JPH046834A - Method of forming silicon nitride film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming a silicon nitride film.

[Conventional technology]

Silicon nitride films are used as gate insulating films for thin film transistors, MO5 type integrated circuit elements, and the like.

This silicon nitride film is generally formed using a plasma CVD apparatus, and conventionally, the power density of RF discharge is controlled to about 120 to 130 mW/cm2, and silicon atoms S+ and nitrogen atoms N are combined. Composition ratio Si/
A silicon nitride film is formed in which the amount of nitrogen atoms N is slightly larger than the stoichiometric ratio (Si/N-0.75).

[Problem to be solved by the invention]

However, the silicon nitride film formed by the conventional film forming method described above has a problem of poor dielectric breakdown voltage.

That is, FIG. 2 shows a breakdown voltage histogram of a silicon nitride film formed by a conventional film formation method, and FIGS. 3 and 4 show the test object used to measure the breakdown voltage of a silicon nitride film. It shows.

As shown in FIGS. 3 and 4, the test object has a large number of striped lower electrodes 2 formed in parallel to each other on one surface of a glass substrate, and a silicon nitride film 3 formed thereon.
On this silicon nitride film 3, a large number of strip-shaped upper electrodes 4 are formed in parallel to each other, perpendicular to the lower electrode 2. By applying a voltage to each lower electrode 2 and sequentially checking the presence or absence of current flowing to each upper electrode 4 each time a voltage is applied to one lower electrode 2, the electrode facing portion where the lower electrode 2 and the upper electrode 4 intersect can be checked. All were measured.

In addition, as for the above-mentioned object, the total number of electrode facing parts is 691.
, 200, the total area of all electrode facing parts is 2.07 cm2
and the silicon nitride film 3 at the substrate temperature
; 250℃ process gas; 5IH430CCM
NH, 60CCM N2 390CCM Pressure; Q, 5TorrRF
Discharge frequency; 13.56MH2 discharge power density;
A film formed to a thickness of 1000 by a plasma CVD apparatus under film forming conditions of 127 mW/cm2 was used. The composition ratio of this silicon nitride film 3 is St/N=0.69.

The dielectric breakdown voltage of the silicon nitride film 3 was measured for the test object while continuously changing the electric field strength applied between the electrodes 2 and 4. At each applied electric field strength of the silicon nitride film 3, The dielectric breakdown occurrence rate (ratio of the number of electrode facing parts where dielectric breakdown occurred to the total number of electrode facing parts) was as shown in FIG. In addition, here, l
The electrode facing part through which a current of X10-6 A or more flowed was determined to be a defective part where dielectric breakdown occurred.

As shown in the dielectric breakdown voltage histogram in Figure 2, the silicon nitride film formed by the conventional film forming method has a dielectric breakdown voltage of 3 MV.
A generated at weak applied electric field strengths below / cm2
Mode failure (initial failure due to pinhole) is I M
Approximately 5% in V/cm2, 2MV/cm2
2 occurs at a large rate of about 2.5%, and 3MV/
B-mode defects (defects due to weak spots) that occur at applied electric field strengths greater than cm2 are 5 M V /
About 5.2% in cm2, 6 MV/cm2
about 14.3% at 7 MV/cm2, about 2.3% at 7 MV/cm2.
This occurred at a fairly large rate of 6%. Note that although Fig. 2 shows a dielectric breakdown voltage histogram of a silicon nitride film formed by controlling the power density of RF discharge to 127 mW/cm2, it is also possible to
All silicon nitride films deposited by the conventional film deposition method controlling the dielectric breakdown voltage to about 2 show dielectric breakdown voltages substantially similar to those shown in FIG.

As described above, the silicon nitride film formed by the conventional film forming method has a poor dielectric breakdown voltage, and therefore, thin film transistors and MO
S-type integrated circuit devices have a high incidence of insulation failure, and have low manufacturing yield and reliability.

The present invention has been made in view of the above circumstances, and its purpose is to provide a method for forming a silicon nitride film that can obtain a silicon nitride film having a high dielectric breakdown voltage. be.

[Means to solve the problem]

In the present invention, when forming a silicon nitride film using a plasma CVD apparatus, the power density of RF discharge is set to 60 to 100 m.
It is characterized by being controlled to W/cm2.

[Effect]

In this way, the power density of RF discharge can be increased to 60 to 100 mW/
A silicon nitride film formed with a controlled thickness of cm2 has an extremely high dielectric breakdown voltage.

〔Example〕

An embodiment of the present invention will be described below.

In this example, the silicon nitride film was deposited at a substrate temperature of 250°C and a process gas of 250°C.
SiSiH430CCH, 60CCM N2 390CCM Pressure: 0. 5TorrRF
Discharge frequency; 13.56MHz discharge power density;
A film was formed to a thickness of 1000 using a plasma CVD apparatus under film forming conditions of 84 mW/cm2. Note that this film formation condition reduces the power density of RF discharge to 84 mW/cm
2, the film forming conditions were the same as those used when forming the silicon nitride film of the object to be tested using the conventional film forming method.

In this way, the power density of RF discharge was reduced to 84 mW/c
The composition ratio of the silicon nitride film formed by controlling m2 is St
/N-0,83, and this silicon nitride film has a composition in which the amount of silicon Si is slightly larger than the stoichiometric ratio (Si /N-0,75).

The silicon nitride film formed by the film forming method of the above embodiment has an extremely high dielectric breakdown voltage with almost no A-mode defects and very few B-mode defects.

That is, in FIG. 1, the silicon nitride film 3 of the test object shown in FIGS. This is a breakdown voltage histogram showing the results of measuring the breakdown voltage of the silicon nitride film 3 while continuously changing the electric field strength. This dielectric breakdown voltage measurement was performed under the same conditions as the dielectric breakdown voltage measurement of a silicon nitride film formed by a conventional film deposition method, and the dielectric breakdown voltage was measured at the electrode facing part where a current of I x 10-6 A or more passed. This was determined to be a defective part.

As shown in the dielectric breakdown voltage histogram in FIG.
A-mode defects that occur at weak applied electric field strengths of V/cm2 or less are almost completely eliminated, and 3 M V/cm2 or less
B-mode defects that occur at applied electric field strengths greater than cm2 are also approximately 0.4% at 5 MV/cm2,
Approximately 0,6% at 6 MV/cm2, 7 MV
Approximately 0.4% at /cm2, 9 MV/c
It was generated only at a very small rate of about 13% O per m 2 .

As described above, the silicon nitride film formed by the film forming method of the above embodiment has an extremely high dielectric breakdown voltage. Therefore, if this silicon nitride film is used as a gate insulating film of a thin film transistor or an MO5 type integrated circuit element, It is possible to significantly reduce the incidence of insulation defects in thin film transistors and MO5 type integrated circuit devices, and improve their manufacturing yield and reliability.
Since the dielectric breakdown voltage of the semiconductor layer is high, the film thickness can be reduced, so even if the gate voltage applied to the gate electrode is the same, a stronger electric field can be applied to the semiconductor layer to increase the on-current.

Furthermore, the silicon nitride film formed by the film forming method of the above embodiment has a composition ratio of Sl/N-0.83, which is a composition in which the amount of silicon St is slightly larger than the stoichiometric ratio. Thin film transistors, etc. that use a film as a gate insulating film have that V.

The ID characteristics will have hysteresis, but when the composition ratio of the silicon nitride film is about 51/N-0.83, the systeresis is slight, so it will not greatly affect the operating characteristics of thin film transistors, etc. .

In addition, in the above example, the power density of the RF discharge was set to 84 m
W/cm2, but this discharge power density is 60 to 1
The discharge power density may be in the range of 00 mW/cm2, and any silicon nitride film formed with a discharge power density in this range exhibits a dielectric breakdown voltage substantially similar to that shown in FIG.

〔Effect of the invention〕

As in the present invention, when forming a silicon nitride film using a plasma CVD apparatus, the power density of RF discharge is set to 60 to 1.
If controlled to 00 mW/cm2, a silicon nitride film having a high dielectric breakdown voltage can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a dielectric breakdown voltage histogram of a silicon nitride film formed by an embodiment of the present invention, and FIG. 2 is a diagram showing a dielectric breakdown voltage histogram of a silicon nitride film formed by a conventional film formation method. , FIG. 3, and FIG. 4 are a plan view and an enlarged cross-sectional view of a portion of the test object used for measuring the dielectric breakdown voltage of a silicon nitride film. Applicant Casio Computer Co., Ltd. Figure Applied Electric Field Silver 4 (MV/cry?)

Claims (1)

[Claims] When forming a silicon nitride film using a plasma CVD device, the power density of RF discharge is set at 60 to 100 mW/cm.
A method for forming a silicon nitride film characterized by controlling the film to ^2.