JP2012191028A - Thin film formation device and thin film formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film formation device capable of forming an Si thin film with more excellent quality characteristics at a low cost as compared with the conventional devices, and to provide a thin film formation method.SOLUTION: A thin film forming device is configured to perform: a step of supplying a first gas obtained by adjusting flow rates of a material gas, a dilution gas, and a krypton gas to a film formation space; a step of processing a substrate by generating a plasma by supplying a high-frequency power to an electrode plate and applying a bias voltage to a mounting table in the film formation space to which the first gas was supplied; a step of supplying a second gas obtained by adjusting the flow rates of the material gas and the dilution gas to the film formation space; and a step of forming a thin film on the substrate by generating a plasma by supplying a high-frequency power to the electrode plate in the film formation space to which the second gas was supplied. The ratio of the flow rate of the material gas to the total flow rate of the material gas and the dilution gas in the first gas is smaller than the ratio in the second gas.

Description

  The present invention relates to a thin film forming apparatus and a thin film forming method for forming a thin film on a substrate using plasma.

Conventionally, a CVD (Chemical Vapor Deposition) apparatus is used to form a thin film on a substrate. In particular, a process of forming a Si thin film used for a thin film solar cell or TFT (Thin Film Transistor) on a glass substrate by using a CVD apparatus has attracted attention. In the formation of the Si thin film, for example, monosilane (SiH ₄ ) is turned into plasma to form the Si thin film on the glass substrate. In recent years, thin-film solar cell panels have been increased in size, and it is desired to form a microcrystalline Si thin film having high quality characteristics and uniform characteristics on a large glass substrate at low cost.

  For example, in order to reduce the manufacturing cost when forming the microcrystalline Si thin film, it is desired that the temperature of the substrate on which the film is formed be 250 ° C. or lower. However, when a microcrystalline Si thin film is formed at a substrate temperature of 250 ° C. or lower, there is a problem in characteristics of the microcrystalline Si thin film, such that the crystallinity of the thin film is poor and the carrier mobility is low.

On the other hand, a method for efficiently producing a photovoltaic device using a microcrystalline semiconductor for a photoelectric conversion layer, which achieves a higher conversion efficiency than conventional ones, is known (Patent Document 1).
In this method, the step of forming an i-type μc-Si: H layer to be a photoelectric conversion layer by a plasma CVD method is divided into two steps. In the first half step, the hydrogen dilution rate of the source gas (SiH ₄ ) is increased and the power for plasma generation is increased to effectively generate microcrystalline silicon nuclei. In the second half step, the source gas is diluted with hydrogen. The deposition rate is increased by reducing the rate and reducing the power for plasma generation.
Thereby, it is supposed that the photoelectric converting layer which consists of a high quality microcrystalline semiconductor layer can be formed efficiently.

JP 2003-37278 A

In the above method, in the first half step, the hydrogen dilution rate of the source gas (SiH ₄ ) is increased and the power for plasma generation is increased to effectively generate microcrystalline Si nuclei. As a result, the microcrystalline Si thin film can be formed with the substrate temperature at 230 ° C.
However, in the current situation where it is desired to form a microcrystalline Si thin film having high quality characteristics at a lower cost, the above method cannot sufficiently meet the above requirements.

  Accordingly, an object of the present invention is to provide a thin film forming apparatus and a thin film forming method for forming an Si thin film having higher quality characteristics than conventional ones at a lower cost.

One embodiment of the present invention is a thin film forming apparatus for forming a thin film over a substrate. The device is
A film forming container having a film forming space for forming a thin film on a substrate placed on a mounting table in a reduced pressure state;
A gas introduction part for introducing a gas used for forming a thin film into the film formation space of the film formation container;
A plasma electrode section for generating plasma in the film formation space using the gas in the film formation space;
A bias voltage section for applying a bias voltage to the mounting table;
A control unit that controls application of the bias voltage.
The gas introduction part is
A Kr reservoir for storing krypton gas;
A raw material gas storage section for storing a raw material gas containing a thin film component;
A dilution gas storage unit for storing a dilution gas for diluting the source gas when supplying the source gas to the film formation container;
A gas flow rate adjusting unit for supplying gas to the film formation container by adjusting the flow rates of the source gas, the dilution gas, and the krypton gas.
The control unit controls the adjustment of the flow rate in addition to the control of the bias voltage.

At that time, the gas flow rate adjusting unit supplies the first gas and the second gas having different flow rate ratios of the source gas and the dilution gas in different processes, and the gas flow rate adjusting unit is configured to supply the first gas. After the supply of the second gas,
The ratio of the flow rate of the source gas to the total flow rate of the source gas and the dilution gas in the first gas is smaller than the ratio in the second gas, and the krypton gas is included in the first gas. Is preferably included.

  Moreover, it is preferable that the upper limit of the ratio of the flow rate of the source gas in the first gas is 30%, and the lower limit of the ratio of the flow rate of the source gas in the second gas is 40%.

  The control unit preferably controls the bias voltage unit to apply the bias voltage to the mounting table when the gas flow rate adjusting unit supplies the first gas.

Another embodiment of the present invention is a thin film forming method for forming a thin film on a substrate. The method is
Supplying a first gas obtained by adjusting the flow rates of the source gas, the dilution gas, and the krypton gas to the film formation space in a reduced pressure state where the substrate is placed on the placement table;
In the film formation space supplied with the first gas, high-frequency power is supplied to an electrode plate provided on the substrate to generate plasma, and by applying a bias voltage to the mounting table, Processing the substrate;
Removing the first gas from the film formation space and supplying a second gas obtained by adjusting the flow rates of the source gas and the dilution gas to the film formation space;
Forming a thin film on the substrate by generating a plasma by supplying high-frequency power to the electrode plate in the film formation space supplied with the second gas.
The ratio of the flow rate of the source gas to the total flow rate of the source gas and the dilution gas in the first gas is smaller than the ratio of the second gas.

  In that case, the upper limit of the ratio of the flow rate of the source gas in the first gas is preferably 30%, and the lower limit of the ratio of the flow rate of the source gas in the second gas is preferably 40%. .

  In the above-described thin film forming apparatus and thin film forming method, it is possible to form an Si thin film having higher quality characteristics than conventional methods at a lower cost.

It is the schematic showing the structure of the thin film forming apparatus which is this embodiment. It is a figure explaining the control system by the control part shown in FIG. It is a figure explaining the plasma electrode part shown in FIG. It is a figure explaining the flow of the thin film formation apparatus which is this embodiment.

Hereinafter, the thin film forming apparatus of the present invention will be described in detail.
FIG. 1 is a schematic diagram showing a configuration of a thin film forming apparatus 10 according to an embodiment of the present invention.

Hereinafter, the thin film forming apparatus of the present invention will be described in detail.
FIG. 1 is a schematic diagram showing a configuration of a thin film forming apparatus 10 according to an embodiment of the present invention.

  A thin film forming apparatus 10 shown in FIG. 1 is a CVD apparatus that forms a thin film on a substrate using generated plasma. The thin film forming apparatus 10 is a system that generates plasma by a magnetic field generated by a current flowing through an electrode plate. This method is different from a method in which plasma is generated by a high voltage generated by resonance of an antenna element such as a monopole antenna. For this reason, it is not necessary to adjust the frequency of the electric power supplied so that the element which produces | generates a plasma may resonate.

(Thin film forming equipment)
Hereinafter, the thin film forming apparatus 10 will be described using an example of forming a microcrystalline Si thin film as a thin film.
The thin film forming apparatus 10 includes a power supply unit 12, a film forming container 14, a gas supply unit 16, a gas exhaust unit 18, and a control unit 19.

The power supply unit 12 includes a high-frequency power source 22, a high-frequency cable 24, a matching box 26, transmission lines 28 a, 28 b, 29 a, and 29 b, a plasma electrode unit 30, and a bias voltage unit 31.
The high frequency power supply 22 supplies, for example, high frequency power of several tens of MHz at 100 to 2000 W to the electrode plates 30 a and 30 b (see FIG. 3) of the plasma electrode unit 30. The matching box 26 matches impedance so that the electric power provided through the high-frequency cable 24 is efficiently supplied to the electrode plates 30a and 30b. The matching box 26 includes a known matching circuit provided with elements such as a capacitor and an inductor.
The transmission lines 28a and 28b extending from the matching box 26 are, for example, copper plate-shaped transmission lines having a certain width, and a current of several tens of amperes can flow through the electrode plates 30a and 30b. The transmission lines 29a and 29b extend from the electrode plates 30a and 30b and are grounded.

Each of the electrode plates 30 a and 30 b is a plate member fixed on a partition wall 32 to be described later, and the first main surface (surface having the maximum area) of the plate member is a film formation space in the film formation container 14. It is arranged to face. The electrode plates 30a and 30b flow current along the longitudinal direction of the plate member between the end face to which the transmission lines 28a and 28b are connected and the end face to which the transmission lines 29a and 29b are connected.
The bias voltage unit 31 is connected to the susceptor 42 and applies a pulse voltage of 0.1 to 10 kHz to the substrate 20 during film formation under the control of the control unit 19.

  The film forming container 14 has an internal space 38 in the container. The internal space 38 is divided into an upper space and a lower film formation space 40 by the partition walls 32 and the electrode plates 30a and 30b. The film formation container 14 is formed of a material such as aluminum, for example, and is sealed so that the internal space 38 can be in a reduced pressure state of 0.1 Pa or less. A matching box 26, transmission lines 28a, 28b, 29a, 29b, and electrode plates 30a, 30b are provided in the upper space of the film forming container 14. Electrode plates 30a and 30b are fixed to the side of the partition wall 32 facing the upper space. An insulating member 34 is provided around the electrode plates 30a and 30b to insulate the surrounding partition walls 32 from each other. On the other hand, an electrode plate shielding part 36 made of a dielectric is provided on the side of the partition wall 32 facing the film formation space 40. For the electrode plate shielding part 36, for example, a quartz plate is used as a member. The reason why the electrode plate shield 36 is provided is to prevent the electrode plates 30a and 30b from being corroded by plasma and to efficiently supply electromagnetic energy to the plasma.

In the film formation space 40 of the film formation container 14, a heater 42, a susceptor 44, and an elevating mechanism 46 are provided.
The heater 42 heats the glass substrate 20 placed on the susceptor 44 to a predetermined temperature, for example, about 250 ° C.
The susceptor 44 has a mounting table on which the substrate 20 is mounted.
The elevating mechanism 46 moves the susceptor 44 on which the glass substrate 20 is placed together with the heater 42 freely in the film forming space 40. In the film forming process stage, the glass substrate 20 is set at a predetermined position so as to be close to the electrode plates 30a and 30b.
The susceptor 44 is connected to the bias power supply unit 31, and a bias voltage is applied to the substrate 20 during the film forming process using plasma.

The gas supply unit 16 includes gas tanks 48a, 48b, 48c, mass flow controllers 50a, 50b, 50c, and valves 51a, 51b, 51c.
The gas tank 48a stores hydrogen gas as a dilution gas for diluting monosilane gas (SiH ₄ ), which is a thin film raw material gas. The gas tank 48b stores monosilane gas (SiH ₄ ) that is a raw material gas for a thin film. The gas tank 48c stores krypton gas. As will be described later, the krypton gas is used in an initial film formation process during film formation.
The mass flow controllers 50a, 50b, and 50c adjust the flow rates of hydrogen gas, monosilane gas, and krypton gas. The valves 51a, 51b, 51c turn on / off (flow rate 0) the supply of hydrogen gas, monosilane gas, and krypton gas. That is, the mass flow controllers 50a, 50b, and 50c and the valves 51a, 51b, and 51c are flow rate adjusting units that adjust the flow rates of hydrogen gas, monosilane gas, and krypton gas. A mixed gas of these gases is supplied into the film formation space 40 from the side wall of the film formation container 14.

  The gas exhaust unit 18 includes an exhaust pipe extending from a side wall in the film formation space 40, a turbo molecular pump 52, and a dry pump 54. The dry pump 54 roughens the inside of the film formation space 40, and the turbo molecular pump 52 maintains the pressure in the film formation space 40 in a predetermined reduced pressure state. The turbo molecular pump 52 and the dry pump 54 are connected by an exhaust pipe.

  The control unit 19 controls operations of the high-frequency power source 22, the bias voltage unit 31, the mass flow controllers 50a, 50b, and 50c, and the valves 51a, 51b, and 51c. FIG. 2 is a diagram for explaining a control system by the control unit 19. Specifically, in the thin film forming apparatus 10, gases having different component ratios are used in the first process at the initial stage of film formation and the second process performed thereafter. In the first treatment, a first gas obtained by mixing hydrogen gas, monosilane gas, and krypton gas is used. At this time, the high frequency power supply 22 is controlled so as to supply high frequency power to the electrode plates 30a and 30b. Further, the bias voltage unit 31 is controlled so as to apply a bias voltage to the susceptor 42.

  On the other hand, in the second treatment, a second gas obtained by mixing hydrogen gas and monosilane gas is used. The second gas does not include krypton gas. Although the krypton gas may be included in the second gas, it is preferable that the krypton gas is not included in the second gas because the krypton gas does not function in the second treatment. At this time, the high frequency power supply 22 is controlled so as to supply high frequency power to the electrode plates 30a and 30b. In the second process, unlike the first process, no bias voltage is applied to the susceptor 42.

In the first process, the nucleus of the microcrystalline Si thin film is formed on the substrate 20, and in the second process, the microcrystalline Si thin film grows on the formed nucleus.
At this time, the ratio of the flow rate of the monosilane gas to the total flow rate of the monosilane gas and the hydrogen gas in the first gas is preferably smaller than the ratio in the second gas. That is, the first gas has less monosilane gas component than the second gas. For example, the ratio of the flow rate of monosilane gas to the total flow rate of monosilane gas and hydrogen gas in the first gas is 0 to 30%, and the ratio of flow rate of monosilane gas to the total flow rate of monosilane gas and hydrogen gas in the second gas is 40% or more. The first gas may have the above ratio of 0%, that is, the monosilane gas may not be contained at all. This is because, by using the thin film forming apparatus 10, the core of the microcrystalline Si thin film can be formed on the substrate 20 in the first process using the Si thin film deposited on the wall surface in the film forming space 40. Because.
As described above, the control unit 19 controls the operations of the high-frequency power source 22, the bias voltage unit 31, the mass flow controllers 50a, 50b, and 50c, and the valves 51a, 51b, and 51c.

FIG. 3 is an enlarged cross-sectional view in which the electrode plates 30a and 30b and the electrode plate shielding portion 36 are enlarged.
The electrode plates 30a and 30b of the plasma electrode unit 30 are provided on the susceptor 44 in the film formation space 40, and generate plasma using the first gas or the second gas. The electrode plates 30a and 30b are plate members elongated in one direction of a rectangular shape. In the electrode plates 30a and 30b, a current flows from one end face connected to the feed lines 28a and 28b to the other end face 31b connected to the feed lines 29a and 29b, that is, in the X direction. One main surface of the electrode plates 30 a and 30 b (the largest surface among the electrode plates 30 a and 30 b) faces the film formation space 40. The feed lines 29a and 29b are grounded as shown in FIG. For example, copper or aluminum is used for the electrode plates 30a and 30b. For example, a high frequency voltage of 500 V to 1 kV is applied to the electrode plates 30a and 30b.
The electrode plate shielding part 36 has a dielectric plate. The dielectric plate shields the entire main surface of the electrode plates 30 a and 30 b facing the film formation space 40.

  In the present embodiment, the electrode plates 30a and 30b are used, but the number of electrode plates is not limited to two. There may be one electrode plate, or three or more electrode plates. In the present embodiment, an example in which a microcrystalline Si thin film is formed is shown, but the present invention is not limited to this.

(Thin film formation method)
FIG. 4 is a diagram showing a flow of the thin film forming method of the present embodiment.
First, the control unit 19 controls the valve 51b to be closed and the valves 51a and 51c to be opened, and further controls the mass flow controllers 50a and 50c to generate the first gas. The first gas includes hydrogen gas and krypton gas, and does not include monosilane gas. For example, the flow rate (sccm) of krypton gas is set to a quarter of the flow rate of hydrogen gas. Since the generated first gas does not contain monosilane gas, the flow rate of monosilane gas is 0% with respect to the total flow rate of monosilane gas and hydrogen gas. In the present embodiment, the first gas can contain up to 30% of monosilane gas with respect to the total flow rate of monosilane gas and hydrogen gas. In this state, the thin film forming apparatus 10 supplies the first gas to the film forming space 40 in a reduced pressure state (step S10).

  Thereafter, the control device 19 controls the high frequency power supply 22 so that the high frequency power supply 22 supplies high frequency power to the electrode plates 30 a and 30 b, and the control device 19 applies a bias voltage to the substrate 20. A bias voltage is applied to the susceptor 42. At this time, a magnetic field is formed in the film formation space 40 by the current flowing through the electrode plates 30a and 30b, and the first gas is ionized by this magnetic field, and plasma is generated above the substrate 20 in the film formation space 40. Is done. Using this plasma, nuclei of a microcrystalline Si thin film are generated on the surface of the substrate 20 (step S20).

  Specifically, since krypton gas is included in the first gas, the density of plasma is increased, thereby increasing the density of hydrogen ions and hydrogen radicals generated from hydrogen gas. Further, since a negative bias voltage is applied to the substrate 20, hydrogen ions and krypton ions are attracted onto the substrate 20, and the substrate 20 receives energy by ion bombardment at this time. On the other hand, the generated plasma etches Si thin film components deposited on the other wall surfaces in the film formation space 40, and the Si components diffuse into the film formation space 40. This Si component is deposited on the substrate 20. At this time, hydrogen radicals or hydrogen ions drawn into the substrate 20 etch the deposited Si and cause an exothermic reaction. Therefore, the surface temperature of the substrate 20 is greatly increased as compared with the conventional case, and the crystallinity of the formed microcrystalline Si thin film is increased.

  Note that in order to increase the plasma density, it is preferable to use a rare gas having a larger atomic radius such as xenon. However, if the atomic radius is large and the mass is large, the momentum of ions colliding with the substrate 20 increases, and the microcrystalline Si Damages the crystallinity of the thin film nuclei. On the other hand, in order not to damage the crystallinity, it is preferable to use a rare gas having a smaller atomic radius such as argon. However, in this case, there is little effect of increasing the plasma density, and the hydrogen ions and radicals received by the substrate 20 are less effective. Irradiation is small and the surface temperature of the substrate 20 is not so high. For the above reasons, the first gas contains krypton gas in the present embodiment. The process of step S20 is performed for 5 to 20 seconds under the conditions of, for example, hydrogen gas 10 sccm, krypton gas 20 sccm, and high-frequency power 1000 to 20000 W in a reduced pressure state of 0.1 to 100 Pa.

Thus, after the nuclei of the microcrystalline Si thin film are formed on the substrate 20, the first process is completed, and the first gas is exhausted from the gas exhaust unit 18 (step S30).
Next, the control unit 19 controls the valve 51c to be closed and the valves 51a and 51b to be opened, and further controls the mass flow controllers 50a and 50b to generate the second gas. The second gas contains hydrogen gas and monosilane gas, and does not contain krypton gas. For example, the flow rate (sccm) of monosilane gas is set to 50% of the total flow rate of monosilane gas and hydrogen gas. Since the generated second gas does not include krypton gas, the flow rate of monosilane gas can be 40% or more with respect to the total flow rate of monosilane gas and hydrogen gas. In this state, the thin film forming apparatus 10 supplies the second gas to the film forming space 40 in a reduced pressure state (step S40).

Thereafter, the control device 19 controls the high frequency power supply 22 so that the high frequency power supply 22 supplies high frequency power to the electrode plates 30a and 30b. At this time, a magnetic field is formed in the deposition space 40 by the current flowing through the electrode plates 30a and 30b, and the second gas is ionized by this magnetic field, and plasma is generated above the substrate 20 in the deposition space 40. Is done. By this plasma, microcrystalline Si can be grown on the nucleus of the microcrystalline Si thin film formed on the substrate 20. At this time, no bias voltage is applied to the substrate 20. Thus, a microcrystalline Si thin film is formed (step S50). The process of step S50 is performed for 1 to 10 minutes under conditions of hydrogen gas 10 sccm, monosilane gas 10 sccm, and high-frequency power 100 to 2000 W, for example, in a reduced pressure state of 0.1 to 100 Pa.
Thus, after the microcrystalline Si thin film is formed on the substrate 20, the second process is completed, and the second gas is exhausted from the gas exhaust unit 18 (step S60).

  As described above, in step S20, since the first treatment with plasma is performed by adjusting the flow rate of krypton gas and applying a bias voltage to the substrate, the surface temperature of the substrate 20 becomes high, and the crystal of the nucleus of the microcrystalline Si thin film Can increase the sex. For this reason, it is possible to form a Si thin film with higher quality characteristics at a lower cost than in the prior art.

  As described above, the thin film forming apparatus and the thin film forming method of the present invention have been described in detail. However, the present invention is not limited to the above embodiment, and various improvements and modifications may be made without departing from the gist of the present invention. Of course.

DESCRIPTION OF SYMBOLS 10 Thin film formation apparatus 12 Power supply unit 14 Film formation container 16 Gas supply part 18 Gas exhaust part 19 Control part 20 Substrate 22 High frequency power supply 24 High frequency cable 26 Matching box 28a, 28b, 29a, 29b Transmission line 30 Plasma electrode part 30a, 30b Electrode Plate 31 Bias voltage section 32 Partition 34 Insulating member 36 Electrode plate shielding section 38 Inner space 40 Deposition space 42 Heater 44 Susceptor 46 Lifting mechanisms 48a, 48b, 48c Gas tanks 50a, 50b, 50c Mass flow controllers 51a, 51b, 51c Valve 52 Turbo Molecular pump 54 Dry pump

Claims (6)

A thin film forming apparatus for forming a thin film on a substrate,
A film forming container having a film forming space for forming a thin film on a substrate placed on a mounting table in a reduced pressure state;
A gas introduction part for introducing a gas used for forming a thin film into the film formation space of the film formation container;
A plasma electrode section for generating plasma in the film formation space using the gas in the film formation space;
A bias voltage section for applying a bias voltage to the mounting table;
A control unit for controlling the application of the bias voltage,
The gas introduction part is
A Kr reservoir for storing krypton gas;
A raw material gas storage section for storing a raw material gas containing a thin film component;
A dilution gas storage unit for storing a dilution gas for diluting the source gas when supplying the source gas to the film formation container;
A gas flow rate adjusting unit for supplying gas to the film forming container by adjusting the flow rates of the source gas, the dilution gas, and the krypton gas;
The control unit controls the adjustment of the flow rate in addition to the control of the bias voltage. The gas flow rate adjustment unit supplies a first gas and a second gas having different flow rate ratios of the source gas and the dilution gas in different processes, and the gas flow rate adjustment unit supplies the first gas. Later, supplying the second gas,
The ratio of the flow rate of the source gas to the total flow rate of the source gas and the dilution gas in the first gas is smaller than the ratio in the second gas, and the krypton gas is included in the first gas. The thin film forming apparatus according to claim 1, wherein:   The upper limit of the ratio of the flow rate of the source gas in the first gas is 30%, and the lower limit of the ratio of the flow rate of the source gas in the second gas is 40%. Thin film forming equipment.   The said control part controls the said bias voltage part so that the said bias voltage may be applied to a mounting table when the said gas flow volume adjustment part supplies the said 1st gas, The any one of Claims 1-3 The thin film forming apparatus according to the item. A thin film forming method for forming a thin film on a substrate,
Supplying a first gas obtained by adjusting the flow rates of the source gas, the dilution gas, and the krypton gas to the film formation space in a reduced pressure state where the substrate is placed on the placement table;
In the film formation space supplied with the first gas, high-frequency power is supplied to an electrode plate provided on the substrate to generate plasma, and by applying a bias voltage to the mounting table, Processing the substrate;
Removing the first gas from the film formation space and supplying a second gas obtained by adjusting the flow rates of the source gas and the dilution gas to the film formation space;
Forming a thin film on the substrate by generating a plasma by supplying high-frequency power to the electrode plate in the film formation space supplied with the second gas, and
A method of forming a thin film, wherein a ratio of a flow rate of the source gas to a total flow rate of the source gas and the dilution gas in the first gas is smaller than the ratio of the second gas.   The upper limit of the ratio of the flow rate of the source gas in the first gas is 30%, and the lower limit of the ratio of the flow rate of the source gas in the second gas is 40%. Thin film forming method.

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