JPH0594954A - Forming method of semiconductor film - Google Patents

Abstract

PURPOSE:To provide a method of forming a semiconductor film which enables an element provided with an amorphous silicon film to be enhanced in characteristics by a method wherein the amorphous silicon film is subjected to a thermal treatment process and then enlarged in grain diameter when it is recrystallized. CONSTITUTION:When an amorphous silicon film is formed on an insulating film 12 provided onto a semiconductor wafer 10, a process where the semiconductor wafer 10 is inserted into the reaction tube of a reduced pressure type or a normal pressure type CVD device, the reaction tube is kept in a reduced pressure or a normal pressure state, and oxidizing gas is made to flow through the reaction tube to execute the oxygen purge of the surface of the wafer and another process where an amorphous silicon film is successively formed on the surface of the wafer by deposition in the above reaction tube are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a semiconductor film on a semiconductor wafer, and more particularly to a method for forming a semiconductor film containing a polycrystalline silicon film as a main component.

[0002]

2. Description of the Related Art A conventional method for forming an amorphous silicon film on an insulating film formed on a semiconductor wafer in a semiconductor device manufacturing process will be described. That is, a semiconductor wafer is inserted into a reaction tube of a low pressure CVD (chemical vapor deposition) apparatus, the reaction tube is heated to 500 to 560 ° C. by an external heater, and the inside of the reaction tube is heated to 0.1 to 1.0 T by a vacuum pump.
Amorphous silicon film is formed on the wafer by reducing the pressure to orr and flowing silane gas into the reaction tube for thermal decomposition.

FIG. 4 is an enlarged sectional view showing a part of the structure of a thin film transistor (TFT) as an example of an element using an amorphous silicon film formed by a conventional method.

Here, 10 is a P-type wafer substrate, and 11
Is an element isolation region (SiO ₂ film), 12 is a gate insulating film formed on the surface of the substrate, 13 is an N + diffusion layer (which becomes the gate electrode of the TFT) formed in the substrate, and 14 is formed on the substrate. The amorphous silicon film is recrystallized by heat treatment. A part of the polycrystalline silicon film 14 becomes the P + diffusion layer (drain region and source region of the TFT) 15, and the remaining part becomes the channel region 16 of the TFT. 41 denotes a grain boundary of the channel region 16. The grain boundary 41 of the channel region 16 is generated by growing grains (grain size) of the amorphous silicon film when the amorphous silicon film is heat-treated and recrystallized.

During the heat treatment, the amorphous silicon film formed by the conventional method is apt to become a crystal nucleus for the impurities (particularly carbon) adsorbed on the wafer surface to grow grains, and the grain growth occurs simultaneously from a large number of places. It becomes difficult to obtain a large grain. In other words, the amorphous silicon film formed by the conventional method has an increased grain boundary 41 in the channel region when recrystallized through the heat treatment process.

Therefore, such grain boundary 4
In the TFT having the channel region 16 in which the number of 1 is large, the probability that the holes 42 are trapped in the grain boundary 41 when the gate is turned on increases, and the on-current decreases.
Further, in the TFT having the channel region 16 in which the grain boundary 41 is large as described above, the grain boundary 41 causes a leak current, so that the off current increases.

The dotted line in FIG. 3 shows the current switch characteristics of the TFT when the amorphous silicon film to be the polycrystalline silicon film 14 in FIG. 1 is formed by the conventional method, and the on-current / off-current ratio is shown. There is a problem that is small.

[0008]

As described above, according to the conventional method of forming a semiconductor film, it becomes difficult to obtain a large grain size when the amorphous silicon film is recrystallized through the heat treatment process, and the grain boundary is reduced. However, there is a problem that it is difficult to improve the characteristics of the element using the amorphous silicon film.

The present invention has been made to solve the above problems, and it becomes possible to make the grain size large and uniform when the amorphous silicon film is recrystallized through a heat treatment process. An object of the present invention is to provide a method for forming a semiconductor film, which can improve the characteristics of a device using a silicon film.

[0010]

According to the method for forming a semiconductor film of the present invention, when an amorphous silicon film is formed on an insulating film formed on a semiconductor wafer, the semiconductor wafer is processed in a reduced pressure type or normal pressure type CVD apparatus. Inserting into the reaction tube, keeping the inside of the reaction tube at a reduced pressure or normal pressure, and purging the wafer surface with oxygen by flowing an oxidizing gas, and subsequently, an amorphous silicon film on the wafer surface in the reaction tube. And a step of depositing and forming.

[0011]

Function: Oxygen purging before depositing and forming the amorphous silicon film reduces carbon impurities adsorbed on the base insulating film. As a result, the number of crystal nuclei necessary for grain growth in the amorphous silicon film when the amorphous silicon film is recrystallized through the heat treatment process is decreased, and the grain size is increased, resulting in an element using the amorphous silicon film. Characteristics (for example, current switching characteristics of TFT) are improved.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an example of a device using an amorphous silicon film formed on a semiconductor wafer as T
It is sectional drawing which shows an example of the structure of FT.

Here, 10 is a P-type wafer substrate, and 11
Is an element isolation region (SiO ₂ film), 12 is a gate insulating film formed on the surface of the substrate, 13 is an N + diffusion layer (which becomes the gate electrode of the TFT) formed in the substrate, and 14 is formed on the substrate. The amorphous silicon film is recrystallized by heat treatment. A part of the polycrystalline silicon film 14 becomes a P + diffusion layer (a drain region and a source region of the TFT) 15, and the remaining part (a part on the gate insulating film 12) becomes a channel region 16 of the TFT. Reference numeral 17 is a CVD insulating film formed on the substrate, and 18 and 19 are a drain electrode and a source electrode which are in contact with the P + diffusion layer 15 through contact holes formed in the CVD insulating film 17.

Next, an embodiment of a method of forming the TFT of FIG. 1 will be described. First, the element isolation region 11 is formed on the P-type wafer substrate 10 by a shape selective oxidation method so as to leave the element formation region. Next, a thin (for example, 6 nm) gate insulating film (oxide film) is formed on the element formation region by dry oxidation at 900 ° C., and As ions are implanted into the wafer substrate 10 through this gate oxide film, and N + Diffusion layer 1
3 is formed. Next, the gate oxide film damaged by the ion implantation on the N + diffusion layer 13 is removed by chemical treatment. The gate insulating film (oxide film) 12 is formed again by dry oxidation at 900 ° C.

Next, in order to form an amorphous silicon film, the wafer substrate is subjected to depressurization type or normal pressure type CV.
It is inserted into the reaction tube of the apparatus D, the reaction tube is heated to approximately 530 ° C. by an external heater, and the pressure inside the reaction tube is reduced to 0.5 Torr by a vacuum pump or kept at normal pressure. Then, an oxidizing gas (for example, oxygen) is flown at a flow rate of 10 cc / min to purge the oxide film 12 on the wafer surface with oxygen. As a result, the carbon impurities adsorbed on the underlying oxide film 12 react with oxygen and are removed in the form of CO and CO ₂ .

Next, following the above steps, silane gas (SiH ₄ ) is caused to flow in the reaction tube at a flow rate of 200 cc / min for thermal decomposition to deposit an amorphous silicon film to a thickness of 30 nm on the wafer surface. Next, the amorphous silicon film is recrystallized (polycrystallized) by heat treatment at 600 ° C. in an N ₂ atmosphere, and the channel region 1
P + type impurities are ion-implanted into the portions other than 6 to form a P + diffusion layer (drain region and source region of TFT) 15.

Next, a CVD oxide film 17 as an interlayer insulating film is deposited to a thickness of 200 nm on the wafer substrate using an atmospheric pressure type CVD apparatus, and then the CVD oxide film 17 is selectively etched to open a contact hole. Make a hole. Further, an aluminum / silicon film is formed on the entire surface of this CVD oxide film and then patterned to form the P + diffusion layer 1
A drain electrode 18 and a source electrode 19 that contact the electrode 5 are formed.

FIG. 2 is an enlarged sectional view showing a part of the structure of the TFT formed by the method of the above embodiment. Two
1 is a grain boundary of the channel region 16. The grain boundary 21 of this channel region 16
Is that when the amorphous silicon film is heat-treated and recrystallized, the larger the grain (grain size) of the amorphous silicon film, the smaller the decrease.

According to the method of the above embodiment, the oxygen purge before forming and depositing the amorphous silicon film reduces the carbon impurities adsorbed on the underlying insulating film. The number of crystal nuclei necessary for grain growth in the amorphous silicon film is reduced, and the grain size is large and uniform. As a result, it can be seen that the area of the grain boundary 21 per unit area of the channel region 16 is reduced as compared with the TFT formed by the method of the conventional example (the structure shown in FIG. 4). Therefore, when the gate of the TFT is turned on, the probability that the holes 22 are trapped in the grain boundary 21 is reduced,
The decrease in on-current is suppressed. Further, in the TFT having the channel region 16 with a small amount of grain boundary 21 as described above, the off current is suppressed.

The solid line in FIG. 3 is a characteristic diagram showing an example of the current switch characteristic of the TFT of FIG. Here, the on-current / off-current ratio of the TFT formed by the method of this embodiment is sufficiently larger than the on-current / off-current ratio of the TFT formed by the conventional method. It can be seen that good properties are obtained with the example method.

Although oxygen is used as the oxidizing gas in the oxygen purging step in the above embodiment, carbon impurities adsorbed on the underlying insulating film are removed even if ozone is flowed, as in the above embodiment. The effect of removing is obtained. Further, it has been confirmed that the effect of removing carbon impurities adsorbed on the base insulating film is further enhanced by flowing the oxygen in a plasma state.

[0022]

As described above, according to the method for forming a semiconductor film of the present invention, it is possible to increase the grain size when the amorphous silicon film is recrystallized through the heat treatment process, and the amorphous silicon film is formed. The characteristics of the element used (for example, the current switching characteristics of the TFT) can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of the structure of a TFT.

FIG. 2 is a TF when the amorphous silicon film in FIG. 1 is formed by an embodiment of the method for forming a semiconductor film of the present invention.
Sectional drawing which expands and shows the structure of T.

3 is a characteristic diagram showing an example of a current switch characteristic of the TFT of FIG.

FIG. 4 is a cross-sectional view showing an enlarged structure of a TFT when the amorphous silicon film in FIG. 1 is formed by a conventional semiconductor film forming method.

[Explanation of symbols]

10 ... P-type wafer substrate, 11 ... Element isolation region, 12 ...
Gate insulating film, 13 ... N + diffusion layer (gate electrode of TFT), 14 ... Polycrystalline silicon film (amorphous silicon film recrystallized through heat treatment), 15 ... P + diffusion layer (TFT drain region) And source region), 16
... TFT channel region, 17 ... CVD insulating film, 18 ...
Drain electrode, 19 ... Source electrode, 21 ... Grain boundary, 22 ... Hole.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinji Miyazaki, 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Stock company Toshiba Research Institute

Claims (4)

[Claims] 1. When forming an amorphous silicon film on an insulating film formed on a semiconductor wafer, the semiconductor wafer is inserted into a reaction tube of a decompression type or atmospheric pressure type chemical vapor deposition apparatus, and the pressure inside the reaction tube is reduced. Alternatively, the method comprises a step of keeping an atmospheric pressure and flowing an oxidizing gas to purge the wafer surface with oxygen, and a step of successively depositing and forming an amorphous silicon film on the wafer surface in the reaction tube. And a method for forming a semiconductor film. 2. The method for forming a semiconductor film according to claim 1, wherein the oxidizing gas is oxygen. 3. The method for forming a semiconductor film according to claim 2, wherein the oxygen is made to flow in a plasma state. 4. The method for forming a semiconductor film according to claim 1, wherein the oxidizing gas is ozone.