JPH01312838A - Formation of insulating film - Google Patents

Abstract

PURPOSE:To decrease density of generated trap level and to improve durability of an insulating film by forming an oxide film on a nitride film by CVD method. CONSTITUTION:After a silicon oxide film 2 is grown on a main surface of a single crystalline silicon substrate 1, a silicon nitride film 3 is selectively formed on the silicon oxide film 2 and an isolated oxide film is selectively formed. After the silicon oxide film 2 and the silicon nitride film 3 are eliminated, the silicon nitride film 3 is formed by vacuum CVD method. A natural oxide film 6 is also formed at the same time. Then a top oxide film 9 which consists of a silicon oxide film is formed on a silicon nitride 5 by vacuum CVD method. Accordingly to this constitution, density of trap level generated during the process is extremely small and does not have a detrimental effect on a multilayer insulating film, thus forming a durable multilayer insulating film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an insulating film forming method for forming a multilayer insulating film consisting of a nitride film and an oxide film on a semiconductor substrate.

[Conventional technology]

FIGS. 3(a) to 3(e) are cross-sectional views showing a method of manufacturing a conventional MIS capacitor having a multilayer insulating film made of a nitride film and an oxide film, respectively. The manufacturing method will be described below with reference to the same figure.

First, a silicon oxide film 2 that will become a pad oxide film is grown on the main surface of a single-crystal silicon substrate 1, and then a silicon nitride film 3 is selectively grown on this silicon oxide film 2, as shown in FIG. to form.

Next, by thermally oxidizing the silicon substrate 1, the silicon substrate 1 is thermally oxidized (
As shown in b), an oxide film 4 is selectively formed.

After removing the silicon oxide film 2 and the silicon nitride film 3, for example, the silicon nitride film 3 is formed into a film with a thickness of 100 g! by low pressure CVD method. ! form 5. At this time, since oxygen in the air adheres to the silicon substrate 1-[ after the removal of the silicon oxide film 2 and before the deposition of the silicon nitride film 5, as shown in FIG.
As shown in , naturally oxidized FJ6 is formed at the same time.

Next, the silicon nitride film 5 is oxidized by a thermal oxidation method at a temperature of about 900° C. to form a top oxide film 7, which is a silicon oxide film of about 30% thickness, as shown in FIG. 3(d).

Next, a polysilicon film doped with phosphorus is grown on the top oxide film 7 and patterned.
A gate electrode 8 is formed as shown in FIG. In this way, the top oxide film 7. A MIS transistor having a multilayer insulating film consisting of a silicon nitride film 5 and a natural oxide film 6 can be manufactured. By forming the insulating film into multiple layers in this manner, the durability of the insulating film is improved, and the reliability of the MIS type semiconductor device is improved.

(Problem to be Solved by the Invention) Formation of a multilayer insulating film using a nitride film and an oxide film has conventionally been performed as described above. The top oxide film 7 has been formed. Therefore, during the formation of the top oxide film 7, trap units with a high density are generated at the interface between the top oxide film 7 and the silicon nitride film 5. The connecting beam is t for this trap unit.
The captured charge generates an electric field in the top oxide film 7 or silicon nitride film 5, which impedes the durability of the multilayer insulating film.
There is a problem in that it adversely affects the lifespan of MIS type semiconductor devices such as capacitors.

This invention was made in order to solve the problems mentioned in J of -1-, and its purpose is to promote a method for forming a highly durable multilayer insulating film consisting of a nitride film and an oxide film. do.

[Means to solve the problem]

The method for forming an insulating film according to the present invention is a method for forming a multilayer insulating film composed of a nitride film and an oxide film, and includes a step of forming the nitride film on a semiconductor substrate, and a step of forming the nitride film on the nitride film. The method includes a step of forming the oxide film by a CVD method.

[Effect]

In this invention, since the oxide film is formed on the nitride film by the CVD method, the density of trap levels generated by this process is small.

[Real 1M 1A] FIGS. 1A to 1E are cross-sectional views showing a method of manufacturing an MIS capacitor having a multilayer insulating film made of a nitride film and an oxide film, which is an embodiment of the present invention.

Hereinafter, the manufacturing method will be explained with reference to the same figure.

First, a silicon oxide film 2 that will become a pad oxide film is grown on the main surface of a single crystal silicon substrate 1, and then a silicon nitride film 3 is grown on this silicon oxide film 2 as shown in FIG. Form selectively.

Next, by thermally oxidizing the silicon substrate 1, the silicon substrate 1 is thermally oxidized (
As shown in b), minute 1i11F! A chemical film 4 is selectively formed.

Then, after removing the silicon oxide film 2 and the silicon nitride film 3, a silicon nitride film 5 with a thickness of 100 mm is formed by, for example, a low pressure CVD method. At this time, silicon oxidation g!
Since oxygen in the air adheres to the silicon substrate 1 after the removal of the silicon nitride film 2 and before the deposition of the silicon nitride film 5, a natural oxide film 6 is simultaneously formed as shown in FIG.

Next, about 30% of
A top oxide film 9 made of a silicon oxide film is formed. With advances in technology, the i-tube oxide film 9 with a thickness of about 30 mm can be formed with sufficient accuracy by low pressure CVD.

Next, a polysilicon film doped with phosphorus is grown on the top oxide film 9, and by forming a vacuum, as shown in FIG.
A gate electrode 8 is formed as shown in FIG. In this way, the top oxide film 9. Silicon nitride F! 5. It is possible to manufacture a MIS kit t1 vacitor having a multilayer insulating film made of natural oxide pattern 6.

By forming the top oxide l119 by the low pressure CVD method in this manner, the 1-wrap density generated at the interface between the top oxide film 9 and the silicon nitride film 7 when the top oxide film 9 is formed becomes considerably small. Therefore, the amount of charge trapped in top oxide film 9 and silicon nitride film 5 by trap levels is very small. For this reason, top oxidation F! The electric field generated in 9 or the silicon nitride film 5 does not affect the multilayer insulating film, and does not adversely affect the life of MIS type semiconductor devices such as MrS capacitors formed of this multilayer insulating film.

FIG. 2 shows an MIS capacitor manufactured by the manufacturing method shown in FIG. 1, which is an embodiment of the present invention, and a third MIS capacitor, which is a conventional example.
The lifespan of the MIS capacitor manufactured using the manufacturing method shown in the figure is TOD B (Time Dependent
1 is a graph showing experimental results measured using the Dielcctic Breakdown method. Note that the active region area of both MIS capacitors at this time is 400μ.
m2, and the experiment was conducted by keeping the silicon substrates 1 of both ~118 capacitors at ground potential and setting the gate electrodes 8 at negative or positive potential, thereby creating a negative high electric field (-8 ~
-10M V/cjI) or positive high electric field (12
-14MV/I:Jl) and measured the time until dielectric breakdown occurred.

In Figure 2, the solid line e! 1.12 indicates the life of M I S t = Yabashita manufactured by the conventional insulating film forming method, 11 indicates a negative high electric field, and 12 indicates a positive high electric field between the substrate 1 and the gate 111i electrode 8. This is the case when it is generated. On the other hand, 13.14 shown by the broken line indicates the life of the MrS capacitor manufactured by the insulating film forming method shown in the example of the present invention, where I3 is a negative high electric field and i4 is a positive high electric field. This is a case in which it is generated between the gate electrode 8 and the gate electrode 8. J3 and Eaf indicate the voltage applied to the gate electrode 8,
Lifespan is a normalized value.

As shown in the figure, regardless of the - field applied to the gate electrode 8, which is 1.0, the life of this embodiment C is longer than that of the conventional example, and the reliability is improved.1. / I can see that there is a T.

Although this example shows the case where the top oxide film 9 formed on the silicon nitride film 5 is formed by low pressure CVD, this method may also be applied to other CVD methods such as atmospheric pressure CVD. The invention can be applied to achieve similar effects.

〔Effect of the invention〕

As explained below, according to the present invention, carbon is deposited on the nitride film.
Since a multilayer insulating film is formed by forming an oxide film using the VD method, the density of trap levels generated during this process is very small and does not adversely affect the multilayer insulating film. Therefore, it is possible to form a more durable multilayer insulating film.

[Brief explanation of the drawing]

FIGS. 1(a) to 1(e) each illustrate a multilayer insulating film made of a nitride film and an oxide film according to an embodiment of the present invention.
A cross-sectional view showing a method of manufacturing an IS capacitor, FIG.
Graph showing the DDB measurement results of S-# separator, 3rd
Figures (a) to (e) are cross-sectional views showing a conventional manufacturing method of a MIS capacitor having a multilayer insulating film made of a nitride film and an oxide film, respectively. In the figure, 1 is a silicon substrate, 5 is a silicon nitride film,
9 is a silicon oxide film formed by a low pressure CVD method. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Masuo OiwaFigure 1 (a))
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Claims (1)

[Claims] (1) A method for forming a multilayer insulating film composed of a nitride film and an oxide film on a semiconductor substrate, the method comprising: forming the nitride film on the semiconductor substrate; and forming the nitride film on the nitride film by a CVD method. A method for forming an insulating film, including the step of forming the oxide film.