JPH0766150A - Fabrication of semiconductor device - Google Patents

Abstract

PURPOSE:To provide a method for fabricating a semiconductor device in which high activation ratio is realized in an ion implanted layer while preventing breakage of protective film when annealing is effected in order to activate the ion implanted layer. CONSTITUTION:In the method for fabricating a semiconductor device comprising an annealing step for activating an ion implanted layer 2 formed on a semiconductor substrate 1, an SiNx film 8 having a continuously varied film quality is formed on the substrate 1 by single film deposition step of plasma CVD and then annealing for activating the ion implanted layer 2 is effected using the SiNx film 8 as a protective film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly, to a method of manufacturing a semiconductor device having a step of performing annealing for activating an ion-implanted layer after ion-implanting a semiconductor substrate.

[0002]

2. Description of the Related Art Conventionally, in the manufacture of field effect transistors (hereinafter referred to as FETs), in order to improve the characteristics (high frequency characteristics and high speed characteristics) of FETs and increase the integration density of semiconductor integrated circuit devices including FETs. In general, a self-alignment method is performed in which ion implantation is performed using a gate electrode or a dummy gate as a mask and then annealing (heat treatment) is performed to activate the ion implantation layer. For example, GaAs Schottky gate FET (hereinafter, Ga
(Hereinafter referred to as AsMESFET), after performing ion implantation by the self-alignment method, annealing at a high temperature for activating the ion implantation layer is performed.

FIG. 4 shows a manufacturing process of a GaAs MESFET using the dummy gate type self-alignment method. First, as shown in FIG.
Si ions are implanted on the semiconductor substrate 1 made of As to form the n-type implantation layer 2. Next, Si on the n-type injection layer 2
An insulating film made of Nx or the like is formed by a CVD method or the like and patterned to form a dummy gate 3 as shown in FIG. Then, in order to reduce the parasitic resistance, Si ions are implanted, and as shown in FIG.
The n-type high concentration injection layer 4 is formed. At this time, the position of the n-type high-concentration injection layer 4 is also determined by the position of the dummy gate 3, and the n-type high-concentration injection layer 4 is formed in a self-aligned manner.

Next, after the activation annealing of the n-type injection layer 2 and the n-type high concentration injection layer 4 is performed, the source electrode 5 is formed on the n-type high concentration injection layer 4 as shown in FIG. And the drain electrode 6 is formed. Then, after removing the dummy gate 3 by etching, as shown in FIG.
To form.

By the way, in order to activate the n-type injection layer 2 and the n-type high-concentration injection layer 4, after forming the n-type high-concentration injection layer 4, high-temperature annealing at 800 ° C. or higher is required. At this time, in order to suppress thermal decomposition of the surface of the semiconductor substrate 1 due to this annealing, a protective film is formed so as to cover the n-type high concentration implantation layer 4 and the dummy gate 3, and then annealing is performed. Is frequently used. The important point in this cap annealing method is
It is to efficiently activate the implanted ions.

Conventionally, it is known that a SiNx film formed by a CVD method is effective as the protective film.
However, this SiNx film easily causes film damage due to high temperature annealing, and it is necessary to limit the film stress and film thickness in order to prevent film damage. On the other hand, a cap annealing method using a SiO ₂ film as a protective film, which hardly causes film damage and can be formed by relatively freely changing film stress and film thickness, has been attempted. However, in this case, there is a problem that the characteristics of the ion-implanted layer deteriorate due to the diffusion of As and the like.

Therefore, as shown in FIG. 5, a first protective film 8a made of SiNx is formed so as to cover the n-type high concentration injection layer 4 and the dummy gate 3, and the second protective film 8a is formed on the first protective film 8a. A protective film having a two-layer structure in which 8b is formed has been proposed. The first protective film 8a is a relatively soft film having a small refractive index (about 0.95) in order to prevent thermal damage. In addition, the second protective film 8b is formed from the semiconductor substrate 1
In order to prevent s escape, the film has a large refractive index (about 2.05) and is made of a relatively hard film.

[0008]

However, the formation of a protective film having a two-layer structure as shown in FIG. 5 of the above-mentioned conventional example requires two film forming steps, resulting in a high manufacturing cost. is there. Further, since the film has a two-layer structure, the film quality changes discontinuously, stress is generated at the interface between the first protective film and the second protective film, and film damage such as cracking is likely to occur.

Therefore, an object of the present invention is to eliminate the above-mentioned various problems of the conventional cap annealing protective film when performing annealing for activation of the ion-implanted layer, and perform protection by annealing. It is possible to prevent damage to the film and realize a high activation rate of the ion implantation layer.
It is to provide a method for manufacturing a semiconductor device.

[0010]

In order to achieve the above object, the present invention provides a method of manufacturing a semiconductor device including a step of performing annealing for activating an ion-implanted layer after ion-implanting a semiconductor substrate. , By plasma CVD method,
A SiNx film having a continuously changing film quality is formed on the semiconductor substrate in a single film forming step, and the SiNx film is used as a protective film to perform annealing for activation of the ion implantation layer. It is a thing.

[0011]

According to the above construction, the protective film for cap annealing whose film quality is continuously changed can be formed in one film forming step, and the film under the protective film is damaged by the heat of annealing. It is possible to form a film having a film quality that does not cause the above phenomenon, and a film having a film quality that prevents As from coming out of the semiconductor substrate on the upper layer portion of the protective film.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a GaAs MESFET according to an embodiment of the present invention will be described below with reference to the drawings. In the figure, the same parts as those of the conventional example shown in FIGS. 4 and 5 are designated by the same reference numerals, and the description thereof will be omitted.

Also in this embodiment, as described in FIG. 4 of the conventional example, first, Si ions are implanted into the semiconductor substrate 1 made of GaAs to form the n-type implantation layer 2. next,
After forming the dummy gate 3 made of SiNx on the n-type implantation layer 2, Si ions are implanted to form the n-type high concentration implantation layer 4. Next, the n-type injection layer 2 and the n-type high concentration injection layer 4
After performing annealing for activating, the source electrode 5 and the drain electrode 6 are formed. Then, after removing the dummy gate 3 by etching, the gate electrode 7 is formed.

The n-type injection layer 2 and the n-type high concentration injection layer 4
A protective film for cap annealing is formed when the annealing for activating is performed. The formation of this protective film will be specifically described below.

After forming the n-type high-concentration implantation layer 4, as shown in FIG. 1, plasma CVD is used to cover the n-type high-concentration implantation layer 4 and the dummy gate 3 by using a SiNx film as a protective film for annealing. 8 is formed. Table 1 shows the film forming conditions at this time.

[0016]

[Table 1]

Under these conditions, when the SiNx film 8 is formed, the temperature of the semiconductor substrate 1 is about 30 seconds after the introduction of each gas shown in Table 1 at about room temperature, as shown in FIG.
It reaches 95 ° C., and after about 1 minute it reaches 300 ° C. The refractive index of the formed SiNx film 8 is 2 when the temperature of the semiconductor substrate 1 is 2.
It becomes 1.90 to 1.95 when the temperature is 95 ° C., and becomes 2.00 to 2.05 when the temperature of the semiconductor substrate 1 is 300 ° C.

Here, S having a refractive index of 1.90 to 1.95
The iNx film is relatively soft and is less likely to be damaged by high temperature annealing. On the other hand, since the SiNx film having a refractive index of 2.00 to 2.05 is relatively hard and dense, it prevents As from coming out from the semiconductor substrate.

Therefore, when the film formation is started about 30 seconds after the introduction of each gas at about room temperature and the film formation is continued for several minutes, as shown in FIG. 3, the refractive index is changed for about 1 minute from the start of the film formation. The continuously changed SiNx film 8 is formed for a few minutes after that, and the SiNx film 8 having a constant refractive index is formed.
The iNx film 8 is obtained.

In other words, according to the above method, since the film on the semiconductor substrate 1 is relatively soft and does not cause film damage due to high temperature annealing, it is relatively hard and dense, and As
It is possible to form the SiNx film 8 consisting of one layer whose film quality is continuously changed on the film capable of preventing omission in one film forming step.

In the above embodiment, the SiNx film was formed under the film forming conditions shown in Table 1 and the above film forming start time. However, the SiNx film is not limited to this. A SiNx film having a desired film quality can be continuously formed. Further, although the manufacturing method by the dummy gate self-alignment method has been described, the present invention is not limited to this, and the present invention can be applied to the manufacturing method by the heat-resistant gate self-alignment method in which ion implantation is performed after the gate electrode is formed. it can.

Further, in the above embodiment, GaAs MES is used.
Although the FET has been described, the present invention can be applied to general semiconductor devices such as HEMTs or other compound semiconductor elements that perform activation annealing after ion implantation.

[0023]

As described above, according to the manufacturing method of the protective film for annealing of the present invention, it is effective to activate the ion-implanted layer from the film that does not cause the film damage due to the high temperature annealing. As a film for preventing the loss of As, a SiNx film having a single-layer structure in which the film quality continuously changes,
It can be formed in a single film forming process. That is, the manufacturing cost of the annealing protective film can be reduced.

The SiNx film as a protective film thus obtained does not cause film damage due to heat of annealing, etc., works effectively for activation of the ion-implanted layer, and has a continuously changing film quality. Also, film damage such as cracking due to discontinuity of film quality does not occur. Therefore, when annealing for activation of the ion-implanted layer is performed using this SiNx film as a protective film, thermal decomposition of the semiconductor substrate surface due to the annealing is suppressed and a high activation rate of the ion-implanted layer is realized. it can. That is, a high-performance and high-quality semiconductor device can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a GaAs MESFET on which a protective film for cap annealing of the present invention is formed.

FIG. 2 is a graph showing the relationship between the semiconductor substrate temperature and the elapsed time when the cap annealing protective film of the present invention is formed.

FIG. 3 is a graph showing the relationship between the refractive index of the protective film and the elapsed time when the protective film for cap annealing of the present invention is formed.

FIG. 4 is a GaAsM according to an embodiment of the present invention and a conventional example.
It is a figure which shows each manufacturing process of ESFET.

FIG. 5 is a cross-sectional view of a GaAs MESFET having a conventional cap annealing protective film formed thereon.

[Explanation of symbols]

 1 semiconductor substrate 2 n-type injection layer 3 dummy gate 4 n-type high concentration injection layer 5 source electrode 6 drain electrode 7 gate electrode 8 SiNx film (protective film)

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/338 29/812

Claims (1)

[Claims] 1. A method of manufacturing a semiconductor device comprising a step of performing annealing for activation of an ion-implanted layer after ion-implantation on a semiconductor substrate, wherein a film quality is continuously formed on the semiconductor substrate by a plasma CVD method. A method for manufacturing a semiconductor device, comprising: forming a changed SiNx film in a single film forming step, and performing annealing for activating the ion implantation layer using the SiNx film as a protective film.