JPH0555587A - Mos device and its manufacture - Google Patents

Abstract

PURPOSE:To provide a MOS device which consists of a silicon nitride film with an improved insulation breakdown voltage and a gate insulation film where an interface state with a silicon substrate is stable and its manufacturing method. CONSTITUTION:A double-layered gate insulation film is formed by depositing a first silicon nitride film 2 and a second silicon nitride film 3, are on the other, by direct nitriding on a silicon substrate 1. The first silicon nitride film 2 is formed by heating the silicon substrate rapidly and in a short time within ammonium environment and the second silicon nitride film 3 is formed by a normal vapor growth method. An interface between silicon and silicon nitride film can be stabilized by direct nitriding and a sufficient gate insulation breakdown voltage can be obtained by the deposited second silicon nitride film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to a MOS field effect transistor and a manufacturing method thereof.

[0002]

2. Description of the Related Art A silicon oxide film has been used as a gate insulating film of a conventional silicon MOS transistor. The gate insulating film is becoming thinner with the performance and miniaturization of transistors. When the insulating film thickness reaches a level of 10 nm or less, it is becoming difficult to guarantee the withstand voltage of the gate insulating film due to defects such as pinholes in a silicon oxide film formed by a normal thermal oxidation method. ..

In order to deal with this problem, a technique using a silicon nitride film-based material as a gate insulating film has been proposed. Since the silicon nitride film has a dielectric constant about twice that of the silicon oxide film, when it is used as a gate insulating film of a MOS transistor, if it has a physically same film thickness, it is electrically about 1 times as thick as the silicon oxide film. It is possible to reduce the thickness to 1/2. That is, since the electrically insulating gate insulating film can be realized by a film physically thicker than the silicon oxide film, it is easy to form a film having few defects such as pinholes. As a gate insulating film using a silicon nitride film, MNOS in which a silicon nitride film is formed on a silicon oxide film by vapor phase epitaxy
The (metal / nitride / oxide / semiconductor) structure is well known. Recently, a nitridide oxide structure in which a silicon nitride film is directly formed on the surface of a silicon oxide film by a nitriding method is published in 1980, Journal of Electrochemical Society, 127, 2053-2057 (J. Select).
rochem. Soc. , Vol. 127, pp. 20
53-2057, (1980)), or the 21st SDC Conference held in 1989, Proceedings 19
7-200 pages (Extended Abstract)
ts of the 21st Conf. SSDM,
pp. 197-200, 1989) and the like.

[0004]

The conventional technique using a silicon nitride film has the following problems because it has a laminated structure with a silicon oxide film.

(1) In the case of the MNOS structure, a large amount of charge traps are formed at the interface between the silicon oxide film and the silicon nitride film, and the charge injection type threshold voltage instability when used as a gate insulating film of a MOS type transistor. cause. That is, it exhibits an unstable interface state.

(2) The nitridide oxide structure is essentially a silicon oxide film, and the advantages of a silicon nitride film having a large dielectric constant are not fully utilized.

The present invention uses the gate insulating film composed only of the silicon nitride film to realize the above (1),
It is intended to solve the problem of (2). However, even when the gate insulating film is composed of only the silicon nitride film, there are the following problems to be solved.

(1) When a silicon nitride film is deposited on a silicon substrate by a normal vapor phase growth method, a thin natural oxide film is formed before the silicon nitride film grows, and eventually the MNO is formed.
The S structure is formed, the interface with the silicon substrate becomes unstable, and the threshold voltage fluctuates.

(2) The silicon nitriding technique can be used to directly form a silicon nitride film on silicon.
Only a very thin silicon nitride film can be formed within a practical temperature and time range, and it cannot be used as a gate insulating film.

Therefore, a main object of the present invention is to provide a structure of a gate insulating film which is made of a silicon nitride film having an excellent withstand voltage and has a stable interface with a silicon substrate, and a method for manufacturing the same. That is.

[0011]

The semiconductor device of the present invention comprises:
At least a first silicon nitride film formed by directly nitriding silicon and a second silicon nitride film deposited by a physical or chemical method on the first conductivity type silicon substrate are laminated. It has a gate insulating film. Further, in a manufacturing method for realizing such a structure, a step of forming a first silicon nitride film by rapidly heating a surface of a silicon substrate in an ammonia atmosphere for a short time, and a step of forming a second silicon nitride film thereon. The step of depositing a silicon nitride film is included. Further, the manufacturing method as described above particularly includes a step of forming a silicon oxide film on the surface of the second silicon nitride film. Further, the manufacturing method as described above particularly includes a step of depositing the second silicon nitride film by a low pressure chemical vapor deposition method.

[0012]

The present invention will be described below with reference to the drawings. 1 is a sectional view of a semiconductor device according to a first embodiment of the present invention. The p-type silicon substrate 1 is heated at 1000 ° C. for 3 hours in an ammonia atmosphere by rapid heating using a halogen lamp.
When heated for 0 seconds, the first silicon nitride film 2 having a thickness of about 2 nm is formed. Then, a second silicon nitride film 3 having a thickness of 10 nm is deposited by a normal chemical vapor deposition method using silane gas and ammonia. Next, a gate electrode 5 made of polycrystalline silicon containing phosphorus, which is an n-type impurity.
To form. After that, the n-type source and drain 6, the interlayer insulating film 7,
Aluminum source and drain electrodes 8 are formed.

The gate insulating film of the completed device has a laminated structure of a first silicon nitride film 2 obtained by directly nitriding silicon and a second silicon nitride film 3 deposited by chemical vapor deposition, The film thickness converted to the entire silicon oxide film was about 7 nm. The method for forming the first and second silicon nitride films in this embodiment is not limited to this. The purpose of the direct nitridation of silicon for forming the first silicon nitride film is to realize a state in which there is no natural oxide film on silicon or a state where it is as small as possible, and can be appropriately changed in relation to other requirements. .. For example, from the viewpoint of directly converting the natural oxide film existing before the nitriding treatment into a silicon nitride film, heating at the highest temperature is desirable, and from the viewpoint of removing such a natural oxide film, it is preferable to use a vacuum or reduced pressure atmosphere. High temperature treatment is effective. However, extreme high-temperature treatment causes adverse effects such as thermal strain in the silicon gas and roughening of the substrate surface. The condition of this embodiment is one of the optimum conditions in consideration of the above problems. For depositing the second silicon nitride film, a sputtering method or the like can be used in addition to the chemical vapor deposition method.
Although the present embodiment has been described with reference to the n-channel type MOS transistor, it can be similarly applied to the p-channel type MOS transistor by changing the conductivity type.

FIG. 2 is a sectional view of a semiconductor device according to the second embodiment of the present invention. After depositing the second silicon nitride film 3 as in the first embodiment, an oxidation treatment was performed in a steam atmosphere at 900 ° C. to form a silicon oxide film 4 of about 2 nm on the surface. Others are the same as those in the first embodiment. With the addition of this step, a part of the silicon nitride film was converted into the silicon oxide film 4, so that the thickness of the gate insulating film converted into the silicon oxide film was increased to about 8 nm. However, a pinhole-like defect of the silicon nitride film can be filled by the oxidation treatment, and the withstand voltage can be improved.

FIG. 3 is a sectional view of a semiconductor device according to the third embodiment of the present invention. A MOS transistor was manufactured in a vertical direction in a groove 9 that was dug vertically to the surface of the p-type silicon substrate 1. In this embodiment, as in the first embodiment, about 2n
m of the first silicon nitride film 2 is formed, and then 1/10
10 nm by low pressure chemical vapor deposition method of about 00 atm
The second silicon nitride film 3 having a thickness of 1 was deposited. When the silicon nitride film 3 is deposited in the narrow groove 9 as in this embodiment, the film coverage on the bottom and side walls of the groove 9 becomes a problem. It can be greatly improved by using vapor deposition at low pressure.

[0016]

As described above, the present invention uses a gate insulating film which is a stack of a silicon nitride film formed by direct nitriding of silicon and a silicon nitride film formed by a deposition type growth method by a physical or chemical method. Has the following effects.

(1) Since there is almost no silicon oxide film at the interface between the silicon and silicon nitride films, the instability of the charge injection type threshold voltage of the MOS transistor can be suppressed. This development can be evaluated by examining the CV characteristics of the MOS structure. FIG. 4 shows a MOS diode using a 12 nm silicon nitride film as a gate insulating film, which was manufactured at the same time as the first embodiment, and a 12 nm film formed by a normal vapor phase growth method.
MOS formed by using the above silicon nitride film as a gate insulating film
The CV characteristic of a diode is shown. The diode manufactured in the ordinary vapor phase growth method exhibits hysteresis when a gate voltage is applied, whereas the diode of the first embodiment exhibits stable characteristics. This indicates that the present invention has excellent resistance to threshold voltage fluctuations due to charge injection.

(2) A second silicon layer is formed on the first silicon nitride thin film having a thickness of about 2 nm by direct nitriding of silicon by an ordinary method.
Since the silicon nitride film can be deposited to an arbitrary thickness, a desired film thickness, that is, a film thickness of about 8 to 15 nm required for a normal MOS transistor can be easily realized. It is almost impossible to achieve such a film thickness by direct nitriding of silicon.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining a first embodiment of the present invention.

FIG. 2 is a sectional view for explaining a second embodiment of the present invention.

FIG. 3 is a sectional view for explaining a third embodiment of the present invention.

FIG. 4 is a diagram for explaining the effect of the present invention by comparison with the prior art and is a graph showing the CV characteristic of a MOS diode.

[Explanation of symbols]

 1 p-type silicon substrate 2 first silicon nitride film 3 second silicon nitride film 4 silicon oxide film 5 gate electrode 6 n-type source / drain 7 interlayer insulating film 8 aluminum source / drain electrode 9 groove

Claims (4)

[Claims] 1. A first conductivity type silicon substrate, a first silicon nitride film formed by directly nitriding the silicon substrate, and a physical or chemical method for depositing on the first silicon nitride film. A MOS type semiconductor device comprising a gate insulating film having at least a second silicon nitride film as a constituent element. 2. A first silicon nitride film is formed by heating the surface of a silicon substrate in an ammonia atmosphere for a short period of time, and a second silicon film is formed by a physical or chemical method.
A method of manufacturing a semiconductor device, comprising forming a gate insulating film by a process including depositing a silicon nitride film. 3. The method of manufacturing a semiconductor device according to claim 2, further comprising the step of forming a silicon oxide film on the surface of the second silicon nitride film. 4. The method of manufacturing a semiconductor device according to claim 2, wherein the second silicon nitride film is deposited by a low pressure chemical vapor deposition method.