JP7665545B2 - Negative ion generator - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies. Publication date: June 30, 2016 Publication: High-Hall-Mobility Al-Doped ZnO Films Having Textured Polycrystalline Structure with a Well-Defined (0001) Orientation, Nanoscale Research Letters [Publications, etc.] Publication date: August 19, 2016 Publication: Correlation between carrier transport and orientation evolution of polycrystalline transparent conductive Al-doped ZnO films

The present invention relates to a film formation system and a film formation method.

A conventional film formation method is shown in Patent Document 1. Patent Document 1 describes the manufacture of an LED element by forming a semiconductor film on a semiconductor substrate.

JP 2008-147608 A

As described above, by forming a semiconductor film on a semiconductor substrate, it is possible to form a high-quality semiconductor film having high orientation and low vacancy defect concentration. However, while the above-mentioned semiconductor substrate can provide a high-quality semiconductor film, there is a problem in that the single crystal semiconductor substrate itself is expensive. Furthermore, polishing scratches on the substrate surface and carbides that adhere during polishing must be removed by etching, which increases the process cost.

The present invention aims to provide a film formation system and a film formation method that can obtain high-quality semiconductor films while keeping costs down.

In order to solve the above problems, the film formation system according to the present invention is a film formation system that forms a film on a non-single crystal substrate, and includes a first film formation device that forms a film by an ion plating method, and a second film formation device that forms a film downstream of the first film formation device, and the first film formation device forms a first semiconductor film containing a first semiconductor material on the non-single crystal substrate, and the second film formation device forms a second semiconductor film containing a second semiconductor material on the first semiconductor film on the non-single crystal substrate.

In the film formation system according to the present invention, before the second semiconductor film is formed by the second film formation device, the first film formation device forms a first semiconductor film on a non-single crystal substrate by an ion plating method. In this way, by forming a film by the ion plating method, a first semiconductor film can be formed as a highly oriented polycrystalline film (called a uniaxial crystal texture or uniaxial crystal texture film) having an orientation order close to that of a single crystal (each crystallite has the same orientation order as the other crystallites). By forming a second semiconductor film on such a first semiconductor film, a second semiconductor film can be obtained that is aligned with the highly oriented first semiconductor film. Therefore, by forming the second semiconductor film on the first semiconductor film, the second film formation device can obtain a highly oriented second semiconductor film compared to the case of directly forming a film on a non-single crystal substrate. In this way, even if a non-single crystal substrate, which is less expensive than a single crystal semiconductor substrate, is used, the quality of the second semiconductor film can be improved by forming the first semiconductor film with the first film formation device. In other words, it is possible to obtain a semiconductor film with a high degree of orientation equivalent to that of the semiconductor film obtained by the conventional method of forming a semiconductor film after etching a single crystal semiconductor substrate to remove polishing scratches and carbides. As a result, it is possible to obtain a high-quality semiconductor film while keeping costs down.

The first film forming apparatus may form the first semiconductor film thinner than the second semiconductor film. In this way, even if the first semiconductor film is thin, the film quality of the second semiconductor film can be sufficiently improved.

In the film formation system, the first semiconductor film is a polycrystalline oriented film, and the second semiconductor film may have an orientation order in the same direction as the growth direction of the first semiconductor film. As a result, the second semiconductor film formed in the film formation system has an orientation aligned along the first semiconductor film, since the orientation of the first semiconductor film formed on the non-single crystal substrate is aligned. Since the crystallites of the second semiconductor film are aligned in a single direction, it can be treated as a polycrystalline film having the same orientation that is almost single crystal (single orientation).

The film formation system may further include a negative ion irradiation unit that irradiates the first semiconductor film with negative ions after the first film formation device has formed the first semiconductor film. By the negative ion irradiation unit irradiating the first semiconductor film with negative ions, the orientation order of the first semiconductor film can be further improved and the density of atomic vacancy point defects in the first semiconductor film can be reduced. This can further improve the film quality of the second semiconductor film.

The film formation method according to the present invention is a film formation method for forming a film on a non-single crystal substrate, and includes a first film formation process in which a film is formed by an ion plating method, and a second film formation process in which a film is formed after the first film formation process. In the first film formation process, a first semiconductor film containing a first semiconductor material is formed on the non-single crystal substrate, and in the second film formation process, a second semiconductor film containing a second semiconductor material is formed on the first semiconductor film on the non-single crystal substrate.

This deposition method can achieve the same effects and benefits as the deposition system described above.

The present invention makes it possible to obtain high-quality semiconductor films while keeping costs down.

1 is a conceptual diagram illustrating a film forming system according to an embodiment of the present invention. 1 is a cross-sectional view showing the configuration of a film formed on a non-single crystal substrate in an embodiment and a comparative example. FIG. 1 is a conceptual diagram of the crystal structure of a film in an embodiment and a comparative example. 1 is a schematic cross-sectional view showing a configuration of a first film forming apparatus. 1 is a schematic cross-sectional view showing a configuration of a first film forming apparatus. FIG. 4 is a schematic cross-sectional view showing the configuration of a second film forming apparatus. 1 is a transmission electron microscope image of the membranes of the comparative example and the example. 1 shows reciprocal lattice maps obtained by measuring the films of the comparative example and the example using an X-ray diffraction measurement method. FIG. 13 is a diagram showing the distribution of the inclination of the orientation plane of crystals in the films of the comparative example and the example. 1 is a graph showing electrical properties of films of a comparative example and an example. 1 is a graph showing electrical properties of films of a comparative example and an example. FIG. 2 is a diagram for explaining a crystal lattice of ZnO.

Below, a film forming system according to one embodiment of the present invention will be described with reference to the attached drawings. Note that in the description of the drawings, the same elements are given the same reference numerals, and duplicated descriptions will be omitted.

Figure 1 is a conceptual diagram showing a film formation system according to an embodiment of the present invention. Also, Figure 2 is a cross-sectional view showing the configuration of a film formed on a non-single crystal substrate, where Figure 2(a) shows the configuration of a film formed in the film formation system shown in Figure 1, and Figure 2(b) shows the configuration of a film formed in a film formation system according to a comparative example. As shown in Figure 1, a film formation system 100 according to an embodiment of the present invention includes a first film formation device 1 that forms a film by an ion plating method, and a second film formation device 2 that forms a film downstream of the first film formation device 1. The first film formation device 1 and the second film formation device 2 are connected to each other by a conveying device or the like, and the non-single crystal substrate 3 may be conveyed automatically, or may be conveyed manually by an operator.

As shown in FIG. 2(a), the film forming system 100 forms a first semiconductor film 4 on a non-single crystal substrate 3, and forms a second semiconductor film 5 on the first semiconductor film 4. The first semiconductor film 4 has a function of aligning the crystal plane orientation of the second semiconductor film 5 as an underlayer for the second semiconductor film 5. The second semiconductor film 5 formed on the non-single crystal substrate 3 and the first semiconductor film 4 in this manner is used as a sensitive film for hydrogen sensors, a light-emitting diode light-emitting layer film, a window layer for silicon heterojunction solar cells, a window layer for CIGS thin-film solar cells, a semiconductor layer for power electronics, a plasmonics material layer for near-infrared wavelength communication, and an antibacterial/bactericidal functional film, etc.

The first film forming apparatus 1 forms a first semiconductor film 4 containing a first semiconductor material on a non-single crystal substrate 3. The first film forming apparatus 1 employs an ion plating method in which ionized metal is evaporated onto the surface of an object as a film forming method. Ga-doped ZnO (GZO) is employed as the first semiconductor material. Other examples of the first semiconductor material include B (boron)-doped ZnO, Al (aluminum)-doped ZnO, In (indium)-doped ZnO, transition metal-doped ZnO, GaN (gallium nitride), metal element-doped GaN, Ga2O3 (gallium oxide), and other metal oxides, metal nitrides, and metal oxide nitrides (e.g., CrON, etc.). The non-single crystal substrate 3 may be a substrate made of a material other than a single crystal semiconductor, such as a glass substrate, a resin substrate, or a substrate made of a non-single crystal semiconductor. The non-single crystal substrate 3 may be a glass substrate formed into a plate shape. The type of glass used as the material of the glass substrate is not particularly limited, and may be any type of glass such as blue plate glass, white plate glass, non-alkali glass, and quartz glass. Examples of resin substrates and non-single crystal semiconductor substrates include sheet polymers (acrylic resins, cycloolefin polymers, etc.) and flexible polymer films (polyethylene terephthalate, polyethylene naphthalate, etc.). The first film forming device 1 forms the first semiconductor film 4 thinner than the second semiconductor film 5. Specifically, the thickness of the first semiconductor film 4 may be, for example, 50 nm or less, and may further be 10 nm or less. The lower limit of the thickness of the first semiconductor film 4 is not particularly limited, but the thickness of the first semiconductor film 4 may be, for example, 2 nm or more. It is desirable to make the thickness of the first semiconductor film 4 thinner within a range that does not affect the function of the second semiconductor film 5.

The film forming system 100 further includes a negative ion irradiation unit 24 that irradiates the first semiconductor film 4 with negative ions after the first film forming apparatus 1 forms the first semiconductor film 4. In this embodiment, the negative ion irradiation unit 24 is incorporated in the first film forming apparatus 1, and the first film forming apparatus 1 can perform the first semiconductor film 4 and the irradiation of the first semiconductor film 4 with negative ions. However, the negative ion irradiation unit 24 does not have to be incorporated in the first film forming apparatus 1, and may be configured as a device separate from the first film forming apparatus 1. The negative ions are substances with positive electron affinity, and negative ions of oxygen may be used. In addition, as the negative ions, H, C, O, F, Si, S, Cl, Br, and I may be adopted as atoms, and O ₂ , Cl ₂ , Br ₂ , I ₂ , CH, OH, CN, HCl, HBr, NH ₂ , N ₂ O, NO ₂ , CCl ₄ , and SF ₆ may be adopted as molecules. The negative ions to be irradiated are not limited to the same elements as those contained in the first semiconductor film 4 or the second semiconductor film 5, and may be different elements. There is no particular limit to the amount of negative ions that the negative ion irradiation unit 24 irradiates the first semiconductor film 4 with, but for example, the irradiated film may be irradiated with an amount of negative ions of 1×10 ¹⁹ cm ⁻³ or more. The amount of irradiation of the negative ions may be an amount that causes surface precipitation or grain boundary precipitation. In this case, the irradiated negative ions diffuse from the first semiconductor film 4 to the second semiconductor film and function as an effective dopant. The detailed configuration of the negative ion irradiation unit 24 will be described later together with the description of the first film forming apparatus 1 .

The second film forming apparatus 2 forms a second semiconductor film 5 containing a second semiconductor material on a first semiconductor film 4 on a non-single crystal substrate 3. The sputtering method may be used as the film forming method of the second film forming apparatus 2. The sputtering method is a method in which the second semiconductor material is placed in a vacuum chamber as a target, and ionized rare gas elements or the like are collided with the target surface to eject atoms of the second semiconductor material and attach them to the surface of the object. However, the film forming method of the second film forming apparatus 2 is not limited to the sputtering method, and various film forming methods such as molecular beam epitaxy (MBE) and electron beam evaporation may be used. Al-added ZnO (AZO) is used as the second semiconductor material. Other examples of the second semiconductor material _that may be used include GaN, AlN, _Ga2O3 , B (boron)-doped ZnO, Al (aluminum)-doped ZnO, In (indium)-doped ZnO, transition metal-doped ZnO, GaN (gallium nitride), metal element-doped GaN, Ga2O3 (gallium oxide), and other metal oxides, metal nitrides, and metal oxynitrides. The thickness of the second semiconductor film 5 is not particularly limited, but may be, for example, 50 nm or more.

(First Film Forming Apparatus 1)
Next, an example of the configuration of the first film forming apparatus 1 will be described with reference to Figures 4 and 5. As shown in Figures 4 and 5, the first film forming apparatus 1 is an ion plating apparatus used in a so-called ion plating method. For convenience of explanation, an XYZ coordinate system is shown in Figures 4 and 5. The Y-axis direction is the direction in which a non-single crystal substrate 3, which will be described later, is transported. The X-axis direction is the position where the non-single crystal substrate 3 and a hearth mechanism, which will be described later, face each other. The Z-axis direction is the direction perpendicular to the Y-axis direction and the X-axis direction.

The first film forming apparatus 1 is a so-called vertical type film forming apparatus in which the non-single crystal substrate 3 is placed and transported in the vacuum chamber 10 with the non-single crystal substrate 3 standing upright or tilted from the upright state so that the thickness direction of the non-single crystal substrate 3 is horizontal (the X-axis direction in Figures 4 and 5). In this case, the X-axis direction is the horizontal direction and the thickness direction of the non-single crystal substrate 3, the Y-axis direction is the horizontal direction, and the Z-axis direction is the vertical direction. The first film forming apparatus 1 may be a so-called horizontal type film forming apparatus in which the non-single crystal substrate 3 is placed and transported in the vacuum chamber so that the thickness direction of the non-single crystal substrate 3 is approximately vertical. In this case, the Z-axis and Y-axis directions are horizontal, and the X-axis direction is vertical and the thickness direction. Below, a vertical film forming apparatus will be described as an example.

The first film forming apparatus 1 includes a vacuum chamber 10, a transport mechanism 13, a film forming section 14, a negative ion irradiation section 24, and a magnetic field generating coil 30.

The vacuum chamber 10 contains the non-single crystal substrate 3 and performs the film formation process. The vacuum chamber 10 has a transfer chamber 10a for transferring the non-single crystal substrate 3 on which a film of the film formation material Ma is formed, a film formation chamber 10b for diffusing the film formation material Ma, and a plasma port 10c for receiving plasma P irradiated in a beam form from the plasma source 7 into the vacuum chamber 10. The transfer chamber 10a, the film formation chamber 10b, and the plasma port 10c are interconnected. The transfer chamber 10a is set along a predetermined transfer direction (arrow A in the figure) (Y axis). The vacuum chamber 10 is made of a conductive material and is connected to ground potential.

The deposition chamber 10b has, as the wall portion 10w, a pair of side walls aligned along the transport direction (arrow A), a pair of side walls 10h, 10i aligned along a direction (Z-axis direction) intersecting the transport direction (arrow A), and a bottom wall 10j arranged intersecting the X-axis direction.

The transport mechanism 13 transports the non-single crystal substrate holding member 16, which holds the non-single crystal substrate 3 while facing the film forming material Ma, in the transport direction (arrow A). For example, the non-single crystal substrate holding member 16 is a frame that holds the outer edge of the non-single crystal substrate 3. The transport mechanism 13 is composed of multiple transport rollers 15 installed in the transport chamber 10a. The transport rollers 15 are arranged at equal intervals along the transport direction (arrow A) and transport the non-single crystal substrate holding member 16 in the transport direction (arrow A) while supporting it. The non-single crystal substrate 3 is, for example, a plate-shaped member such as a non-single crystal substrate or a plastic substrate.

Next, the configuration of the film-forming unit 14 will be described in detail. The film-forming unit 14 adheres particles of the film-forming material Ma to the non-single crystal substrate 3 by ion plating. The film-forming unit 14 has a plasma source 7, a steering coil 25, a hearth mechanism 22, and a ring hearth 6.

The plasma source 7 is, for example, a pressure gradient type plasma gun, and its main body is connected to the film formation chamber 10b via a plasma port 10c provided on the side wall of the film formation chamber 10b. The plasma source 7 generates plasma P in the vacuum chamber 10. The plasma P generated in the plasma source 7 is emitted in the form of a beam from the plasma port 10c into the film formation chamber 10b. This generates plasma P in the film formation chamber 10b.

One end of the plasma source 7 is closed by a cathode 60. A first intermediate electrode (grid) 61 and a second intermediate electrode (grid) 62 are concentrically arranged between the cathode 60 and the plasma port 10c. An annular permanent magnet 61a for converging the plasma P is built into the first intermediate electrode 61. An electromagnetic coil 62a for converging the plasma P is also built into the second intermediate electrode 62. The plasma source 7 also functions as a negative ion irradiation unit 24, which will be described later. Details of this will be described later in the explanation of the negative ion irradiation unit 24.

The steering coil 25 is provided around the plasma port 10c to which the plasma source is attached. The steering coil 25 guides the plasma P into the deposition chamber 10b. The steering coil 25 is excited by a power supply (not shown) for the steering coil.

The hearth mechanism 22 holds the film-forming material Ma. The hearth mechanism 22 is provided in the film-forming chamber 10b of the vacuum chamber 10, and is disposed in the negative direction of the X-axis as viewed from the transport mechanism 13. The hearth mechanism 22 has a main hearth 17 which is a main anode that guides the plasma P emitted from the plasma source 7 to the film-forming material Ma, or a main anode to which the plasma P emitted from the plasma source 7 is guided.

The main hearth 17 has a cylindrical filling section 17a that extends in the positive direction of the X-axis and is filled with the film-forming material Ma, and a flange section 17b that protrudes from the filling section 17a. The main hearth 17 is maintained at a positive potential with respect to the ground potential of the vacuum chamber 10, and therefore draws in plasma P. A through hole 17c for filling the film-forming material Ma is formed in the filling section 17a of the main hearth 17, into which the plasma P is incident. The tip portion of the film-forming material Ma is exposed to the film-forming chamber 10b at one end of the through hole 17c.

When the film-forming material Ma is made of an insulating material, when the main hearth 17 is irradiated with plasma P, the main hearth 17 is heated by the current from the plasma P, the tip of the film-forming material Ma evaporates or sublimes, and the film-forming material particles (evaporated particles) Mb ionized by the plasma P diffuse into the film-forming chamber 10b. When the film-forming material Ma is made of a conductive material, when the main hearth 17 is irradiated with plasma P, the plasma P directly enters the film-forming material Ma, the tip of the film-forming material Ma is heated and evaporated or sublimated, and the film-forming material particles Mb ionized by the plasma P diffuse into the film-forming chamber 10b. The film-forming material particles Mb diffused into the film-forming chamber 10b move in the positive direction of the X-axis of the film-forming chamber 10b and adhere to the surface of the non-single crystal substrate 3 in the transport chamber 10a. The first semiconductor material described above is used as the film-forming material Ma. GZO, which is exemplified as the first semiconductor material, is a conductive material. The film forming material Ma is a solid object formed into a cylindrical shape of a predetermined length, and multiple pieces of film forming material Ma are loaded into the hearth mechanism 22 at one time. Then, as the film forming material Ma is consumed, the film forming material Ma is sequentially pushed out from the negative X-direction side of the hearth mechanism 22 so that the tip of the film forming material Ma on the most forward side maintains a predetermined positional relationship with the upper end of the main hearth 17.

The annular hearth 6 is an auxiliary anode having an electromagnet for inducing plasma P. The annular hearth 6 is arranged around the filling section 17a of the main hearth 17 that holds the film-forming material Ma. The annular hearth 6 has an annular coil 9, an annular permanent magnet section 20, and an annular container 12, and the coil 9 and the permanent magnet section 20 are housed in the container 12. In this embodiment, the coil 9 and the permanent magnet section 20 are installed in the negative X direction as viewed from the transport mechanism 13, but the permanent magnet section 20 and the coil 9 may be installed in the negative X direction. The annular hearth 6 controls the direction of the plasma P incident on the film-forming material Ma or the direction of the plasma P incident on the main hearth 17 depending on the magnitude of the current flowing through the coil 9.

Next, the configuration of the negative ion irradiation unit 24 will be described in detail. The negative ion irradiation unit 24 has a plasma source 7, a raw material gas supply unit 40, a control unit 50, and a circuit unit 34. Note that some of the functions included in the control unit 50 and the circuit unit 34 also belong to the aforementioned film formation unit 14.

The plasma source 7 used is the same as the plasma source 7 of the film forming unit 14 described above. That is, in this embodiment, the plasma source 7 of the film forming unit 14 is also used as the plasma source 7 of the negative ion irradiation unit 24. The plasma source 7 functions as the film forming unit 14 and also as the negative ion irradiation unit 24. Note that the film forming unit 14 and the negative ion irradiation unit 24 may have different plasma sources.

The plasma source 7 intermittently generates plasma P in the deposition chamber 10b. Specifically, the plasma source 7 is controlled by the control unit 50 described below so as to intermittently generate plasma P in the deposition chamber 10b. This control will be described in detail in the explanation of the control unit 50 described below.

The raw gas supply unit 40 is disposed outside the vacuum chamber 10. The raw gas supply unit 40 supplies oxygen gas, which is a raw gas for oxygen negative ions, into the vacuum chamber 10 through a gas supply port 41 provided in a side wall (e.g., side wall 10h) of the film formation chamber 10b. The raw gas supply unit 40 starts supplying oxygen gas when, for example, the film formation processing mode is switched to the oxygen negative ion generation mode. The raw gas supply unit 40 may also continue to supply oxygen gas in both the film formation processing mode and the oxygen negative ion generation mode.

The position of the gas supply port 41 is preferably near the boundary between the film formation chamber 10b and the transfer chamber 10a. In this case, oxygen gas from the raw material gas supply unit 40 can be supplied near the boundary between the film formation chamber 10b and the transfer chamber 10a, so that oxygen negative ions, which will be described later, are generated near the boundary. Therefore, the generated oxygen negative ions can be suitably attached to the non-single crystal substrate 3 in the transfer chamber 10a. The position of the gas supply port 41 is not limited to near the boundary between the film formation chamber 10b and the transfer chamber 10a.

The control unit 50 is disposed outside the vacuum chamber 10. The control unit 50 switches the switching unit of the circuit unit 34. The switching of the switching unit by the control unit 50 will be described in detail below together with the explanation of the circuit unit 34.

The circuit section 34 has a variable power supply 80, a first wiring 71, a second wiring 72, resistors R1 to R4, and short-circuit switches SW1 and SW2.

The variable power supply 80 applies a negative voltage to the cathode 60 of the plasma source 7 and a positive voltage to the main hearth 17 of the hearth mechanism 22 across the vacuum chamber 10, which is at ground potential. As a result, the variable power supply 80 generates a potential difference between the cathode 60 of the plasma source 7 and the main hearth 17 of the hearth mechanism 22.

The first wiring 71 electrically connects the cathode 60 of the plasma source 7 to the negative potential side of the variable power supply 80. The second wiring 72 electrically connects the main hearth 17 (anode) of the hearth mechanism 22 to the positive potential side of the variable power supply 80.

One end of the resistor R1 is electrically connected to the first intermediate electrode 61 of the plasma source 7, and the other end is electrically connected to the variable power supply 80 via the second wiring 72. That is, the resistor R1 is connected in series between the first intermediate electrode 61 and the variable power supply 80.

One end of the resistor R2 is electrically connected to the second intermediate electrode 62 of the plasma source 7, and the other end is electrically connected to the variable power supply 80 via the second wiring 72. That is, the resistor R2 is connected in series between the second intermediate electrode 62 and the variable power supply 80.

One end of resistor R3 is electrically connected to the wall 10w of the deposition chamber 10b, and the other end is electrically connected to the variable power supply 80 via the second wiring 72. That is, resistor R3 is connected in series between the wall 10w of the deposition chamber 10b and the variable power supply 80.

One end of resistor R4 is electrically connected to the ring hearth 6, and the other end is electrically connected to the variable power source 80 via the second wiring 72. In other words, resistor R4 is connected in series between the ring hearth 6 and the variable power source 80.

The short-circuit switches SW1 and SW2 are switching units that are switched between ON/OFF states by receiving a command signal from the control unit 50 described above.

The short-circuit switch SW1 is connected in parallel to the resistor R2. The short-circuit switch SW1 is switched ON/OFF by the control unit 50 depending on whether the mode is the film formation processing mode or the oxygen negative ion mode. The short-circuit switch SW1 is turned OFF in the film formation processing mode. As a result, in the film formation processing mode, the second intermediate electrode 62 and the variable power supply 80 are electrically connected to each other via the resistor R2, so that it is difficult for a current to flow between the second intermediate electrode 62 and the variable power supply 80. As a result, the plasma P from the plasma source 7 is emitted into the vacuum chamber 10 and enters the film formation material Ma (see FIG. 4).

On the other hand, in the oxygen negative ion generation mode, the short-circuit switch SW1 is switched between ON and OFF states at predetermined intervals by the control unit 50 in order to intermittently generate plasma P from the plasma source 7 within the vacuum chamber 10. When the short-circuit switch SW1 is switched to the ON state, the electrical connection between the second intermediate electrode 62 and the variable power supply 80 is short-circuited, and a current flows between the second intermediate electrode 62 and the variable power supply 80. In other words, a short-circuit current flows through the plasma source 7. As a result, plasma P from the plasma source 7 is no longer emitted into the vacuum chamber 10.

When the short-circuit switch SW1 is switched to the OFF state, the second intermediate electrode 62 and the variable power supply 80 are electrically connected to each other via the resistor R2, and therefore current does not easily flow between the second intermediate electrode 62 and the variable power supply 80. As a result, plasma P from the plasma source 7 is emitted into the vacuum chamber 10. In this way, the ON/OFF state of the short-circuit switch SW1 is switched at predetermined intervals by the control unit 50, so that plasma P from the plasma source 7 is intermittently generated in the vacuum chamber 10. In other words, the short-circuit switch SW1 is a switching unit that switches between supplying and blocking plasma P into the vacuum chamber 10.

The short-circuit switch SW2 is connected in parallel to the resistor R4. The short-circuit switch SW2 is switched ON/OFF by the control unit 50 depending on whether the mode is a standby mode, which is a state before the non-single crystal substrate 3 is transported and before the film formation processing mode is entered, or the film formation processing mode. The short-circuit switch SW2 is set to the ON state in the standby mode. This shorts the electrical connection between the annular hearth 6 and the variable power supply 80, making it easier to pass current through the annular hearth 6 than through the main hearth 17, and preventing unnecessary consumption of the film formation material Ma.

On the other hand, the short-circuit switch SW2 is turned OFF in the film formation processing mode. This electrically connects the annular hearth 6 and the variable power supply 80 via the resistor R4, making it easier to pass current through the main hearth 17 than through the annular hearth 6, and the emission direction of the plasma P can be preferably directed toward the film formation material Ma. Note that the short-circuit switch SW2 may be turned either ON or OFF in the oxygen negative ion generation mode.

The magnetic field generating coil 30 is provided in the vacuum chamber 10 between the film formation chamber 10b and the transport chamber 10a. The magnetic field generating coil 30 is disposed, for example, between the hearth mechanism 22 and the transport mechanism 13. More specifically, the magnetic field generating coil 30 is positioned so as to be interposed between the end of the film formation chamber 10b on the transport chamber 10a side and the end of the transport chamber 10a on the film formation chamber 10b side. The magnetic field generating coil 30 has a pair of coils 30a, 30b facing each other. The coils 30a, 30b face each other in a direction that intersects, for example, the direction from the film formation chamber 10b to the transport chamber 10a (the direction from the hearth mechanism 22 to the transport mechanism 13).

The magnetic field generating coil 30 is not excited in the film formation mode, and is excited by a power supply (not shown) for the magnetic field generating coil 30 in the oxygen negative ion generation mode. Here, the film formation mode is a mode in which a film formation process is performed on the non-single crystal substrate 3 in the vacuum chamber 10. The oxygen negative ion generation mode is a mode in which oxygen negative ions are generated to be attached to the surface of the film formed on the non-single crystal substrate 3 in the vacuum chamber 10. The magnetic field generating coil 30 is excited in the oxygen negative ion generation mode to form a sealing magnetic field M in the vacuum chamber 10 having magnetic field lines extending in a direction intersecting the direction from the film formation chamber 10b to the transfer chamber 10a (the direction from the hearth mechanism 22 to the transfer mechanism 13) (see FIG. 5). By generating such a sealing magnetic field M, the magnetic field generating coil 30 suppresses the inflow of electrons in the film formation chamber 10b into the transfer chamber 10a. The magnetic field lines of the sealing magnetic field M may have a portion that extends in a direction that is approximately parallel to the transport direction (arrow A) of the non-single crystal substrate 3. The ON/OFF state of the power supply for the magnetic field generating coil 30 may be controlled by a control unit 50, which will be described later. The magnetic field generating coil 30 is covered with a case 31 to prevent deposition of the film forming material Ma. The magnetic field generating coil 30 does not have to be covered with the case 31.

(Second Film Forming Apparatus 2)
FIG. 6 is a schematic diagram of the second film forming apparatus 2. FIG. 6 illustrates a configuration in which the sputtering method is adopted as the film forming method of the second film forming apparatus 2. As shown in FIG. 6, the second film forming apparatus 2 forms a second semiconductor film 5 on a non-single crystal substrate 3 by a sputtering method. Although a first semiconductor film 4 is formed on the surface of the non-single crystal substrate 3, in the following description, the non-single crystal substrate 3 will simply be referred to as a "non-single crystal substrate 3". The second film forming apparatus 2 includes a vacuum chamber 102, a target 103 provided in the vacuum chamber 102, a power source 106 that generates plasma by discharge, a heating unit 118 that heats the non-single crystal substrate 3, and a control unit 130 that controls the second film forming apparatus 2. The second film forming apparatus 2 generates plasma in a vacuum under a dilute argon atmosphere, and causes positive ions in the plasma to collide with the film forming material (target 103), ejecting metal atoms, which are then deposited on the non-single crystal substrate 3 to form a film.

The vacuum chamber 102 is a container capable of accommodating the non-single crystal substrate 3, and includes a sputtering chamber 107 in which sputtering is performed, an exhaust chamber 108 adjacent to the front side of the sputtering chamber 107, and a vent chamber 109 adjacent to the rear side of the sputtering chamber 107. The vacuum chamber 102 is capable of arranging the non-single crystal substrate 3, and is provided with a non-single crystal substrate placement section 120 capable of transporting the placed non-single crystal substrate 3 in a predetermined transport direction A. The non-single crystal substrate placement section 120 includes a plurality of transport rollers 111 arranged along the transport direction A. The non-single crystal substrate 3 is placed on the transport rollers 111 and transported in the transport direction A by the transport rollers 111. The non-single crystal substrate 3 may be placed in the non-single crystal substrate placement section 120 while being placed on a transport tray.

The target 103 is a flat plate-shaped member made of the film-forming material or a part of the film-forming material (composition material). A cylindrical member can also be used as the target 103. The target 103 is placed facing the non-single crystal substrate 3 in the sputtering chamber 107. The target 103 has a front surface 103a facing the non-single crystal substrate placement portion 120 (facing the non-single crystal substrate 3), and a back surface 103b on the opposite side. A sputtering space C is formed between the target 103 and the non-single crystal substrate 3. The target 103 is formed by sintering powder of the second semiconductor material.

The second film forming apparatus 2 also includes turbo molecular pumps (TMPs) 112 connected to the sputtering chamber 107, exhaust chamber 108, and vent chamber 109 for evacuating the insides of the chambers, gate valves 113 provided between the sputtering chamber 107, exhaust chamber 108, and vent chamber 109, at the inlet of the exhaust chamber 108, and at the outlet of the vent chamber 109, and dry pumps 114 connected to the exhaust chamber 108 and vent chamber 109, respectively.

The second deposition apparatus 2 further includes an argon cylinder 116 filled with argon (Ar) gas as an inert gas, which is an atmospheric gas, and a mass flow controller (MFC) 117, which is a gas flow controller that supplies the argon gas in the argon cylinder 116 to the sputtering chamber 107 at a predetermined flow rate. Xenon (Xe) or krypton (Kr) may also be used as the atmospheric gas. The second deposition apparatus 2 further includes an oxygen cylinder 122 filled with oxygen gas, and a mass flow controller 121, which is a gas flow controller that supplies the oxygen gas in the oxygen cylinder 122 to the sputtering chamber 107 at a predetermined flow rate.

In the vacuum chamber 102, below the non-single crystal substrate 3 (behind the deposition surface), heating units 118 composed of heaters are arranged in parallel in the transport direction A. Heating units 118 are provided in each of the sputtering chamber 107, the exhaust chamber 108, and the vent chamber 109, but some of the heating units 118 may be omitted. In addition, the mounting position of the heating units 118 in the vacuum chamber 102 is not particularly limited, and they may be placed anywhere as long as they can heat the non-single crystal substrate 3.

The power source 106 supplies power to the target 103 to generate a discharge. The power source 106 includes a DC power source and a high-frequency power source. The high-frequency power source can superimpose a high frequency on the power supplied by the DC power source 33. The frequency of the high-frequency power source 36 is 13 to 41 MHz.

A film formation method using the film formation system 100 as described above will be described. The film formation method includes a first film formation process in which a film is formed by an ion plating method, and a second film formation process in which a film is formed after the first film formation process. In the first film formation process, a first semiconductor film 4 containing a first semiconductor material is formed on a non-single crystal substrate 3. In the second film formation process, a second semiconductor film 5 containing a second semiconductor material is formed on the first semiconductor film 4 on the non-single crystal substrate 3. Note that between the first film formation process and the second film formation process, a negative ion irradiation process is performed in which negative ions are irradiated onto the first semiconductor film 4.

Next, the operation and effects of the film forming system 100 and film forming method according to this embodiment will be described.

First, as a comparative example, a film formation system in which a second semiconductor film 5 is formed directly on a non-single crystal substrate 3 as shown in FIG. 2(b) will be described. The non-single crystal substrate 3 is an inexpensive substrate compared to semiconductor substrates such as silicon wafers and sapphire. However, unlike these semiconductor substrates, the non-single crystal substrate 3 is not a substrate with good crystal orientation, so even if the second semiconductor film 5 is formed on the non-single crystal substrate 3 by sputtering or other film formation methods, it will have a polycrystalline (mixed orientation) structure with no uniform orientation. For example, as shown in FIG. 3(b), the crystallites 5a are finely oriented in many directions. In this configuration, many grain boundaries with no uniform orientation are formed. When electrons E pass through such a second semiconductor film 5, in addition to scattering due to passing through the crystallites, the effect of scattering occurring at the grain boundaries is also present.

In contrast, in the film formation system 100 according to the present embodiment, before the second semiconductor film 5 is formed by the second film formation device 2, the first film formation device 1 forms the first semiconductor film 4 on the non-single crystal substrate 3 by the ion plating method. In this way, by forming the first semiconductor film 4 containing the first semiconductor material by the ion plating method, the first semiconductor film 4 can be made into a highly oriented polycrystalline film (called a uniaxial crystal texture or uniaxial crystal texture film) having an orientation order close to that of a single crystal (each crystallite has the same orientation order with respect to each other). By forming the second semiconductor film 5 on such a first semiconductor film 4, the second semiconductor film 5 can be obtained along the highly oriented first semiconductor film 4. Therefore, the second film formation device 2 can form the second semiconductor film 5 on the first semiconductor film 4, thereby obtaining a highly oriented second semiconductor film 5, compared to the comparative example in which film formation is performed directly on the non-single crystal substrate 3. In this way, even if a non-single crystal substrate 3, which is less expensive than a single crystal semiconductor substrate, is used, the first semiconductor film 4 is formed in the first film forming apparatus 1, and the film quality of the second semiconductor film 5 can be improved. In other words, a highly oriented semiconductor film can be obtained that is equivalent to the high orientation of a semiconductor film obtained by a conventional method of forming a semiconductor film after etching a single crystal semiconductor substrate to remove polishing scratches and carbides. As described above, a high-quality semiconductor film can be obtained while suppressing costs. Furthermore, the film forming method according to this embodiment can also obtain the same actions and effects as the film forming system 100.

The first semiconductor film 4 is a polycrystalline oriented film, and the second semiconductor film 5 has an orientation order in the same direction as the growth direction of the first semiconductor film 4. For example, as shown in FIG. 3(a), the second semiconductor film 5 formed by the film formation system 100 has an orientation aligned along the first semiconductor film 4 since the orientation of the first semiconductor film 4 formed on the non-single crystal substrate 3 is aligned. Since the crystallites 5a of the second semiconductor film 5 are aligned in a single direction, it can be treated as a polycrystalline film having the same orientation that is almost single crystal (single orientation). In such a good quality second semiconductor film 5, it is possible to reduce scattering at grain boundaries to almost zero, and high carrier mobility can be achieved.

Furthermore, as a comparative example, there is a method of forming a lattice-matching buffer layer (ZnO layer) on a high-quality silicon or sapphire substrate, but when forming the buffer layer, it is necessary to not only simply form the buffer layer, but also to anneal the buffer layer at a high temperature of, for example, 600°C or higher. Since the film formation temperature in the first film formation device 1 using the ion plating method according to this embodiment is only about 200°C, there is no need to provide an annealing device, etc., and therefore handling is improved even in the line process.

The first film forming apparatus 1 also forms the first semiconductor film 4 thinner than the second semiconductor film 5. That is, the first semiconductor film 4 has the function of aligning the orientation of the second semiconductor film 5 formed on its upper surface, so it may be as thin as possible as long as it can perform this function. In this way, even a thin first semiconductor film 4 can sufficiently improve the film quality of the second semiconductor film 5.

The film formation system 100 further includes a negative ion irradiation unit 24 that irradiates the first semiconductor film 4 with negative ions after the first film formation device 1 forms the first semiconductor film 4. By the negative ion irradiation unit 24 irradiating the first semiconductor film 4 with negative ions, the orientation order of the first semiconductor film 4 can be further improved and the density of atomic vacancy point defects in the first semiconductor film 4 can be reduced. This can further improve the film quality of the second semiconductor film 5.

The present invention is not limited to the above-described embodiments.

For example, in FIG. 1, the first film forming apparatus 1 and the second film forming apparatus 2 are shown as being connected in a line, but the first film forming apparatus 1 and the second film forming apparatus 2 may be provided in different facilities. In other words, the non-single crystal substrate 3 formed in the first film forming apparatus 1 may be transported to another facility and then filmed in the second film forming apparatus 2.

Furthermore, the configuration of the film forming apparatus shown in Figures 4 to 6 is merely an example, and other configurations may be adopted without departing from the spirit of the invention.

In addition, by using a single crystal semiconductor substrate instead of a non-single crystal substrate, forming a first semiconductor film on the single crystal semiconductor substrate by a first film formation apparatus, and then forming a second semiconductor film on the first semiconductor film on the single crystal semiconductor substrate by a second film formation apparatus, there is an advantage that the process temperature can be significantly reduced compared to conventional methods.

[Example]
Hereinafter, a film forming system according to one embodiment of the present invention will be specifically described based on an embodiment, but the configuration of the film forming system is not limited to the following embodiment.

(Comparative Example 1)
The film formation system according to Comparative Example 1 was equipped with only the second film formation device. The film formation system according to Comparative Example 1 formed a second semiconductor film directly on a non-single crystal substrate. DC-magnetron sputtering was used as the film formation method of the second film formation device. Al-added ZnO was used as the second semiconductor material. The thickness of the second semiconductor film was set to 500 nm. A glass substrate made of alkali-free glass (Corning Eagle-XG) was used as the non-single crystal substrate. Various conditions of the second film formation device are shown below.
<Model of second film forming apparatus (DC-magnetron sputtering)>
ULVAC CS-L
<Film formation conditions>
Process gas: Argon gas Pressure: 1 Pa
・Substrate temperature: 200℃
Power: 200W

(Comparative Example 2)
As a film formation system according to Comparative Example 2, a system including a third film formation apparatus that forms a buffer layer on a non-single crystal substrate by a sputtering method upstream of the second film formation apparatus, and the second film formation apparatus was used. RF-magnetron sputtering was adopted as the film formation method of the third film formation apparatus. The third film formation apparatus adopted Ga-doped ZnO as the semiconductor material of the buffer layer. The thickness of the buffer layer was set to 10 nm. The second film formation apparatus formed a second semiconductor film with a thickness of 490 nm on the buffer layer. Other conditions for film formation by the second film formation apparatus were the same as those of Comparative Example 1. Various conditions for the third film formation apparatus are shown below.
<Model of the third film forming apparatus (RF-magnetron sputtering)>
ULVAC CS-L
<Film formation conditions>
Process gas: Argon gas Pressure: 1 Pa
・Substrate temperature: 200℃
Power: 200W

(Example)
As the film formation system according to the embodiment, a first film formation apparatus using an ion plating method for forming a first semiconductor layer on a non-single crystal substrate upstream of the second film formation apparatus and a second film formation apparatus were used. The first film formation apparatus adopted Ga-doped ZnO as the semiconductor material of the first semiconductor layer. The thickness of the first semiconductor layer was set to 10 nm. The second film formation apparatus formed a second semiconductor film having a thickness of 490 nm on the buffer layer. Other conditions for film formation by the second film formation apparatus were the same as those of Comparative Example 1. Various conditions for the first film formation apparatus are shown below.
<Model of the first film forming apparatus (ion plating method)>
RPD equipment manufactured by Sumitomo Heavy Industries, Ltd. <Film formation conditions>
Discharge current: 150A
Total pressure: 0.3 Pa (process gas is argon gas and oxygen gas, oxygen ratio is about 7%)

(Cross-section observation)
The cross section of each film was observed with reference to the images of the cross section of the film obtained in Comparative Example 1, Comparative Example 2, and Example taken with a transmission electron microscope (TEM). An example of the cross section image is shown in FIG. 7. The upper part of FIG. 7 shows the cross section of the entire semiconductor film, and the lower part of FIG. 7 shows an enlarged cross section of the semiconductor film near the lower end of the second semiconductor film. The dashed line in the lower part of FIG. 7 shows the boundary between the first semiconductor layer or the second semiconductor layer and the non-single crystal substrate. As shown in FIG. 7(a), it can be seen that the crystals are not aligned in the vicinity of the non-single crystal substrate 3 in Comparative Example 1. As shown in FIG. 7(b), it can be seen that the crystals are aligned in Comparative Example 2 compared to Comparative Example 1, but the crystal arrangement is changed diagonally in the crystallite compared to the Example. As shown in FIG. 7(c), it can be seen that the Example has a highly oriented first semiconductor film 4, and thus the crystals are aligned compared to each Comparative Example. As described above, it was observed that the crystallinity of the second semiconductor film was uniformed by forming the first semiconductor film on a non-single crystal substrate as in the embodiment.

(Measurement by X-ray diffraction)
The films obtained in Comparative Example 1, Comparative Example 2, and Example were measured by X-ray diffraction (XRD: X-Ray Diffraction) measurement. A model "Rigaku SmatLab" was used as the X-ray diffraction measurement device. The measurement results are shown in Figs. 8 and 9. Fig. 8 shows a reciprocal lattice map obtained by the measurement. The upper part of Fig. 9 is a pole figure showing the distribution of the 0001 component, and the lower part is a graph showing the distribution of the inclination of the 0001 component with respect to the C-axis direction (0°). Note that the "0001 component" means a plane through which the (0001) vector shown by the (a1, a2, a3, c) vectors in the ZnO crystal lattice shown in Fig. 12 passes perpendicularly. ZnO is prone to grow in the C-axis direction in a hexagonal wurtzite structure, and the "C-axis" and the substrate perpendicular direction may be regarded as the same. In Fig. 8, the part indicated by "P" in the figure spreads and does not draw an arc, and the closer it is to the point, the closer the second semiconductor film is to single crystals and the higher the orientation. In Fig. 9, the peaks of the 0001 component are concentrated in the C-axis direction (0°), and the sharper the peak in the C-axis direction, the higher the orientation order is close to single crystals. For example, when the film has a random orientation as shown in Fig. 3(b), it has a peak near 66° because it grows in an oblique direction relative to the substrate perpendicular direction, but when the film has the same orientation order as shown in Fig. 3(a), such a peak is not detected.

As shown in FIG. 8, in Comparative Example 1 and Comparative Example 2, the portion indicated by "P" drew an arc. In comparison, in the Example, the portion indicated by "P" had a shape closer to a point than in Comparative Example 1 and Comparative Example 2. From this, it can be understood that the Example has a structure closer to a single crystal than in Comparative Example 1 and Comparative Example 2. Also, as shown in FIG. 9, in the Example, the 0001 components were mostly concentrated in the C-axis direction, and a sharp peak was drawn in the C-axis direction. The half-width of the 0001 components was 1.8°, and most of the 0001 components were present in the range of -0.9° to +0.9° from the C-axis direction (0°). On the other hand, in Comparative Example 1, the peak of the 0001 components was present in a ring shape not only in the C-axis direction but also near other angles (near 66°). From this, it can be understood that the crystal grew in an oblique direction when viewed from the C-axis. Also, in Comparative Example 2, the 0001 components were not concentrated in the C-axis direction compared to the Example. That is, it can be seen that in the examples, a polycrystalline film with the same orientation order close to that of a single crystal was obtained, while in comparative examples 1 and 2, a randomly oriented polycrystalline film was obtained.

(Electrical characteristics)
The electrical properties of the films obtained in Comparative Example 1, Comparative Example 2, and Example were measured by Hall effect measurement under room temperature environment. The measurement results are shown in Figures 10 and 11. "N: carrier density" indicates the carrier density. "μ _H : Hall mobility" indicates the carrier mobility in the entire bulk. The higher the value, the higher the carrier mobility. "ρ: resistivity" indicates the resistivity of the film. "μ _opt : optical mobility" indicates the carrier mobility in the grain. The higher the value, the higher the carrier mobility. "μ _GB : grain boundary scattering" indicates the degree of scattering at the grain boundary. Since the relationship "1/μ _H = 1/μ _opt + 1/μ _GB " holds, the Hall mobility is determined by grain boundary scattering and intragranular migration. "μ _opt /μ _GB " indicates the grain boundary scattering contribution. The closer the value is to 0, the less scattering at the grain boundary.

As shown in FIG. 10, the carrier density N of the embodiment is higher than the carrier density N of the comparative example 1 and the carrier density N of the comparative example 2. This indicates that the orientation order is improved by the effect of the first semiconductor film, and the dopant efficiency is improved and the carrier density N is increased. In addition, the hole mobility μ _H of the embodiment is higher than the hole mobility μ _H of the comparative example 1 and the hole mobility μ _H of the comparative example 2. This indicates that the presence of the first semiconductor film results in the same orientation order and reduces grain boundary scattering, so that the hole mobility μ _H is increased. In addition, the presence of the first semiconductor film improves the dopant efficiency and increases the carrier density N, and grain boundary scattering is reduced and the hole mobility μ _H is increased, so that the resistivity ρ is also reduced. While the optical mobility μ _opt is almost the same in each comparative example and the embodiment, the "μ _opt /μ _GB " indicating the grain boundary scattering contribution is lower in the embodiment than in each comparative example, and is close to 0. From this, it can be understood that since the embodiment has a uniform orientation order close to that of a single crystal, scattering at grain boundaries is small and high carrier mobility can be achieved.

REFERENCE SIGNS LIST 1... first film formation apparatus, 2... second film formation apparatus, 3... non-single crystal substrate, 4... first semiconductor film, 5... second semiconductor film, 24... negative ion irradiation section, 100... film formation system.

Claims (6)

A negative ion generating device for irradiating a target with negative ions, comprising:
A plasma source for generating plasma;
a vacuum chamber having a space capable of supplying the plasma generated from the plasma source to a raw material of negative ions;
a magnetic field generating means for generating a magnetic field that suppresses the inflow of electrons of the plasma into the object disposed in the vacuum chamber;
a control unit that controls the supply of the plasma into the vacuum chamber to be performed intermittently;
having
The magnetic field generating means is a negative ion generating device that applies a magnetic field between the plasma, the electron temperature of which has been reduced, and the target object within the vacuum chamber. The negative ion generating device according to claim 1 , wherein the plasma source emits plasma in the form of a beam into the space. The plasma supply device further includes a switching unit that switches between supplying and blocking the plasma into the vacuum chamber,
The negative ion generating device according to claim 1 , wherein the control unit supplies the plasma intermittently by switching the switching unit. The negative ion generating device according to any one of claims 1 to 3, wherein the magnetic field generating means forms a sealing magnetic field within a vacuum chamber having magnetic field lines extending in a direction intersecting a direction from the space toward the target object. 5. The negative ion generating device according to claim 1, wherein the plasma source is a pressure gradient type plasma gun. The plasma source has an electrode for focusing the plasma,
The negative ion generating device according to claim 1 , further comprising a switching unit for switching the ease with which a current flows to the electrode.

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