JP3045945B2 - Method of forming silicon nitride thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a so-called plasma silicon nitride thin film (hereinafter referred to as a p-SiN film) used as a final protective film (passivation film) of a semiconductor integrated circuit device. In particular, silane (SiH ₄ ), ammonia (NH ₃ ), nitrogen (N ₂ ) are used as raw material gases.
And a method of forming a silicon nitride film by a plasma enhanced chemical vapor deposition method using the method.

[0002]

2. Description of the Related Art In recent years, as the integration and miniaturization of LSI devices have progressed, device reliability has become an important issue. In order to improve the reliability of the semiconductor device, the quality of a so-called final protective film for protecting the semiconductor device is important. This final protective film is for protecting the active region and the like of the semiconductor device from the outside atmosphere to provide protection. For example, plasma enhanced chemical vapor deposition (Plasma Enhanced Chemical)
al Vapor Deposition, hereinafter PEC
VD) is widely used. The characteristics of this p-SiN film are as follows:
There are points.

(1) Less occurrence of so-called cracks,
It can be grown on aluminum (Al) wiring with a film thickness of about 1 μm. (2) High step coverage. (3) Excellent moisture resistance. (4) Can be grown at low temperature. For example, it can be grown at a temperature of 400 ° C. or lower. In particular, this low film forming temperature is a very advantageous condition in a semiconductor device manufacturing process. For example,
Another widely used film forming method is a thermal CVD method. However, when a film is formed by this thermal CVD method, the film forming temperature reaches 700 ° C. or more. Therefore, there is a possibility that the aluminum used for the wiring itself may be seriously damaged.

[0004]

As described above, p
-SiN film has excellent characteristics,
With the progress of high integration and miniaturization of devices, MOSFET using hydrogen contained in this p-SiN film
, A large problem that impairs the reliability of the semiconductor device, such as fluctuation of the threshold voltage (hot carrier effect).

It is generally believed that this problem is caused by hydrogen mixed into the p-SiN film. That is,
Hydrogen in the p-SiN film moves to the MOS interface, traps hot electrons, and changes the threshold voltage of the MOSFET. Such a phenomenon is observed as a phenomenon such as a remarkable shift in threshold voltage when a certain stress voltage is applied to a polysilicon gate MOSFET on which a p-SiN film is stacked. Generally, the p-SiN film contains 18 to 25 atom% of hydrogen atoms in the form of Si-H or NH. Among them, the Si—H bond has a weaker bonding force than the N—H bond, and easily releases hydrogen in a later heat treatment step or the like. Therefore, it is considered that it is necessary to reduce the hydrogen content in the film in order to solve this problem.

In order to solve such a problem, for example, according to the invention described in JP-A-63-52419,
The content of hydrogen is reduced by replacing Si—H bonds in the film with Si—F bonds using SiH ₂ F _{2 in} which hydrogen atoms of silane of the source gas are replaced by halogen atoms such as fluorine. However, the behavior of halogen atoms in a film in a semiconductor device has not been elucidated yet, and cannot be said to be an essential solution. At the same time, etching may be performed by the fluorine.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for forming a p-SiN film having a reduced hydrogen content.

[0008]

According to a first aspect of the present invention, at least silane, ammonia,
A method of growing a silicon nitride thin film by plasma enhanced chemical vapor deposition using nitrogen as a raw material, including a control step of controlling the amount of decomposition of ammonia to be about 4% to about 10%. A method for forming a silicon nitride thin film.

According to a second aspect of the present invention, there is provided a method of growing a silicon nitride thin film by a thermal chemical vapor deposition method using at least silane, ammonia and nitrogen as raw materials. Is 4% or more 1
A control step of controlling the concentration to be 0% or less.

According to a third aspect of the present invention, there is provided a method for forming a silicon nitride thin film according to the first or second aspect of the present invention, wherein the amount of decomposition of ammonia is detected using infrared laser spectroscopy. The control step is a method for forming a silicon nitride thin film, wherein control is performed based on the detected amount of decomposition of ammonia.

[0011]

According to the first aspect of the present invention, in the plasma-enhanced chemical vapor deposition method, the amount of ammonia decomposed is 4% or more.
%. As a result, the hydrogen content in the silicon nitride thin film can be reduced.

Also in the second invention, the decomposition amount of ammonia in the thermal chemical vapor deposition method is 4% or more and 10% or less.
Control is performed as follows.

In the third aspect of the present invention, infrared laser spectroscopy is used to detect the amount of ammonia decomposed. For this reason, the decomposition amount of ammonia can be easily detected.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

The method for forming a silicon nitride thin film according to the present invention is characterized in that the decomposition amount of ammonia is controlled within a certain range.
Reduces the hydrogen content in the p-SiN film to provide high quality p-
This is a method for forming a SiN film. In particular, as a method for detecting the amount of decomposition of ammonia, it is preferable to detect the amount of decomposition of ammonia by infrared semiconductor laser spectroscopy.

The following embodiment is an example in which silane (diluted with 80% of nitrogen) and ammonia are used as raw material gases. A p-type or n-type silicon substrate is used as a substrate when a p-SiN film is formed using these materials. An apparatus for forming a thin film is a single-wafer RF (Radio)
(Frequency) plasma CVD apparatus. FIG. 1 shows the configuration of this single-wafer RF plasma CVD apparatus. The plasma excitation frequency of this plasma CVD apparatus is, for example, 13.56 MHz, and an infrared ray crosses the reaction region for in-situ (in-situ) observation by an infrared semiconductor laser spectroscope. (KCl) window 10 is provided with a flange. Also, as shown in FIG. 1B, the infrared light incident on the device is multiply reflected by concave mirrors M1, M2, and M3 provided outside the flange (not shown). It is incident on a detector, from which the gas concentration is calculated. FIG.
As shown in (b), the concave mirrors M1, M2 and M3 are provided outside the film forming chamber, but may be provided inside the film forming chamber. The number of multiple reflections of the infrared ray and the distance that the infrared ray traverses the reaction region are adjusted according to the intensity of the semiconductor laser used. By this adjustment, the setting is made so that the sensitivity of the gas concentration is improved as much as possible.

In this embodiment, for example, the ammonia concentration is changed by fixing the flow rate of silane to 10 sccm and the flow rate of nitrogen to 40 sccm, and changing the flow rate of ammonia in the range of 10 to 50 sccm. FIG.
As shown in FIG. 1A, an electrode 12 with a gas outlet and a susceptor 14 with a heater are provided in a film forming chamber of the plasma CVD apparatus. With the susceptor 14 having the heater, the substrate temperature is about 35 in this embodiment.
Heat to 0 ° C. The raw material gas flows from the gas outlet of the electrode 12 with gas outlet, and so-called RF power is applied to the electrode 12 with gas outlet. In this embodiment, for example, the gas pressure is set to 0.8 Torr, and the RF power is set to 30 W. First, the inventor of the present application conducted an experiment on how the decomposition amount of ammonia changes depending on the ammonia concentration. First, the results will be described.

FIG. 2 is a graph showing the result of an examination on the relationship between the ammonia concentration and the amount of decomposition of ammonia. In the present embodiment, the decomposition amount of ammonia is determined by monitoring one of the absorption lines (726.944 cm ⁻¹ ) of ammonia in the infrared region before and during the reaction. In the graph of FIG. 2, the horizontal axis represents the ammonia concentration (%), and the vertical axis represents the ammonia decomposition amount (%). As shown in the graph of FIG. 2, when the concentration of ammonia is increased, the amount of decomposition of ammonia starts to increase at first. The amount is decreasing.

Next, when the hydrogen content of the p-SiN thin film obtained in the above experiment was determined by FTIR or the like, the result shown in FIG. 3 was obtained. FIG. 3 is a graph showing the relationship between the concentration of ammonia and the hydrogen content of the p-SiN thin film obtained by the method. The horizontal axis of the graph shown in FIG. 3 is the ammonia concentration, and the vertical axis is the hydrogen content in the film. As can be understood from the graph shown in FIG. 3, as the concentration of ammonia increases, the hydrogen content initially increases, but when the ammonia concentration further increases and exceeds about 30%, the hydrogen content decreases. Tend to.

When the above results are integrated using the ammonia concentration as a mediation parameter, the relationship shown in FIG. 4 is obtained. FIG. 4 shows the decomposition amount of ammonia and
A graph showing the relationship between the p-SiN thin film and the hydrogen content in the film is shown. In the graph shown in FIG. 4, the horizontal axis represents the amount of ammonia decomposed, and the vertical axis represents the hydrogen content in the film. As can be understood from the graph shown in FIG.
An almost proportional relationship is recognized between the hydrogen content in the p-SiN film. Therefore, it can be understood that the hydrogen content can be easily controlled by monitoring the decomposition amount of ammonia.

The characteristic feature of the present invention is that, in view of the fact that the amount of decomposition of ammonia and the hydrogen content in the film are substantially proportional to each other, the amount of decomposition of ammonia is controlled by controlling the amount of decomposition of ammonia. That is, the hydrogen content was controlled. By forming a p-SiN film using such a method, a p-SiN film having a small hydrogen content can be obtained.

Further, in order to obtain optimum film forming conditions for reducing the hot carrier effect, the relationship between the amount of decomposition of ammonia and the amount of variation between the threshold voltage of the MOS transistor and the amount of ammonia was investigated. The result of this experiment is shown in FIG. The horizontal axis of the graph shown in FIG. 5 represents the amount of decomposition of ammonia, and the vertical axis represents the amount of change in the threshold voltage.
As shown in the graph of FIG. 5, when the amount of decomposition of ammonia is about 4% or more and less than 10%, the fluctuation amount of the threshold voltage becomes 0.05 volt or less, and generally, It can be said that the variation is sufficiently small. Therefore, it can be understood that when the decomposition amount of ammonia is about 4% or more and 10% or less, the hot carrier resistance increases.

As described above, the characteristic feature of the present embodiment is that the concentration of ammonia is controlled in consideration of the fact that the concentration of ammonia is substantially proportional to the hydrogen content in the film. Thus, the hydrogen content in the film was controlled. Further, what is characteristic in the present embodiment is that the amount of change in the threshold voltage of the MOS transistor is sufficiently reduced by specifically setting the decomposition amount of ammonia to 4% or more and 10% or less. As described above, according to the present embodiment, it is possible to realize a method of forming a silicon nitride thin film in which the threshold voltage of the MOS transistor does not fluctuate easily only by adding an apparatus for detecting the concentration of ammonia.

In this embodiment, the concentration of ammonia and the amount of decomposition thereof were measured by an infrared semiconductor laser spectroscopy method to form a silicon nitride thin film. However, any method which can detect the concentration of ammonia is known in the art. Any method that has been adopted can be adopted. Further, in this embodiment, the PECVD method has been described for determining the reaction conditions of the silicon nitride thin film. However, the present invention can also be used for determining the reaction conditions of the silicon nitride thin film by the thermal CVD method.

[0025]

As described above, according to the first aspect of the present invention, a p-SiN film having a small hydrogen content can be obtained. Therefore, when this film is used as a final protective film of an LSI, there is an effect that a semiconductor device having high hot carrier resistance can be manufactured.

According to the second aspect of the present invention, the same effects as in the first aspect of the present invention can be obtained in the thermal chemical vapor deposition method.

According to the third aspect of the present invention, since the amount of ammonia decomposed is detected using infrared laser spectroscopy, there is an effect that the first aspect of the present invention can be easily realized.

[Brief description of the drawings]

FIG. 1 is a structural explanatory view of a thin film forming apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between an ammonia concentration and an ammonia decomposition amount in the present embodiment.

FIG. 3 is a graph showing a relationship between an ammonia concentration and a hydrogen content in a film in the present embodiment.

FIG. 4 is a graph showing the relationship between the amount of decomposed ammonia and the hydrogen content in a film in this example.

FIG. 5 shows the amount of ammonia decomposed and MO in this example.
9 is a graph showing a relationship between a threshold voltage of an S transistor and an amount of change.

[Explanation of symbols]

10 KCl window, 12 electrode with gas outlet, 14
Susceptor with heater.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/318

Claims (3)

(57) [Claims] 1. A method for growing a silicon nitride thin film by plasma enhanced chemical vapor deposition using at least silane, ammonia and nitrogen as raw materials, wherein the amount of decomposition of ammonia is controlled to be 4% or more and 10% or less. A method for forming a silicon nitride thin film, comprising: 2. A method for growing a silicon nitride thin film by a thermal chemical vapor deposition method using at least silane, ammonia and nitrogen as raw materials, wherein the decomposition amount of ammonia is about 4% or more and about 10% or less. A method for forming a silicon nitride thin film, comprising: a controlling step of controlling. 3. The method for forming a silicon nitride thin film according to claim 1, further comprising: detecting an amount of ammonia decomposed using infrared laser spectroscopy. A method for forming a silicon nitride thin film, wherein control is performed based on the amount of decomposition of silicon nitride.