, but O ⁺ ₂ ions are most suitable. After the oxygen ions 2 are implanted into the silicon wafer 1 to form an ion-implanted layer in this manner, heating is performed by laser irradiation, as shown in FIG. 1b. Figure 1b
In this case, the silicon wafer 1 is attached to a part of the inner wall of the container 3 using a supporting method such as a vacuum chuck. For example, dry O ₂ is supplied to this container 3 from an inlet 4 in order to create an oxidizing atmosphere inside the container 3 and exits from an outlet 5. The flow rate of O ₂ at the inlet 4 and outlet 5 is By adjusting it, the oxygen partial pressure can be freely controlled. In this case, when closing the outlet 5, the oxygen pressure can be monitored with the pressure gauge 6, and if a flow meter is provided before the inlet 4, the partial pressure can be controlled while flowing _O2 . In any case, the oxygen pressure inside the container 3 is maintained at a desired value, but this pressure may be 1 atm or less, or may be higher than this when increasing the growth rate.

On the other hand, the wall of the container 3 opposite to the wall to which the silicon wafer 1 is attached is made of a material that is transparent to the wavelength of the laser beam, such as glass or other transparent reinforced resin when using an argon gas laser. There is. Further, various kinds of lasers can be used as the laser 7, but in order to obtain irradiation light of uniform intensity over the entire surface of the silicon wafer 1, a continuous wave type argon ion laser is preferable. The light emitted from this laser 7 is narrowed down to a narrow beam diameter by a lens 7a, and is further focused by a Y-axis direction mirror sweeper 7b and an
The beam is deflected by an axial mirror sweeper 7c and irradiated in a sweeping manner over the entire surface of the silicon wafer 1. At this time, the diameter of the beam spot is about 10 to 200 μm, but the overlap of the sweeping laser beams is adjusted well to obtain uniform irradiation. In this example, the sweep could be completed in about 2 minutes for the silicon wafer 1 having a diameter of 3 inches.

Incidentally, since the composition ratio of a silicon oxide film (SiO ₂ ) is Si:O=1:2, ion implantation and laser heating can be set so as to satisfy this condition. For example, when forming a silicon oxide film with a thickness of 100 Å on the surface of the silicon wafer 1, if the amount of silicon is approximately 5×10 ²² /cm ³ , the amount of oxygen is 5×10 ²² ×2×100×10 ^-8 = 1×10 ¹⁷ /cm ²
becomes. If 0 ⁺ ₂ ions are to be implanted, the amount of oxygen will be half this amount, that is, 5×10 ¹⁶ /cm ² . Also, the thickness of silicon consumed is approximately 50 Å. Therefore, O ⁺ ₂ ions are implanted with such energy that they enter a depth of about 50 Å.

FIG. 2a is a graph showing the relationship between the depth from the surface of the silicon wafer 1 (horizontal axis) and the oxygen concentration (vertical axis). In this example, when ion implantation is performed with an energy of 2.5 KV, an ion implantation layer (portion shown by hatching) is formed with a Gaussian distribution of oxygen concentration as shown in the figure. However, in this state, the silicon oxide film has not yet been formed. Therefore, next, this ion-implanted layer is melted with energy from a laser beam. In this case, the power level of the laser is set so that the silicon on the surface of the silicon wafer 1 is melted to a depth of about 50 Å.

Figure 2b shows the depth from the surface of the silicon wafer 1 (horizontal axis) and oxygen concentration (vertical axis), as in Figure 2a.
It is a graph showing the relationship between Note that the depth is set at 0 at the surface of the silicon wafer 1, and portions protruding above this are indicated by a negative sign. In this example,
The power level of the laser was set to 14.5 watts, and the surface of the ion-implanted layer was swept with light having a laser beam diameter of 150 μm to provide energy and heat. In this case, the diffusion of oxygen in the melted silicon is extremely fast, and the distribution of oxygen is almost constant in the melted layer even after a short heat treatment with a laser. A silicon oxide film (portion indicated by hatching) is formed.
Note that the silicon oxide film is formed to protrude from the surface of the silicon wafer 1 by approximately 50 Å.

In this case, as described in FIG. 1B, since laser heating is performed in an oxygen atmosphere, outward diffusion of oxygen, etc. is suppressed, and a high quality silicon oxide film can be obtained.
In addition, it is generally believed that selecting the power level of a laser for melting silicon is difficult and difficult to control, but in reality, an ion-implanted layer with O ⁺ ₂ ions absorbs less energy due to damage from the implanted ions. The coefficient is sufficiently large compared to the single-crystal silicon portion, and it is not very difficult to dissolve the ion-implanted layer and the single-crystal silicon at the interface. Such an increase in the absorption coefficient is particularly noticeable for light with a wavelength of around 1.06 μm produced by an Nd:YAG laser, making it very easy to control, but it is also possible to increase the absorption coefficient with light produced by argon or ruby lasers. .

In this embodiment, an example in which a silicon oxide film with a thickness of 100 Å is formed has been described, but the film thickness can be formed arbitrarily. In this case, the amount of ion implantation, implantation energy, laser power level, etc. may be changed depending on the film thickness. Moreover, even if the ion-implanted layer is heated to a high temperature of 1200 to 1300°C using a laser without melting the silicon, a somewhat satisfactory silicon oxide film can be obtained.

FIG. 3 is a sectional view of a semiconductor device to which another embodiment of the present invention is applied. As shown in FIG. 3a, a resist 8 is formed on the surface of the silicon wafer 1, and patterned by removing the resist 8 only in the region where the oxide film is to be formed. Next, as shown in FIG. 3B, O ⁺ ₂ ions are implanted using the resist 8 as a mask to partially form an ion implantation layer 9. Next, as shown in FIG. 3c, after the resist 8 is completely removed, laser light is irradiated and heat treatment is performed to form an oxide film 10 in a predetermined area.

FIG. 4 is a sectional view of a semiconductor device to which another embodiment is applied. As shown in FIG. 4a, the oxide film 11
Next, as shown in FIG. 4B, O ⁺ ₂ ions are implanted using the oxide film 11 as a mask to form an ion implantation layer 9. Next, the fourth
As shown in FIG. c, the oxide film 10 can be formed by laser beam irradiation and heat treatment. Note that in addition to the oxide film 11, a nitride film can also be formed.

As described above, according to the oxide film forming method of the present invention,
It can be used not only to oxidize the entire surface of a semiconductor substrate, but also to partially oxidize any region. Moreover, it can be used to form thin oxide films such as gate oxide films accurately and uniformly, and also to oxidize contact areas etc. It is also effective in reducing surface steps, and can be applied to a wide variety of fields in the manufacturing process of semiconductor devices.
In addition, it is possible to use materials such as GaAs, which were previously difficult to oxidize.
It is also effective for group semiconductors such as - group semiconductors and CdS. As described above, the present invention has many excellent effects.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the oxide film forming method according to the present invention, FIG. 2 is a graph showing the relationship between the depth from the surface of the silicon wafer and the oxygen concentration, and FIGS. 3 and 4 are diagrams showing other examples, respectively. FIG. 3 is a cross-sectional view of the applied semiconductor device. In each figure, the same numbers indicate the same or corresponding parts. 1... Silicon semiconductor substrate, 2... Oxygen ions, 3... Container, 4... Inlet, 5... Outlet, 6...
...Pressure gauge, 7...Laser, 7a...Lens,
7b...Y-axis direction mirror sweeper, 7c...X-axis direction mirror sweeper.

Claims (1)

[Claims] 1 Form an ion-implanted layer by implanting oxygen ions into the main surface of a semiconductor substrate to a depth of about half the thickness of the oxide film to be formed; An oxide film forming method characterized by irradiation with laser light at a power level that melts a semiconductor substrate to approximately half the depth of the semiconductor substrate.