Method for forming p-type tin oxide film, and film deposition device

Abstract

[Problem] To easily produce p-type tin(II) oxide. [Solution] A first film, which is made of tin metal, and a second film, which is made of tin(IV) oxide, are alternately deposited to form a multilayer object, and the multilayer object is subjected to a heat treatment to produce p-type tin(II) oxide from the multilayer object.

Description

Method and apparatus for forming p-type tin oxide film

[0001] The present disclosure relates to a method and apparatus for forming a p-type tin oxide film.

[0002] Tin oxide, an oxide semiconductor, is sometimes used in battery anodes. In this case, divalent tin oxide (SnO) is first mechanically synthesized to produce disproportionated tin oxide, in which zero-valent metallic tin (Sn) and tetravalent tin oxide (SnO2) are dispersed. The disproportionated tin oxide is then mixed with carbon (C) powder, and a disproportionated tin oxide-carbon composite is then mechanically synthesized. This disproportionated tin oxide-carbon composite is suitable for use in battery anodes (see, for example, Patent Document 1).

[0003] Korean Patent No. 10-1836311

[0004] The techniques disclosed herein readily produce p-type tin(II) oxide.

[0005] One aspect of the technology disclosed herein is a method for forming a p-type tin oxide film, which includes a step of alternately stacking first films made of metallic tin and second films made of tin(IV) oxide to form a laminate, and a step of subjecting the laminate to a heat treatment to produce p-type tin(II) oxide from the laminate.

[0006] According to the technology of the present disclosure, p-type tin(II) oxide can be easily produced.

[0007] FIG. 1 is a cross-sectional view schematically showing the structure of a film forming apparatus according to an embodiment of the technology disclosed herein. FIG. 2 is a diagram for explaining the relationship between the atomic ratio of tin to oxygen and the conductivity type of tin oxide to be produced. FIG. 3 is a process diagram showing a method for forming a p-type tin oxide film according to the present embodiment. FIG. 4 is a process diagram showing a method for forming a p-type tin oxide film according to the present embodiment. FIG. 5 is a process diagram showing a method for forming a p-type tin oxide film according to the present embodiment. FIG. 6 is a graph showing the level intensity at 3 eV corresponding to the binding energy of p-type tin(II) oxide when the temperature of heat treatment is changed. FIG. 7 is a graph showing the carrier density of p-type tin(II) oxide when the temperature of heat treatment is changed. FIG. 8 is a graph showing the mobility of p-type tin(II) oxide when the temperature of heat treatment is changed. FIG. 9 is a process diagram showing a first modified example of a method for forming a p-type tin oxide film using a protective film. FIG. 10 is a process diagram showing a first modified example of a method for forming a p-type tin oxide film using a protective film. FIG. 11 is a process diagram showing a second modified example of a method for forming a p-type tin oxide film using a protective film.

[0008] In addition, since the conductivity type of tin oxide can be changed to p-type or n-type depending on the valence of tin, it has recently been suitably used for the channel of tunnel field effect transistors. Incidentally, p-type tin oxide is divalent tin oxide (SnO), but its cohesive energy is high, and even if you try to produce p-type tin oxide by crystallizing tin (Sn) and oxygen (O), it is difficult to produce n-type tetravalent tin oxide (SnO2) or SnO3, which have lower cohesive energy. ５ O6 is preferentially produced, so it is difficult to produce p-type tin oxide.

[0009] In contrast, the technology disclosed herein produces p-type tin oxide by alternately stacking films of metallic tin (Sn) and tetravalent tin oxide (SnO) and strictly controlling the elemental composition ratio of tin and oxygen in the stack. Hereinafter, divalent tin oxide (SnO) will be referred to as "tin(II) oxide" and tetravalent tin oxide (SnO) will be referred to as "tin(IV) oxide."

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present disclosure will now be described with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view schematically illustrating the structure of a film deposition apparatus according to the present embodiment;

[0011] The film forming apparatus 10 is a magnetron sputtering apparatus that uses physical vapor deposition (PVD) and forms a first film 53 made of metallic tin and a second film 54 made of tin(IV) oxide on a wafer W (substrate) by sputtering. The film forming apparatus 10 can also form the first film 53 and the second film 54 on a substrate made of glass, for example, instead of the wafer W. As will be described later, the film forming apparatus 10 alternately stacks the first film 53 and the second film 54 to form a stacked body 55. However, as long as the first film 53 and the second film 54 are alternately stacked, the film formed first may be either the first film 53 or the second film 54.

[0012] The film forming apparatus 10 includes a processing chamber 11 , a stage unit 12 , a first cathode unit 13 , a second cathode unit 14 , a gas supply unit 15 , a shutter 16 , and a control unit 17 .

[0013] The processing vessel 11 is made of, for example, aluminum and accommodates a wafer W therein. The processing vessel 11 has a vessel body 18 connected to a ground potential and having an open top, and a lid 19 provided to close the top opening of the vessel body 18. The vessel body 18 has a substantially cylindrical shape, and the lid 19 has a substantially truncated cone shape.

[0014] An exhaust port 20 is opened at the bottom of the processing vessel 11, and an exhaust device 21 is connected to the exhaust port 20. The exhaust device 21 has a pressure control valve and a vacuum pump (neither of which are shown), and evacuates the inside of the processing vessel 11 to reduce the internal pressure to a predetermined vacuum level. In addition, a load / unload port 22 is opened at the sidewall of the processing vessel 11 for loading and unloading the wafer W, and the load / unload port 22 is opened and closed by a gate valve 23.

[0015] The stage unit 12 has a generally circular disk shape and is disposed near the bottom of the processing vessel 11 to horizontally hold the wafer W. The stage unit 12 includes a base 24 and an electrostatic chuck 25. The base 24 is made of, for example, aluminum, and the electrostatic chuck 25 is made of a dielectric material, for example, yttria (YO), and is provided with an electrode 26 therein. A DC voltage is applied to the electrode 26 from a DC power supply (not shown), and the wafer W is electrostatically attracted to the surface of the electrostatic chuck 25 by electrostatic force generated by the electrode 26. A temperature control mechanism, such as a refrigerant flow path for circulating a refrigerant and a heater (neither of which are shown), is also disposed within the stage unit 12.

[0016] The stage unit 12 is connected to a driving device 28 provided below the processing vessel 11 via a shaft 27. The shaft 27 passes through the bottom wall of the processing vessel 11 from the driving device 28, and its tip is connected to the center of the bottom surface of the stage unit 12. The driving device 28 raises and lowers the stage unit 12 via the shaft 27, and also rotates the stage unit 12 within a horizontal plane.

[0017] The gap between the shaft 27 and the bottom wall of the processing vessel 11 is sealed by a sealing member 29. The sealing member 29 maintains the degree of vacuum inside the processing vessel 11 when the shaft 27 rotates and moves up and down. The sealing member 29 is, for example, a magnetic fluid seal.

[0018] The first cathode unit 13 is provided on the inclined surface of the lid 19 of the processing vessel 11. The first cathode unit 13 has a first target 30 made of metallic tin, a first target electrode 31 that holds the first target 30, and a first power supply 32 that supplies power to the first target 30 via the first target electrode 31. In the first cathode unit 13, as will be described later, a voltage is applied to the first target 30, causing tin sputtered particles (first sputtered particles) to be emitted from the first target 30.

[0019] The first target electrode 31 is attached via a first insulating member 34 to the inside of a first hole 33 formed in the inclined surface of the lid 19 of the processing vessel 11. The first power supply 32 is a DC power supply and applies a negative DC voltage to the first target electrode 31, so that the first target electrode 31 functions as a cathode electrode.

[0020] A first shield member 35 is provided on the outer periphery of the first target 30. The first shield member 35 prevents the tin sputter particles emitted from the first target 30 from reaching the inner wall of the processing vessel 11 or the back surface of the first target electrode 31, and regulates the emission direction of the tin sputter particles emitted from the first target 30.

[0021] A first cathode magnet 36 is provided on the rear side of the first target electrode 31. The first cathode magnet 36 realizes magnetron sputtering by forming a leakage magnetic field around the first target 30. The first cathode magnet 36 is provided outside the processing vessel 11 and is driven by a first magnet driving unit 37.

[0022] The second cathode unit 14 is also provided on the inclined surface of the lid 19 of the processing vessel 11. The second cathode unit 14 has a second target 38 made of tin (IV) oxide, a second target electrode 39 that holds the second target 38, and a second power supply 40 that supplies power to the second target 38 via the second target electrode 39. In the second cathode unit 14, as will be described later, when a voltage is applied to the second target 38, sputtered particles of tin (IV) oxide (second sputtered particles) are emitted from the second target 38.

[0023] The second target electrode 39 is attached via a second insulating member 42 to the inside of a second hole 41 formed in the inclined surface of the lid 19 of the processing vessel 11. The second power supply 40 is also a DC power supply and applies a negative DC voltage to the second target electrode 39, so that the second target electrode 39 also functions as a cathode electrode.

[0024] A second shield member 43 is provided on the outer periphery of the second target 38. The second shield member 43 also prevents the sputtered particles of tin (IV) oxide emitted from the second target 38 from reaching the inner wall of the processing vessel 11 or the back surface of the second target electrode 39. In other words, the second shield member 43 also regulates the emission direction of the sputtered particles of tin (IV) oxide emitted from the second target 38.

[0025] A second cathode magnet 44 is provided on the rear side of the second target electrode 39. The second cathode magnet 44 realizes magnetron sputtering by forming a leakage magnetic field around the second target 38. The second cathode magnet 44 is provided outside the processing vessel 11 and is driven by a second magnet driving unit 45.

[0026] The number of first cathode units 13 and second cathode units 14 is not limited to one each, and may be two or more. However, the number of first cathode units 13 and the number of second cathode units 14 are set to be the same.

[0027] The gas supply unit 15 includes a gas supply source 46, a gas supply pipe 47 extending from the gas supply source 46, a flow rate controller 48 provided on the gas supply pipe 47, and a gas introduction pipe 49. The gas supply source 46 supplies an inert gas, such as a rare gas such as argon (Ar) gas or oxygen (O) gas, as a plasma generation gas to be excited inside the processing vessel 11 via the gas supply pipe 47 and the gas introduction pipe 49 into the processing vessel 11.

[0028] When forming the first film 53 made of metallic tin on the wafer W, the first power supply 32 applies a negative DC voltage to the first target 30 via the first target electrode 31. At this time, the gas supplied into the processing vessel 11 is excited due to the application of the negative DC voltage to the first target 30. At the same time, the first cathode magnet 36 driven by the first magnet driving unit 37 forms a leakage magnetic field around the first target 30, thereby generating magnetron plasma concentrated around the first target 30. Then, positive ions in the magnetron plasma are attracted by the negative DC voltage and collide with the first target 30, causing tin atoms to be emitted from the first target 30 as sputtered particles.

[0029] Furthermore, when forming the second film 54 made of tin(IV) oxide on the wafer W, the second power supply 40 applies a negative DC voltage to the second target 38 via the second target electrode 39. At this time, the gas supplied into the processing vessel 11 is excited due to the application of the negative DC voltage to the second target 38. At the same time, the second cathode magnet 44 driven by the second magnet driving unit 45 forms a leakage magnetic field around the second target 38, thereby generating magnetron plasma concentrated around the second target 38. Positive ions in the magnetron plasma are attracted by the negative DC voltage and collide with the second target 38, causing tin(IV) oxide molecules to be emitted from the second target 38 as sputtered particles.

[0030] As will be described later, in the film formation apparatus 10, a first film 53 made of metallic tin and a second film 54 made of tin(IV) oxide are alternately stacked to form a laminate 55. Therefore, while the first target 30 emits tin sputter particles to form the first film 53, it is necessary to prevent positive ions from being attracted to the second target 38. Also, while the second target 38 emits tin(IV) oxide sputter particles to form the second film 54, it is necessary to prevent positive ions from being attracted to the first target 30.

[0031] Accordingly, the film formation apparatus 10 includes a shutter 16 that shields the first target 30 or the second target 38 that is not contributing to film formation from the magnetron plasma. The shutter 16 has a truncated cone shape that conforms to the inner inclined surface of the lid 19 of the processing vessel 11 and is large enough to cover the facing areas of the first target 30 and the second target 38. Furthermore, openings 50 that are slightly larger than the first target 30 and the second target 38 are formed on the inclined surface of the shutter 16 at positions facing the first target 30 and the second target 38. The number of openings 50 is the same as the number of first cathode units 13 and second cathode units 14. For example, when two first cathode units 13 and two second cathode units 14 are disposed, two openings 50 are formed in the shutter 16.

[0032] The shutter 16 is attached to the lid 19 by a rotation shaft 51 provided at the center of the ceiling surface of the lid 19. The rotation shaft 51 is connected to a rotation mechanism 52 provided above the processing vessel 11, and the rotation mechanism 52 rotates the shutter 16 horizontally via the rotation shaft 51. When the first film 53 is formed, the shutter 16 rotates so that the opening 50 faces the first target 30 and covers the facing region of the second target 38. When the second film 54 is formed, the shutter 16 rotates so that the opening 50 faces the second target 38 and covers the facing region of the first target 30.

[0033] The control unit 17 controls the operation of each component of the film forming apparatus 10, such as the first power supply 32, the second power supply 40, the exhaust device 21, the first magnet driving unit 37, the second magnet driving unit 45, the gas supply unit 15, and the rotation mechanism 52. The control unit 17 also has input devices such as a keyboard and a mouse, an output device, a display device, and a storage device (none of which are shown). The control unit 17 causes each component of the film forming apparatus 10 to perform a predetermined operation based on, for example, a processing recipe retrieved from a storage medium.

[0034] Incidentally, because p-type tin(II) oxide is divalent tin oxide (SnO), when producing p-type tin(II) oxide, the atomic ratio of the raw materials tin to oxygen should be approximately 1:1 before crystallizing the tin and oxygen. However, p-type tin(II) oxide has a high cohesive energy, and during crystallization, n-type tin(IV) oxide, which has a lower cohesive energy, tends to be produced.

[0035] For example, in a crystal, the formation energy of oxygen defects (oxygen vacancies) is much lower than that of tin defects (tin vacancies). Therefore, when the atomic ratio of tin to oxygen is 1 when tin is taken as 1, i.e., when tin is rich (oxygen is poor), donor oxygen defects are more likely to occur than acceptor tin defects. As a result, even if tin(II) oxide is generated, its conductivity type will be n-type (Figure 2).

[0036] Furthermore, for example, because the formation energy of interstitial tin atoms in a crystal is negative, donor interstitial tin atoms are likely to occur. When interstitial tin atoms occur, the number of tin atoms that make up the crystal decreases. Therefore, when the atomic ratio of tin to oxygen is greater than 1.4 when tin is 1, i.e., when oxygen is excessively rich, tin atoms in the crystal need to bond with many oxygen atoms, and tin(IV) oxide is naturally produced. Because this tin(IV) oxide contains interstitial tin atoms that act as donors, its conductivity type is n-type (Figure 2).

[0037] On the other hand, when the atomic ratio of tin to oxygen is 1:1 to 1:1.4, the mixture becomes slightly oxygen-rich (slightly tin-poor), making it difficult for interstitial tin atoms and oxygen defects to form as donors, while making it easier for tin defects and interstitial oxygen atoms to form as acceptors. Furthermore, by narrowing down the conditions for producing p-type tin(II) oxide within this atomic ratio range using resistance measurements, Hall effect measurements, etc., it becomes possible to produce p-type tin(II) oxide stably and with good reproducibility in a variety of environments.

[0038] From the above, in order to produce p-type tin(II) oxide by crystallizing tin and oxygen, it is necessary to strictly control the atomic ratio of tin to oxygen as raw materials so that it is an atomic ratio that allows the production of p-type tin(II) oxide, within a range of 1:1 to 1:1.4.

[0039] To crystallize tin and oxygen, it is conceivable to use a sputtering method in an oxygen atmosphere to emit sputtered tin particles from a target made of metallic tin. In this case, it is necessary to control the atomic ratio of tin to oxygen by adjusting the flow rate of oxygen gas flowing into the processing vessel. However, it is very difficult to control the oxidation state of tin to a metastable divalent state by adjusting the gas flow rate.

[0040] Therefore, in this embodiment, a film whose atomic number can be accurately adjusted by adjusting the thickness is used, and the number of tin and oxygen atoms to be crystallized is accurately controlled. Specifically, when forming a stack of first films 53 and second films 54 in the film forming apparatus 10, the first films 53 and second films 54 are alternately stacked so that the atomic ratio (atomic ratio) of tin to oxygen in the stack is in the range of 1:1 to 1:1.4, and the atomic ratio of tin to oxygen falls within the range of atomic ratios that can produce p-type tin(II) oxide. The method for controlling the atomic ratio of tin to oxygen at this time includes, for example, adjusting the film thickness of each first film 53 and each second film 54.

[0041] 3A to 3D are process diagrams illustrating a method for forming a p-type tin oxide film according to this embodiment. The formation methods of FIGS. 3A to 3D are performed by a sputtering apparatus. For example, the formation methods of FIGS. 3A to 3D may be performed by the film formation apparatus 10, in which case the control unit 17 controls the operation of each component of the film formation apparatus 10 based on a process recipe.

[0042] First, the temperature of the wafer W is maintained at room temperature, for example, 20° C., and the internal pressure of the processing vessel accommodating the wafer W is increased to, for example, 1.5×10 -5 The pressure is reduced to less than 1000 kJ / cm2.

[0043] Next, argon gas is supplied as a plasma generating gas into the processing chamber. At this time, since it has been confirmed that adding an appropriate amount of oxygen gas improves crystallinity, the supplied plasma generating gas may contain a small amount (about 1%) of oxygen gas.

[0044] Thereafter, a first film 53 is formed by sputtering (FIG. 3A). When the film formation apparatus 10 performs the formation methods of FIGS. 3A to 3D, the shutter 16 is first rotated to position the opening 50 opposite the first target 30 and cover the opposing area of ​​the second target 38. The first power supply 32 applies a negative DC voltage to the first target 30, and the first cathode magnet 36 forms a leakage magnetic field around the first target 30. At this time, magnetron plasma is generated from the plasma generation gas, and positive ions in the magnetron plasma attracted by the negative DC voltage collide with the first target 30, thereby releasing tin sputtered particles from the first target 30. The tin sputtered particles are then deposited on the surface of the wafer W to form the first film 53. Thereafter, the formation of the first film 53 is stopped.

[0045] Next, a second film 54 is formed on the first film 53 by sputtering ( FIG. 3B ). When the film-forming apparatus 10 performs the formation method shown in FIGS. 3A to 3D , the shutter 16 is first rotated to position the opening 50 facing the second target 38 and cover the area facing the first target 30. The second power supply 40 applies a negative DC voltage to the second target 38, and the second cathode magnet 44 forms a leakage magnetic field around the second target 38. At this time, magnetron plasma is generated from the plasma generating gas, and positive ions in the magnetron plasma attracted by the negative DC voltage collide with the second target 38, releasing sputtered particles of tin(IV) oxide from the second target 38. The sputtered particles of tin(IV) oxide then deposit on the first film 53, forming the second film 54. The formation of the second film 54 is then stopped.

[0046] Next, the formation of the first film 53 and the formation of the second film 54 are alternately repeated to alternately stack the first film 53 and the second film 54 to form a stacked body 55 (FIG. 3C). Note that, although the first film 53 is formed first in the formation methods shown in FIGS. 3A to 3D, the second film 54 may be formed first as long as the first film 53 and the second film 54 are alternately stacked.

[0047] 3A to 3D, each of the first films 53 and each of the second films 54 are formed so that the elemental composition ratio of tin to oxygen in the stack 55 falls within the range of 1:1 to 1:1.4. At this time, the formation time of each of the first films 53 and each of the second films 54 is adjusted so that the ratio of the film thickness of each of the first films 53 to the film thickness of each of the second films 54 is a ratio that indicates p-type conductivity (for example, 7:1).

[0048] 3A to 3D , in order to achieve uniform mixing when the first films 53 and the second films 54 are melted and mixed, as described below, it is preferable that the film thicknesses of the first films 53 and the second films 54 are also the same. However, the film thicknesses of the first films 53 and the second films 54 formed at the interface with the surface of the wafer W may be different from those of the other first films 53 and second films 54 in order to maintain the composition of the interface or to change the composition for the purpose of achieving electrical contact. Furthermore, in the formation methods of FIGS. 3A to 3D , the formation times of the first films 53 and the second films 54 are adjusted so that the film thicknesses of the first films 53 and the second films 54 correspond to an appropriate atomic ratio (composition ratio) of tin to oxygen to obtain p-type characteristics.

[0049] Next, the wafer W is transferred from the processing chamber and into a heating device (not shown) separate from the film-forming apparatus 10, where the stack 55 formed on the wafer W is subjected to a heat treatment by the heating device. This heat treatment is performed, for example, inside a processing chamber (not shown) of the heating device, which is filled with an inert gas such as argon gas or nitrogen (N) gas. The wafer W is heated to 200°C to 400°C by the heat treatment. At this time, the first films 53 and the second films 54 mutually diffuse, and tin and oxygen mix in the stack 55. Then, as the stack 55 cools, the tin and oxygen crystallize. However, because the elemental composition ratio of tin to oxygen is within the range of 1:1 to 1:1.4, p-type tin(II) oxide is preferentially generated, forming a tin oxide film 56 made of p-type tin(II) oxide (FIG. 3D). The tin oxide film 56 formed at this time is not composed only of p-type tin (II) oxide, but also contains small amounts of n-type tin (IV) oxide and SnO, which have low cohesive energy, in addition to p-type tin (II) oxide. However, because p-type tin (II) oxide is dominant (approximately 90% or more by mass) in the tin oxide film 56, the tin oxide film 56 as a whole has p-type properties.

[0050] Regarding the heat treatment temperature, the present applicant formed tin oxide films 56 by changing the heat treatment temperature and confirmed the abundance ratio of p-type tin(II) oxide in each tin oxide film 56. Specifically, the composition of each tin oxide film 56 was confirmed by XPS (X-ray photoelectron spectroscopy). FIG. 4 is a graph showing the level intensity at 3 eV, which corresponds to the binding energy of p-type tin(II) oxide, when the heat treatment temperature was changed. As shown in the graph of FIG. 4, the level intensity is highest when the heat treatment temperature is 300°C. Here, since the level intensity corresponds to the abundance ratio of the corresponding component, it was found that the largest amount of p-type tin(II) oxide was generated when the heat treatment temperature was 300°C. In other words, it was found that a heat treatment temperature of 300°C is preferable from the viewpoint of the efficiency of generating p-type tin(II) oxide.

[0051] The applicant also formed tin oxide films 56 by changing the heat treatment temperature and checked the carrier density and mobility in each tin oxide film 56. In this case, the elemental composition ratio of tin to oxygen in the laminate 55 for forming the tin oxide film 56 was often close to 1:1.2.

[0052] 5A is a graph showing the carrier density of p-type tin (II) oxide when the temperature of the heat treatment is changed, and FIG. 5B is a graph showing the mobility of p-type tin (II) oxide when the temperature of the heat treatment is changed. In the graphs of FIGS. 5A and 5B, "◯" corresponds to p-type tin (II) oxide constituting the tin oxide film 56, and "×" corresponds to antimony-doped p-type tin (Sn 4+ Sb 3+

[0033] A reference document in which p-type conductivity is exhibited by replacing ZnO with ZnO (see, for example, "The Optimum Fabrication Condition of p-Type Antimony Tin Oxide Thin Films Prepared by DC Magnetron Sputtering," co-authored by Huu Phuc Dang, Quang Ho Luc, Tran Le, and Van Hieu Le, Hindawi Publishing Corporation, Journal of Nanomaterials, Volume 2016, Article ID 7825456, 11 The data corresponds to antimony-doped tin oxide (hereinafter referred to as "ATO") in the data disclosed in the references (http: / / dx.doi.org / 10.1155 / 2016 / 7825456), and "*" corresponds to p-type tin(II) oxide in the data disclosed in the references.

[0053] 5A and 5B, the carrier density and mobility of p-type tin(II) oxide are highest when the heat treatment temperature is 300° C. Therefore, it was found that a heat treatment temperature of 300° C. is preferable from the viewpoint of improving the carrier density and mobility of the generated p-type tin(II) oxide.

[0054] 5A and 5B, the carrier density and mobility of the tin oxide film 56 are almost equal to or higher than those of ATO and p-type tin(II) oxide (hereinafter abbreviated as "ATO, etc.") in the data disclosed in the reference documents. Here, the heat treatment temperature required to produce ATO, etc. is 400° C. or higher. Therefore, it was found that the p-type tin(II) oxide constituting the tin oxide film 56 can ensure carrier density and mobility equal to or higher than those of ATO, etc., by heat treatment at a temperature lower than that of ATO, etc.

[0055] According to this embodiment, a laminate 55 is formed by alternately stacking first films 53 made of metallic tin and second films 54 made of tin(IV) oxide, and the laminate 55 is then heat-treated to form a tin oxide film 56. When producing tin oxide by crystallizing tin and oxygen, the atomic ratio of tin to oxygen must be strictly controlled to obtain a desired conductivity type. However, the number of atoms contained in the film can be accurately adjusted by adjusting the thickness. In this embodiment, in which the first films 53 and the second films 54 are alternately stacked, the elemental composition ratio of tin to oxygen in the laminate 55 can be strictly controlled by adjusting the film thicknesses of the first films 53 and the second films 54 to form the laminate 55. As a result, when the laminate 55 is mixed and crystallized by heat treatment to produce the tin oxide film 56, the desired conductivity type can be easily obtained in the tin oxide film 56.

[0056] In particular, in this embodiment, first films 53 and second films 54 are alternately laminated so that the elemental composition ratio of tin to oxygen in stacked body 55 falls within the range of 1:1 to 1:1.4, and therefore p-type tin(II) oxide can be easily produced in tin oxide film 56. As described above, when tin oxide film 56 is produced, the conductivity type of tin oxide film 56 changes in response to changes in the elemental composition ratio of tin to oxygen in stacked body 55. Therefore, in order to reliably produce p-type tin(II) oxide, it is preferable that the elemental composition ratio of tin to oxygen in stacked body 55 be within a range in which p-type tin(II) oxide is preferentially produced (for example, approximately 1:1.2).

[0057] Furthermore, in this embodiment, first films 53 made of metallic tin and second films 54 made of tin(IV) oxide are alternately laminated, so that when laminate 55 is mixed by heat treatment, tin and oxygen tend to be distributed evenly in laminate 55. As a result, tin atoms and oxygen atoms tend to bond in a 1:1 ratio, which can promote the production of p-type tin(II) oxide.

[0058] Furthermore, in this embodiment, the temperature of the wafer W is maintained at room temperature when forming the stack 55. This suppresses tin precipitation due to high temperatures, prevents a decrease in the number of tin atoms that constitute the crystal, and promotes the subsequent generation of p-type tin(II) oxide.

[0059] Furthermore, in this embodiment, when first film 53 and second film 54 are laminated to form laminate 55, a small amount of oxygen gas of about 1% may be contained in the supplied plasma generating gas. This allows the oxidation state of tin to be controlled appropriately, and in the subsequent generation of p-type tin(II) oxide, the crystallinity of the tin(II) oxide can be improved.

[0060] Although the preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications and changes are possible within the scope of the gist of the present disclosure.

[0061] 3A to 3D, the stacked body 55 and the tin oxide film 56 are not covered with a protective film, but after the tin oxide film 56 is formed as shown in Fig. 6A, a protective film 57 may be formed to entirely cover the tin oxide film 56 (Fig. 6B). This prevents oxygen from being taken into the tin oxide film 56 from the outside during the transfer of the wafer W to a subsequent process after the formation of the tin oxide film 56, which would cause some of the p-type tin (II) oxide to change into n-type tin (IV) oxide.

[0062] Furthermore, after the stack 55 is formed, a protective film 58 may be formed to completely cover the stack 55 before the stack 55 is subjected to a heat treatment ( FIG. 7A ). Then, a tin oxide film 56 is formed from the stack 55 by a heat treatment ( FIG. 7B ). However, because the stack 55 is covered by the protective film 58, oxygen is prevented from entering the stack 55 from the outside when the first films 53 and the second films 54 are mixed and crystallized. This prevents the elemental composition ratio of tin to oxygen in the stack 55 from falling outside the range of 1:1 to 1:1.4, thereby preventing the generation of n-type tin(IV) oxide. The protective films 57 and 58 may be formed, for example, of an oxide film or a nitride film.

[0063] 3A to 3D may be performed not only by a sputtering apparatus but also by other types of film formation apparatuses. Examples of other types of film formation apparatuses that perform the formation methods of FIGS. 3A to 3D include film formation apparatuses that use chemical vapor deposition (CVD), atomic layer deposition (ALD), and pulsed laser deposition (PLD). The film formation apparatuses that use chemical vapor deposition and atomic layer deposition may be either plasma-based or non-plasma-based.

[0064] 3A to 3D, p-type tin(II) oxide was produced, but the methods of FIG. 3A to 3D can also be applied to the production of metal oxide films made of other tin oxides or oxide semiconductors other than tin oxide. In this case, the compositions and thicknesses of the first and second films to be stacked are determined depending on the composition of the metal oxide film to be produced.

[0065] This application claims priority based on Japanese Patent Application No. 2024-139600, filed on August 21, 2024, the entire contents of which are incorporated herein by reference.

[0066] W wafer 10 film forming apparatus 11 processing vessel 17 control unit 30 first target 38 second target 53 first film 54 second film 55 laminate 56 tin oxide film

Claims

1. A method for forming a p-type tin oxide film, comprising the steps of: forming a laminate by alternately stacking a first film made of metallic tin and a second film made of tin (IV) oxide; and heat treating the laminate to produce p-type tin (II) oxide from the laminate.

2. A method for forming a p-type tin oxide film according to claim 1, wherein the first film and the second film are alternately laminated so that the elemental composition ratio of tin to oxygen in the laminate falls within the range of 1:1 to 1:1.

4.

3. The method for forming a p-type tin oxide film according to claim 1, wherein the heat treatment involves heating the laminate to 200°C to 400°C.

4. The method for forming a p-type tin oxide film according to claim 1, wherein p-type tin (II) oxide is produced by crystallizing the p-type tin oxide from the laminate.

5. The method for forming a p-type tin oxide film according to claim 1, wherein the first film and the second film are formed by any one of PVD including sputtering, CVD, and ALD.

6. The method for forming a p-type tin oxide film according to claim 5, wherein the first film and the second film are formed by sputtering.

7. A film formation apparatus comprising: a processing vessel that accommodates a substrate; a first target made of metallic tin that is placed inside the processing vessel; a second target made of tin (IV) oxide that is placed inside the processing vessel; and a control unit, wherein the control unit forms a laminate by alternately repeating a step of depositing first sputtered particles emitted from the first target onto the substrate to form a first film made of metallic tin, and a step of depositing second sputtered particles emitted from the second target onto the substrate to form a second film made of tin (IV) oxide.

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