JPS593869B2 - Method for manufacturing silicon gate field effect semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a silicon gate field effect semiconductor device.

Field effect transistor using polycrystalline silicon (hereinafter referred to as M
OS) is commonly known as silicon gate MOS, and this polycrystalline silicon is an insulator that does not contain impurities except in special cases, and if necessary, phosphorus, boron, arsenic, gallium, etc. are added as impurities. It is added to polycrystalline silicon by techniques such as diffusion or doping, or by ion implantation techniques, and is used as a conductor.

Generally, the selection of impurities is phosphorus for the N-channel silicon gate M05 and boron for the P-channel silicon gate, and in most cases, when the impurity is diffused into the silicon substrate, it is simultaneously diffused into the polycrystalline silicon. be done. In special cases, an impurity different from that diffused into the substrate may be diffused into the polycrystalline silicon, but in either case, only a single impurity is contained in the polycrystalline silicon. In this way, when a single impurity, particularly boron, is contained in polycrystalline silicon, it becomes a cause of deterioration of the characteristics of the MOS, as will be described later. The purpose of the present invention is to provide a silicon gate MO with stable characteristics.
An object of the present invention is to provide a method for manufacturing S.

The present invention deals with two types of impurities contained in polycrystalline silicon,
In particular, the behavior of each of the 20 impurities when boron and phosphorus are contained at the same time is based on new experimental results when a silicon oxide film is used as a gate insulating film.

Taking a P-channel silicon gate MOS as an example, when it is heat-treated in an atmosphere containing hydrogen and an atmosphere containing steam, the threshold voltage VT of the MOS transistor becomes negative as shown in Figure 1a and b. The phenomenon is known.

In FIG. 1, VTo indicates the initial value of VT, and indicates the heat treatment time. This phenomenon occurs because boron, an impurity added to polycrystalline silicon, thermally diffuses into the silicon oxide film and is accelerated by hydrogen. On the other hand, taking an N-channel silicon gate MOS as an example, it is much more stable than a P-channel silicon gate MOS, and no change in the threshold voltage of the MOS transistor 35 is observed during heat treatment. This is shown in FIG. This shows that phosphorus is extremely difficult to diffuse into the silicon oxide film. Generally, when boron enters a silicon oxide film, it forms a glass layer, but the presence of boron makes the silicon oxide film easier to crystallize and the film density becomes sparse.On the other hand, a silicon oxide film containing phosphorus becomes more amorphous and has a lower film density. It is known that the density increases, and the above phenomenon can be understood as an effect of this.
FIG. 3 shows what happens when phosphorus is diffused into a silicon oxide film in which boron has been diffused.

In the figure, t', T. "t'2 indicates phosphorus diffusion time,
a', a! a' indicates the corresponding VT. That is, with the phosphorus diffusion as a boundary, the P channel silicon gate MOS becomes unstable before that, and the N channel silicon gate MOS becomes stable after that. This can be understood by considering that the silicon oxide film, which had once become sparse due to boron, becomes dense again due to phosphorus, as described above.
The present invention applies this new phenomenon shown in FIG. 3 to a semiconductor device. For example, taking a P channel silicon gate MOS as an example, boron is doped into the polycrystalline silicon gate at the same time as it is diffused into the source and train.

After that, in order to take advantage of the multilayer wiring technology that is a feature of silicon gate MOS, an insulating film must be formed on the polycrystalline silicon to separate the polycrystalline silicon from other wiring electrodes. For this reason, when thermal oxidation is performed, boron invades the silicon oxide film from polycrystalline silicon, deteriorates the oxide film quality, creates charge traps, promotes instability in high temperature bias processing, and finally reduces the threshold voltage of the MOS transistor. It is known that the value of
This effect is more pronounced when the process is carried out in an atmosphere containing hydrogen. In reality, therefore, a boron-impermeable film such as a silicon nitride film is sandwiched between the polycrystalline silicon and the silicon oxide film, or an insulating film is grown by vapor phase growth at low temperatures. According to the present invention. In a method for manufacturing a silicon gate field effect semiconductor device in which a silicon oxide film is used as a gate insulating film and a polycrystalline silicon gate is provided thereon, boron or gallium is introduced through the silicon oxide film onto the surface of the substrate that is to become a channel. A silicon gate field effect semiconductor comprising a first step of introducing phosphorus into a polycrystalline silicon gate, and a second step of introducing phosphorus into a polycrystalline silicon gate, thereby obtaining a predetermined constant threshold voltage. A method for manufacturing the device is obtained.
When boron penetrates the silicon oxide film through heat treatment, MOS
The threshold voltage of the transistor changes.

It is known that this phenomenon can be used to control the threshold voltage of a MOS transistor. However, the addition of boron alone is difficult to put into practical use due to the instability of the MOS transistor described above. Therefore, according to an embodiment of the present invention, boron is added to polycrystalline silicon at a concentration of 1018 to 1019 Ad during or after the growth of polycrystalline silicon, respectively, by doping diffusion, and then heated at 900°C to 1100°C in an atmosphere containing hydrogen. Boron, which is heat-treated at a vorticity of , is diffused through a silicon oxide film onto the surface of the substrate that is to become a channel of a MOS transistor.

When phosphorus is diffused into polycrystalline silicon at a concentration of about 1020/Cd after an appropriate period of time, the threshold voltage of the MOS transistor changes in proportion to the square root of the heat treatment time, and does not change during heat treatment after phosphorus diffusion. In this way, any MOS transistor with good stability can be obtained.
Although this method is possible with a P-channel silicon gate MOS, it is effective when applied to an N-channel silicon gate MOS. Although the above embodiments have been described for phosphorus-boron systems, the present invention is also effective when applied to phosphorus-gallium, etc.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the square root of the heat treatment time and the threshold voltage for a P-channel silicon gate MOS and Figure 2 for an N-channel silicon gate MOS, where A, b, and C are respectively shown in each figure. Hydrogen atmosphere, steam atmosphere, and inert gas atmosphere are shown.

Claims (1)

[Claims] 1. In a method for manufacturing a silicon gate field effect semiconductor device in which a silicon oxide film is used as a gate insulating film and a polycrystalline silicon gate is provided thereon, boron or gallium is introduced through the silicon oxide film into the surface of the substrate that is to become a channel. A silicon gate field effect semiconductor device comprising a first step and a second step of introducing phosphorus into a polycrystalline silicon gate, thereby obtaining a predetermined constant threshold voltage. manufacturing method.