Silicon film forming method and apparatus

Abstract

To provide a method for forming a silicon film which can crystallize a silicon film at a low temperature in a short time and form a silicon film with high flatness.SOLUTION: A film forming method includes the steps of supplying a silicon-containing gas onto a seed layer to deposit an amorphous silicon film onto the seed layer, and supplying chlorosilane gas onto the amorphous silicon film to crystallize the amorphous silicon film while forming a chlorosilane cap layer on the amorphous silicon film.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for forming a silicon film. [Background technology]

[0002] Conventionally, a method for forming a silicon film has been known that includes a step (step 1) of supplying a high-order aminosilane gas containing two or more silicon atoms in its molecular formula onto a surface to be treated, thereby adsorbing silicon onto the surface to be treated to form a seed layer, and a step (step 2) of supplying a silane gas not containing an amino group onto the seed layer, thereby depositing silicon onto the seed layer to form a silicon film, in which the treatment temperature in step 1 is in the range of 350°C or lower and room temperature (25°C) or higher (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-45082 A Summary of the Invention [Problem to be solved by the invention]

[0004] A method for forming a silicon film is provided that can form a silicon film having high flatness at a high temperature. [Means for solving the problem]

[0005] In order to achieve the above object, a method for forming a silicon film according to one aspect of the present invention includes the steps of: supplying a silicon-containing gas onto a seed layer; and depositing an amorphous silicon film on the seed layer. supplying a chlorosilane gas onto the amorphous silicon film to deposit a cap layer of chlorosilane on the amorphous silicon film. Effect of the Invention

[0006] According to the present disclosure, a silicon film with excellent flatness can be formed. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 illustrates a film forming apparatus according to an embodiment of the present disclosure. [Diagram 2] 1A to 1C are diagrams for explaining an example of a method for forming a silicon film according to an embodiment of the present disclosure. [Diagram 3] 1A and 1B are diagrams showing a comparison between a silicon film formed by the silicon film forming method according to the embodiment and other silicon films. [Figure 4] 1 is a diagram for explaining surface roughness in an example in which the silicon film forming method according to the embodiment was carried out; FIG. [Diagram 5] FIG. 1 shows the results of measuring surface roughness by AFM. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0009] [Film forming equipment] FIG. 1 is a diagram showing a film forming apparatus according to an embodiment of the present disclosure. In this embodiment, an example in which the film forming apparatus is configured as a vertical heat treatment apparatus will be described. The film forming apparatus according to the present disclosure is not limited to a vertical heat treatment apparatus, and can be applied to various film forming apparatuses. Applicable film forming apparatuses include single-wafer type film forming apparatuses and semi-batch type film forming apparatuses. In this embodiment, an example in which the film forming apparatus is configured as a vertical heat treatment apparatus will be described.

[0010] The vertical heat treatment apparatus performs CVD (Chemical Vapor Deposition) film formation to form a crystallized silicon film on an underlayer of a silicon oxide film.

[0011] The vertical heat treatment apparatus includes a reaction tube 11, which is a substantially cylindrical vacuum vessel with its longitudinal direction oriented vertically. The reaction tube 11 has a double-tube structure consisting of an inner tube 12 and an outer tube 13 with a ceiling that covers the inner tube 12 and is formed to have a certain distance from the inner tube 12. The inner tube 12 and the outer tube 13 are made of a heat-resistant material, for example, quartz. The reaction tube 11 may be called a processing chamber because it forms a closed space in which substrates are processed.

[0012] A cylindrical manifold 14 made of stainless steel (SUS) is disposed below the outer tube 13. The manifold 14 is airtightly connected to the lower end of the outer tube 13. The inner tube 12 protrudes from the inner wall of the manifold 14 and is supported by a support ring 15 formed integrally with the manifold 14.

[0013] A lid 16 is disposed below the manifold 14, and the lid 16 can be raised and lowered between an upper position and a lower position by the boat elevator 10. FIG. 1 shows the lid 16 in the upper position, and in this upper position, the lid 16 closes an opening 17 of the reaction tube 11 below the manifold 14, making the inside of the reaction tube 11 airtight. A wafer boat 3 made of, for example, quartz is placed on the lid 16. The wafer boat 3 is configured to hold a number of wafers W to be processed as substrates horizontally at a predetermined interval in the vertical direction. A heat insulator 18 is provided around the reaction tube 11 so as to surround the reaction tube 11, and a heater 19 made of, for example, a resistance heating element, which is a heating unit, is provided on the inner wall surface of the heat insulator 18, which can heat the inside of the reaction tube 11.

[0014] In the manifold 14, the process gas introduction pipe 21 and the purge gas introduction pipe 31 are inserted below the support ring 15, and the downstream ends of the gas introduction pipes 21 and 31 are arranged so as to supply gas to the wafer W in the inner pipe 12. For example, the upstream side of the process gas introduction pipe 21 branches to form branch paths 22A to 22C, and the upstream ends of the branch paths 22A to 22C are connected to a disilane (Si2H6) gas supply source 23A, a monosilane (SiH4) gas supply source 23B, and a chlorosilane gas supply source 23C. Gas supply mechanisms 24A to 24C are respectively provided in the branch paths 22A to 22C. The gas supply mechanisms 24A to 24C each include a valve and a mass flow controller, and are configured so as to be able to control the flow rate of the process gas supplied from the gas supply sources 23A to 23C to the process gas introduction pipe 21.

[0015] The Si2H6 gas is a seed layer forming gas for forming a seed layer on the surface of the silicon oxide film, and the gas supply source 23A and the gas supply mechanism 24A constitute a Si2H6 (disilane) gas supply unit.

[0016] The Si2H6 gas may also be used as a silicon-containing gas to further deposit an amorphous silicon film on the second seed layer, as will be described in detail later.

[0017] The disilane gas supply unit is a gas supply unit for forming a seed layer, and therefore may be called a seed layer forming gas supply unit.

[0018] In this embodiment, an example is described in which one type of gas is used for forming a seed layer, but two or more types of gases may be used for forming a seed layer. In addition, when forming a film on a wafer W on which a seed layer has already been formed, the seed layer forming gas supply unit may not be required. Furthermore, even when the seed layer forming gas supply unit is used, a gas other than Si2H6 gas may be used. For example, DIPAS (diisopropylaminosilane gas) may be used. In this way, the disilane gas supply unit given as an example and the seed layer forming gas supply unit may be provided as necessary.

[0019] The SiH4 gas is a film-forming gas for forming a silicon (Si) film on the wafer W on which the sheet layer is formed, and the gas supply source 23C and the gas supply mechanism 24C constitute a silicon-containing gas supply unit. Note that since the silicon-containing gas is a gas used in film formation, the silicon-containing gas supply unit may also be called a film-forming gas supply unit.

[0020] The chlorosilane gas is a gas for forming a cap layer on the surface of the silicon film, and contains silicon and chlorine. The gas supply source 23C and the gas supply mechanism 24C constitute a chlorosilane gas supply unit. Since the chlorosilane gas is a gas used for forming the cap layer, the chlorosilane gas supply unit may be called a capping gas supply unit.

[0021] As the chlorosilane gas, various chlorosilane gases such as DCS (SiH2Cl2, dichlorosilane, hereinafter also referred to as "DCS"), trichlorosilane gas, tetrachlorosilane, HCD (disilicon hexachloride), and the like may be used.

[0022] The upstream side of the purge gas introduction pipe 31 is connected to a supply source 32 of nitrogen (N2) gas, which is a purge gas. A gas supply mechanism 33 is provided in the purge gas introduction pipe 31. The gas supply mechanism 33 is configured similarly to the gas supply mechanisms 24A to 24C, and controls the flow rate of the purge gas to the downstream side of the introduction pipe 31.

[0023] Further, the manifold 14 has an exhaust port 25 opening on a side surface above the support ring 15, and exhaust gas generated in the inner tube 12 is exhausted to the exhaust port 25 through a space formed between the inner tube 12 and the outer tube 13. An exhaust pipe 26 is airtightly connected to the exhaust port 25. A valve 27 and a vacuum pump 28 are installed in the exhaust pipe 26 from its upstream side in this order. By adjusting the opening of the valve 27, the pressure inside the reaction tube 11 is controlled to a desired pressure.

[0024] The vertical heat treatment apparatus is provided with a control unit 30 configured by a computer, and the control unit 30 is provided with a program. This program is structured with a group of steps so that a series of processing operations described below can be performed on the wafer W by outputting control signals to each part of the vertical heat treatment apparatus 1 to control the operation of each part. Specifically, control signals are output so that the boat elevator 10 raises and lowers the lid 16, the output of the heater 19 (i.e., the temperature of the wafer W), the opening of the valve 27, the supply flow rate of each gas into the reaction tube 11 by the gas supply mechanisms 24A to 24C and 33, and the like are controlled. This program is stored in the control unit 30 in a state of being stored in a storage medium such as a hard disk, a flexible disk, a compact disk, a magnet optical disk (MO), or a memory card.

[0025] The control unit 30 controls the temperature of the heater 19, and when forming a silicon film, adjusts the temperature of the heater 19 to a temperature suitable for depositing a silicon film, and when forming a cap layer made of chlorosilane on the silicon film, adjusts the temperature of the heater 19 to a temperature suitable for forming a chlorosilane layer.

[0026] [Film forming method] 2 is a diagram for explaining an example of a method for forming a silicon film according to an embodiment of the present disclosure, with reference to FIG. 1 showing an apparatus configuration as appropriate.

[0027] An example will be described in which disilane (Si2H6) is used as the gas for forming the seed layer, monosilane (SiH4) is used as the gas for forming the silicon bulk layer, and DCS (dichlorosilane) is used as the chlorosilane gas. In this embodiment, for ease of understanding, the gas is specified for description, but the gas for forming the seed layer may be any of various gases capable of forming a seed layer, the gas for forming the silicon bulk layer may be any of various gases capable of forming a silicon bulk layer, and the chlorosilane gas may be any of various chlorosilane gases, and the types of gases are not limited to those in this embodiment.

[0028] Fig. 2(a) is a diagram showing an initial state of the wafer W. As shown in Fig. 2(a), a silicon oxide film (SiO2) is formed on the surface of the wafer W. The silicon oxide film serves as a base film.

[0029] First, the wafer W shown in FIG. 2(a) is transferred to the wafer boat 3 by a transfer mechanism (not shown) and held thereon. Then, the wafer boat 3 is placed on the lid 16 located at the lowered position. Then, the lid 16 is raised to the raised position, the wafer boat 3 is carried into the reaction tube 11, and the opening 17 of the reaction tube 11 is closed by the lid 16, making the reaction tube 11 airtight. Next, a purge gas is supplied into the reaction tube 11, and the reaction tube 11 is evacuated to a vacuum atmosphere of a predetermined pressure, and the wafer W is heated by the heater 19 to a predetermined temperature. The temperature at this time is set to a predetermined film formation temperature suitable for depositing a silicon film on the wafer W. The temperature of the heater 19 may be controlled by the control unit 30.

[0030] FIG. 2(b) illustrates an example of a seed layer forming step.

[0031] After the wafer W is heated, the supply of the purge gas is stopped, and disilane gas is supplied into the reaction tube 11. This disilane gas is deposited on the surface of the silicon oxide film 40 of the wafer W, and a seed layer 50 is formed so as to cover the silicon oxide film 43 (not shown).

[0032] FIG. 2(c) shows an example of a silicon film deposition step.

[0033] After the seed layer formation process, the supply of the purge gas is stopped, and SiH4 gas is supplied into the reaction tube 11. As shown in FIG. 2(c), the SiH4 gas is deposited on the seed layer 50, and a Si film 60 is formed on the entire surface of the wafer W so as to cover the seed layer 50. Then, the deposition of the SiH4 gas continues, and the silicon film 60 grows. That is, the thickness of the silicon film 60 increases. The silicon film 60 may be called a silicon bulk layer 60.

[0034] In the silicon film deposition process, the temperature of the heater 19 is set to a temperature suitable for forming the silicon film 60. The temperature suitable for forming the silicon film 60 is, for example, a temperature equal to or higher than 450° C. and lower than 540° C. For example, when monosilane gas is used as the silicon-containing gas, the temperature of the heater 19 may be set to 480° C. to form the silicon film 60.

[0035] Also, Si2H6 gas may be used instead of SiH2 gas. In this case, the seed layer forming process and the silicon film depositing process may be performed consecutively.

[0036] An amorphous silicon film 60 is formed on the surface of the wafer W in a silicon film deposition process.

[0037] After the supply of the SiH4 gas or Si2H6 gas is stopped, a purge gas is supplied into the reaction tube 11, and the SiH4 gas or Si2H6 gas is purged from the reaction tube 11.

[0038] 2(d) shows an example of the capping step, in which the temperature of the heater 19 is set to a temperature higher than that of the silicon film deposition step, and chlorosilane gas is supplied into the reaction tube 11 to form a cap layer 70 made of chlorosilane.

[0039] The temperature of the heater 19 in the capping step is set to a temperature suitable for forming a cap layer 70 of chlorosilane, for example, at 500° C. or higher and 700° C. or lower.

[0040] By forming the cap layer 70 of chlorosilane, the crystallization is performed while maintaining the flatness of the silicon film 60. In the capping step, a temperature is set higher than that during the deposition of the silicon film 60, and the crystallization of the silicon film 60 also progresses.

[0041] Conventionally, when crystallizing the silicon film 60, chlorosilane is not supplied, but the silicon film 60 is simply heated to crystallize the silicon film 60. In this case, crystal grains are formed on the surface of the silicon film 60, and the crystallization proceeds with the crystal grains as cores, which causes unevenness on the surface of the silicon film 60, which makes it difficult to use the silicon film 60 as a device.

[0042] In the silicon film forming method according to this embodiment, the silicon film 60 is heated while supplying chlorosilane, for example, DCS, onto the surface of the silicon film 60. Then, the silicon film 60 is crystallized while maintaining its flatness at a temperature of 550° C. to 600° C., for example, 560° C. to 580° C.

[0043] This is believed to be because chlorine has the effect of promoting crystallization without forming such crystal grains. Therefore, by performing low-temperature annealing while supplying chlorosilane, it is possible to obtain a crystallized silicon film 60 with high flatness.

[0044] 2(d), annealing may be performed at a higher temperature if necessary. In that case, it may be performed in the film forming apparatus, or the wafer W may be moved to the annealing apparatus. The additional annealing step may be set at any temperature higher than the temperature in the capping step, and may be set at a predetermined temperature within the range of 600° C. to 700° C., for example. By providing such an additional annealing step, the crystallization of the silicon film 60 can be further promoted.

[0045] FIG. 3 is a diagram showing a comparison between the silicon film formed by the silicon film forming method according to the present embodiment and other silicon films.

[0046] 3(a) is a diagram showing silicon films 60, 70 formed by the silicon film forming method according to this embodiment. By forming a cap layer 70 made of chlorosilane on the surface, crystallization of the silicon film 60 can be performed at a low temperature while maintaining flatness.

[0047] Fig. 3(b) is a diagram showing an uncrystallized silicon film. As shown in Fig. 3(b), simply depositing the silicon film 60 does not crystallize the silicon film 60, and the device is not yet completed.

[0048] Fig. 3(c) shows a silicon film crystallized by conventional heating. As shown in Fig. 3(c), if heating is performed directly after Fig. 3(b), surface 61 of silicon film 60 is crystallized. However, since crystal grains are formed on surface 61, unevenness is formed, and flat silicon film 60 cannot be crystallized. In addition, the heating temperature needs to be set to a temperature higher than 600°C.

[0049] [Example] Hereinafter, examples of the silicon film forming method according to this embodiment will be described.

[0050] FIG. 4 is a diagram for explaining the surface roughness of an example in which the silicon film forming method according to the present embodiment was carried out.

[0051] Figure 4(a) is an image showing the state of a silicon film that has just been deposited as reference data. As shown in Figure 4(a), the surface state of the amorphous silicon film is clean. However, the silicon film is not crystallized.

[0052] Figure 4(b) is an image showing the surface state when an amorphous silicon film is heated to 550°C or higher and 580°C or lower to crystallize it. As shown in Figure 4(b), crystal grains are formed on the surface. For this reason, the flatness of the surface cannot be maintained.

[0053] Figure 4(c) is an image showing the state when the silicon film forming method according to this embodiment is carried out. Here, an example is shown in which annealing is carried out while supplying chlorosilane gas at 550°C or more and 580°C or less. As shown in Figure 4(c), no crystal grains are present on the surface, and the surface remains flat.

[0054] Figure 5 shows the results of measuring surface roughness with an AFM. The vertical axis shows the average surface roughness Ra [nm] and the maximum surface roughness Rmax [nm].

[0055] FIG. 5(a) shows the state of the reference data where only a silicon film was deposited, and the average surface roughness Ra was 0.16 and the maximum average roughness Rmax was 2.08, which are low values ​​for the surface roughness.

[0056] Figure 5(b) shows an example in which a silicon film was deposited, followed by deposition of SiH4 at 580°C. In Figure 5(b), crystal grains were generated, and the average surface roughness Ra rose to 2.02, while the maximum surface roughness Rmax rose to 46.96. Thus, it was shown that when deposition is performed while supplying chlorosilane, crystallization is possible while maintaining flatness, compared to the case of depositing SiH4 at a high temperature.

[0057] 5(c) shows an example of deposition at 580° C. while supplying chlorosilane in the silicon film deposition method according to this embodiment. The average surface roughness Ra is also low at 0.18, and the maximum surface roughness Rmax is 1.70, showing that crystallization is certainly achieved while maintaining flatness.

[0058] As described above, the silicon film forming method and the silicon film forming apparatus according to the present embodiment make it possible to crystallize the silicon film while maintaining the surface flatness of the silicon film. Such flatness of the surface makes it possible to obtain good device characteristics.

[0059] Furthermore, when crystal grains are formed, if the silicon film is thin, the silicon film is pulled by the crystal grains, exposing the underlying silicon oxide film; however, the silicon film forming method and film forming apparatus according to this embodiment are applicable regardless of the thickness of the silicon film.

[0060] Although the preferred embodiments and examples of the present disclosure have been described in detail above, the present disclosure is not limited to the above-described embodiments and examples, and various modifications and substitutions can be made to the above-described embodiments and examples without departing from the scope of the present disclosure. [Explanation of symbols]

[0061] 11 Reaction tube 19 Heater 21, 31 Gas inlet pipe 23A~23C, 32 Gas supply source 24A~24C, 33 Gas supply mechanism 27 Valve 30 Control section 42 Recess 40 Silicon oxide film 50 Seed Layer 60 Silicone membrane W wafer

Claims

1. supplying a silicon-containing gas onto the seed layer to deposit an amorphous silicon film on the seed layer; supplying chlorosilane gas onto the amorphous silicon film, and crystallizing the amorphous silicon film while forming a cap layer of chlorosilane on the amorphous silicon film.

2. The amorphous silicon film is formed at a first temperature; 2. The method of claim 1, wherein the chlorosilane cap layer is formed at a second temperature higher than the first temperature.

3. the first temperature is less than 540° C.; 3. The method for forming a silicon film according to claim 2, wherein the second temperature is within a temperature range of 500° C. to 700° C.

4. The first temperature is equal to or higher than 450° C. and equal to or lower than 500° C.

4. The method for forming a silicon film according to claim 3, wherein the second temperature is 560° C. or more and 580° C. or less.

5. the silicon-containing gas is monosilane or disilane; 5. The method for forming a silicon film according to claim 1, wherein the chlorosilane gas is dichlorosilane.

6. A processing chamber; a substrate holder for holding a substrate disposed in the processing chamber; A heater for heating the substrate holder; a silicon-containing gas supply unit that supplies a silicon-containing gas to the substrate holder and deposits an amorphous silicon film on the substrate; a chlorosilane gas supply unit that supplies chlorosilane gas to the substrate holder and forms a cap layer of chlorosilane on the amorphous silicon film; a control unit that sets the heater to a first temperature when the silicon-containing gas is supplied from the silicon-containing gas supply unit, and sets the heater to a second temperature higher than the first temperature when the chlorosilane gas is supplied from the chlorosilane gas supply unit, the second temperature is a temperature that crystallizes the amorphous silicon film while forming a cap layer of the chlorosilane on the amorphous silicon film; Film deposition equipment.

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