JPH05145068A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To provide a manufacturing method capable of forming the MIS structured part of the semiconductor device having metal-oxide.nitride insulating film-semiconductor (MIS) structured part more easily than any other conventional method. CONSTITUTION:A tungsten oxide film 13 is formed on a prospective MIS structured part formation region of a silicon substrate 11. Next, the substrate 11 with the tungsten oxide film 13 formed thereon is heat-treated in hydrogen atmosphere containing N2O or NH3 gas. The mixing amount of N2O gas or NH3 gas is specified so that the water content range may be 0,01-1% in partial pressure ratio while the temperature range may be 500-1200 deg.C. Through these procedures, an oxide.nitride insulating film 15 can be formed on the part of the silicon substrate 11 in contact with the tungsten oxide film 13. Furthermore, the tungsten oxide film 13 is reduced to be turned into a tungsten film 13a thus making it usable as a gate electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention is applied to MIS (Metal Insu
The present invention relates to a method for manufacturing a semiconductor device having a lator semiconductor) structure portion, and more particularly to a method for manufacturing a semiconductor device characterized by the step of forming a MIS structure portion.

[0002]

2. Description of the Related Art MIS field effect transistors (hereinafter
It may also be abbreviated as “MISFET”. ), MIS diode, EPROM (Electrically Programmable RO)
M), E ² PROM (Electrically Erasable Programm
A semiconductor device such as an able ROM) has a structure portion (hereinafter referred to as “MIS structure portion”) in which a semiconductor, an insulating film, and a metal are laminated.

A silicon oxide film (SiO ₂ ) formed by thermally oxidizing a silicon substrate is generally used as an insulating film in the MIS structure portion of such a semiconductor device. However, with the miniaturization of this type of semiconductor device, it is necessary to reduce the thickness of the insulating film, and as an insulating film that replaces the silicon oxide film, for example, the document a relating to the applicant of the present application can be used.
(IEEE (IE) IEDM Tech.
Dig. (IDM Technical Digest), (1990), pp. 425-428), an oxynitride insulating film has been proposed.

In this document a, a silicon substrate is heated by an infrared lamp in an oxygen atmosphere (so-called RTP (Rapid Ther.
mal process) to form a silicon oxide film on the surface of the substrate, and then further heat the substrate in an N ₂ O atmosphere to form an oxynitride insulating film, and the evaluation results of this film and the gate insulating film. MOS (Metal Oxide S
EMI) FET evaluation results are disclosed. It has been shown that the oxynitride insulating film is superior to the silicon oxide film in reliability against electric stress.

[0005]

However, the method of forming an oxynitride insulating film disclosed in the above document a requires a step of thermally oxidizing the silicon substrate, such as previously thermally oxidizing the silicon substrate and then nitriding the silicon substrate. there were.

Considering that reduction of the number of steps is effective for improving the manufacturing yield of semiconductor devices and cost reduction, and reduction of the number of steps is generally effective for improving the quality of semiconductor devices, It is desired to reduce the number of steps.

The present invention has been made in view of the above points, and therefore an object of the present invention is to form a semiconductor device using an oxynitride insulating film as an insulating film of a MIS structure portion when the insulating film is formed. It is intended to simplify the forming process of the.

[0008]

In order to achieve this object, the inventor of this application has conducted various studies. As a result, Document b ("Electronic Material Series VLSI Thin Film Technology" (September 1986), Maruzen Co., pp.163-).
It was thought that the above object could be achieved by applying the technology disclosed in 165). This technique was a technique in which a refractory metal is not oxidized and only silicon is selectively oxidized in a system in which a refractory metal film and silicon coexist. Hereinafter, a specific description will be given with reference to FIG.

FIG. 2 shows that in a hydrogen atmosphere containing water vapor,
It is a thermal equilibrium curve of tungsten (W) and silicon (Si). It is quoted from the above-mentioned document b. (A) in FIG. 2 is a reaction of W, that is, W + 3H ₂ O = WO ₃ + 3H.
₂ represents the thermal equilibrium of ₂ and (b) is the reaction of Si, that is, Si
It represents the thermal equilibrium of + 2H ₂ O = SiO ₂ + 2H ₂ .

The characteristic diagram shown in FIG. 2 shows that when the conditions of the temperature and the water content of the hydrogen atmosphere containing water vapor are above the curves (a) and (b) shown in FIG. It is shown that the reaction of Si proceeds in the right side direction of the corresponding reaction equation. This means that Si is oxidized in the range sandwiched by the curves (a) and (b) in FIG. 2 (the shaded area in FIG. 2), but W is not strongly oxidized in the reduction reaction. This means that selective oxidation is possible.

However, as it is, the reduction of the tungsten oxide film and the formation of the silicon oxide film are performed, and the nitriding is not performed, so that the object of the present invention is not achieved.

[0012] Therefore, the inventor of this application is WO ₃
If a metal oxide film such as MoO ₃ or MoO _{3 is} brought into contact with the silicon substrate and heat treatment is performed in this state in a reducing atmosphere containing nitrogen,
For example, in the case of using a WO _3, 2WO ₃ + 3Si
→ It was thought that the nitridation of the SiO ₂ film would occur along with the reaction of 2W + 3SiO ₂ , and an oxynitride insulating film that could be used as an insulating film of the MIS structure portion would be formed on the silicon substrate in contact with this WO ₃ .

Therefore, according to the present invention, in manufacturing a semiconductor device having a structure portion in which an oxynitride insulating film and a metal film are laminated in this order on a silicon substrate, formation of the above-mentioned structure portion is performed by forming the structure portion of the silicon substrate. It is characterized in that it is performed in a step including a step of forming a metal oxide film on the formation planned region and a step of heat-treating the silicon substrate on which the metal oxide film has been formed in a reducing atmosphere containing nitrogen.

In implementing the present invention, a tungsten oxide film or a molybdenum oxide film is used as the metal oxide film, and the reducing atmosphere containing nitrogen is N ₂ O.
It is preferably formed by introducing (dinitrogen monoxide) gas or NH ₃ (ammonia) gas into a hydrogen atmosphere.

The silicon substrate referred to in the present invention is
The silicon substrate itself, the one in which an epitaxial layer such as a silicon layer or a polysilicon layer is formed on the silicon substrate, and the one in which a silicon-based epitaxial layer (for example, a Si-Ge layer) containing an element other than silicon is formed. I will say.

[0016]

According to the present invention, the metal oxide film is in direct contact with the region for forming the MIS structure portion of the silicon substrate. Then, in this state, since the structure is heat-treated in a reducing atmosphere containing nitrogen, oxygen is supplied from the metal oxide film to the silicon substrate side in the form of H ₂ O or OH and is in contact with the metal oxide film of the silicon substrate. A silicon oxide film is formed on the exposed portion. Further, in parallel with the formation of such a silicon oxide film, nitrogen in the reducing atmosphere acts on a portion of the silicon substrate which is in contact with the metal oxide film, and an oxynitride insulating film is formed on this portion.
For example, FIG. According to the results of SIMS (Secondary Ion Mass Spectroscopy) described in 1 (b) and (c), nitrogen is unevenly distributed at the interface between the silicon substrate and the silicon oxide film. It is thought to occur. The oxynitride insulating film thus formed is
It becomes the insulating film of the IS structure part. Further, the metal obtained by reducing the metal oxide film when the silicon oxide film is formed is the metal of the MIS structure portion, that is, the MOSFE.
If it is T, it can be a gate electrode, and if it is a MOS diode, it can be an electrode gate electrode. As a result, the metal and oxynitride insulating film in the MIS structure portion are formed in self alignment.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a method for manufacturing a semiconductor device of the present invention will be described below with reference to the drawings. Here, MO
An example in which the method of the present invention is applied when forming the MIS structure portion of an SFET or a MOS diode will be shown. Figure 1
(A)-(D) is a process drawing used for the description, and is a process drawing shown by a cross section of the sample cut in the thickness direction of the silicon substrate. It should be noted that each of these drawings merely schematically shows the shape, size, and arrangement relationship of each component so that the present invention can be understood.

First, a silicon substrate 11 is prepared (see FIG. 1).
(A)). An insulating film (not shown) for element isolation is usually formed on the silicon substrate 11 by, for example, the LOCOS method. Further, in the case of forming a MOSFET, impurities are introduced into the channel formation planned region of the substrate 11 for controlling the threshold voltage.

Next, a tungsten oxide film (for example, WO ₃ ) in this case is formed as a metal oxide film 13 in a predetermined thickness on the MIS structure portion formation planned region of the silicon substrate 11 (FIG. 1B). Here, the MIS structure portion formation planned region is a gate electrode formation region, M
If it is an OS diode, since it is a metal electrode formation region,
The planar shape of the tungsten oxide film 13 is, for example, MO.
The shape corresponds to the gate electrode of the SFET and the shape of the electrode of the MOS diode. Further, the stoichiometric ratio and the film thickness of the tungsten oxide film 13 are one of the factors that determine the film thickness of the silicon oxide film to be formed later on the silicon substrate 11, and therefore are set to appropriate values according to the design. However, if the thickness of the tungsten oxide film 13 is too thick, nitriding may not be performed well, so this point is also taken into consideration when determining the film thickness.

The tungsten oxide film 13 can be formed, for example, by forming the film by a sputtering method or a CVD method and then patterning this film into a predetermined shape by a known photolithography technique and etching technique. Specific examples of the film forming method include a sputtering method using a target made of a tungsten oxide film, a sputtering method using a target made of tungsten and mixing an oxygen gas with a sputtering gas, or a WF ₆ gas and an oxygen gas. SiH
A CVD method using ₄ gases and the like can be mentioned.

Next, the silicon substrate 11 on which the tungsten oxide film 13 is formed is heat-treated in a reducing atmosphere containing nitrogen. In this embodiment, the heat treatment is performed in a hydrogen atmosphere containing N ₂ O gas or NH ₃ gas. Atmosphere and temperature conditions at that time are such that the metal oxide film can be reduced and a portion of the silicon substrate in contact with the metal oxide film can be selectively oxidized (hereinafter, referred to as "selective oxidation") and can be nitrided. Set the conditions. For example, the condition of the region sandwiched between the curve (a) and the curve (b) shown in FIG. 2 may be satisfied and nitriding may occur. Among these conditions, the atmospheric condition is sandwiched between the curve (a) and the curve (b) in FIG. 2 by oxygen (O ₂ ) or hydrogen (H ₂ ) contained in N ₂ O gas or NH ₃ gas. It can be formed by optimizing the partial pressure ratio of the N ₂ O gas or the NH ₃ gas to the hydrogen gas so that the amount of water defined in the defined region can be obtained.
However, if the partial pressure of N ₂ O gas or NH ₃ gas is too high, the reduction of the tungsten oxide film will not be performed well, so the upper limit is determined by this. N ₂ O gas or NH
A suitable partial pressure ratio of ₃ gases to hydrogen gas is N ₂ used.
Although it varies depending on the purity of the O gas or NH ₃ gas, it is considered to be about several percent to several dozen percent.

Under such conditions, 2WO ₃ + 3Si
→ The reaction of 2W + 3SiO ₂ progresses, and further this SiO ₂
Nitriding of the film proceeds. As a result, the oxynitride insulating film 1 is formed on the portion of the silicon substrate 11 that is in contact with the tungsten oxide film 13.
5 is formed. The oxynitride insulating film 15 becomes an insulating film in the MIS structure portion. On the other hand, since the tungsten oxide film 13 is reduced by the heat treatment in the reducing atmosphere, it becomes the tungsten film 13a. This tungsten film 13a
Serves as the gate electrode of the MOSFET or the electrode of the MOS diode (FIG. 1 (C)). Here, FIG. 1D is an enlarged cross-sectional view of a P portion of the sample illustrated in FIG. In the oxynitride insulating film 15, nitrogen atoms are unevenly distributed in the vicinity of the interface between the silicon substrate 11 and the oxynitride insulating film 15 (see FIG. 1 (b) and (c) in Document a).
by. ), A portion 17 in which a large amount of nitrogen is taken in is formed in the vicinity of this interface.

According to the experiment conducted by the inventor of this application,
The condition of the heat treatment in the hydrogen atmosphere containing nitrogen is that both the temperature and the water content are in the region between the curve (a) and the curve (b) shown in FIG. It is known that if it is too low, the oxynitride insulating film cannot be formed at an industrial rate, and if it is too high, the quality of the oxynitride insulating film deteriorates. And the temperature of the heat treatment is 500 to 12
The temperature is preferably in the range of 00 ° C., and the water content (H ₂ O) in a hydrogen atmosphere is 0.01 to 100 in terms of partial pressure ratio.
It has been found that a range of 5% is preferable. However, it has been found that even in such a preferable range, the water content is more preferably in the range of 0.01 to 1%, and the temperature is better on the high temperature side.
This is because nitriding can be performed better and a high-quality oxynitride insulating film can be obtained. Such a suitable range is shown by adding Q in FIG.

Although the embodiment of the invention has been described above, the invention is not limited to the embodiment.

For example, although the tungsten oxide film is used as the metal oxide film in the above-mentioned embodiments, another metal oxide film may be used as long as it can selectively oxidize. However, when it is considered that the metal film obtained by reducing the metal oxide film is used as it is as the gate electrode or the electrode for the diode, the MO
Heat resistance is required considering the manufacturing process of the S element.
Therefore, a high melting point metal oxide film is preferable. For example, a molybdenum oxide film is suitable.

Further, in the above-mentioned embodiments, the heat treatment in the reducing atmosphere containing nitrogen is explained as a special step, but this heat treatment is usually carried out in the semiconductor device manufacturing process, for example, impurity activation. Of course, it may be performed by devising the conditions for the heat treatment for conversion.

In the above embodiment, the MOSFET and M
Although the example of forming the MIS structure of the OS diode has been described, the method of the present invention uses an EPROM having a MIS structure including a floating gate made of polysilicon, and an insulating film and a control gate formed on the floating gate. E ²
It is considered that the method can be applied to the case of forming the MIS structure portion of the PROM.

[0028]

As is apparent from the above description, according to the method for manufacturing a semiconductor device of the present invention, the thermal oxidation step in forming the oxynitride insulating film of the MIS structure portion is combined with other steps. Therefore, the manufacturing process of the semiconductor device having the MIS structure portion can be simplified as compared with the conventional case by forming the insulating film portion with the oxynitride insulating film.

Further, the electrode portion and the insulating film portion of the MIS structure portion can be formed in a self-aligned manner, which is also advantageous in this respect.

Further, the film thickness of the oxynitride insulating film in the MIS structure portion can be controlled by controlling the stoichiometric ratio and / or the film thickness of the metal oxide film. Therefore, it is possible to form an extremely thin gate insulating film.

[Brief description of drawings]

1A to 1D are process drawings for explaining an embodiment of the present invention, which is a process drawing of forming a MIS structure portion.

FIG. 2 is a thermal equilibrium diagram of W (tungsten) and Si (silicon).

[Explanation of symbols]

 11: Silicon Substrate 13: Metal Oxide Film (Tungsten Oxide Film) 13a: Metal Film (Tungsten Film) 15: Oxynitride Insulation Film 17: Portion with Large Amount of Nitrogen

Claims (2)

[Claims] 1. When manufacturing a semiconductor device having a structure portion in which an oxynitride insulating film and a metal film are laminated in this order on a silicon substrate, the formation of the structure portion is performed by forming a metal on the region where the structure portion is to be formed on the silicon substrate. A method of manufacturing a semiconductor device, comprising: a step of forming an oxide film; and a step of heat-treating the silicon substrate on which the metal oxide film has been formed in a reducing atmosphere containing nitrogen. 2. The method of manufacturing a semiconductor device according to claim 1, wherein a tungsten oxide film or a molybdenum oxide film is used as the metal oxide film, and the reducing atmosphere containing nitrogen is N ₂ O (dinitrogen monoxide). ) Gas or NH ₃ (ammonia) gas is introduced into a hydrogen atmosphere to form the semiconductor device.