JP2011241471A - Method and apparatus of forming conductive thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique of sputtering film deposition which satisfies various film properties at the same time.SOLUTION: In a method of forming a conductive thin film on a substrate using a sputtering phenomenon, at least one of deposition parameters including sputter electric power, sputter gas, and reactive gas is shifted to two values and its time division ratio is controlled during the thin film deposition. A method of forming the conductive thin film on a semiconductor having either p-type or n-type conductivity, in which an intense plasma irradiation is performed when starting deposition onto the semiconductor, can also be employed.

Description

  The present invention relates to a method for forming a conductive thin film used for a light emitting device or a display device and an apparatus used therefor, and more particularly to a method for forming an oxide transparent conductive thin film and an apparatus used therefor.

  As a transparent conductive thin film (hereinafter, also simply referred to as a thin film or a conductive thin film), IZO, ZnO, AZO, GZO and the like are known in addition to ITO widely used in various display devices. As a method for forming these thin films, various methods such as a vacuum deposition method and a sputtering method, a PLD (Pulsed Laser Deposition) method, and a sol-gel method have been tried. These thin films are generally binary or ternary compounds such as oxides, and the electrical conductivity, optical transparency, and surface flatness, as well as the film composition and crystallinity, vary greatly depending on the formation method. For this reason, even for the same ITO, for example, the formation method and conditions are changed according to the device to be applied, and necessary characteristics are extracted and used for each device.

  Conventionally, the most commonly used methods for forming an ITO film are sputtering and vacuum deposition. Sputtering is widely used in display devices such as liquid crystal panels and touch panels because it can be uniformly formed on a large area substrate and has excellent film quality. On the other hand, when the deposition substrate is a semiconductor, such as an LED, sputtering is avoided for reasons such as concerns about damage to the semiconductor and difficulty in ohmic contact with the semiconductor, and vacuum deposition has been used for many years. Has been.

  However, ITO films formed by vapor deposition tend to be unstable films such as needle crystals in general, have insufficient chemical resistance in device processes, and require characteristics for thin film characteristics such as transmittance and flatness. Attempts to replace it with other film forming methods have been made.

  In addition, in both sputtering and vacuum deposition, characteristics such as conductivity and permeability are ensured by adding a small amount of oxygen during film formation, so the accuracy of gas flow controllability and residual moisture in vacuum As a result, film formation stability and reproducibility were extremely difficult.

Japanese Patent No. 1553959 Japanese Patent No. 1462543

  Thus, in recent years, the characteristics required for transparent conductive thin films are extremely diverse, and the required characteristics are greatly different depending on the device to be applied. For example, in a liquid crystal display device, characteristics such as conductivity and transmittance are mainly required, but in addition to these, an LED requires low contact resistance with a semiconductor. In particular, it is very difficult to obtain a good contact for p-type GaN having a low carrier concentration.

  An ITO film formed by vacuum evaporation can obtain an ohmic contact relatively easily, but the film quality is insufficient. On the other hand, the sputter method can provide good film quality, but it is difficult to make ohmic contact. In any of the forming methods, it is difficult to add a small amount of oxygen, and it is extremely difficult to satisfy all the characteristics such as flatness as well as resistivity and transmittance.

  In view of such a problem, an object of the present invention is to provide a technique for simultaneously satisfying all film characteristics in sputtering film formation.

  In order to solve the above problems, the present invention is a method of forming a conductive thin film on a substrate using a sputtering phenomenon, and includes sputtering power, sputtering gas, and reactive gas during the thin film formation. It is a method for forming a conductive thin film characterized in that at least one of the deposition parameters is changed to two values and the time division ratio is controlled.

According to a second aspect of the present invention, in the method for forming a conductive thin film according to the first aspect, ECR is used as a plasma generation method, and the film formation parameter further includes microwave power. According to the invention described in the above item, in the method for forming a conductive thin film on a semiconductor having p-type or n-type conductivity, plasma irradiation is intensely performed at the start of film formation on the semiconductor. Is a method for forming a conductive thin film.

  According to a fourth aspect of the present invention, in the method for forming a conductive thin film according to the third aspect, the plasma generation method is ECR.

  The invention according to claim 5 is an apparatus for forming a conductive thin film on a substrate using a sputtering phenomenon, and the film formation parameters including sputtering power, sputtering gas, and reactive gas are reduced during thin film formation. It is a conductive thin film forming apparatus characterized by having means for changing at least one of the two values into two values and controlling the time division ratio.

  According to a sixth aspect of the present invention, in the conductive thin film forming apparatus according to the fifth aspect of the present invention, ECR is used as a plasma generation method, and the film formation parameter further includes microwave power.

It is a figure which shows the cross-section of a typical solid source ECR plasma film-forming apparatus. It is a figure which shows the resistivity and surface flatness of the ITO film | membrane by the film-forming method of the comparative example 1. It is a figure which shows the permeation | transmission characteristic of the ITO film | membrane formed in the comparative example 1 and Example 1. FIG. It is a figure which shows the IV characteristic of the ITO / p-GaN contact in the case where the contact layer by this invention is inserted, and the case where it does not insert.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The present invention provides a method for forming a conductive thin film using a sputtering phenomenon. First, in order to ensure controllability and reproducibility of film quality, at least one of gas flow rate and power is applied during film formation. It is characterized in that means for changing the value and controlling the time division ratio is used. The conventional method of controlling a very small amount of film formation parameters in analogy has the disadvantage that the film quality changes greatly due to slight fluctuations in film formation conditions and residual gas, etc. Highly accurate film quality control is possible. Further, the second means of the present invention is characterized in that the substrate is irradiated with intense plasma at the time of starting the film formation, whereby a good ohmic contact between the conductive thin film and the semiconductor can be obtained.

  When using only the film properties of the conductive film itself, for example, when applied to a device such as a touch panel, a sufficient effect can be obtained only by the first means, but a device that requires contact with a semiconductor, such as an LED. Then, both the first means and the second means are used.

(First embodiment)
In the present embodiment, the ITO film is formed by sputtering using a solid source type ECR plasma film forming apparatus. ECR is an abbreviation for Electron Cyctron Resonance, or electron cyclotron resonance. The solid source type ECR plasma film forming apparatus can generate a plasma flow by utilizing this ECR phenomenon. By applying a voltage to the target placed around the generated plasma flow, ions in the plasma are accelerated and incident on the target to cause a sputtering phenomenon, and the released target particles are deposited on a sample substrate placed nearby. A technique for forming a thin film has already been patented (see Patent Documents 1 and 2).

  Here, a solid source ECR plasma apparatus that can be used in the ECR sputtering method will be described. FIG. 1 shows a typical structure of a solid source ECR plasma apparatus. In the figure, the plasma generation chamber 1 is attached to the sample chamber 2 at an angle, and is connected to the sample chamber via the plasma extraction window 3. Both are sealed spaces isolated from the atmosphere.

  In order to form a thin film on the sample substrate 5 placed on the rotating sample stage 4, first, the plasma generation chamber 1 and the sample chamber 2 are evacuated by a vacuum pump (not shown) through the exhaust passage 6, A gas is introduced from the gas inlet 7 or the gas inlet 8 and maintained at a predetermined pressure.

  Next, a current is passed through the two magnetic coils 9 placed around the plasma generation chamber 1 to generate a magnetic field, and then the microwave 11 guided to the rectangular waveguide 10 is converted into a microwave below the plasma generation chamber 1. It introduces to the vacuum side through the introduction window 12. As a result, electron cyclotron resonance occurs in the plasma generation chamber 1, and ECR plasma is generated.

  The plasma generated in the plasma generation chamber 1 flows as a plasma flow 13 from the plasma extraction window 3 to the sample substrate 5 along the divergent magnetic field. When the sputtering power supply 14 is turned on and a voltage is applied to the target 15 in this state, ions in the ECR plasma are accelerated toward the target 15 and target constituent atoms are released into the vacuum by the ion bombardment. At this time, direct current (DC), alternating current (RF), DC pulse, or the like is used as a sputtering power source applied to the target.

  The particles that have jumped out of the target 15 travel in all directions to form a thin film on the sample substrate 5 and also adhere to the inner wall of the plasma generation chamber 1. Any solid material can be used as the target material. Typical examples include silicon, aluminum, titanium, zirconium, zinc, carbon, tantalum, molybdenum, tungsten, and compounds such as ITO, IZO, and STO. . In addition, when using oxygen or nitrogen in addition to an inert gas such as argon or xenon when forming a film, a compound thin film such as silicon oxide, silicon nitride, or alumina can be formed even when the target is a single metal. it can.

  The shutter 16 is normally closed and is controlled to be opened and closed when plasma irradiation or sputter film formation processing is performed on the sample substrate 5 for a predetermined time.

  The ITO film formation in this embodiment uses an ITO target having a Sn composition of 10% as the target 15 and argon and oxygen as the gas in the apparatus shown in FIG. At least one is changed to two values such as ON / OFF (1/0), for example, and a means for controlling the time division ratio is used. Specifically, the control means includes a sputtering power source 14, a gas introduction valve (not shown) connected to the gas introduction port 7 or 8, and a microwave generator for introducing the microwave 11 into the rectangular waveguide 10 ( (Not shown) and means for controlling the shutter 16 respectively. As a result, the controllability and reproducibility of the film quality are ensured, and all required characteristics such as electric conductivity, surface flatness, and optical transparency are satisfied. For comparison, the following Comparative Example 1 and Example 1 were performed.

(Comparative Example 1)
First, as Comparative Example 1, an ITO film was formed by the conventional method using the apparatus shown in FIG. The film formation conditions at this time were a microwave 11 power of 300 W, a sputtering power of 300 W applied to the target 15, an argon gas flow rate of 25 sccm, a current 26 A of two magnetic coils, and a substrate rotation of 15 rpm, and the substrate was not heated. A plurality of ITO films were obtained by changing the flow rate of oxygen gas. Argon gas and oxygen gas were introduced from the gas inlet 7. As the sample substrate 5, a Si wafer cleaved to 5 to 20 mm square on a 6-inch diameter SUS disc and a sapphire wafer cleaved in the same manner were screwed. The ITO film was formed by adjusting the film formation time so that the film thickness was about 100 nm at each oxygen gas flow rate.

  For the ITO film formed by the method of Comparative Example 1, the ITO film formed on the Si wafer was irradiated with a helium-neon laser, and the ITO film thickness and refractive index were measured by ellipsometry. The sapphire substrate was annealed after film formation, and the resistivity, surface roughness, and transmittance were measured before and after that. The annealing was performed at 450 ° C. for 20 minutes in nitrogen using a gold furnace. The resistivity was measured using the four-probe method, the surface roughness was measured using AFM, and the transmittance was measured using spectroscopic analysis.

  FIG. 2 plots the resistivity and surface flatness of the ITO film annealed after being deposited on the sapphire substrate by the method of Comparative Example 1 against the oxygen flow rate during deposition. In FIG. 2, 2a indicates the average roughness Ra, and 2b indicates the resistivity ρ. According to the figure, it can be seen that the resistivity ρ increases rapidly with a slight addition of oxygen, while the average roughness Ra is significantly reduced. At an oxygen flow rate of 0 sccm, the resistivity is at a practical level, but the unevenness (average roughness Ra) is large, which may cause a problem. As a conventional general method, the oxygen flow rate has been set to 0.3 to 0.4 sccm so that various characteristics satisfy practical levels. However, these characteristics are not satisfactorily satisfactory, and the characteristics fluctuate greatly due to slight changes in flow rate, and thus there is a problem in reproducibility.

  In Example 1, an ITO film was formed by the method of the present invention using the apparatus shown in FIG. In this example, film formation was attempted under the same conditions as in Comparative Example 1 except that the oxygen flow rate was 1.5 sccm and ON / OFF was repeated only for that flow rate. The oxygen flow ON / OFF is fixed at 1.5 sccm for the mass flow connected to the gas inlet 7 and the piping is changed so that the two valves installed before and after the piping can be turned ON / OFF simultaneously. Film formation was performed under a plurality of conditions with different ON / OFF times (duty ratios). The film quality of the ITO film formed by this method was evaluated in the same manner as in Comparative Example 1 above.

As a result, when the ON time was 1 second and the OFF time was 4 seconds, conditions with a low resistivity and good flatness were obtained. After annealing, the ITO film had a resistivity of 5.7 × 10 ⁻⁴ Ωcm and a Ra of 0.22 nm, satisfying both characteristics of resistivity and flatness, and can be controlled with good reproducibility. . In addition, when both the ON time and OFF time were set to 2.5 seconds, almost the same data was obtained, and the film quality was extremely good in terms of both resistivity and flatness.

  In addition, the optical transmittance was compared between the sample formed in Comparative Example 1 with an oxygen flow rate of 2 sccm and the sample formed in Example 1 under the conditions of both ON time and OFF time of 2.5 seconds. FIG. 3 is a diagram showing optical transmission characteristics of the ITO film. In the figure, 3a represents the optical transmission characteristics of Example 1, and 3b represents the optical transmission characteristics of Comparative Example 1. As shown in FIG. 3, the ITO film according to the present invention also has an optical transmittance of 99.5% or more at a wavelength of 500 nm, which is equivalent to or better than that of the conventional method, and the transmission wavelength region is on the short wavelength side. It was confirmed to spread.

  As described above, according to the present invention, the physical properties of the conductive thin film can be controlled with high accuracy, and can be optimized to satisfy all required characteristics such as electrical conductivity, surface flatness, and optical transparency. In addition, the reproducibility is easily ensured.

  As an example of film forming conditions other than the above, even when the microwave power is 700 W, the sputtering power is 500 W, the argon gas flow rate is 40 sccm, the current of the two magnetic coils is 26 A, the substrate rotation is 15 rpm, and the substrate is not heated, the oxygen flow rate is 1.5 sccm. In addition to an ON time of 1 second and an OFF time of 4 seconds, when an oxygen flow rate of 0.5 sccm was set to an ON time of 3 seconds, an OFF time of 7 seconds, an ITO film superior to the conventional method was obtained. The oxygen flow rate and the time division ratio are determined by optimizing while evaluating the film quality.

  In addition to the parameters shown above, the same oxygen flow rate control was performed with various changes in the microwave power and sputtering power. It became clear that the ON / OFF time division ratio can be selected. As the tendency, the optimum condition was obtained by increasing the oxygen flow rate to a maximum of about 2 sccm or relatively increasing the ON time of oxygen as the microwave power was increased.

  In the above embodiment, as a method for controlling the time division ratio by changing at least one of the film formation parameters during film formation to two values, the oxygen flow rate and the ON / OFF time division ratio are controlled. However, the film quality can be controlled even if the time division ratio of two values other than ON / OFF is controlled for not only the oxygen flow rate but also the sputtering power, microwave power, and argon flow rate as the sputtering gas. It was possible to improve the controllability. Further, not only these film formation parameters but also a case where opening and closing of the shutter 16 is required as required. When the film formation parameters are changed, the oxygen adsorption state on the target surface changes, and when it is desired to avoid film formation on the substrate in the transition state, the shutter 16 is closed.

  In the above embodiment, ITO was described as an example of the conductive thin film. However, the conductive thin film is not limited to ITO, but also ternary compounds such as IZO, AZO, and GZO, and oxides such as ZnO. The same effect can be obtained with a thin film.

  Further, although ECR plasma film formation is used in this embodiment, the same method can be applied to film formation by general sputtering, counter sputtering, unbalanced magnetron sputtering, ion beam, or the like. For example, in conventional ITO film formation by sputtering, a small amount of oxygen has been conventionally added to argon, which is a sputtering gas, but controllability and reproducibility are greatly improved by oxygen flow rate control according to the present invention.

(Second Embodiment)
In this embodiment, the ITO film is formed as a contact layer by irradiating the surface of the film formation substrate with a strong plasma at the start of film formation, that is, before film formation or during initial film formation.

  Here, the examination performed in advance for applying the ITO film to the p-type GaN contact electrode of the LED will be described. First, using the apparatus shown in FIG. 1, a p-GaN substrate is also set on a 6-inch SUS substrate, and ITO is formed in the same manner as the Si wafer and sapphire wafer used in Example 1 to obtain a sample. Samples were evaluated.

The P-GaN substrate is used for evaluating contact resistance mainly by IV characteristics. After growing Mg-doped GaN on the sapphire substrate by MOCVD, activation annealing is performed to obtain a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ level. It is a thing. In order to remove the natural oxide film on the GaN surface, light etching was performed with dilute hydrofluoric acid before forming the ITO film. In addition, a thin SUS plate with a large number of holes having a diameter of about 0.1 to 1 mm was used as a mask when forming the ITO film so that a circular electrode was formed on the p-GaN substrate. The IV characteristics were measured by applying a voltage between two adjacent electrodes among them.

  In the above sample formed by the same method as in Example 1, excellent ITO film characteristics were obtained, and the reproducibility of the film formation was ensured. However, the evaluation result of the ITO / p-GaN contact using the p-GaN substrate formed by the same method as in Example 1 shows the same Schottky characteristic as the conventional film forming method, which is completely improved. There wasn't.

  Therefore, when the contact characteristics were examined by changing all film formation parameters, the contact characteristics were improved and the low voltage was reduced when the oxygen flow rate was reduced to about 0.5 sccm or less and the microwave power was increased to 500 W or more. However, it became clear that current tends to flow easily. However, even when the oxygen flow rate and the microwave power were changed to the maximum, all showed Schottky characteristics and no ohmic characteristics were obtained.

  On the other hand, when an attempt was made to vary the oxygen flow rate and microwave power only for ITO having a film thickness of about 5 nm to 10 nm at the ITO / p-GaN interface, the contact characteristics were determined by the ITO film forming conditions on the interface side. It was found that the influence of the film formation conditions of the distant ITO was small. Based on these results, the ITO film forming method of Example 1 was used, and only a portion in contact with the p-GaN interface was devised to examine whether an ohmic contact could be obtained. As a result, ohmic characteristics can be obtained by irradiating the p-GaN surface with a sufficient ECR plasma flow (intensity plasma) at the start of film formation, that is, before film formation or during initial film formation. Formed). There are the following three methods (A) to (C) as specific implementation methods for irradiating plasma intensely at the start of film formation on the substrate.

  (A) Before film formation, an ECR plasma flow having a pressure of about 0.1 Pa or more and about 500 W or more is irradiated for at least several seconds to about 10 minutes.

  (B) Under conditions of pressure of about 0.1 Pa or more and microwave power of about 500 W or more, the ITO film formation rate is suppressed to about 5 nm / min or less by reducing the sputtering power to the target, etc. 20 nm ITO is formed.

  (C) After depositing an ITO film of one atomic layer or more, repeat the sequence of stopping the sputtering power supply to the target and irradiating the ECR plasma flow under the same conditions as in (A). 20 nm ITO is formed.

  The above three methods are all expected to be effective in irradiating a low energy, high density ion beam when forming the ITO / p-GaN interface. The higher the microwave power, the longer the irradiation time. The longer the length, the better the contact characteristics improvement effect. Typically, an ohmic contact that is sufficiently satisfactory for practical use has been realized by irradiating an ECR plasma flow of about 3 minutes at a microwave power of 800 W until the formation of an ITO film having a thickness of 5 nm is completed.

  The IV characteristics of the ITO / p-GaN contact made of ITO with the contact layer formed by the method of the present embodiment are shown in the IV characteristics of the ITO / p-GaN contact made of ITO without the contact layer formed by the method of the first embodiment. Compared with characteristics.

  The ITO without the interface contact layer can be formed by the same method as the film forming method of Example 1, and using the apparatus of FIG. 1, the microwave power 700 W, the sputtering power 500 W, the argon gas flow rate 40 sccm, and the two magnetic coils An ITO film having a film thickness of 100 nm was formed under the conditions of current 26A, substrate rotation 15 rpm, substrate heating, oxygen flow rate 1.5 sccm, ON time 1 second, and OFF time 4 seconds.

  The ITO contact layer of this embodiment is formed by using the apparatus of FIG. 1 to form a film for 20 seconds at a microwave power of 900 W, a sputtering power of 100 W, an argon gas flow rate of 40 sccm, and an oxygen flow rate of 0 sccm, and then turn off the sputtering power. Then, the sequence of plasma flow irradiation for 20 seconds was repeated four times to form an ITO layer having a total thickness of about 5 nm. The method for forming the ITO layer of about 5 nm to 100 nm thereon is the same as that without the contact layer.

  4A and 4B are diagrams showing the IV characteristics of the ITO / p-GaN contact. FIG. 4A shows the case where the ITO contact layer is not formed, and FIG. 4B shows the case where the ITO contact layer is formed. ing. In the figure, the plot line a is before annealing of the ITO without the contact layer, the plot line b is after annealing of the ITO without the contact layer, the plot line c is before annealing of the ITO with the contact layer, Plot lines d indicate the IV characteristics in each of the ITO layers with contact layers after annealing.

  The annealing after the ITO film formation was performed at 550 ° C. for 10 minutes in nitrogen. Before the annealing, all IV characteristics show Schottky characteristics (plot line a, plot line c). One sample with a contact layer showed linearity (plot line d) by annealing, and an ohmic contact was obtained.

  The method for forming the ITO contact layer in this example was confirmed to have a great effect even in the following three-layer structure, for example. As a first step, a film was deposited for 15 seconds at a microwave power of 900 W, a sputtering power of 150 W, an argon gas flow rate of 40 sccm, and an oxygen flow rate of 0 sccm, and then the sputtering power was turned off and plasma flow irradiation was repeated three times for a total of 3 times. An ITO layer of about 5 nm is formed. As a second step, an ITO film having a film thickness of 10 nm is formed by processing for 90 seconds at a microwave power of 900 W, a sputtering power of 150 W, an argon gas flow rate of 40 sccm, and an oxygen flow rate of 0.5 sccm. As a third step, an ITO film having a thickness of 100 nm is formed with a microwave power of 700 W, a sputtering power of 500 W, an argon gas flow rate of 40 sccm, an oxygen flow rate of 1.5 sccm, an ON time of 1 second, and an OFF time of 4 seconds. In these three steps, the current of the two magnetic coils was 26 A, the substrate rotation was 15 rpm, and the substrate heating was performed.

  As described above, there are many variations in setting the contact layer formation parameters, such as the methods (A), (B), and (C). However, the strength is increased at the time of starting film formation on the substrate. In order to irradiate the plasma, some considerations are necessary in addition to irradiating the plasma for a predetermined time or longer with high microwave power. For example, if the pressure is reduced to about 0.05 Pa or less, the energy of argon ions is increased and the ITO film formed on the substrate is ion-etched, and the contact improvement effect cannot be obtained. Therefore, the pressure is maintained at a predetermined value or more. It is necessary to pay attention such as In fact, it was confirmed that the ITO film was etched at a speed of about 10 nm / min by ECR plasma flow irradiation with a microwave power of 500 W and a pressure of about 0.03 Pa.

  In the apparatus used this time, the area irradiated with the plasma flow is approximately 30 cm in diameter. Therefore, when using another apparatus, the microwave power can be normalized using the power density per unit area.

  Up to now, the reason why contact between ITO and p-GaN formed by sputtering has not been obtained is generally due to sputtering damage, but at least in the examples of the present invention, such a result Was not seen. Even if contact characteristics may deteriorate due to damage, the target surface of the device used this time is facing, and the substrate is in a distant position so that it does not face the target. Therefore, it is considered that the influence of high energy particles jumping out from the target surface is small.

  Also, as is well known, the ion energy in the ECR plasma flow is an extremely low energy of about 20 eV-30 eV and does not cause fatal damage to the semiconductor surface. Rather, it is considered that the contact characteristics are greatly improved by high-density and low-energy ion irradiation, such as an interface reaction promoting action between ITO and p-GaN.

  In the case of the above method (A), the ITO / p-GaN reaction cannot be promoted before the ITO film is formed. However, due to the resputtering phenomenon, a very small amount of ITO is formed on the p-GaN substrate. Adherence to the surface is also envisaged. As a contact improvement mechanism, in addition to the above, a chemical action such as breaking the Mg-hydrogen bond of the p-GaN substrate by plasma irradiation or a thermal action by increasing energy at the atomic level may be considered. For the above reason, it is interpreted that the effect of improving the contact characteristics is further promoted by performing the plasma irradiation while heating the substrate as well as performing the plasma irradiation.

  In addition, in order to effectively perform the method (C), there may be a case where a sequence control means different from that generally used in the apparatus configuration is required. As an example, by repeating ON / OFF of the sputtering power to the target while opening the shutter 16 to perform film formation, it is possible to effectively reduce the film formation speed and enhance the ECR plasma flow irradiation effect. At this time, when the ON time is 10 seconds and the OFF time is 10 seconds, the film formation speed is ½. However, if the OFF time is 20 seconds, the film formation speed can be reduced to 1/3, and the irradiation effect is high by that amount. Become. In this way, the required characteristics can be easily obtained by controlling the ON / OFF time in units of seconds.

  In this example, when the sputtering power is turned on, changes in the oxygen adsorption state on the target surface, plasma instability, particle generation, etc. may become problems. In this case, the shutter 16 is temporarily closed and the sputtering power is temporarily closed. There is also a method in which the shutter 16 is opened after being turned on and stabilized. In that case, after the microwave power and the sputtering power are turned on to make a film ready state, “maintain 10 seconds after opening the shutter 16 → maintain 20 seconds after turning off the sputtering power → close the shutter 16 and turn on the sputtering power 20 This is a sequence example such as “second maintenance”.

  In the above example, the time division ratio is controlled in the same manner as in the first embodiment by turning on / off the power. However, the present invention is not limited to this, and the method of controlling the time division ratio by raising and lowering the power to two values. Can also be adopted. The power ON / OFF includes the power source and the cycle control mechanism of the shutter 16 as described above.

  According to the present embodiment, ohmic contact with a semiconductor, which has conventionally been difficult by sputtering, can be realized without using another film forming method such as vapor deposition.

  In the present embodiment described above, an example of ITO as a contact electrode and p-GaN as a semiconductor is shown. However, the present invention is not limited to this, and in any combination of electrodes other than ITO and any semiconductor including, for example, an n-type semiconductor. The effects of the invention can be obtained. As electrodes, for example, ternary compounds such as IZO, AZO, and GZO, oxide thin films such as ZnO, and all metals such as Ni, Au, and Pd are assumed. On the other hand, semiconductors include InP, GaP, and GaAs. All semiconductor materials such as Si, SiC, etc. are applied.

DESCRIPTION OF SYMBOLS 1 Plasma production chamber 2 Sample chamber 3 Plasma extraction window 4 Sample stand 5 Sample substrate 6 Exhaust path 7, 8 Gas inlet 9 Magnetic coil 10 Rectangular waveguide 11 Microwave 12 Microwave introduction window 13 Plasma flow 14 Sputtering power source 15 Target 16 Shutter

Claims (6)

  A method for forming a conductive thin film on a substrate by utilizing a sputtering phenomenon, wherein at least one of film formation parameters including sputtering power, sputtering gas, and reactive gas is changed to two values during thin film formation. And a method of forming a conductive thin film, wherein the time division ratio is controlled.   The method for forming a conductive thin film according to claim 1, wherein ECR is used as a plasma generation method, and microwave power is further included in the film formation parameter.   A method for forming a conductive thin film on a semiconductor having a p-type or n-type conductivity, wherein the plasma irradiation is intensely performed at the start of film formation on the semiconductor.   The method for forming a conductive thin film according to claim 3, wherein the plasma generation method is ECR.   An apparatus for forming a conductive thin film on a substrate using a sputtering phenomenon, wherein at least one of deposition parameters including sputtering power, sputtering gas, and reactive gas is set to two values during thin film formation. A conductive thin film forming apparatus characterized by having means for changing and controlling the time division ratio.   6. The conductive thin film forming apparatus according to claim 5, wherein ECR is used as a plasma generation method, and microwave power is further included in the film formation parameters.

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