Method for forming polycrystalline silicon film

Abstract

To provide a technology that can form a film of polycrystalline silicon having a large grain size.SOLUTION: A method for forming a polycrystalline silicon film includes the steps of: forming a first amorphous silicon film having an island shape on a substrate; forming a second amorphous silicon film that covers the first amorphous silicon film; forming a third amorphous silicon film on the second amorphous silicon film; and heating the substrate to a first temperature. The first amorphous silicon film is a film that is crystallized at a lower temperature than the second amorphous silicon film, and the first temperature is a temperature at which the first amorphous silicon film is more easily crystallized than the second amorphous silicon film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for forming a polycrystalline silicon film. [Background technology]

[0002] A technique is known in which an amorphous silicon film doped with impurities that suppress the progress of crystallization and an undoped amorphous silicon film are stacked in this order on an insulating film, and then the stacked amorphous silicon films are crystallized (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-255894 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides a technique that allows for the formation of large-grain polycrystalline silicon films. [Means for solving the problem]

[0005] A method for forming a polycrystalline silicon film according to one embodiment of the present disclosure includes the steps of forming a first amorphous silicon film having an island shape on a substrate, forming a second amorphous silicon film covering the first amorphous silicon film, forming a third amorphous silicon film on the second amorphous silicon film, and heating the substrate to a first temperature, wherein the first amorphous silicon film is a film that crystallizes at a lower temperature than the second amorphous silicon film, and the first temperature is a temperature at which the first amorphous silicon film crystallizes more easily than the second amorphous silicon film. [Effects of the Invention]

[0006] According to the present disclosure, a polycrystalline silicon film with a large grain size can be formed. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a flowchart illustrating a method for forming a polycrystalline silicon film according to an embodiment. [Figure 2] 1A and 1B are cross-sectional views illustrating steps in a method for forming a polycrystalline silicon film according to an embodiment of the present invention; [Figure 3] 1A and 1B are cross-sectional views illustrating steps in a method for forming a polycrystalline silicon film according to an embodiment of the present invention; [Figure 4] 1A and 1B are cross-sectional views illustrating steps in a method for forming a polycrystalline silicon film according to an embodiment of the present invention; [Figure 5] 4 is a cross-sectional view showing a process of forming a polycrystalline silicon film according to an embodiment of the present invention; [Figure 6] 1 is a schematic diagram showing an example of a processing apparatus for performing a method for forming a polycrystalline silicon film according to an embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, non-limiting exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. In all the accompanying drawings, the same or corresponding reference numerals are used to designate the same or corresponding members or components, and redundant descriptions will be omitted.

[0009] [Method for forming polycrystalline silicon film] A method for forming a polycrystalline silicon film according to an embodiment will be described with reference to Figures 1 to 5. In the following, an example will be described in which a polycrystalline silicon film is formed on an insulating film formed on a substrate.

[0010] As shown in FIG. 1, the method for forming a polycrystalline silicon film according to the embodiment includes performing a first film-forming step S1, a second film-forming step S2, a third film-forming step S3, and a crystallization step S4 in this order.

[0011] (First film formation step S1) As shown in FIG. 2, the first film formation process S1 includes forming a first amorphous silicon film 121 having an island shape on an insulating film 110 formed on the surface of a substrate 100. The first amorphous silicon film 121 is a film that crystallizes at a lower temperature than a second amorphous silicon film 122 (described later). The first amorphous silicon film 121 is formed by supplying a first silicon-containing gas to the substrate 100. Monosilane (SiH4) is preferably used as the first silicon-containing gas. The first film formation process S1 is preferably performed in a process chamber maintained at a higher pressure than the second film formation process S2. This allows the thermal decomposition temperature of the first silicon-containing gas to be lower. For example, in a commonly used pressure range (e.g., 1 Pa or higher and 1000 Pa or lower), the thermal decomposition temperature of monosilane is approximately 450°C to 530°C, while the thermal decomposition temperature of disilane, an example of a higher order silane (described later), is approximately 350°C to 420°C. Therefore, when the first film formation process S1 is performed in a processing chamber maintained at the same pressure as the second film formation process S2, the film formation temperature of the first film formation process S1 is set to a temperature higher than the film formation temperature of the second film formation process S2. On the other hand, by performing the first film formation process S1 in a processing chamber maintained at a higher pressure than the second film formation process S2, the thermal decomposition temperature of monosilane can be lowered. For example, by performing the first film formation process S1 in a processing chamber maintained at a pressure of 1.3 kPa to 13 kPa (10 Torr to 100 Torr), monosilane can be thermally decomposed at a temperature of 350°C to 420°C. As a result, the first film formation process S1 and the second film formation process S2 can be performed at the same temperature. The preferred process conditions for the first film formation process S1 are as follows:

[0012] First silicon-containing gas: monosilane Substrate temperature: 350℃ or more and 420℃ or less Pressure inside the treatment vessel: 1.3kPa or more and 13kPa or less

[0013] (Second film formation process S2) As shown in FIG. 3, the second film formation process S2 includes forming a second amorphous silicon film 122 covering the first amorphous silicon film 121. The second amorphous silicon film 122 is formed by supplying a second silicon-containing gas to the substrate 100. As the second silicon-containing gas, a high-order silane gas containing two or more silicon (Si) atoms in one molecule can be suitably used. The high-order silane gas has a large number of silicon atoms in one molecule, allowing smooth film formation at low temperatures. Therefore, by using a high-order silane gas, the second amorphous silicon film 122 is formed so as to cover the insulating film 110 and the first amorphous silicon film 121. Examples of high-order silane gases include disilane (Si2H6), trisilane (Si3H8), and tetrasilane (Si4H 10 ) or a mixed gas of two or more of these. The preferred process conditions for the second film-forming step S2 are as follows.

[0014] Second silicon-containing gas: disilane Substrate temperature: 350℃ or more and 420℃ or less Pressure inside the processing vessel: 1 Pa or more and 1000 Pa or less

[0015] (Third film formation process S3) As shown in FIG. 4, the third film-forming step S3 includes forming a third amorphous silicon film 123 on the second amorphous silicon film 122. The third amorphous silicon film 123 is formed by supplying a third silicon-containing gas to the substrate 100. Examples of the third silicon-containing gas include monosilane, a higher-order silane gas, a halogen-containing silicon gas, or a mixture of two or more of these. Examples of the halogen-containing silicon gas include fluorine-containing silicon gases such as SiF, SiHF, SiH, F, and SiH; chlorine-containing silicon gases such as SiCl, SiHCl, SiHCl (DCS), and SiHCl; and bromine-containing gases such as SiBr, SiHBr, SiHBr, and SiHBr. Monosilane is preferably used as the third silicon-containing gas because of its high film-forming rate and low cost. The third film-forming step S3 may be performed at the same temperature as the second film-forming step S2, or may be performed at a temperature different from that of the second film-forming step S2. The preferred process conditions for the third film-forming step S3 are as follows.

[0016] Third silicon-containing gas: monosilane Substrate temperature: 450℃ or higher and 530℃ or lower Pressure inside the processing vessel: 1 Pa or more and 1000 Pa or less

[0017] (Crystallization step S4) The crystallization step S4 includes heating the substrate 100 to a first temperature to crystallize the first amorphous silicon film 121, the second amorphous silicon film 122, and the third amorphous silicon film 123, thereby forming a polycrystalline silicon film. The first temperature is a temperature at which the first amorphous silicon film 121 crystallizes more easily than the second amorphous silicon film 122. In this case, as shown in FIG. 5, the crystallization of the first amorphous silicon film 121, the second amorphous silicon film 122, and the third amorphous silicon film 123 progresses with the island-shaped first amorphous silicon film 121 as a nucleus. As a result, a polycrystalline silicon film with a large grain size can be formed. Note that reference numeral 124 in FIG. 5 schematically illustrates the grain boundaries between adjacent single-crystal regions. For example, when monosilane gas is used in the first film-forming step S1 and disilane gas is used in the second film-forming step S2, the first temperature may be 550° C. or higher and 600° C. The crystallization step S4 is performed in an inert gas atmosphere such as a nitrogen atmosphere or an argon atmosphere, or a reducing gas atmosphere such as a hydrogen atmosphere.

[0018] According to the method for forming a polycrystalline silicon film of the embodiment described above, first, a first amorphous silicon film 121 having an island shape is formed on the substrate 100. Next, a second amorphous silicon film 122 is formed to cover the first amorphous silicon film 121. Next, a third amorphous silicon film 123 is formed on the second amorphous silicon film 122. Next, the substrate 100 is heated to a first temperature. The first amorphous silicon film 121 is a film that crystallizes at a lower temperature than the second amorphous silicon film 122, and the first temperature is a temperature at which the first amorphous silicon film 121 crystallizes more easily than the second amorphous silicon film 122. As a result, crystallization of the first amorphous silicon film 121, the second amorphous silicon film 122, and the third amorphous silicon film 123 progresses with the island-shaped first amorphous silicon film 121 as a nucleus. As a result, a polycrystalline silicon film with a large grain size can be formed.

[0019] [Processing device] An example of a processing apparatus for carrying out the method for forming a polycrystalline silicon film according to the embodiment will be described with reference to Fig. 6. The processing apparatus 1 is a batch-type apparatus that processes a plurality of substrates at once. The substrates may be, for example, semiconductor wafers (hereinafter simply referred to as "wafers W").

[0020] The processing apparatus 1 includes a processing vessel 10, a gas supply unit 30, an exhaust unit 40, a heating unit 50, a control unit 80, and the like.

[0021] The processing vessel 10 can be depressurized and accommodates a wafer W. The processing vessel 10 has a cylindrical inner tube 11 with a ceiling and an open lower end, and a cylindrical outer tube 12 with a ceiling and an open lower end that covers the outside of the inner tube 11. The inner tube 11 and the outer tube 12 are made of a heat-resistant material such as quartz, and are arranged coaxially to form a double-tube structure.

[0022] The ceiling of the inner pipe 11 is, for example, flat. A storage section 13 for storing a gas nozzle is formed on one side of the inner pipe 11 along its longitudinal direction (vertical direction). The storage section 13 is an area within a protrusion 14 formed by protruding part of the side wall of the inner pipe 11 outward.

[0023] A rectangular opening 15 is formed in the side wall of the inner tube 11 opposite the housing portion 13 along its longitudinal direction (vertical direction).

[0024] The opening 15 is a gas exhaust port formed so as to be able to exhaust gas from the inner tube 11. The length of the opening 15 is the same as the length of the wafer boat 16, or is formed so as to extend in the vertical direction longer than the length of the wafer boat 16.

[0025] The lower end of the processing vessel 10 is supported by a cylindrical manifold 17 made of, for example, stainless steel. A flange 18 is formed at the upper end of the manifold 17, and the lower end of the outer tube 12 is placed on the flange 18 to support it. A seal member 19 such as an O-ring is interposed between the flange 18 and the lower end of the outer tube 12 to keep the inside of the outer tube 12 airtight.

[0026] An annular support 20 is provided on the inner wall of the upper portion of the manifold 17, and the lower end of the inner tube 11 is placed and supported on the support 20. A lid 21 is airtightly attached to the opening at the lower end of the manifold 17 via a sealing member 22 such as an O-ring, so as to airtightly close the opening at the lower end of the processing vessel 10, i.e., the opening of the manifold 17. The lid 21 is made of, for example, stainless steel.

[0027] A rotating shaft 24 that rotatably supports the wafer boat 16 via a magnetic fluid seal 23 penetrates the center of the lid 21. A lower portion of the rotating shaft 24 is rotatably supported by an arm 25A of a lifting mechanism 25 that is a boat elevator.

[0028] A rotating plate 26 is provided at the upper end of the rotating shaft 24, and a wafer boat 16 holding wafers W is placed on the rotating plate 26 via a quartz heat retention table 27. Therefore, by raising and lowering the lifting mechanism 25, the lid 21 and the wafer boat 16 move up and down as a unit, allowing the wafer boat 16 to be inserted into and removed from the processing vessel 10. The wafer boat 16 can be accommodated in the processing vessel 10, and holds a plurality of wafers W (e.g., 50 to 150 wafers) approximately horizontally with spacing between them in the vertical direction.

[0029] The gas supply unit 30 supplies process gases used in the first film formation process S1, the second film formation process S2, and the third film formation process S3 described above into the inner tube 11. The process gases include a first silicon-containing gas, a second silicon-containing gas, a third silicon-containing gas, a purge gas, etc. The gas supply unit 30 has a gas nozzle 31.

[0030] The gas nozzle 31 is made of, for example, quartz, and is provided inside the inner tube 11 along its longitudinal direction, with its base end bent into an L-shape and supported so as to penetrate through the manifold 17. The gas nozzle 31 has a plurality of gas holes 32 formed along its longitudinal direction, and discharges processing gas from the gas holes 32 in a horizontal direction. The plurality of gas holes 32 are arranged at intervals equal to the intervals between wafers W supported on the wafer boat 16, for example. A processing gas with a controlled flow rate is introduced into the gas nozzle 31.

[0031] 6 shows a case where the gas supply unit 30 has one gas nozzle 31, the form of the gas supply unit 30 is not limited thereto, and for example, the gas supply unit 30 may have a plurality of gas nozzles. In this case, the first silicon-containing gas, the second silicon-containing gas, the third silicon-containing gas, and the purge gas may be supplied into the inner pipe 11 from the same gas nozzle or from different gas nozzles.

[0032] The exhaust unit 40 exhausts gas that is discharged from the inner tube 11 through the opening 15 and then discharged from a gas outlet 41 via a space P1 between the inner tube 11 and the outer tube 12. The gas outlet 41 is formed on the side wall of the upper part of the manifold 17, above the support unit 20. An exhaust passage 42 is connected to the gas outlet 41. A pressure adjustment valve 43 and a vacuum pump 44 are sequentially disposed in the exhaust passage 42, so that the inside of the processing vessel 10 can be exhausted.

[0033] The heating unit 50 is provided around the outer tube 12. The heating unit 50 is provided, for example, on the base plate 28. The heating unit 50 has a cylindrical shape so as to cover the outer tube 12. The heating unit 50 includes, for example, a heating element and heats the wafer W in the processing vessel 10.

[0034] The control unit 80 controls the operation of each unit of the processing device 1. The control unit 80 may be, for example, a computer. A computer program that controls the operation of each unit of the processing device 1 is stored in a storage medium 90. The storage medium 90 may be, for example, a flexible disk, a compact disk, a hard disk, a flash memory, a DVD, or the like.

[0035] [Operation of the Processing Device] A description will be given of a case where the method for forming a polycrystalline silicon film according to the embodiment is carried out in the processing apparatus 1. The method for forming a polycrystalline silicon film described below is carried out by a control unit 80 controlling the operation of each unit of the processing apparatus 1.

[0036] First, wafer boat 16 loaded with a plurality of wafers W is loaded into processing vessel 10. Next, the opening at the bottom end of manifold 17 is closed with lid 21, thereby making the interior of processing vessel 10 an airtight space.

[0037] Next, the first film formation process S1 is performed. In the first film formation process S1, the processing chamber 10 is first evacuated to maintain a first process pressure, and the power supplied to the heating unit 50 is controlled to raise the wafer temperature to a first process temperature. The first process pressure is set to, for example, 1.3 kPa or more and 13 kPa or less. The first process temperature is set to, for example, 350°C or more and 420°C or less. After the processing chamber 10 is stabilized at the first process pressure and the wafer temperature is stabilized at the first process temperature, monosilane is supplied as a first silicon-containing gas into the processing chamber 10 while rotating the wafer boat 16. This forms island-shaped first amorphous silicon films 121 on the wafers W. After the island-shaped first amorphous silicon films 121 are formed on the wafers W, the supply of the first silicon-containing gas into the processing chamber 10 is stopped. Note that the rotation of the wafer boat 16 continues.

[0038] Next, the second film formation process S2 is performed. In the second film formation process S2, the pressure inside the process chamber 10 is first adjusted from the first process pressure to the second process pressure, and the power supplied to the heating unit 50 is controlled to adjust the wafer temperature to the second process temperature. The second process pressure is set to, for example, 1 Pa or more and 1000 Pa or less. The second process temperature is set to, for example, the same as the first process temperature. This eliminates the need for temperature changes in the second film formation process S2, thereby improving productivity. However, the second process temperature may be different from the first process temperature. After the pressure inside the process chamber 10 is stabilized at the second process pressure and the wafer temperature is stabilized at the second process temperature, disilane is supplied as a second silicon-containing gas into the process chamber 10 while the wafer boat 16 continues to rotate. This forms a second amorphous silicon film 122 covering the first amorphous silicon film 121. After the first amorphous silicon film 121 is completely covered with the second amorphous silicon film 122, the supply of the second silicon-containing gas into the processing chamber 10 is stopped. Note that the wafer boat 16 continues to rotate.

[0039] Next, the third film formation process S3 is performed. In the third film formation process S3, the pressure inside the processing chamber 10 is first adjusted from the second process pressure to the third process pressure, and the wafer temperature is adjusted to the third process temperature by controlling the power supplied to the heating unit 50. The third process pressure is set to, for example, 1 Pa or more and 1000 Pa or less. The third process temperature may be the same as or different from the second process temperature. After the pressure inside the processing chamber 10 is stabilized at the third process pressure and the wafer temperature is stabilized at the third process temperature, monosilane is supplied as a third silicon-containing gas into the processing chamber 10 while the wafer boat 16 continues to rotate. As a result, a third amorphous silicon film 123 is formed on the second amorphous silicon film 122. The third amorphous silicon film 123 is formed to be thicker than the second amorphous silicon film 122, for example. After the third amorphous silicon film 123 having a desired thickness is formed, the supply of the third silicon-containing gas into the processing chamber 10 is stopped. The wafer boat 16 continues to rotate.

[0040] Next, a crystallization step S4 is performed. In the crystallization step S4, the inside of the processing chamber 10 is first adjusted to an inert gas atmosphere, and the wafer temperature is adjusted to a fourth process temperature by controlling the power supplied to the heating unit 50. The inert gas atmosphere may be, for example, a nitrogen atmosphere or an argon atmosphere. Alternatively, a reducing gas atmosphere such as a hydrogen atmosphere may be used instead of the inert gas atmosphere. The fourth process temperature is set to a temperature at which the first amorphous silicon film 121 is more easily crystallized than the second amorphous silicon film 122, for example, 550°C to 600°C. This allows the first amorphous silicon film 121, the second amorphous silicon film 122, and the third amorphous silicon film 123 to crystallize, with the island-shaped first amorphous silicon film 121 acting as a nucleus. As a result, a polycrystalline silicon film with a large grain size can be formed.

[0041] After the polycrystalline silicon film is formed, the wafer W is unloaded from the processing chamber 10 in the reverse order of the procedure for loading the wafer W into the processing chamber 10.

[0042] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive, and the above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

[0043] In the above embodiment, the processing apparatus is a batch type apparatus that processes multiple wafers at once, but the present disclosure is not limited to this. For example, the processing apparatus may be a single-wafer type apparatus that processes wafers one by one. [Explanation of symbols]

[0044] 100 boards 121 First amorphous silicon film 122 Second amorphous silicon film 123 Third amorphous silicon film S1 1st film formation process S2 2nd film formation process S3 Third film formation process S4 Crystallization process

Claims

1. forming a first amorphous silicon film having an island shape on a substrate; forming a second amorphous silicon film covering the first amorphous silicon film; forming a third amorphous silicon film on the second amorphous silicon film; heating the substrate to a first temperature; and the first amorphous silicon film is a film that crystallizes at a lower temperature than the second amorphous silicon film, the first temperature is a temperature at which the first amorphous silicon film is more easily crystallized than the second amorphous silicon film; A method for forming a polycrystalline silicon film.

2. The first amorphous silicon film is formed by depositing SiH ４ It is formed by supplying a gas, the second amorphous silicon film is formed by supplying a high-order silane gas to the substrate; 2. The method for forming a polycrystalline silicon film according to claim 1.

3. The higher silane gas is disilane, trisilane, tetrasilane, or a mixed gas of two or more thereof.

3. The method for forming a polycrystalline silicon film according to claim 2.

4. The first temperature is 550°C or higher and 600°C or lower.

4. The method for forming a polycrystalline silicon film according to claim 1.

5. the step of forming the first amorphous silicon film is performed in a processing chamber maintained at a higher pressure than the step of forming the second amorphous silicon film; 5. The method for forming a polycrystalline silicon film according to claim 1.

6. the step of forming the first amorphous silicon film and the step of forming the second amorphous silicon film are performed at the same temperature; 6. The method for forming a polycrystalline silicon film according to claim 1.

7. an insulating film is formed on the substrate, the first amorphous silicon film is formed on the insulating film; 7. The method for forming a polycrystalline silicon film according to claim 1.

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