JPH10189575A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen a thermal load imposed on a BPSG film in a reflow process so as to planarize the BPSG film by a method wherein a silicon oxide doped with impurities is formed on a semiconductor substrate where a device is formed, and then the semiconductor substrate is subjected to a thermal treatment in an ammonia atmosphere. SOLUTION: A transistor structure equipped with a polysilicon gate electrode 2 is formed on a silicon semiconductor substrate 1. An undoped silicon oxide film 3 of comparatively high quality is formed thereon as a protective film 3. For instance, a BPSG film 5 is formed as an interlayer insulating film on all the surface by a CVD method. The silicon semiconductor substrate 1 is introduced into an oven filled with N2 at an atmospheric pressure, and then the oven is filled with NH3 replacing N2 , treated up to a temperatures of 700 to 800 deg.C, and then kept at a constant temperature. NH3 is fed into the oven at a flow rate of 10 to 50slm or so, and the BPSG film 5 is subjected to a reflow process for 20 to 50 minutes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and is particularly suitably applied to, for example, a method for forming an interlayer insulating film in a multilayer wiring structure.

[0002]

2. Description of the Related Art An interlayer insulating film in a multilayer wiring structure includes:
A boron-phosphorus silicate glass (BPSG) film, which is a silicon oxide film containing boron (B) and phosphorus (P), is generally used. This is because the BPSG film is subjected to a heat treatment after the CVD film formation. This is because the film is a high-performance insulating film having a feature that a flow phenomenon of a film called reflow occurs to greatly flatten the element surface.

In a conventional method of manufacturing a semiconductor device using a BPSG film, for example, as shown in FIG. 3A, a transistor structure (not shown) having a gate electrode 2 formed on a silicon substrate 1 is formed. A non-doped silicon oxide film 3 is formed thereon as a protective film by, for example, a plasma enhanced chemical vapor deposition (plasma CVD) method.
As shown in FIG. 3B, a BPSG film 5 is deposited by a CVD method, and then, as shown in FIG. 3C, in a nitrogen (N ₂ ) atmosphere at about 700 to 900 ° C. for 20 to 50 minutes. Is performed, and a reflow process for flattening the BPSG film 5 is performed.

Alternatively, as shown in FIG. 4A, after a transistor structure (not shown) having a gate electrode 2 is formed on a silicon substrate 1, a silicon nitride film 4 is formed thereon as a protective film. Next, as shown in FIG. 4B, a BPSG film 5 is deposited by a CVD method.
As shown in (c), the BPSG film 5 is reflowed in a water vapor atmosphere.

[0005]

However, for the purpose of reducing the deterioration of the element characteristics in the manufacturing process of the semiconductor device, for example, the transistor characteristics (Vt characteristics, etc.), after the formation of the elements such as the transistors, the heat treatment is preferably performed as much as possible. It is necessary to suppress the load, and it is an important subject to reduce the temperature in the reflow process.

In the above-described conventional reflow treatment in a nitrogen atmosphere, the impurity concentration (B, P concentration) in the BPSG film is
It is possible to lower the temperature of the reflow process by increasing the temperature and lowering the phase transition temperature of the film itself to improve the fluidity of the film.
There is a limit on the film quality such as the problem of occurrence of deposition. Further, the conventional reflow treatment in a steam atmosphere is effective as a method for lowering the temperature, but in this method, it is necessary to provide a silicon nitride film under the BPSG film as a protective film,
There are problems such as film peeling due to internal stress of the silicon nitride film and a problem that a refresh effect in a hydrogen sintering process in a later process is hindered by the silicon nitride film and is reduced.

[0007]

According to the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: forming a silicon oxide film doped with an impurity on a semiconductor substrate having elements formed thereon; And a second step of heat-treating the semiconductor substrate in an ammonia atmosphere after the first step.

[0008] In one embodiment of the present invention, in the second step,
The semiconductor substrate is heat-treated at a temperature of 700 to 800C.

In one embodiment of the present invention, the silicon oxide film contains boron and phosphorus.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described according to preferred embodiments.

First, as shown in FIG. 1A, a transistor structure having a gate electrode 2 made of, for example, polysilicon is formed on a silicon semiconductor substrate 1. Note that a gate insulating film, a source / drain diffusion layer, and the like having a transistor structure are not shown. Next, on it, as a protective film,
For example, a non-doped silicon oxide film 3 having relatively good film quality is formed by a plasma CVD method.

Next, for example, as shown in FIG.
A BPSG film 5 is formed on the entire surface as an interlayer insulating film by a CVD method. Here, for example, the BPSG film 5 contains boron (B) in an amount of about 2.0 to 4.0 wt% and phosphorus (P) in an amount of 5.5 to 5.5%.
It contains about 7.0% by weight.

Next, as shown in FIG. 1 (c), after the silicon semiconductor substrate 1 is placed in a furnace in which N _{2 has been} replaced at atmospheric pressure, the atmosphere in the furnace has been replaced with NH ₃ and the furnace temperature has been reduced. 70
Raise the processing temperature to about 0 to 800 ° C and stabilize it. Then, while supplying NH ₃ into the furnace at a flow rate of about 10 to 50 slm, the BP is maintained at atmospheric pressure for about 20 to 50 minutes.
The reflow process of the SG film 5 is performed. After the reflow process is completed, lower the furnace temperature to below the reflow temperature and set the atmosphere to N
After sufficiently replacing H _{3 with} N ₂ , the furnace body is opened and the silicon semiconductor substrate 1 is left in an air atmosphere to lower the temperature.

FIG. 2 shows the nitrogen (N) concentration distribution in the wafer thickness direction in the BPSG film after the reflow in the case of the NH ₃ atmosphere reflow according to the present invention and in the case of the conventional N ₂ atmosphere reflow. FIG. 2 also shows the concentration distributions of boron (B), phosphorus (P), silicon (Si), and oxygen (O) for reference. The concentration in the film is indicated by a relative value.

As can be seen from FIG. 2, the NH according to the invention
_{In the three} atmosphere reflow, more nitrogen (N) diffuses into the BPSG film than in the conventional N ₂ atmosphere reflow. This means that the film fluidity of the BPSG film is improved. As a result, in the NH ₃ atmosphere reflow according to the present invention, the reflow processing temperature is reduced by about 50 to 100 ° C. in the same processing time as the conventional N ₂ atmosphere reflow in which the concentrations of boron and phosphorus in the BPSG film are the same. Can be.

[0016]

According to the present invention, a BPSG film formed on a semiconductor substrate, for example, is heat-treated in an ammonia atmosphere and reflowed, whereby the BPSG film is more reflowed in a nitrogen atmosphere than in the conventional case. A large amount of nitrogen diffuses into the membrane, and the membrane fluidity is improved. Therefore, for example, the concentration of boron and phosphorus in the BPSG film and the reflow processing time remain the same, and the reflow processing temperature can be made lower than before. As a result, the thermal load in the reflow process is reduced, so that the deterioration of the device characteristics, for example, the transistor characteristics (Vt characteristics, etc.) is suppressed, and further, while the impurity deposition of the BPSG film is suppressed as in the related art, The flattening of the BPSG film equivalent to the conventional one can be achieved.

Also, unlike the conventional case of performing reflow treatment in a water vapor atmosphere, for example, there is no need to form a silicon nitride film as a protective film on the gate electrode. Does not occur.

[Brief description of the drawings]

FIG. 1 is a process sectional view illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a graph showing an impurity concentration distribution in a film of a semiconductor device.

FIG. 3 is a process sectional view showing a conventional method for manufacturing a semiconductor device.

FIG. 4 is a process sectional view illustrating another conventional method for manufacturing a semiconductor device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 silicon semiconductor substrate 2 gate electrode 3 silicon oxide film 4 silicon nitride film 5 BPSG film

Claims (3)

[Claims] A first step of forming a silicon oxide film to which an impurity is added on a semiconductor substrate on which an element is formed; and a heat treatment of the semiconductor substrate in an ammonia atmosphere after the first step. 2. A method for manufacturing a semiconductor device, comprising: 2. The method according to claim 1, wherein in the second step,
A method for manufacturing a semiconductor device, wherein the semiconductor substrate is heat-treated at a temperature of 700 to 800C. 3. The method according to claim 1, wherein the silicon oxide film contains boron and phosphorus.