JPH06232116A - Formation of silicon oxide film - Google Patents

Abstract

PURPOSE:To obtain a silicon oxide film having the smooth surface, on which hazes (They are considered to be silicon particles.) do not exist, when the silicon oxide film (the so-called HTO film) is formed at high temperature by a low- pressure CVD method. CONSTITUTION:When a silicon oxide film (an HTO film) is formed by a CVD method using SiH4 gas and N2 gas, the interior of a chamber is filled with an N2O gas atmosphere and thereafter, the silicon oxide film is formed in such a way that the SiH4 gas is introduced into the chamber while being increased in a stepwise form to a set flow rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a silicon oxide film used in a semiconductor device.

[0002]

2. Description of the Related Art As a silicon oxide film of a semiconductor device, a silicon oxide film generally called an HTO film which is formed at a high temperature of about 800 ° C. by a low pressure CVD (chemical vapor deposition) method is used. There is. This HTO film is excellent in uniformity and film quality and is used as a gate oxide film or the like.

When the HTO film is formed, haze, which is considered to be silicon grains, is likely to occur, and the film surface is likely to be a silicon oxide film having irregularities. It is generally known that the cause of haze in the HTO film is very sensitive to the flow rate ratio of SiH ₄ and N ₂ O, that is, the abundance ratio of the reaction gas at a certain place, and the flow rate ratio: N ₂ O / As the SiH ₄ is smaller, haze is more likely to occur, which can occur mainly in the initial stage of film formation.

The HTO film is produced by introducing nitrous oxide (N ₂ O) gas into the furnace in which the semiconductor wafer is placed, filling the inside of the furnace with N ₂ O gas, and then introducing silane (SiH ₄ ) gas. Although a film is formed, the SiH ₄ gas is usually introduced through the mass flow controller in the sequence shown in FIG. 4, and the flow rate ratio of the reaction gas is N ₂ O / SiH ₄ = 40/1. The soft start of the general-purpose mass flow controller during the sequence takes up to 1 minute. However, this sequence can sometimes cause haze.

In order to prevent the generation of haze, it is possible to deal with it by increasing the original flow rate ratio, and two methods are available: (i) a method of increasing the flow rate of N ₂ O. (ii) There is a method of reducing the flow rate of SiH ₄ .

[0006]

However, in the above method (i) of increasing the flow rate of N ₂ O, the total flow rate of the reaction gas is increased, and the film formation on the wafer is uniform near the gas inlet. Property (uniformity within the wafer surface) deteriorates. Also (i
In the method i) of reducing the flow rate of SiH _{4, when} the flow rate of SiH ₄ decreases, the SiH ₄ is sufficiently transferred to the wafer near the gas outlet.
₄ Gas is not supplied, and the film formation rate varies greatly depending on the position of the wafer in the furnace, resulting in poor film formation uniformity (uniformity between wafers).

As described above, if the N ₂ O / SiH ₄ flow rate ratio alone is used (the flow rate ratio is set to 40/1 or more), it becomes difficult to control the film formation uniformity, and a very delicate condition regarding the presence or absence of haze. The current situation is that the film is formed in.

At present, the inside of the furnace is initially N₂Fill with O gas
Every time, in this state SiH_FourI am trying to flush. this
SiH_FourWhen flowing, vacuum the line and open the valve.
SiH_FourFlow or N on the line₂Flow O gas
Open the valve and SiH_FourThere is a method such as pouring, but whichever
Even, SiH_FourThe initial stage of introducing gas is SiH _Four
Flow rate is higher than the set value and the desired SiH_FourAnd N₂
The flow rate ratio of O cannot be obtained. Mass flow controller for flow control
Although using a controller, the current mass flow controller
The performance of the controller can control the flow rate ratio in the initial stage.
Can not.

That is, as shown by the broken line a in FIG._Four
Immediately after introducing the gas, SiH is suddenly introduced into the furnace. _FourGas is introduced
Therefore, at the beginning of film formation, N₂O / SiH_FourFlow rate or
The ratio will change. Haze is generated in the initial stage of film formation.
Is a floor and is a general-purpose mass flow controller in the sequence of FIG.
Only the soft start function which is one of the functions of the tracker
Is hard to deal with.

In view of the above points, the present invention provides a method for forming a silicon oxide film having a haze-free smooth surface without affecting the film formation uniformity.

[0011]

According to the present invention, when a silicon oxide film 8 is formed by a CVD method using a silane-based gas 7 and a gas 5 containing oxygen, the inside of a so-called chamber 2 such as a furnace or a reaction vessel is After making the gas atmosphere containing oxygen, stepwise (A ₁ , A ₂ , A ₃ ) up to the set flow rate of the silane-based gas 7.
Then, a silicon oxide film 8 is formed.

[0012]

In the present invention, the silane-based gas is introduced into the chamber 2 in a stepwise manner (A ₁ , A ₂ , A ₃ ) up to the set flow rate after the chamber 2 is set to a gas atmosphere containing oxygen. Even if the gas 7 is rapidly introduced immediately after the start of introduction, there is no problem because the flow rate of the silane-based gas 7 in the first stage A ₁ does not reach the set value A ₃ at the time of film formation.

Then, even if the silane-based gas increases step by step thereafter, at that time, it is accurately controlled by the flow rate of the silane-based gas 7 by the mass flow controller 6. Therefore, at the time when the silane-based gas 7 reaches the set flow rate, that is, the flow rate ratio between the gas 5 containing oxygen and the silane-based gas 7 at the initial stage of film formation does not become small, but becomes the set flow rate ratio, and the haze Does not occur.

That is, the silicon oxide film 8 having a smooth surface without haze can be obtained without increasing the flow rate ratio of the gas containing oxygen / silane-based gas.

[0015]

Embodiments of the method for forming a silicon oxide film according to the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a silicon oxide film forming apparatus 1 according to the present invention. A semiconductor wafer (for example, a silicon wafer) 3 is placed in a furnace 2, and a first wafer is placed in the furnace 2. A gas containing oxygen whose flow rate is set by the mass flow controller 4, for example, nitrous oxide (N ₂ O) gas 5
And the second mass flow controller 6
A silane-based gas whose flow rate is set by, for example, silane (SiH ₄ ) gas 7 is introduced.

Therefore, in the present invention, the set value of the SiH ₄ gas mass flow controller 5 is set to at least two, and the flow rate of the SiH ₄ gas is increased stepwise to the set value.

In this example, SiH_FourGas and N₂Use O gas
By the low pressure CVD method, that is, below the temperature at which silane decomposes.
For example, when forming a silicon oxide film at about 800 ° C.
The inside of the furnace 2₂After making O gas atmosphere, as shown in FIG.
Set the mass flow controller 6 in 3 steps
A₁, A₂, A₃And SiH_FourGas flow rate is value A₁，
A ₂And A₃And the set value A during film formation₃Increased in steps
Let

For example, if the set value A ₃ is 30 cc, 10 cc
Assuming that the flow rate is increased stepwise at / min, it takes 3 minutes from the start of SiH ₄ gas introduction to reach the set value A ₃ .

According to the above method, the set value of the mass flow controller 6 is set to three levels A ₁ , A ₂ and A ₃ and Si is set.
By increasing the flow rate of the H ₄ gas to the set value A ₃ at the time of film formation stepwise, the SiH ₄ gas is introduced at the initial stage.
_{Even if the 4} gases are suddenly introduced into the furnace 2 as shown by the broken line b in FIG. 2, there is no direct influence because the set value is less than the set value A ₃ at the time of film formation, and thereafter the flow rate control of the mass flow controller is accurate. Often done.

Therefore, N ₂ O at the initial stage of film formation with the set value A ₃
The flow rate ratio of / SiH ₄ can be set to a target setting value, for example, N ₂ O / SiH ₄ = 40/1 without decreasing, and the haze-free surface on the semiconductor wafer 2 is H.
The TO film 8 is formed.

Further, according to the sequence shown in FIG. 2, the degree of freedom in film forming conditions can be increased without being restricted by the flow rate ratio and total flow rate of the reaction gas during film formation.

The present invention can also be applied to a film forming apparatus 9 in which the N ₂ O gas 5 and the SiH ₄ gas 7 are mixed outside the furnace 2 and introduced into the furnace 2 as shown in FIG. .

Although the furnace is used in the above example, the present invention can also be applied to the case where the silicon oxide film is formed in a reaction vessel such as atmospheric pressure CVD without using the furnace.

[0025]

According to the present invention, it is possible to surely form a silicon oxide film having a smooth surface without haze.
Further, the degree of freedom in film forming conditions can be increased without being restricted by the flow rate ratio and total flow rate of the reaction gas during film formation.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of a silicon oxide film forming apparatus according to the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the flow rate and the time when SiH ₄ gas is introduced in this example.

FIG. 3 is a configuration diagram showing another example of a silicon oxide film forming apparatus according to the present invention.

FIG. 4 is a characteristic diagram showing a relationship between a flow rate and time when a conventional SiH ₄ gas is introduced.

[Explanation of symbols]

1,9 Film forming device 2 Furnace 3 Semiconductor wafer 4,6 Mass flow controller 5 N ₂ O gas 7 SiH ₄ gas 8 Silicon oxide film (HTO film)

Claims (1)

[Claims] 1. When forming a silicon oxide film by a CVD method using a silane-based gas and a gas containing oxygen, the chamber is made to have a gas atmosphere containing the oxygen, and then the silane-based gas is supplied up to a set flow rate. A method for forming a silicon oxide film, which is characterized in that the silicon oxide film is introduced stepwise.