JPH08269708A - Formation of thin film - Google Patents

Abstract

PURPOSE: To form a thin film with the fine adjustment of the amt. of dopant, etc., facilitated by depositing the particle sputtered from a subtarget on a main target and sputtering both particles from the main target. CONSTITUTION: A rotary plate 81 provided with a substrate 22 and a first subtarget 93 and a rotary plate 82 furnished with a second subtarget 94 and an opening 82 are set on a rotating shaft 15 in a chamber 11. When the subtarget 93 is opposed to the opening 82, Ar is introduced into the chamber 11 to a specified pressure, am RF power is impressed on a main target electrode 31 to generate an electric discharge, Ar ion is struck against the subtarget 93 to sputter the particle, and the particle is deposited on the main target 91. The rotary plate 81 is then turned through an angle of 180 deg. to oppose the substrate 22 to the opening 82a, Ar ion is hit against the main target 91, hence the particle of the main target and that of the subtarget 93 are sputtered and deposited on the substrate 22, and a thin film is formed.

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 thin film of conductive oxide or metal.

[0002]

2. Description of the Related Art Semiconductor devices such as photovoltaic devices are
A transparent electrode such as SnO ₂ , ITO, or ZnO or A
A metal electrode of g, Al, platinum, copper titanium alloy or the like is formed into a thin film. These electrode thin films are mainly formed by a sputtering method using those electrode materials as a target. The sputtering method is, for example, a method in which argon ions are made to collide with a target that is a cathode during glow discharge, and particles knocked out of the target are deposited on a substrate arranged facing the target. Further, in recent years, a magnetron sputtering method has been devised in order to improve throughput. The magnetron sputtering method is a method of arranging a magnetic field orthogonal to the electric field to confine the generated plasma in the vicinity of the target to improve the sputtering efficiency and increase the deposition rate.

FIG. 5 is a schematic view showing a schematic configuration of an apparatus for carrying out a conventional thin film forming method. Chamber 11
1, an exhaust device 112 is connected to the chamber 1 so that the pressure inside the chamber 111 can be reduced when sputtering is performed.
Further, in the chamber 111, a rotary plate 181 and a rotary shutter 113 are arranged at a predetermined interval in the vertical direction, and are individually rotated around a rotary shaft 115.

A substrate electrode 121 is attached to the lower surface of the rotary plate 181. A bias power source 161 is connected to the substrate electrode 121. Also, the substrate electrode 1
A substrate 122 is set at 21.

The rotary shutter 113 has an opening 113.
a is formed. The opening 113a has an opening shape corresponding to the substrate 122. Therefore, when the rotary shutter 113 rotates and the opening 113a is located below the substrate 122, the shutter state of the rotary shutter 113 with respect to the substrate 122 is released. By forming the shutter state, it is possible to prevent the problem of discharge state control at the start of discharge.

At the lower position in the chamber 111,
A first target electrode 131 and a second target electrode 132 are arranged. First target electrode 131
Is connected to the RF power supply 151 and the second target electrode 1
32 is connected to the RF power supply 152. And the first
The first target 191 is set on the target electrode 131, and the second target 192 is set on the second target electrode 132.

In such an apparatus, a thin film made of the material of the first target 191 and the second target 192 are used.
It is possible to form a thin multilayer film made of the above material on the substrate 22.

By the way, when forming a thin film of a transparent electrode by the above-mentioned sputtering method, in order to control the conductivity of this transparent electrode, it is necessary to change the amount of a dopant (for example, Al) with respect to the main electrode material (for example, ZnO). There is. However, since the amount of dopant is very small compared to the main electrode material, conventionally, several types of targets with different amounts of dopant were prepared, and the amount of dopant should be adjusted by replacing the target itself. I was doing. Alternatively, the dopant amount is adjusted by setting two or more targets having different dopant amounts (for example, two dopant amounts of 1% and 5%) and adjusting the applied voltage of each target to carry out the co-sputtering. Was doing. Further, in the case of forming a multilayer film in which the doping amount is continuously changed, it is necessary to prepare an electrode targeting a solid which is a raw material of each layer.

[0009]

However, if many kinds of targets are prepared and replaced as in the conventional case, the production efficiency becomes poor and the production cost becomes expensive. Further, in the method of adjusting the amount of dopant by adjusting the power applied to each of the targets when performing simultaneous sputtering for two or more targets, it is difficult to easily obtain a desired thin film because the adjustment control is difficult, and the productivity is improved. Has the disadvantage that it decreases.

In view of the above circumstances, it is an object of the present invention to provide a thin film forming method capable of easily performing fine adjustment of the dopant amount and the like without requiring many kinds of targets having different dopant amounts.

[0011]

In order to solve the above-mentioned problems, a thin film forming method of the present invention is a method of forming a thin film on a substrate by a sputtering phenomenon. The first step of depositing the particles of the sub-target that are knocked out by the impact on the main target and the ions are collided with the main target on which the particles of the sub-target are deposited, and knocked out by the impact A second step of depositing particles of the primary target and particles of the secondary target on the substrate.

Further, the first step and the second step are continuously performed by changing the potential difference between the substrate electrode, the main target electrode, and the sub-target electrode while maintaining the applied state of the discharge power. It may be performed.

[0013]

According to the above arrangement, the amount of sub-target particles deposited on the main target can be adjusted by changing the degree of sputtering from the sub-target to the main target in the first step. Then, in the sputtering from the main target to the substrate in the second step, the particles of the main target and the particles of the sub target are deposited on the substrate in a component ratio that reflects the deposition amount of the sub target particles.

Therefore, the component ratio of the thin film deposited on the substrate can be easily adjusted by adjusting the deposition amount of the sub-target material in the first step, so that many kinds of targets having different dopant amounts are prepared. Without this, fine adjustment of the amount of dopant can be easily performed. Further, in the repetition of the first step and the second step, by varying the deposition amount of the target material depending on the repetition, it is possible to easily form a multilayer film having different component ratios. Further, by preparing a plurality of sub-targets and main targets, it is possible to form a multilayer film made of different materials.

By the way, the transition from the first step to the second step or the transition from the second step to the first step may be performed by once stopping the discharge state and then causing the discharge state again. However, in this case, the film quality may be slightly deteriorated due to the influence of the initial discharge when the discharge is restarted.

If the first step and the second step are continuously performed while maintaining the discharge state, the influence of the initial discharge can be avoided.

[0017]

【Example】

(Embodiment 1) The present invention will be described below with reference to the drawings showing the embodiment.

FIG. 1 is a schematic view showing a schematic configuration of an apparatus for carrying out the thin film forming method of the present invention. Chamber 1
An exhaust device 12 is connected to 1 so that the pressure inside the chamber 11 can be reduced when sputtering is performed. Further, in the chamber 11, a first rotating plate 81 and a second rotating plate 82 that also serves as a shutter are arranged at a predetermined interval in the vertical direction, and each of the rotating shafts 15
Each of them can be rotated independently about the center of.

On the lower surface of the first rotating plate 81, the first
The secondary target electrode 41 and the substrate electrode 21 are attached. The first sub target electrode 41 is a bias power source 71.
The substrate electrode 21 is connected to the bias power supply 61. In addition, the first sub-target electrode 41 has a first
The secondary target 93 is set, and the substrate 22 is set on the substrate electrode 21.

The lower surface of the second rotating plate 82 has a second
The secondary target electrode 42 is attached. The second secondary target electrode 42 is connected to the bias power source 72. Then, the second secondary target 94 is set on the second secondary target electrode 42. Further, the second rotating plate 82 has an opening 82a formed therein. The opening 82 a has an opening shape corresponding to the first sub target 93 and the substrate 22. Therefore, the second
The rotating plate 82 rotates so that the opening 82a becomes the first
When it is located below the sub target 93 or the substrate 22, the shutter state of the second rotary plate 82 with respect to the sub target 93 or the substrate 22 is released.

A first main target electrode 31 and a second main target electrode 32 are arranged at a lower position in the chamber 11. The first main target electrode 31 is connected to the RF power supply 51, and the second main target electrode 32 is
Is connected to an RF power source 52. Then, the first main target 91 is set on the first main target electrode 31, and the second main target 92 is set on the second main target electrode 32.

A method for forming a thin film of the present invention using the above apparatus will be described. In this embodiment, ZnO is used as the first main target 91, Al is used as the second main target 92, and Al ₂ O _{3 is used} as the first sub-target 93.
Was used as the second sub-target 94.

In the method of forming a thin film of this embodiment, first, Ar is introduced into the chamber 11 to a predetermined pressure, and then the main target electrode 31 is supplied with RF power from the RF power supply 51.
Electric power is applied to cause a discharge state. Then, Ar ions are made to collide with the first sub-target 93, and the particles of the sub-target 93 struck by the impact are deposited on the first main target 91. Hereinafter, this step is referred to as the first step. In the first step, the first rotary plate 81 is rotated by 180 ° from the state shown in FIG. 1, and the first sub-target 93 is attached to the opening 82 a of the second rotary plate 82.
Turn to. The particles knocked out from the first sub target 93 are deposited on the first main target 91 through the opening 82a.

Next, the first primary target 91 on which the particles of the first secondary target 93 are deposited is bombarded with ions, and the particles of the first primary target 91 and the first secondary target that are knocked out by the impact are bombarded. 93 particles are deposited on the substrate 22. Hereinafter, this step is referred to as the second step. In the second step, the state of FIG. 1, that is, the substrate 22 is directed to the opening 82a of the second rotating plate 82. The particles of the first main target 91 and the particles of the first sub-target 93 deposited in the first step are deposited on the substrate 22 through the opening 82a.

The first step and the second step are the same as the second step.
By rotating the first rotary plate 81 with the rotary plate 82 fixed, it is possible to repeatedly perform the discharge while maintaining the discharge state. Then, by the sputtering while rotating, the particles of the first main target 91 and the particles of the first sub-target 93 can be uniformly (about ± 3%) deposited on the substrate 22. In addition, in the repetition of the first step and the second step while rotating,
The potential difference between the electrodes suitable for the first step may be adjusted, and the potential difference between the electrodes suitable for the second step may be adjusted, as will be described later.
It is also possible to perform the first step and the second step without changing the potential difference between the electrodes.

Table 1 below shows various conditions regarding the substrate temperature and the like in the first step and the second step. The numbers in the table correspond to the member numbers in FIG. The self-bias of the first main target electrode 31 was -250V. The unit film thickness on the substrate 22 formed per rotation of the first rotary plate 81 was 5 Å. The final film thickness formed on the substrate 22 was 3000 angstroms.

[0027]

[Table 1]

FIG. 2 is a graph showing the relationship between the bias voltage applied to the secondary target electrode 41 in the first step and the resistivity of the ZnO thin film formed on the substrate.

When the bias voltage to the sub-target electrode 41 is -200 to -300 V, the difference is about 50 V at most, even if it is larger or smaller than the self-bias voltage (-250 V) at the time of discharging the main target electrode 31. Therefore, the particles of the sub target 93 are hardly deposited on the first main target 91. Therefore, the resistivity of the obtained film is almost the same as that when only undoped ZnO is targeted.

On the other hand, when the bias voltage of the secondary target electrode is -350 V or less, the secondary target (Al ₂
O ₃ ) is sputtered onto the main target (ZnO) to form a doped ZnO film on the substrate. The reason why the doped ZnO film is formed on the substrate is that not only sputtering from the sub-target to the main target but also sputtering from the main target to the substrate are alternately and continuously performed. That is, the first step and the second step are alternately and continuously performed without changing the potential difference between the electrodes.
However, as in the present embodiment, since the second rotating plate 82 is fixed and the film is formed while rotating the first rotating plate 81, the first rotating plate 81 is rotated by the first rotation every half rotation.
The step and the second step are switched.

By changing the bias voltage of the sub target electrode, the degree of sputtering from the sub target to the main target in the first step can be adjusted. Figure 2
Then, the lower the bias voltage of the secondary target electrode is, the higher the doping amount of Al is, and the obtained Z
It can be seen that the resistivity of the nO film becomes small. Therefore, the doping amount of the formed ZnO film can be easily changed in the film thickness direction only by changing the bias voltage of the sub target electrode. However, when the bias voltage of the sub target electrode is set lower than -600 V, the crystallinity of the film obtained by excessive doping is lowered, and the resistivity is rather increased.

Further, the bias voltage of the sub target electrode is the self bias voltage (-2 when the main target electrode is discharged).
If it is higher than 50 V), it becomes difficult to maintain the discharge in the first step, and the controllability of the film characteristics becomes poor, which is not preferable.

Here, when performing sputtering from the second sub-target 94 using Al to the first main target (ZnO) 91, a ZnO thin film having a doping amount larger than that in the case of FIG. Although obtained, as a result, the resistivity becomes high, but in the case of forming a multilayer film, there is an advantage that the contact resistance between adjacent layers can be reduced.

When the second sub-target (Al) 94 is used, the first rotary plate 81 is fixed so that the substrate 22 faces the first main target 91, and the second rotary plate 82 is rotated. You can do it. However, as described above, when a multilayer film is formed using the second sub-target (Al) 94, the second rotating plate 82 is not simply rotated for forming each film, but is rotated every half rotation. The rotation is temporarily stopped so that the second sub target 94 or the substrate 22 faces the first main target 91 for a certain period of time, and the first step and the second step are performed separately in time.

Therefore, it is important to adjust the potential difference between the electrodes suitable for the first step and the potential difference between the electrodes suitable for the second step. Since the process is switched for each process, the productivity of film formation is reduced. On the other hand, since the rotation is temporarily stopped and the film is formed under the condition suitable for each process, the controllability of the sputtering is improved, and a high quality multilayer film can be formed by uniform film formation.

The present invention was applied to the case of using a multilayer film of ZnO and Al as a back electrode of an amorphous silicon solar cell. The results are shown below. As the first step, sputtering from the second sub target (Al) 94 to the first main target (ZnO) 91 was performed. Further, the bias voltage to the second secondary target electrode 42 at this time was set to −550V, and the other conditions were the same as those in Table 1. Under these conditions, a 20 Å interface layer was formed at the interface between ZnO and Al. As a result, the series resistance is reduced by 20% compared to the back electrode of the multilayer film made of ZnO and Al formed by the conventional device, and the conversion efficiency of the amorphous silicon solar cell is changed from 11.5% to 12.2%. Improved.

As described above, in the first step, the sub target 93 (or 94) is changed to the main target 91.
By changing the degree of sputtering to (or 92), it is possible to adjust the deposition amount of the particles of the sub target 93 (or 94) deposited on the main target 91 (or 92). Then, the main target 9 in the second step
In the sputtering from 1 (or 92) to the substrate 22,
The primary target particles and the secondary target particles are deposited on the substrate 22 in a component ratio that reflects the deposition amount of the secondary target particles.

Therefore, the component ratio of the thin film deposited on the substrate 22 can be easily adjusted only by adjusting the deposition amount of the secondary target material in the first step. Then, as can be seen from FIG. 2, the adjustment of the component ratio can be performed only by adjusting the bias voltage to the sub target electrode.
In addition, by repeating the first step and the second step,
It is possible to easily form a multilayer film having different component ratios. In addition, by preparing a plurality of sub-targets for one main target or preparing a plurality of main targets themselves, it is possible to easily form a multilayer film in which not only the component ratio but also the main material itself is different.

If the transition between the above two steps is performed by the potential difference among the substrate electrode, the main target electrode and the sub target electrode, the influence of the initial discharge can be eliminated and a higher quality thin film can be formed.

FIG. 3 is a schematic view showing a schematic structure of an apparatus having another structure for carrying out the thin film forming method of the present invention. 1 differs from the device of FIG. 1 in that the device of FIG. 1 is provided with the second sub-target electrode 42 and the second sub-target 94 on the second rotary plate 82, whereas the device of FIG. The point is that the plate 85 is provided with the second sub-target electrode 42 and the second sub-target 94.

The slide plate 85 is used for the chamber 11
Configured to move linearly horizontally within the second
The secondary target 94 can be put in or taken out of the plasma region. Second
In the state in which the secondary target 94 of No. 2 is placed in the plasma region, the spread of plasma to the substrate electrode 21 can be blocked, and the sputtering from the second secondary target 94 to the first primary target 91 can be performed. In the state where the sub-target 94 of the above is emitted from the plasma region, the spread of the plasma to the substrate electrode 21 can be released and the sputtering from the first main target 91 to the substrate 22 can be performed.

In this apparatus, the slide plate 85 is used for inserting the first step and the second step in a series of film forming steps.
It is realized by a linear slide mechanism that moves in and out, and mechanical control becomes simpler than control of rotation of the rotating plate and its stop.

FIG. 4 is a schematic view showing a schematic structure of an apparatus having another structure for carrying out the thin film forming method of the present invention. In the apparatus shown in FIG. 4, the chamber 11 is formed by arranging two chamber chambers 11a and 11b side by side. A substrate loading chamber and a substrate unloading chamber (not shown) are formed at both ends of the chamber 11, and a substrate transfer path (not shown) is secured on the side of the chamber chambers 11a and 11b that are close to each other.
The substrate 22 can be transferred in both chambers 11a and 11b. Then, as in the apparatus of FIG. 3, the second sub-target electrode 42 and the second secondary target electrode 42
The secondary target 94 of the slide plate 8 is further provided.
6, a first sub-target electrode 41 and a second sub-target 93 are provided. In addition, each chamber 11a, 11
Shutters 13 '... Are provided in b.

By using such an apparatus, the multi-layer film can be formed on the substrate 22 continuously by linearly conveying the substrate 22, so that the productivity of film formation is improved.

[0045]

As described above, according to the present invention,
In a series of steps for forming a thin film, a first step for performing sputtering from the sub target to the main target and a second step for performing sputtering from the main target to the substrate are appropriately incorporated, and the first step is performed. In, since the component ratio of the thin film deposited on the substrate can be easily adjusted only by adjusting the deposition amount of the secondary target material, the fine adjustment of the dopant amount can be easily performed without preparing many kinds of targets having different dopant amounts. There is an effect that can be performed.

Further, when the transition between the above two steps is performed by the potential difference between the substrate electrode, the main target electrode and the sub target electrode, the stop of the discharge state can be avoided, so that the influence of the initial discharge is affected. There is an effect that a higher quality thin film can be formed without it.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of an apparatus for carrying out a thin film forming method of the present invention.

FIG. 2 is a graph showing the relationship between the bias voltage applied to the sub target electrode and the resistivity of the formed film.

FIG. 3 is a schematic view showing a schematic configuration of an apparatus having another configuration for carrying out the thin film forming method of the present invention.

FIG. 4 is a schematic diagram showing a schematic configuration of an apparatus having another configuration for carrying out the thin film forming method of the present invention.

FIG. 5 is a schematic diagram showing a schematic configuration of an apparatus for performing a conventional thin film forming method.

[Explanation of symbols]

 11 chamber 21 substrate electrode 22 substrate 31 first main target electrode 32 second main target electrode 41 first slave target electrode 42 second slave target electrode 51 RF power supply 52 RF power supply 61 bias power supply 71 bias power supply 72 bias power supply 91 First Master Target 92 Second Master Target 93 First Slave Target 94 Second Slave Target

Claims (2)

[Claims] 1. In a method of forming a thin film on a substrate by a sputtering phenomenon, ions are made to collide with a sub-target prepared separately from the main target, and particles of the sub-target knocked out by the impact are deposited on the main target. And a second step of causing ions to collide with the primary target on which the particles of the secondary target are deposited, and depositing the particles of the primary target and the particles of the secondary target knocked out by the impact on the substrate. A method of forming a thin film, comprising: 2. The first step and the second step are performed by changing the potential difference between the substrate electrode, the main target electrode, and the sub target electrode while maintaining the discharge state.
The thin film forming method according to claim 1, wherein the thin film forming method is performed continuously.