Film forming method and film forming apparatus

Abstract

The present invention relates to a film forming method and a film forming apparatus. [Subject] A technology for forming a polysilicon film having a large grain size is provided. [Solution] A film forming method according to one embodiment of the present invention comprises the following steps: a step of forming a laminated film on a substrate in which an interface layer, a main layer, and a surface layer are sequentially laminated; and a step of performing a crystallization treatment on the laminated film, wherein the main layer is formed from a film that is easier to crystallize than the interface layer in the crystallization treatment step, and the surface layer is formed from a film that is easier to crystallize than the main layer in the crystallization treatment step.

Description

Technical Field

[0001] The present disclosure relates to a film forming method and a film forming apparatus. Background Art

[0002] Polycrystalline silicon films are sometimes used as channels in three-dimensional NAND structures. Patent Document 1 discloses a method for forming a polycrystalline silicon film by stacking a second amorphous silicon film, whose crystal growth is faster than that of a first amorphous silicon film, on top of a first amorphous silicon film, whose crystal growth is slower, and then performing a crystallization process to form the polycrystalline silicon film.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-115435 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] The present disclosure provides a technology capable of forming a polycrystalline silicon film with large grain size.

[0008] Solutions for solving problems

[0009] A film forming method according to one embodiment of the present invention comprises the following steps: a step of forming a laminated film on a substrate in which an interface layer, a main layer and a surface layer are sequentially stacked; and a step of performing a crystallization treatment on the laminated film, wherein the main layer is formed from a film that is easier to crystallize than the interface layer in the crystallization treatment step, and the surface layer is formed from a film that is easier to crystallize than the main layer in the crystallization treatment step.

[0010] Effects of the Invention

[0011] According to the present disclosure, a polycrystalline silicon film having a large grain size can be formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a flowchart showing a film formation method according to one embodiment.

[0013] Figure 2 To show Figure 1 A flowchart of an example of a process for forming a laminated film in a film formation method.

[0014] Figure 3 To show Figure 1 A cross-sectional view showing an example of a step of forming a laminated film in a film forming method.

[0015] Figure 4 It is a diagram for explaining the effects of the film formation method according to one embodiment.

[0016] Figure 5 It is a longitudinal sectional view showing a configuration example of a vertical heat treatment apparatus.

[0017] Figure 6 For illustration purposes Figure 5 Diagram of the reaction tube of a vertical heat treatment device.

[0018] Figure 7 This is a diagram showing an example of evaluation results based on XRD.

[0019] Figure 8 This is a diagram showing an example of evaluation results based on SIMS.

[0020] Figure 9 This is a diagram showing an example of evaluation results using spectroscopic ellipsometer.

[0021] Figure 10 This is a diagram showing another example of evaluation results using spectroscopic ellipsometer.

[0022] Figure 11 This is a diagram showing an example of evaluation results based on TEM.

[0023] Description of Reference Numerals

[0024] 110 base

[0025] 120 laminated film

[0026] 121 Interface Layer

[0027] 122 Main layer

[0028] 123 surface layer DETAILED DESCRIPTION

[0029] Hereinafter, non-limiting exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. In all the accompanying drawings, identical or corresponding components or parts are denoted by identical or corresponding reference numerals, and duplicate descriptions are omitted.

[0030] [Film formation method]

[0031] The film formation method according to one embodiment will be described by taking the case of forming a polysilicon film as an example. Figure 1 1 is a flow chart showing a film forming method according to one embodiment. The film forming method according to one embodiment includes the following steps: forming a laminated film ( S10 ); performing a crystallization treatment on the laminated film ( S20 ); and reducing the thickness of the laminated film ( S30 ).

[0032] (Step S10 of Forming a Laminated Film)

[0033] Figure 2 To show Figure 1 Flowchart of an example of step S10 of forming a laminated film in the film formation method. Figure 3 To show Figure 1 A cross-sectional view showing an example of step S10 of forming a laminated film in the film forming method of FIG.

[0034] The step S10 of forming a laminated film is a step of forming a laminated film in which an interface layer, a bulk layer, and a surface layer are sequentially stacked. The thickness of the laminated film formed in the step S10 is, for example, thicker than the target thickness in the design. In this embodiment, the step S10 of forming a laminated film includes the step S11 of forming an interface layer, the step S12 of forming a bulk layer, and the step S13 of forming a surface layer.

[0035] In step S11, Figure 3 As shown in (a), an interface layer 121 is formed on a base 110. In this embodiment, the base 110 includes a substrate 111 and an insulating film 112. The substrate 111 can be, for example, a semiconductor wafer such as a silicon wafer. The insulating film 112 is formed on the surface of the substrate 111. The insulating film 112 can be, for example, a silicon oxide film (SiO2 film) or a silicon nitride film (SiN film).

[0036] The interface layer 121 is formed of, for example, an amorphous silicon film containing silicon (Si) and hydrogen (H). The amorphous silicon film is formed, for example, by an atomic layer deposition (ALD) method or a chemical vapor deposition (CVD) method using a high-grade silane gas. As the high-grade silane gas, for example, Si2H6, Si3H8, Si4H 10 Silane-based gases that contain more than two silicon atoms in one molecule. By using high-order silane-based gases, an amorphous silicon film with a high hydrogen concentration in the film can be formed. In addition, the interface layer 121 can be formed, for example, by an amorphous silicon film containing silicon and impurities that hinder crystallization. As impurities that hinder crystallization, for example, oxygen (O), carbon (C), and nitrogen (N) can be cited. The amorphous silicon film can be formed, for example, by an ALD method or a CVD method using a silicon raw material gas and a gas containing impurities that hinder crystallization. As a silicon raw material gas, for example, SiH4, Si2H6, Si3H8, Si4H 10 As the gas containing impurities that hinder crystallization, for example, N2O, NO, C2H4, NH3, N2H4, and monomethylhydrazine (MMH) can be used.

[0037] In step S12, Figure 3As shown in (b) of FIG. 1 , a main layer 122 is formed on the interface layer 121. The main layer 122 is formed by a film that is easier to crystallize than the interface layer 121 in the step S20 of crystallizing the stacked film. The main layer 122 is formed, for example, by an amorphous silicon film containing silicon and hydrogen, in which the hydrogen concentration is lower than that of the amorphous silicon film forming the interface layer 121. The amorphous silicon film is formed, for example, by an ALD method or a CVD method using a silane gas that is lower in order than the high-order silane gas used when forming the interface layer 121. For example, when Si2H6 is used when forming the interface layer 121, SiH4 can be used as the silane gas. The main layer 122 can be, for example, a layer thicker than the interface layer 121. In addition, the main layer 122 can have a multilayer structure. In the above case, each layer of the multilayer structure is formed by a film that is easier to crystallize than the interface layer 121 in the step S20 of crystallizing the stacked film.

[0038] In step S13, Figure 3 As shown in (c) of FIG. 1 , a surface layer 123 is formed on the main layer 122. The surface layer 123 is formed by a film that is easier to crystallize than the main layer 122 in the step S20 of crystallizing the stacked film. The surface layer 123 is formed, for example, by an amorphous silicon film containing silicon and hydrogen, wherein the hydrogen concentration in the film is lower than that of the amorphous silicon film forming the main layer 122. The amorphous silicon film is formed, for example, by an ALD method or a CVD method using a processing condition that is less likely to incorporate hydrogen into the film than the processing condition used when forming the main layer 122. In addition, the surface layer 123 can be formed, for example, by an amorphous silicon film containing silicon and impurities for promoting crystallization. Examples of impurities for promoting crystallization include chlorine (Cl), phosphorus (P), boron (B), germanium (Ge), aluminum (Al), nickel (Ni), and fluorine (F). The amorphous silicon film is formed by an ALD method or a CVD method using a silicon raw material gas and a gas containing impurities for promoting crystallization. As silicon raw material gas, for example, SiH4, Si2H6, Si3H8, Si4H 10 As a gas containing impurities for promoting crystallization, for example, dichlorosilane (DCS), PH3, BCl3, B2H6, GeH4, GeCl4, AlCl3, trimethylaluminum (TMA), and SiF4 can be used. In addition, the surface layer 123 may be formed without silicon and with impurities for promoting crystallization, and may be formed by doping the surface of the main layer 122 with impurities for promoting crystallization.

[0039] Through the above steps S11 to S13 , the laminated film 120 in which the interface layer 121 , the bulk layer 122 , and the surface layer 123 are sequentially laminated is formed on the substrate 110 .

[0040] (Step S20 of Crystallizing the Laminated Film)

[0041] Step S20 of crystallizing the stacked film is performed after step S10 of forming the stacked film. In this embodiment, step S20 of crystallizing the stacked film includes performing a heat treatment (annealing) on ​​the stacked film 120 to crystallize the amorphous silicon film forming the stacked film 120 to form a polycrystalline silicon film. The annealing temperature can be, for example, 550°C to 800°C.

[0042] (Step S30 of Reducing the Thickness of the Laminated Film)

[0043] The step S30 of reducing the thickness of the stacked film is performed after the step S20 of crystallizing the stacked film. In this embodiment, the step S30 of reducing the thickness of the stacked film includes performing an etch back process on the stacked film 120 formed in the step S10 of forming the stacked film, thereby reducing the thickness of the stacked film 120 to a target thickness. The etch back process can be performed, for example, by dry etching or wet etching.

[0044] Through the above steps S10 to S30 , a polysilicon film having a desired film thickness can be formed on the substrate 110 .

[0045] It should be noted that the film forming method of one embodiment may include: a process of forming a seed layer on the substrate 110, which is performed before the process S10 of forming the laminated film. In the present embodiment, the seed layer is formed using an aminosilane-based gas. Hereinafter, the seed layer formed using the aminosilane-based gas is also referred to as an aminosilane seed. As aminosilane-based gases, for example, DIPAS (diisopropylaminosilane), 3DMAS (tris(dimethylamino)silane), and BTBAS (bis-tert-butylaminosilane) can be cited. The seed layer is formed, for example, by a CVD method or an ALD method using an aminosilane-based gas heated to a temperature that does not cause thermal decomposition. By forming the seed layer on the substrate 110 in this way, the roughness of the laminated film 120 formed on the seed layer can be reduced.

[0046] 〔Action / Effect〕

[0047] Figure 4 It is a diagram for explaining the effects of the film formation method according to one embodiment. Figure 4 (a) is a diagram for explaining a mechanism when the amorphous silicon film is crystallized to form the stacked film 120 in which the interface layer 121 , the bulk layer 122 , and the surface layer 123 are stacked in this order. Figure 4 (b) is a diagram for explaining the mechanism of crystallization of an amorphous silicon film forming a stacked film 120X in which an interface layer 121 and a bulk layer 122 are sequentially stacked. Both the stacked film 120 and the stacked film 120X are formed on the insulating film 112 .

[0048] In the stacked film 120, among the amorphous silicon films of the interface layer 121, the main layer 122 and the surface layer 123, the amorphous silicon film of the surface layer 123 is the easiest to crystallize, and the amorphous silicon film of the interface layer 121 is the least likely to crystallize. Figure 4 As shown in (a), crystallization starting from the interface side (the interface layer 121 side of the interface layer 121 and the main layer 122) is suppressed, and crystallization starts from the crystal nucleus 124 generated on the surface side (the surface layer 123 and the surface layer 123 side of the main layer 122). As a result, the crystal grain size of the polycrystalline silicon film on the interface side becomes larger than the crystal grain size of the polycrystalline silicon film on the surface side. In other words, the grain boundaries 125 of the polycrystalline silicon film on the interface side become smaller than the grain boundaries 125 of the polycrystalline silicon film on the surface side. As a result, when the film thickness of the polycrystalline silicon film is reduced to the target film thickness T, a polycrystalline silicon film with a large grain size can be formed.

[0049] On the other hand, in the laminated film 120X, the surface layer 123 is not formed. Figure 4 As shown in (b) of FIG, crystallization easily proceeds starting from crystal nuclei 124X generated on the interface side (the interface layer 121 side of the interface layer 121 and the bulk layer 122). As a result, the crystal grain size of the polycrystalline silicon film on the interface side becomes smaller than the crystal grain size of the polycrystalline silicon film on the surface side. In other words, the number of grain boundaries 125X of the polycrystalline silicon film on the interface side becomes greater than the number of grain boundaries 125X of the polycrystalline silicon film on the surface side. As a result, the grain size of the polycrystalline silicon film decreases when the film thickness of the polycrystalline silicon film is reduced to the target film thickness T.

[0050] [Film forming device]

[0051] As an example of a film-forming apparatus capable of performing the above-described film-forming method, a batch-type vertical heat treatment apparatus for simultaneously heat-treating multiple substrates is used. However, the film-forming apparatus is not limited to a batch-type apparatus and may also be a single-wafer apparatus for processing each substrate.

[0052] Figure 5 It is a longitudinal sectional view showing a configuration example of a vertical heat treatment apparatus. Figure 6 For illustration purposes Figure 5 Diagram of the reaction tube of a vertical heat treatment device.

[0053] like Figure 5 As shown, the vertical heat treatment apparatus 1 includes a reaction tube 34, a cover 36, a wafer boat 38, a gas supply unit 40, an exhaust unit 41, and a heating unit 42. The reaction tube 34, the cover 36, the wafer boat 38, the gas supply unit 40, the exhaust unit 41, and the heating unit 42 constitute a processing unit.

[0054] The reaction tube 34 is a processing container for housing a wafer boat 38. The wafer boat 38 is a substrate holder that holds multiple semiconductor wafers (hereinafter referred to as "wafers W") at predetermined intervals. The reaction tube 34 comprises an inner tube 44, a cylindrical tube with an open lower end and a topped cylindrical tube 46, an outer tube 46 with an open lower end and covering the outside of the inner tube 44. The inner and outer tubes 44, 46, are formed from a heat-resistant material such as quartz and are coaxially arranged to form a double tube structure.

[0055] The top 44A of the inner tube 44 is, for example, flat. A nozzle housing portion 48 for housing a gas nozzle is formed on one side of the inner tube 44 along its longitudinal direction (up and down direction). Figure 6 As shown, a portion of the side wall of the inner tube 44 is protruded outward to form a convex portion 50, and a nozzle housing portion 48 is formed within the convex portion 50. A rectangular opening 52 is formed along the longitudinal direction (vertical direction) of the inner tube 44 on the side wall opposite to the nozzle housing portion 48.

[0056] The opening 52 is a gas exhaust port formed to discharge the gas in the inner tube 44. The opening 52 is formed to have a length equal to or longer than the length of the wafer boat 38 and to extend in both the vertical directions.

[0057] The lower end of the reaction tube 34 is supported by a cylindrical manifold 54 made of, for example, stainless steel. A flange 56 is formed at the upper end of the manifold 54, and the lower end of the outer tube 46 is mounted on and supported by the flange 56. A sealing member 58, such as an O-ring, is interposed between the flange 56 and the lower end of the outer tube 46 to create an airtight state within the outer tube 46.

[0058] An annular support portion 60 is provided on the inner wall of the upper portion of the manifold 54. The lower end of the inner tube 44 is mounted on the support portion 60 and supported. A lid 36 is airtightly attached to the lower opening of the manifold 54 via a sealing member 62, such as an O-ring, to airtightly block the lower opening of the reaction tube 34, i.e., the opening of the manifold 54. The lid 36 is formed, for example, of stainless steel.

[0059] A rotation shaft 66 is provided through the center of the cover 36 via a magnetic fluid seal portion 64. The lower portion of the rotation shaft 66 is rotatably supported by an arm 68A of an elevating portion 68 including a boat elevator.

[0060] A rotating plate 70 is provided at the upper end of the rotating shaft 66 , and a wafer boat 38 holding wafers W is placed on the rotating plate 70 via a quartz heat-retaining table 72 . Therefore, by raising and lowering the lifting unit 68 , the lid 36 and the wafer boat 38 move up and down together, allowing the wafer boat 38 to be inserted and removed from the reaction tube 34 .

[0061] The gas supply unit 40 is provided in the manifold 54 and introduces gas into the inner tube 44. The gas supply unit 40 includes a plurality (e.g., three) of quartz gas nozzles 76, 78, and 80. Each gas nozzle 76, 78, and 80 is provided along the longitudinal direction of the inner tube 44, and its base end is bent into an L-shape and supported so as to penetrate the manifold 54.

[0062] Gas nozzles 76, 78, 80 are as follows Figure 6 As shown, they are arranged in a row along the circumferential direction within the nozzle housing 48 of the inner tube 44. A plurality of gas holes 76A, 78A, 80A are formed at predetermined intervals along the length direction of each gas nozzle 76, 78, 80, so that each gas can be released horizontally from each gas hole 76A, 78A, 80A. The predetermined interval is set, for example, in the same manner as the interval between the wafers W supported by the wafer boat 38. In addition, the height position is set so that each gas hole 76A, 78A, 80A is located in the middle between the wafers W adjacent in the vertical direction, so that each gas can be effectively supplied to the space between the wafers W. As the type of gas, a film forming gas, an etching gas, and a purge gas can be used, and each gas can be supplied as needed through each gas nozzle 76, 78, 80 while controlling the flow rate of each gas.

[0063] A gas outlet 82 is formed on the upper sidewall of the manifold 54, above the support portion 60. This allows the gas within the inner tube 44, which is discharged from the opening 52, to be exhausted through the space 84 between the inner tube 44 and the outer tube 46. An exhaust unit 41 is provided above the gas outlet 82. The exhaust unit 41 includes an exhaust passage 86 connected to the gas outlet 82. A pressure regulating valve 88 and a vacuum pump 90 are sequentially interposed in the exhaust passage 86 to evacuate the interior of the reaction tube 34.

[0064] A cylindrical heating unit 42 is provided on the outer circumference of the outer tube 46 so as to cover the outer tube 46 . The heating unit 42 heats the wafers W accommodated in the reaction tube 34 .

[0065] The overall operation of the vertical heat treatment apparatus 1 is controlled by a control unit 95. The control unit 95 may be, for example, a computer. Furthermore, a computer program for performing the overall operation of the vertical heat treatment apparatus 1 is stored in a storage medium 96. The storage medium 96 may be, for example, a floppy disk, an optical disk, a hard disk, a flash memory, a DVD, or the like.

[0066] An example of a film forming method according to an embodiment, for example, a method of forming a polysilicon film on a wafer W, will be described using the vertical heat treatment apparatus 1 described above.

[0067] First, the control unit 95 controls the lifting unit 68 to carry the wafer boat 38 holding a plurality of wafers W into the reaction tube 34 , and hermetically blocks the lower end opening of the reaction tube 34 with the lid 36 .

[0068] Next, the control unit 95 controls the gas supply unit 40, the exhaust unit 41, the heating unit 42, and the like so as to sequentially execute the aforementioned steps of forming the stacked film S10, crystallizing the stacked film S20, and reducing the thickness of the stacked film S30. Thus, a polycrystalline silicon film with a large grain size can be formed on the wafer W.

[0069] It should be noted that, in the above example, the three steps of forming the stacked film (step S10), crystallizing the stacked film (step S20), and reducing the thickness of the stacked film (step S30) are performed in the vertical heat treatment apparatus 1. However, the present disclosure is not limited to this. For example, if the step S30 of reducing the thickness of the stacked film includes an etch-back process using wet etching, the step of reducing the thickness of the stacked film may also be performed in an apparatus other than the vertical heat treatment apparatus 1.

[0070] [Ease of crystallization]

[0071] (Evaluation based on XRD)

[0072] The results of evaluating the easiness of crystallization of an amorphous silicon film using X-ray diffraction (XRD) will be described.

[0073] First, an aminosilane seed crystal and an amorphous silicon film (hereinafter referred to as "a-Si(SiH4)") formed using SiH4 gas were sequentially stacked on the SiO2 film. The stacked film was then heat treated at 550°C, 600°C, and 650°C, and its crystalline state was evaluated by XRD.

[0074] Separately, an aminosilane seed crystal and a chlorine-doped amorphous silicon film (hereinafter referred to as "a-Si(Cl-dope)") formed using a mixture of SiH4 gas and DCS gas were sequentially stacked on the SiO2 film. The stacked film was then heat treated at 550°C, 600°C, and 650°C, and its crystalline state was evaluated using XRD.

[0075] The evaluation results of the crystal state based on XRD are shown in Figure 7 . Figure 7 This is a diagram showing an example of evaluation results based on XRD. Figure 7 (a) shows the result of a stacked film in which aminosilane seed crystals and a-Si(SiH4) are sequentially stacked on a SiO2 film. Figure 7(b) shows the result of a stacked film in which an aminosilane seed crystal and a-Si(Cl-dope) are sequentially stacked on a SiO2 film. Figure 7 (a) and Figure 7 In (b), the horizontal axis represents the diffraction angle 2θ [degrees], and the vertical axis represents the diffracted X-ray intensity (intensity) [counts].

[0076] In a-Si(SiH4), such as Figure 7 As shown in (a), when heat treated at 600°C, no peak of Si(220) surface appears. On the other hand, in a-Si(Cl-dope), Figure 7 As shown in (b), when heat treatment is performed at 600°C, a peak of the (220) plane of Si appears.

[0077] In addition, in a-Si(SiH4), Figure 7 As shown in (a), when heat treated at 600°C, the peak of Si(311) surface does not appear. On the other hand, in a-Si(Cl-dope), Figure 7 As shown in (a), when heat treatment is performed at 600°C, a peak of the (311) plane of Si appears.

[0078] From the above results, it can be said that a-Si(Cl-dope) is easier to crystallize than a-Si(SiH4).

[0079] (Evaluation based on SIMS)

[0080] The results of analyzing factors affecting the ease of crystallization of an amorphous silicon film using secondary ion mass spectrometry (SIMS) will be described.

[0081] First, the concentration of hydrogen (H) (hereinafter referred to as "hydrogen concentration in the film") and the concentration of chlorine (Cl) (hereinafter referred to as "chlorine concentration in the film") contained in the a-Si (SiH4) and a-Si (Cl-dope) films before heat treatment were measured by SIMS. In addition, the hydrogen concentration and the chlorine concentration in the a-Si (SiH4) and a-Si (Cl-dope) films after heat treatment were measured by SIMS. The measurement results are shown in FIG. Figure 8 .

[0082] Figure 8 This is a diagram showing an example of evaluation results based on SIMS. Figure 8 ] The average value of the hydrogen concentration in the film and the average value of the chlorine concentration in the film at a depth of 15 nm to 20 nm from the surface of the film are shown in FIG.

[0083] like Figure 8As shown in the figure, there is almost no difference in hydrogen concentration between the a-Si(SiH4) film and the a-Si(Cl-dope) film before and after heat treatment. On the other hand, the chlorine concentration in the a-Si(Cl-dope) film is 1 to 2 orders of magnitude higher than that in the a-Si(SiH4) film both before and after heat treatment.

[0084] From the above results, it is considered that chlorine contained in the amorphous silicon film promotes crystallization.

[0085] (Evaluation based on spectroscopic ellipsometer)

[0086] The results of evaluating the easiness of crystallization of an amorphous silicon film using the extinction coefficient (k value) in a spectroscopic ellipsometer will be described.

[0087] First, aminosilane seed crystals and a-Si(SiH4) were sequentially stacked on a SiO2 film. The thickness of the aminosilane seed crystal / a-Si(SiH4) stack was set to 30 nm. The stacked film was then heat treated at 550°C, 575°C, 600°C, 625°C, and 650°C for 12 hours. The k value was then calculated using spectroscopic ellipsometer measurements.

[0088] Separately, aminosilane seed crystals and a-Si(Si2H6) were sequentially stacked on the SiO2 film. The thickness of the aminosilane seed crystal / a-Si(Si2H6) stacked film was set to 30 nm. The stacked film was then heat treated at 550°C, 575°C, 600°C, 625°C, and 650°C for 12 hours, and then measured using spectroscopic ellipsometer to calculate the k value.

[0089] The calculation results of the k value based on the spectroscopic ellipsometer are shown in Figure 9 . Figure 9 This is a diagram showing an example of evaluation results using spectroscopic ellipsometer. Figure 9 In the graph, the horizontal axis represents the heat treatment temperature [° C.], and the vertical axis represents the extinction coefficient (k value). Figure 9 In the figure, the solid line represents the k value of the aminosilane seed crystal / a-Si(SiH4) stacked film, and the dotted line represents the k value of the aminosilane seed crystal / a-Si(Si2H6) stacked film.

[0090] like Figure 9As shown in the figure, when the heat treatment temperature is 600°C, the k value of the aminosilane seed / a-Si (SiH4) stacked film is smaller than the k value of the aminosilane seed / a-Si (Si2H6) stacked film. Based on this result, the aminosilane seed / a-Si (SiH4) stacked film is easier to crystallize than the aminosilane seed / a-Si (Si2H6) stacked film. The amorphous silicon film formed using Si2H6 gas contains more H (hydrogen) than the amorphous silicon film formed using SiH4 gas. It is believed that the difference in hydrogen concentration in the film affects the ease of crystallization.

[0091] [The starting point of crystallization]

[0092] (Evaluation based on spectroscopic ellipsometer)

[0093] The results of evaluating the starting point of crystallization of the amorphous silicon stacked film using the extinction coefficient (k value) in a spectroscopic ellipsometer will be described.

[0094] (Evaluation based on XRD)

[0095] First, an aminosilane seed crystal, an amorphous silicon film formed using Si2H6 gas (hereinafter referred to as "a-Si(Si2H6)"), and a-Si(SiH4) were sequentially stacked on a SiO2 film. The thickness of the aminosilane seed crystal / a-Si(Si2H6) / a-Si(SiH4) stacked film was set to 40 nm. The stacked film was then heat treated at 550°C, 575°C, 600°C, 625°C, and 650°C for 12 hours, and then measured using spectroscopic ellipsometer to calculate the k value.

[0096] Separately, an aminosilane seed crystal, a-Si(Si2H6), a-Si(SiH4), and a-Si(Cl-dope) were sequentially stacked on the SiO2 film. The thickness of the aminosilane seed crystal / a-Si(Si2H6) / a-Si(SiH4) / a-Si(Cl-dope) stack was set to 40 nm. The stacked film was then heat treated at 550°C, 575°C, 600°C, 625°C, and 650°C for 12 hours, and then measured using spectroscopic ellipsometer to calculate the k value.

[0097] The calculation results of the k value based on the spectroscopic ellipsometer are shown in Figure 10 . Figure 10 This is a diagram showing another example of evaluation results using spectroscopic ellipsometer. Figure 10 In the graph, the horizontal axis represents the heat treatment temperature [° C.], and the vertical axis represents the extinction coefficient (k value). Figure 10In the figure, the solid line represents the k value of the aminosilane seed / a-Si(Si2H6) / a-Si(SiH4) / a-Si(Cl-dope) stacked film, and the dotted line represents the k value of the aminosilane seed / a-Si(Si2H6) / a-Si(SiH4) stacked film.

[0098] like Figure 10 As shown in the figure, when the heat treatment temperature is 600°C, the k value of the amorphous silicon stacked film with a-Si(Cl-dope) formed on the outermost surface is lower than the k value of the amorphous silicon stacked film without a-Si(Cl-dope) formed on the outermost surface. This result shows that the formation of a-Si(Cl-dope) on the outermost surface facilitates crystallization of the amorphous silicon stacked film. This is believed to be because the formation of a-Si(Cl-dope) on the outermost surface allows crystallization to proceed from the a-Si(Cl-dope) as the starting point.

[0099] (Evaluation based on TEM)

[0100] The following describes the results of observing a cross section of an amorphous silicon film in the process of crystallization using a transmission electron microscope (TEM).

[0101] First, aminosilane seed crystals, a-Si(Si2H6), a-Si(SiH4), and a-Si(Cl-dope) were stacked in this order on the SiO2 film. Then, the stacked film was heat treated at 600°C for 12 hours, and the cross section of the stacked film was observed by TEM. The results of the cross section observation of the stacked film by TEM are shown in FIG. Figure 11 .

[0102] Figure 11 This is a diagram showing an example of the evaluation results based on TEM. Figure 11 As shown, interference fringes FR, reflecting crystallization, are generated on the surface side of the amorphous silicon (a-Si) film. This result indicates that in the aminosilane seed crystal / a-Si(Si2H6) / a-Si(SiH4) / a-Si(Cl-dope) stacked film, crystal growth readily progresses on the surface side of the stacked film. In other words, it is believed that crystal growth progresses from the surface side of the stacked film.

[0103] The embodiments disclosed herein are by way of example only and should not be construed as limiting. The embodiments described above may be omitted, replaced, or modified in various ways without departing from the scope of the appended claims and the spirit thereof.

[0104] In the above embodiment, the film formed by the film forming method is described as a polysilicon film, but the present disclosure is not limited thereto. For example, the film formed by the film forming method may be a polysilicon germanium film or a polycrystalline germanium film.

Claims

1. A film forming method comprising the following steps: forming a laminated film having an interface layer, a bulk layer, and a surface layer laminated in this order on a substrate; and a step of crystallizing the laminated film, The main layer is formed of a film that is more easily crystallized than the interface layer in the step of performing the crystallization treatment. The surface layer is formed of a film that is more easily crystallized than the main body layer in the step of performing the crystallization treatment.

2. The film forming method according to claim 1, wherein The method further comprises a step of reducing the thickness of the laminated film, which is performed after the step of performing the crystallization treatment.

3. The film forming method according to claim 2, wherein The thickness of the laminated film formed in the step of forming the laminated film is thicker than a target film thickness, The step of reducing the thickness of the stacked film is a step of reducing the thickness of the stacked film to the target thickness.

4. The film forming method according to any one of claims 1 to 3, wherein The main body layer has a multi-layer structure, In the step of performing the crystallization treatment, each layer of the multilayer structure is formed of a film that is more easily crystallized than the interface layer.

5. The film forming method according to any one of claims 1 to 3, wherein The interface layer and the bulk layer are formed of films containing silicon and hydrogen, The hydrogen concentration in the film decreases in the order of the interface layer and the bulk layer. The film forming method according to claim 5 , wherein: The surface layer is formed of a film containing silicon and impurities for promoting crystallization.

7. The film forming method according to claim 5, wherein The surface layer is formed of a film containing silicon and hydrogen, The hydrogen concentration in the film decreases in the order of the interface layer, the bulk layer, and the surface layer.

8. The film forming method according to any one of claims 1 to 3, wherein The interface layer is formed of a film containing silicon and impurities for hindering crystallization, The main body layer is formed of a film containing silicon, The surface layer is formed of a film containing silicon and impurities for promoting crystallization.

9. The film forming method according to claim 8, wherein The impurities for hindering crystallization are oxygen, carbon or nitrogen.

10. The film forming method according to claim 6 or 9, wherein The impurities used to promote crystallization are chlorine, phosphorus, boron, germanium, aluminum, nickel or fluorine.

11. The film forming method according to claim 6 or 9, wherein The surface layer is formed by doping the surface of the bulk layer with the impurity for promoting crystallization.

12. The film forming method according to any one of claims 1 to 3, wherein The surface layer does not contain silicon and is formed of impurities for promoting crystallization.

13. A film forming apparatus comprising a processing unit and a control unit. The control unit is configured to control the processing unit so as to execute the following steps: forming a laminated film having an interface layer, a bulk layer, and a surface layer laminated in this order on a substrate, and subjecting the laminated film to a crystallization treatment, The main layer is formed of a film that is more easily crystallized than the interface layer in the step of performing the crystallization treatment. The surface layer is formed of a film that is more easily crystallized than the main body layer in the step of performing the crystallization treatment.

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