JPS62145821A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To perform an oxidation required for two steps in a conventional method in a single step by concurrently forming oxide films of different thickness in the same step. CONSTITUTION:A buffer oxide film 2 is formed by a thermal oxidation on a substrate 1, covered with a photoresist film 3, exposed, and photosensed to allow the photoresist film 3 of desired pattern to remain. After the semiconductor substrate 1 is exposed, the substrate 1 is thermally oxidized at low temperature to concurrently form oxide films 5 of different thicknesses. That, is, the film 3 is removed by plasma etching, the film 2 is then removed by plasma etching, the surface of the substrate 1 is exposed, and a reoxidized film 5 is adhered by thermal oxidation on the substrate 1 after the substrate 1 is exposed. In this thermal oxidation, the oxidation is accelerated by treating at low temperature, and performs a pyrooxidation (a hydrogen combustion oxidizing method) at 875 deg.C for 20min.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a method for forming a silicon oxide film, particularly a method for forming a thick silicon oxide film in a short time, and further relates to a method for simultaneously forming silicon oxide films of different thicknesses. Regarding the method.

(b) Conventional Technology Silicon oxide films play an important role in the manufacture of semiconductor devices. It is well known that it is used as a surface protection film for elements, a film for selective diffusion, an insulating film between wirings, and the like. There are various methods for forming this silicon oxide film, including thermal oxidation, plasma oxidation, anodic oxidation, and the like. However, the thermal oxidation method is the most practical method, and is often used in the manufacture of current semiconductor devices.

Thermal oxidation methods include dry O6 oxidation method and wet O6 oxidation method. oxidation method,
There are steam oxidation methods, hydrogen combustion oxidation methods, etc. dry O8
The oxidation method uses 0.0% in the diffusion furnace. Gas and N.

A silicon oxide film is formed on the wafer surface by introducing a gas. The wet O3 oxidation method forms a silicon oxide film by introducing O gas passed through water into a diffusion furnace. The steam oxidation method involves introducing water vapor into a diffusion furnace to form a silicon oxide film on the wafer surface.

In the anodic oxidation method, a silicon plate is placed on the anode side electrode using an RF sputtering device, and a silicon plate is placed on the anode side electrode.
The silicon plate is heated to a high temperature of 0 to 1000° C., and the surface of the silicon plate is reacted with oxygen decomposed in plasma to form a silicon oxide film.

In such a thermal oxidation method, when a silicon wafer is heated at approximately 1200°C in a dry O8 atmosphere, 20
000 silicon oxide films can be formed. 10000 again
It takes about 4 hours to form a human silicon oxide film.
°C requires steam oxidation.

(c) Problems to be solved by the invention However, in the thermal oxidation method mentioned above, as shown in Figure 2.2.4 etc. on page 131 of Latest LSI Process Technology, Industrial Research Association, May 1983 issue. It is necessary to perform thermal oxidation for the oxidation time determined by the 1/2 double rule. For this reason, when a particularly thick silicon oxide film is formed by thermal oxidation, it has the disadvantage of requiring a long heat treatment. Another drawback is that silicon oxide films of different thicknesses cannot be simultaneously formed on a substrate by thermal oxidation.

(d) Means for Solving the Problems The present invention has been made in view of the above drawbacks, and involves ion implantation of impurities such that the peak of ion concentration is located on or near the main surface of the semiconductor substrate (1). A semiconductor that improves the drawbacks of conventional semiconductors through the process of selectively forming the layer (4) and the process of exposing the surface of the semiconductor substrate (1) and then thermally oxidizing it at low temperatures to simultaneously form oxide films (5) of different thicknesses. A method for manufacturing the device is provided.

(*) Function According to the present invention, low-temperature accelerated oxidation is performed by utilizing changes in the crystal structure, defects, dislocations, etc. of the substrate surface at the peak position of ion concentration during ion implantation, and a thick layer can be formed in a short time. A silicon oxide film (5) is realized.

As a result, by selectively providing the ion implantation layer (4) on the surface of the substrate (1), oxide films (5) of different thicknesses can be formed in the same oxidation process.

(F) Embodiment An embodiment of the present invention will be described in detail with reference to FIGS. 1 to 7.

The first step of the present invention is to selectively form an ion-implanted impurity layer (4) on the main surface of the semiconductor substrate (1) such that the peak of ion concentration is located at or near the surface ( Figures 1A to 1C).

In this step, as shown in FIG. 1A, a P-type silicon of 10 to 14 Ω is used as the semiconductor substrate (1), and a buffer oxide film (2) is formed on the surface of the substrate (1) by thermal oxidation. The thickness of the buffer oxide film (2) is determined based on the characteristic diagram shown in FIG. 3, and is determined so that the peak of the impurity ion concentration is located on the substrate surface. Specifically, when arsenic (A) is ion-implanted, the thickness is set to 220 people at an acceleration voltage of 40 Key, the thickness is set to 380 people at an acceleration voltage of 80 KeV, and the thickness is set to 620 people at an acceleration voltage of 130 KeV. A polysilicon film or a silicon nitride film may be used instead of the buffer oxide film (2).

Subsequently, in this step, as shown in the opening of FIG. 1, a photoresist film (3) is coated on the buffer oxide film (2) and exposed to light to leave a desired pattern of the photoresist film (3). The photoresist film (3) acts as a mask for ion implantation.

Furthermore, in this step, as shown in Figure 1C, a buffer oxide film (
2) and impurity ions are implanted from above the photoresist film (3) to selectively form an ion implantation layer (4). In this ion implantation, impurity species = 4-class (A, P, B, etc.), dose amount, and acceleration voltage are selected to predetermined values, and the peak position of the ion concentration in the ion implantation layer (4) is set to the substrate (1). ) on or near the surface. The ion concentration due to ion implantation is as shown in Figure 2.
When the average range R of the ions is set to be approximately equal to the thickness of the buffer oxide film (2), a Gaussian distribution is obtained as shown by the solid line. In addition, the dose of ion implantation is selected within the range of more than twice the normal dose to achieve the effect of accelerated oxidation, as shown in the characteristic diagram shown in Figure 6. In the case of arsenic, the dose is 6
In the case of phosphorus, I
X 10 "cm-' or more. In this example, arsenic is used as an impurity, and the dose is 5XIQ"cm-'.
It is set to 1.

The second step of the present invention consists in exposing the surface of the semiconductor substrate (1) and then thermally oxidizing the substrate (1) at a low temperature to simultaneously form oxide films (5) of different thicknesses (Fig. 1, 2). ).

This step is the most characteristic step of the present invention, in which the photoresist film (3) is removed by plasma etching or the like, and then the buffer oxide film (2) is removed by dry etching such as plasma etching or wet etching using HF or the like.
Expose the surface of the substrate (1). After exposing the surface of the substrate (1),
A re-oxidized film (5) is attached to the surface of the substrate by thermal oxidation. In this thermal oxidation treatment, accelerated oxidation is performed by processing at a low temperature, and in the example, pyro oxidation (hydrogen combustion oxidation method) is performed at 875° C. for 20 minutes. The reason for performing the low-temperature treatment will be explained with reference to FIG. 5. This is because the effect of accelerated oxidation cannot be obtained unless the activation rate of arsenic is kept low and thermal oxidation is not performed. When arsenic is ion-implanted at an acceleration voltage of 100 KeV and a dose of 5×10 "an-", heat treatment must be performed at a temperature of 950° C. or less in order to suppress the activation rate to 50% or less. Conventionally, in order to recover defects on the substrate surface formed by ion implantation, annealing is always performed at 1000°C or higher for 30 minutes, but in the present invention, the process is performed at a low temperature and the defects are used as they are for growth. It is characterized by rapid oxidation.

The relationship between the thickness of the re-oxidation film (5) in accelerated oxidation and the thickness of the buffer oxide film (2) in this process will be explained with reference to Figure 4. Figure 4 shows arsenic at a dose of 5X10''. cm-'' and acceleration voltages of 40 KeV, 80 KeV, and 130 Ke. When the oxide film (2) is approximately 140 thick, the thickness of the re-oxidized film (5) reaches a peak of 4000 thick.When the acceleration voltage is 80 KeV, the buffer oxide film (2)
When the number of people is about 350, the thickness of the re-oxidized film (5) reaches a peak of 4000 people. Furthermore, in the case of an accelerating voltage of 130 KeV, when the buffer oxide film (2) is about 600 layers, the re-oxidation film (5)
Its thickness peaks at 4,000 people. From this result, the thickness of the buffer oxide film (2) is accelerated so that the peak of ion concentration is located on the surface of the substrate (1), as shown in Figure 3. 220 people at voltage 40KeV, 380 people at acceleration voltage 80KeV, acceleration voltage 1
It is clear that this value agrees well with the value of 620 people at 30 KeV. The accelerated oxidation of the present invention will now be analyzed as follows. There is a peak of defects caused by ion implantation near the average range R during ion implantation, and the buffer oxide film (2
) is set near π2, a defect peak appears on the surface of the substrate (1).

When the surface of this substrate (1) is thermally oxidized at a low temperature, oxidation proceeds before defects are annealed, and accelerated oxidation continues due to defect peaks.

The dotted line characteristic diagram shown in Figure 4 shows arsenic at an accelerating voltage of 80 Ke.
This is the case where ions were implanted at a dose of 5 x 10 "Cm-" and then annealed at 1000°C for 30 minutes. It is not oxidized quickly and becomes only about 1,700 people thick. Furthermore, the characteristics indicated by the dotted line do not form a peak with respect to the buffer oxide film thickness, indicating that defects on the substrate surface are recovered by annealing.

From this experiment, it is clear that the accelerated oxidation of the present invention depends on defect peaks on the substrate surface.

FIG. 7 shows the speed increase characteristics of the reoxidized film (5) with respect to its atomic weight. This graph shows the oxidation conditions: 20 minutes dry 02
Oxidation, pyrooxidation for 20 minutes, and ion implantation into the substrate in an acceleration chamber JEf 80 Key, dose 5×10I6
Performed with cITl-1, /< y -77 oxide film (2)
The film thickness is set so that the acceleration peaks at an acceleration voltage of 80 KeV. The speed increase is based on the film thickness of a virgin wafer under the same oxidation conditions. As is clear from Figure 7, when boron (B) is used as an impurity, the speed increase is 1.3.
When phosphorus (P) is used, the speed is increased 3.5 times, and when arsenic (A, ) is used, the speed is increased 9 times.

It can be seen from this that the larger the atomic weight, the larger the defects, and the more accelerated oxidation is promoted.

Therefore, in this step, a thick re-oxidized film (6) is formed on the ion-implanted layer (4) through accelerated oxidation, and a thin re-oxidized film (7) is formed on the surface of the other substrate (1) through normal oxidation. It is formed. Specifically, arsenic was applied at a dose of 5 at an acceleration voltage of 80 KeV.
When ion implantation is carried out at X 10 "cm-", if a thick re-oxidized film (6) is attached to floats of about 7000 people, a thin re-oxidized film (7) can be attached to about 100 people at the same time. From now on, the thick reoxidation film (6) can be used as a field oxide film, and the thin reoxidation film (7) can be used as a gate oxide film.

(g) Effects of the Invention According to the present invention, a silicon oxide film can be thickly deposited in a short time by accelerated oxidation, so that the work efficiency can be greatly improved. Specifically, in the present invention, a reoxidation film (5) of about 4000 people can be formed by pyrooxidation at 875°C for 20 minutes, whereas in the conventional method, about 4000 people can be formed by wet O2 oxidation at 1000°C for 1.5 hours. An oxide film can be formed.

Furthermore, in the present invention, since oxide films (5) of different thicknesses can be formed simultaneously in the same process, there is an advantage that the oxidation treatment, which conventionally required two processes, can be realized in a single process. Moreover, in the present invention, a thick reoxidized film (6) can be formed in the oxidation time of a thin reoxidized film (7), resulting in extremely high efficiency.

[Brief explanation of drawings]

1A to 1D are cross-sectional views for explaining the method of manufacturing a semiconductor device of the present invention, FIG. 2 is a cross-sectional view for explaining the peak of ion concentration in the present invention, and FIG. A characteristic diagram explaining the relationship between buffer oxide film thickness and ion concentration,
FIG. 4 is a characteristic diagram illustrating the relationship between buffer oxide film thickness and re-oxidation film thickness in the present invention, and FIG. 5 is a characteristic diagram illustrating the relationship between annealing temperature and arsenic activation rate in the present invention. , FIG. 6 is a characteristic diagram illustrating the relationship between dose amount and re-oxidation film thickness in the present invention, and FIG. 7 is a characteristic diagram illustrating the relationship between atomic weight and re-oxidation film speed increase in the present invention. be. (1) is a semiconductor substrate, (2) is a buffer oxide film, (3)
is a photoresist film, (4) is an ion implantation layer, and (5) is a reoxidation film. Applicant Sanyo Electric Co., Ltd. and one other representative Patent attorney Shizuo Sano Figure 1 A Figure 1 mouth Figure 1 C Figure 1 Design

Claims (1)

[Claims] 1. A step of selectively forming an ion-implanted impurity layer on one main surface of the semiconductor substrate such that the peak of ion concentration is located at or near the surface, and after exposing the surface of the semiconductor substrate, the substrate is thermally oxidized at a low temperature. 1. A method of manufacturing a semiconductor device, comprising the step of simultaneously forming oxide films of different thicknesses.