JPH08109473A - Formation of silicon oxide film - Google Patents

Abstract

PURPOSE: To suppress an arcing phenomenon and to enable the regulation and maintenance of the desired film forming rate, in the formation of a silicon oxide film, by regulating the negative pressure applied to a target to an intermittent one repeated in a specified period. CONSTITUTION: A sputtering gas contg. an oxidizing gas is used, the negative voltage is applied to a target essentially consisting of silicon, and sputtering is executed to form a silicon oxide film. At this time, the negative voltage to be applied is regulated to a periodically repeated intermittent certain voltage at 100Hz to 100kHz, and into a one in the range between a point A in which current increased in accordance with the increase of voltage in the functional relationship of current-voltage transits to the reduction and a point B at which it thereafter transits to the increase. Moreover, it is preferable that the positive voltage is applied in at least a part of the time in which the intermittent negative voltage is not applied from the viewpoint of the suppression of arcing. In this method, by changing the amt. of the sputtering gas to be introduced and the concn. of the oxidizing gas therein, the film forming rate can be regulated.

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 by a direct current reactive sputtering method.

[0002]

2. Description of the Related Art As a method for forming a silicon oxide film, 1)
A so-called CVD method in which a molecular gas containing silicon and a molecular gas containing oxygen are decomposed by an excitation means such as heat or plasma and then reacted to obtain silica, or 2) silicon oxide is targeted and a high-frequency alternating voltage is applied to this. A so-called high-frequency sputtering method is generally used in which a rare gas such as argon is applied to generate plasma, and the rare gas positive ions sputter a silicon oxide target to deposit a silicon oxide film on a substrate.

In the CVD method, since the temperature of the substrate rises during the formation of the silicon oxide film, there is a restriction that it cannot be formed on the substrate having low heat resistance. Further, in the high frequency sputtering method, the substrate is damaged by electrons or negative ions, and RF for forming a film on a large area substrate is used.
It is impossible to increase the power supply.

On the other hand, a reactive gas or a mixed gas of a reactive gas and a rare gas is made to collide with a target to knock out atoms contained in the target, and the process until such atoms are deposited on the substrate and after the deposition, React with gas,
There is a so-called DC reactive sputtering method. The DC reactive sputtering method is preferably used because it has the advantage that the film thickness distribution can be kept small even on a substrate having a large area, the temperature rise of the substrate is small, and that the substrate is less damaged by ions and electrons. There is.

In the conventional DC reactive sputtering method, in order to form a film at a desired rate, the mixing ratio of the sputtering gas, the introduced gas flow rate, the applied voltage, the applied current, and the applied power are changed in various ways. After forming the film on and measuring the film thickness,
Under the assumption of the condition reproducibility that the same film forming rate is obtained when the film forming conditions are the same, a set of film forming parameters (sputtering gas mixture ratio, introduction gas flow rate, applied voltage,
A method of forming a film by setting an applied current and an applied power has been used.

However, in the reactive sputtering method, the sputter gas itself is reactive, and the ionized ions and the dissociated atoms generated as a result of the collision of these with the sputter gas molecules are also reactive. ing.

These sputtering gas molecules, dissociated atoms, and ions (collectively referred to as reactive particles below) are the target surface, the atoms knocked out from the target, the group of such atoms, or the film formed on the substrate. And so on.

The number of reactive particles, and the excited state of each particle, is a state quantity directly related to reactivity, and these are
With slight changes in the electrical resistance of the wall of the container that performs sputtering, the impurity gas contained in the sputtering gas, the exhaust speed, etc.
It will change a lot. In particular, when the film formation rate is increased, the change in the film formation rate due to the change in the state is remarkable.

That is, in the film formation by the conventional reactive sputtering method, particularly when high-speed film formation is aimed, the relationship between the film formation condition and the film formation speed under the condition is unstable. And only by measuring the thickness of the obtained film,
I don't know if this relationship is maintained or not. Further, the film thickness is different each time this relationship is deviated, and it is difficult to always obtain the film having the same film thickness.

When this relationship is deviated, the relationship between the film forming condition and the film forming speed is obtained again by forming the film again while changing the film forming condition and measuring the thickness of the obtained film. After that, a film having a desired film thickness is formed.

On the other hand, the functional relationship among the voltage, current, and power supplied from the power source is obtained, and by grasping the overall state of the reactive sputtering process at that time, the deposition conditions and the deposition rate are It has been proposed that a film can be formed by detecting a shift in the relationship between the films before film formation and modifying the film formation conditions so that a film having a desired film thickness can be obtained (see (Hei 6-3655).

By the way, when a silicon target is used and an oxidizing gas such as oxygen is used as the sputtering gas, a silicon oxide having an extremely high electric insulating property is formed on the surface of the silicon target, which causes Spark discharge from a small part and the accompanying release of silicon clusters, that is, arcing occurs.

This arcing phenomenon causes problems such as the inclusion of silicon in the silicon oxide film during film formation and the deterioration of film thickness uniformity.

On the other hand, DC sputtering is usually performed by continuously applying a constant negative voltage to a target containing silicon as a main component, and intermittent negative repetitions of 100 kHz or less are repeated periodically. It has been proposed that arcing is suppressed and the quality of the obtained silicon oxide film is improved by applying a voltage to perform sputtering (Japanese Patent Application No. 6-175672).

However, when the method of applying the intermittent negative voltage which is repeated in the above-mentioned cycle is used, the voltage applied to the target changes, and the state of the generated plasma including
The state of the entire sputtering process changes, and the functional relationship among the voltage, current, and power supplied from the power supply changes with time. Therefore, even if the arcing phenomenon can be suppressed, the relationship between the film forming conditions and the film forming rate cannot be known from the functional relationship among the voltage, current, and power, and it is difficult to maintain the desired film forming rate. there were.

[0016]

The present invention suppresses the arcing phenomenon, and knows the relationship between the film forming conditions and the film forming rate from the functional relationship between voltage, current and power, and adjusts the desired film forming rate. An object of the present invention is to provide a high-speed deposition method of a silicon oxide film that can be maintained.

[0017]

The present invention relates to a method for forming a silicon oxide film by using a sputtering gas containing an oxidizing gas, applying a negative voltage to a target containing silicon as a main component, and performing sputtering. The negative voltage is 100 Hz or more,
A constant negative voltage that is periodically repeated at 100 kHz or less and has a point A at which the current that increases with an increase in the voltage in the current-voltage functional relationship starts to decrease and a point B at which the current starts to increase again. There is provided a method for forming a silicon oxide film, which is characterized in that the voltage is in the range between.

In the present invention, in particular, from the viewpoint of suppressing arcing, it is preferable that the positive voltage is applied during at least part of the time when the intermittent negative voltage is not applied.

In the target containing silicon as a main component, the current increases as the voltage increases, but a point where the current changes from an increase to a decrease (hereinafter referred to as a specific point A) appears, and then a decrease again starts to increase. A current-voltage functional relationship in which a point (hereinafter referred to as a specific point B) appears is shown.

Specific point A to specific point B in the functional relationship
A transparent silicon oxide film can be formed at a high speed by forming a film with a voltage in the range.

In particular, at the specific point A, the film forming rate per applied electric power has a constant value regardless of any condition, and in the vicinity of the specific point B, the film forming rate of the silicon oxide film per applied electric power is the highest. growing.

As the sputtering gas used in the present invention, a mixed gas of oxygen and argon is used, but a combination of an oxidizing gas and a rare gas other than this can also be used, and further, the refractive index of the silicon oxide film can be adjusted. Depending on the purpose, nitrogen can be added, and other gases can be added.

The target containing silicon as a main component used in the present invention is not particularly limited, and for example, single crystal doped with phosphorus or boron or polycrystalline silicon can be adopted.

[0024]

In general, when a silicon oxide film is formed by a direct current sputtering method using a target containing silicon as a main component and an oxidizing gas such as oxygen as a sputtering gas, silicon having a very high electrical insulating property is formed on the surface of the silicon target. An oxide is formed, which causes arcing. This arcing is suppressed by applying a constant negative voltage to a target containing silicon as a main component to perform direct current sputtering, while applying a negative voltage that is periodically repeated at 100 kHz or less. It was experimentally confirmed that this is possible by performing sputtering. It is considered that the suppression of this arcing phenomenon is obtained by the following mechanism.

Since magnetron discharge is used in ordinary reactive DC sputtering, when a negative potential is applied, the plasma related to sputtering immediately above the target does not spread over the entire surface directly above the target, and the plasma distribution Due to the non-uniformity, a single target is divided into a portion (hereinafter, referred to as an erosion region) in which sputtering is performed exclusively and a portion (hereinafter, referred to as a non-erosion region) other than this.

The erosion region is generated by the positive ions colliding with the target from the plasma immediately above the target and sputtering the target constituent material, while the non-erosion region has very few positive ions colliding with the target, or , Because there is no.

Arcing occurs exclusively near the boundaries of erosion and non-erosion regions on the target. This is because even if an insulating substance is generated in the erosion region, it is removed one after another by sputtering, and conductivity is imparted by the effect of atomic level mixing by colliding positive ions, and this region is given. There is no charge stagnant (hereinafter referred to as charge-up).
On the other hand, in the non-erosion region, an insulating substance is generated on the target surface, but its film thickness increases with time, and arcing hardly occurs.

An insulating substance is generated near the boundary between the erosion region and the non-erosion region, and positive ions collide with the insulating substance, though the amount is smaller than the number of positive ions colliding with the erosion region. Then, the surface of the insulating material is positively charged up.

Further, in this region, since the film thickness of the insulating material is small, the electrical breakdown voltage is small, and the breakdown voltage is caused by the negative voltage applied to the target material and the electric field generated by the positive charge on the surface of the insulating material. Occurrence occurs and arcing occurs from this point.

Therefore, by periodically setting the target to the ground potential or a positive voltage, the constraint of the plasma composed of positive ions and electrons is released, and the positive charge on the surface of the insulating material is the electrons supplied from the plasma. Disappears and the arcing observed near the boundary between the erosion region and the non-erosion region does not occur.

That is, in order to suppress arcing, it is important to control the state of charges near the boundary between the erosion region and the non-erosion region.

On the other hand, in a reactive DC sputtering method in which a target containing silicon as the main component is used and a negative voltage is applied to the target without interruption, a functional relationship among the voltage, current, and power supplied from the power source to the target. Was examined in detail, and what was affected by the film formation rate per input electric power was investigated. As a result, it was clarified that the film formation rate per applied power largely depends on the surface state of the erosion region of the target during sputtering, that is, the oxidation state. Have found that it is necessary to keep the surface state constant.

Therefore, in order to control the film formation rate while suppressing arcing, the state of charges near the boundary between the erosion region and the non-erosion region should be controlled and the oxidation state of the surface of the erosion region should not be changed. is important.

However, in order to suppress the occurrence of the arcing phenomenon while keeping the surface state of the target constant by using the functional relation among the voltage, the current and the power described above, it is simply repeated periodically as described above. When the negative voltage is applied, the following problems occur.

That is, when the target is provided with the time when the negative voltage is not applied, the sputtering phenomenon stops during the time when the negative voltage is not applied, and electrons are generated near the boundary between the erosion region and the non-erosion region. Not only collisions, but also oxygen molecules, atoms, ions, and radicals collide with the erosion region, and the surface state changes. That is, the functional relationship among voltage, current, and power will change with time.

Therefore, 100 is effective for suppressing arcing.
The voltage, current, and power supplied to the target were measured by variously changing the frequency of the intermittent negative voltage that is periodically repeated at or below kHz, and as a result, even for a substance with a large oxidation activity such as silicon, the frequency was 100 Hz. It has been found that with the above frequencies, even if the negative voltage is intermittent, the same functional relationship as in the case where the negative voltage is continuously applied is obtained, and the film formation rate can be adjusted. That is, it was clarified that the oxidation state of the surface of the erosion region of the target containing silicon as a main component did not significantly change for a time of 10 ms or less.

The present invention is based on such a new finding, and by investigating the above-mentioned functional relation, from the form of the function, it is possible to obtain a state in which a high deposition rate in which the target is not completely covered with the reactant is obtained. It is possible to maintain the conditions and know the conditions under which the silicon oxide film is obtained on the substrate before forming the film, and under the conditions, the silicon oxide film can be stably formed at a high speed.

[0038]

【Example】

Example 1 N-type silicon doped with phosphorus having an area of 432 mm × 127 mm and a specific resistance of 1.3 Ω · cm was used as a target, and a mixed gas of oxygen and argon having an oxygen concentration of 10% by volume was used as a sputtering gas. used. The amount of sputter gas introduced was 110 sccm. As shown in the upper part of FIG. 1, a negative voltage was applied to the target for 490 μs, and a positive voltage of 50 V was applied for the subsequent 10 μs to form a silicon oxide film on the soda lime glass. The application of this voltage corresponds to a frequency of 2 kHz.

FIG. 1 shows how the current changes over time. The current gradually decreases while applying a negative voltage, and eventually takes a constant value (hereinafter referred to as a constant current value). However, the change over time of this current varies depending on the impedance of the power source and the impedance of the entire sputtering process. When the impedance of the power source is large, the current may gradually increase from the initial stage of negative voltage application.

In this embodiment, the negative voltage is -260V.
To -470 V, a constant current value was obtained. The current-voltage curve obtained is given in FIG. From FIG. 2, the current increases as the voltage increases, and then decreases,
Again, the increasing current-voltage functional relationship can be read.

Further, the current-voltage functional relationship is a monovalent function of voltage, and all states can be obtained by changing the voltage, but the current-voltage functional relationship is
As is clear from FIG. 2, the multi-valued function of the current is present in a part of the region, and it is understood that one state cannot be stably obtained by controlling the current or the power in this region.

Further, the thickness of the obtained silicon oxide film was measured with a stylus type film thickness meter. FIG. 3 shows the film formation rate per applied electric power with respect to the applied voltage during film formation. From FIG. 3, it can be seen that the film formation rate per applied electric power increases with the voltage. In addition, the voltage at the specific point B in FIG.
When applying a voltage higher than V to form a film, a transparent silicon oxide film could not be obtained.

In this example, by forming the film at a voltage in the range from the specific point A to the specific point B, it was possible to form a transparent silicon oxide film at a high speed while suppressing arcing.

[Embodiment 2] The amount of sputter gas introduced in Embodiment 1 is 110 sccm, 150 sccm, 170.
A silicon oxide film was formed in the same manner as in Example 1 except that the sccm was changed in three ways. The current-voltage curve obtained is given in FIG.

From FIG. 4, it can be seen that in the range from the specific point A to the specific point B, even if the voltage is the same, the current value is different if the amount of sputter gas introduced is different. Therefore, even with the same voltage, the power value can be changed by changing the amount of sputter gas introduced. FIG. 5 shows the relationship between the applied voltage and the film formation rate converted into the applied power. From FIG. 5, even if the introduction amount of the sputtering gas is changed,
It was revealed that the functional relationship between the applied voltage and the film formation rate per applied power is maintained, that is, the film formation rate per applied power depends only on the applied voltage.

Therefore, the conditions other than the introduction amount of the sputtering gas are fixed, and the current value is adjusted by changing the introduction amount of the sputtering gas, whereby the desired film forming rate can be obtained.

[Example 3] A silicon oxide film was formed in the same manner as in Example 1 except that the oxygen concentration in the sputtering gas in Example 1 was changed. FIG. 6 shows the case where the oxygen concentration is 10% by volume and 20% by volume in the obtained current-voltage curve.
Give to.

From FIG. 6, it can be seen that in the range from the specific point A to the specific point B, the current value is higher when the oxygen concentration of the sputter gas is higher even at the same voltage. That is, the conditions other than the oxygen concentration of the sputtering gas are fixed, and the oxygen concentration of the sputtering gas is changed to adjust the current value, whereby the desired film formation rate can be obtained.

When the exhaust speed of the sputtering gas was changed and the same examination as in Examples 2 and 3 was carried out, it was confirmed that the film forming speed also depends on the exhaust speed of the sputtering gas. That is, the conditions other than the sputtering gas exhaust speed are fixed, and the current value is adjusted by changing the sputtering gas exhaust speed, whereby the desired film formation speed is obtained.

[0050]

According to the method for forming a silicon oxide film of the present invention, the arcing phenomenon during film formation can be suppressed, the film can be formed at a high speed, and the film formation speed can be easily adjusted and maintained. It can be carried out.

[Brief description of drawings]

FIG. 1 is a graph showing time variation of applied voltage (upper row) and time variation of current (lower row) used in an example of the present invention.

FIG. 2 is a graph showing the relationship between applied voltage and current value.

FIG. 3 is a graph showing a relationship between an applied voltage and a film forming rate per applied electric power.

FIG. 4 The amount of sputter gas introduced is 110 sccm.
(□), 150 sccm (+), 170 sccm (◇)
The graph which shows the relationship between the applied voltage and the current value in the case of.

FIG. 5: Sputter gas introduction amount is 110 sccm
(□), 150 sccm (+), 170 sccm (◇)
6 is a graph showing the relationship between the film formation rate per applied power and the applied voltage during film formation in the case of.

FIG. 6 The oxygen concentration of the sputtering gas is 10% by volume.
The graph which shows the relationship between an applied voltage and a current value in the case of (+) and 20 volume% (□).

 ─────────────────────────────────────────────────── (72) Inventor Takuji Oyama 1150 Hazawa-machi, Kanagawa-ku, Yokohama, Kanagawa Prefecture Asahi Glass Co., Ltd. (72) Inventor Keido Nishimura 1150, Hazawa-machi, Kanagawa-ku, Yokohama Kanagawa Prefecture Asahi Glass Co., Ltd. Central Research Center

Claims (6)

[Claims] 1. A method of forming a silicon oxide film by using a sputtering gas containing an oxidizing gas, applying a negative voltage to a target containing silicon as a main component, and performing sputtering, wherein the negative voltage is 100 Hz or more. A constant negative voltage that is periodically repeated at 100 kHz or less and has a point A at which the current that increases with an increase in the voltage in the current-voltage functional relationship starts to decrease and a point B at which the current starts to increase again. A method of forming a silicon oxide film, characterized in that the voltage is in the range between. 2. The film forming method according to claim 1, wherein the positive voltage is applied during at least a part of the time when the intermittent constant negative voltage is not applied. 3. The film forming method according to claim 1, wherein the negative voltage is a voltage in the vicinity of the point B at which the current turns to increase again in the current-voltage functional relationship. 4. The film forming rate is adjusted by changing the amount of sputter gas introduced.
2. The film forming method according to any one of 1 above. 5. The film forming method according to claim 1, wherein the film forming rate is adjusted by changing the concentration of the oxidizing gas in the sputtering gas. 6. The film forming method according to claim 1, wherein the film forming speed is adjusted by changing the exhaust speed of the sputtering gas from the film forming chamber.