WO2009002028A2

WO2009002028A2 - Method and apparatus for depositing thin film

Info

Publication number: WO2009002028A2
Application number: PCT/KR2008/003234
Authority: WO
Inventors: Hai-Won Kim; Sang-Ho Woo; Sung-Kil Cho; Keun-Hee Lee
Original assignee: Eugene Technology Co., Ltd.
Priority date: 2007-06-22
Filing date: 2008-06-11
Publication date: 2008-12-31
Also published as: TWI466176B; WO2009002028A3; KR100943426B1; TW200901290A; KR20080112736A

Abstract

Disclosed is a method of depositing a thin film on a substrate loaded in a chamber by chemical vapor deposition (CVD). Source gas including silicon-based gas and nitrogen-based gas is supplied into a chamber. Polycrystalline silicon is deposited on the substrate by the source gas. A mixing ratio of the nitrogen-based gas to the silicon-based gas may be less than 0.05. When the mixing ratio of the nitrogen-based gas is excessive, silicon nitride (SixNy) containing a large amount of silicon is deposited on the substrate. The silicon-based gas may be silane (SiH4) or disilane (Si2H6). The nitrogen-based gas may be ammonia (NH3). According to the method, polycrystalline silicon having very fine size can be deposited and degradation of characteristics can be prevented by improving evenness of electrical characteristic.

Description

METHOD AND APPARATUS FOR DEPOSITING THIN FILM

Technical Field

[1] The present invention relates to method and apparatus for depositing a thin film on a substrate, and more particularly, to method and apparatus for depositing a thin film on a substrate by chemical vapor deposition. Background Art

[2] A semiconductor device includes many layers on a silicon substrate (wafer). The layers are deposited on the substrate through a deposition process. The deposition process is usually divided into two categories, in other words, chemical vapor deposition (CVD) and physical vapor deposition (PVD). In the each deposition process, the wafer is placed in a deposition chamber and a thin film is formed by supplying a component for the thin film in a gas state to the surface of the wafer. In the chemical vapor deposition, reacting gases are supplied into the deposition chamber and the thin film is formed on the surface of the wafer by chemical reaction between the reaction gases.

[3] Polycrystalline silicon used as a gate electrode can be deposited by the following process. First, a wafer is loaded in a deposition chamber and then a thin film is deposited on the wafer by supplying source gas in the chamber. In this time, the source gas supplied in the chamber includes silane (SiH₄) and the thin film is deposited on the wafer by the source gas supplied in the chamber. In this time, the polycrystalline silicon film is deposited on the wafer by thermal decomposition of the silane (SiH₄).

[4] However, by the above described deposition process, it has been difficult to deposit not only a polycrystalline silicon film having silicon crystal structure of thin thickness (less than about 400A) but also an uniform polycrystalline silicon film. Accordingly, when the polycrystalline silicon film is used as a floating gate electrode of a semiconductor flash memory, there is caused a problem such as over erase phenomenon in a manufactured device. Accordingly, evenness, durability and reliability of the device are degraded by threshold voltage shift and very uneven threshold voltage Vt. Thus, characteristics of the device are degraded.

[5] More particularly, first an amorphous silicon thin film is grown at a constant process temperature (usually less than 55⁰C) by using silane (SiH₄) or disilane (Si₂H₆) and then the grown thin film is crystallized by a predetermined heat treatment process (for example, 65O⁰C to 900⁰C). Thus, results as shown in FIGS 1 and 2 are obtained. FIGS 1 and 2 are photographs of the polycrystalline silicone film according to the conventional deposition process, which are taken by a Transmission Electron Microscope (TEM).

[6] When the gate electrode of the device such as the flash memory is formed by the above described process, grain sizes of crystallized grains of the thin film are very irregular and crystal grains having sizes of tens of A or few hundreds of nm are formed. Accordingly, when a transistor is formed by using the thin film, one or two grain boundaries are formed in regions where the size of the grain is large, and on the contrary, many grain boundaries are formed in regions where the size of the grain is very small. Therefore, an oxide valley region is formed by tunnel oxide under the region where the crystal grains are contacted to each other. A larger oxide valley is formed under an interface between large crystal grains. Accordingly, more phosphorus are concentrated in the subsequent process of forming phosphorus polycrystalline silicon to reduce a local barrier height. Thus, it may causes reliability of the device to be largely degraded because the over erase point or electron trap formation site is formed by phosphorus at the time of driving the device. In addition, the difference between moving speeds of electrons causes differences of driving power between transistors. Accordingly, there has been a problem that characteristics of the device are largely degraded because driving powers of transistors included in one chip are largely different from each other when the deivec is driven. Disclosure of Invention

Technical Problem

[7] Accordingly, an object of the present invention is to provide a thin film deposition method that can deposit a thin film having a crystal structure formed of very fine grains.

[8] Additional advantages, objects and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. Technical Solution

[9] According to an aspect of the present invention, there is provided a method of depositing a thin film on a substrate, which includes: depositing a thin film by supplying source gas in a chamber loaded with the substrate, where the source gas includes silicon-based gas and nitrogen-based gas.

[10] A mixing ratio of the nitrogen-based gas to the silicon-based gas may be less than

0.05.

[11] In addition, a content of the nitrogen in the thin film may be less than 10at% (atomic percentage).

[12] On the other hand, pressure of the deposition process may be 100 to 300torr when a temperature of the deposition process is 580 to 65O⁰C.

[13] In addition, the pressure of the deposition process may be 5 to lOOtorr when the temperature of the deposition process is 650 to 75O⁰C.

[14] In addition, the method may further include a heat treatment process for the thin film deposited on the substrate.

[15] The thin film may be polycrystalline silicon.

[16] The silicon-based gas may be silane (SiH₄) or disilane (Si₂H₆).

[17] The nitrogen-based gas may be ammonia (NH₃).

[18] According to another aspect of the present invention, there is provided a method of depositing a thin film on a substrate, which includes: depositing a columnar thin film by supplying source gas in a chamber loaded with the substrate, where the source gas is silicon-based gas, and pressure of the deposition process is less than lOtorr when a temperature of the deposition process is 640 to 68O⁰C.

[19] According to a still another aspect of the present invention, there is provided a method of depositing a thin film on a substrate, which includes: depositing crystalline and amorphous thin film by supplying source gas in a chamber loaded with the substrate, where the source gas is silicon-based gas, and a pressure of the deposition process is 10 to 50torr when a temperature of the deposition process is 640 to 68O⁰C.

[20] According to a further still another aspect of the present invention, there is provided a method of depositing a thin film on a substrate, which includes: depositing an amorphous thin film by supplying source gas in a chamber loaded with the substrate, where the source gas is silicon-based gas, and pressure of the deposition process is more than 50torr when a temperature of the deposition process is 640 to 68O⁰C.

Advantageous Effects

[21] According to the thin film deposition method, the polycrystalline silicon thin film having the very fine crystal grain structure can be deposited in the single wafer type chamber by the chemical vapor deposition process. Silane (SiH₄) gas is used as the silicon source gas. The polycrystalline silicon thin film containing very fine crystallized grains is formed by mixing nitrogen-containing gas such as NH₃ with SiH₄ in a predetermined ratio and supplying and depositing the mixture under predetermined process temperature and pressure.

[22] The method of depositing the polycrystalline silicon thin film according to the present invention produces the following effects.

[23] First, when the polycrystalline silicon thin film is used as the electrode for the floating gate of the flash memory in the semiconductor device, uniform crystal grains are formed. Thus, durability and reliability of the device can be improved.

[24] Second, when the polycrystalline silicon thin film is used in DRAM, SRAM or LOGIC device, excellent device characteristics can be secured. Thus, yield and characteristics of the semiconductor device manufactured by using the polycrystalline silicon thin film are improved. Brief Description of the Drawings

[25] FIGS. 1 and 2 are photographs illustrating a polycrystalline silicon thin film according to a conventional deposition method;

[26] FIG. 3 is a view illustrating a deposition apparatus for performing a deposition process according to one exemplary embodiment of the present invention;

[27] FIG. 4 is a graph illustrating a refractive index of a thin film deposited according to pressure and temperature conditions;

[28] FIGS. 5, 6, 7 and 8 are photographs illustrating crystal structures of thin films deposited according to the exemplary embodiment; and

[29] FIG. 9 is a photographs illustrating a crystal structure of a thin films deposited according to another exemplary embodiment. Best Mode for Carrying Out the Invention

[30] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawing. The aspects and features of the present invention and methods for achieving the aspects and features will be apparent by referring to the embodiments to be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed hereinafter, but can be implemented in diverse forms. The matters defined in the description, such as the detailed construction and elements, are nothing but specific details provided to assist those of ordinary skill in the art in a comprehensive understanding of the invention, and the present invention is only defined within the scope of the appended claims. In the entire description of the present invention, the same drawing reference numerals are used for the same elements across various figures.

[31] Accoridng to one exemplarly embodiment of the present invention, a thin film having a fine columnar crystalline structure is deposited on a semiconductor device in a single chamber by a chemical vapor deposition process. Generally, the "chemical vapor deposition" is a process of forming a thin film on a semiconductor substrate by supplying source gas to the substrate and inducing chemical reaction between the source gas and substrate. Referring to FIG. 3, the thin film deposition according to the embodiment is performed in a single chamber by the chemical vapor deposition. FIG. 3 shows a deposition apparatus 10 for performing a deposition process according to the embodiment.

[32] A chamber 11 includes an internal space isolated from the outside. An introducing unit 12 is provided at an upper part of the chamber to introduce source gas in the internal space. A main supply line 12a and first and second supply lines 18a and 19a are connected to the introducing unit 12. The first supply line 18a supplies a first source gas in the chamber 11, and the second supply line 18b supplies a second source gas in the chamber 11. The first source gas is silicon-based gas including silane or disilane, and the second source gas is nitrogen-based gas including ammonia. However, only one source gas may be supplied into the chamber 11. In addition, a first flow rate controller 18b and a first valve 18c are provided on the first supply line 18a, and a second flow rate controller 19b and a second valve 19c are provided on the second supply line 19a. On the other hand, gas supplied through the introducing unit 12 is ejected into the chamber 11 through a shower head 13. In addition, a wafer 15 for deposition is placed on a heater 14 supported by a heater support 16.

[33] When deposition is completed, unreacted gas and by-products in the chamber 11 are discharged through a vacuum port 17. A discharge line 17a and a vacuum pump 17b are connected to the vacuum port 17 to discharge the unreacted gas and by-products in the chamber 11 forcibly. In addition, the process pressure in the chamber 11 can be controlled by using the discharge line 17a and vacuum pump 17b. The source gas is supplied to the substrate in the chamber 11 by the above described process and a thin film is deposited on the substrate by reaction gas decomposed by thermal decomposition. On the other hand, the heater 14 for controlling the process temperature, the vacuum pump 17b for controlling the process pressure, and the first and second flow rate controllers 18b and 19b for controlling supply amounts (or mixing ratio) of the first and second source gases are controlled by a controller 20.

[34] FIG. 4 is a graph illustrating refractive index of a thin film deposited according to pressure and temperature conditions. Referring to FIG. 4, a horizontal axis corresponds to a process temperature and a vertical axis corresponds to refractive index (R.I.) indicating crystalline characteristic of the deposited thin film. The refractive index value near 4.5 indicates growth of more amorphous silicon thin film. On the other hand, the refractive index value near 4.0 indicates growth of crystalline structure near a crystallized polycrystalline silicon thin film.

[35] On the other hand, the crystalline structure means a solid that has three-dimensional periodicity in an atomic arrangement thereof. A solid having no the periodicity is referred to as "non-crystalline (amorphous) material". A semiconductor using the above described amorphous state includes non-crystalline silicon. The amorphous semiconductor is used in a thin film transistor because it can be deposited in a large area at a low temperature.

[36] Referring to FIG. 4, the measured refractive index is changed according to pressure in a temperature range of 640 to 685⁰C. For example, when the temperature is 655⁰C and the source gas supplied during the process is constant, the measured refractive index is near 4.0 under process pressure lower than lOtorr. Accordingly, a columnar poly crystalline silicon thin film is formed. On the other hand, when the process pressure is higher than lOOtorr, the measured refractive index becomes near 4.5. Accordingly, an amorphous polycrystalline silicon thin film is formed. For another example, even if the process is performed in the lower pressure at the process temperature higher than 685⁰C when the supplied source gas is constant, the amorphous silicone thin film cannot be formed any more as shown in the graph. In other words, the polycrystalline silicon thin film is formed in the pressure less than lOtorr at the process temperature of 685⁰C. In addition, the measured refractive index becomes near 4.0 even under the process pressure more than lOOtorr. Thus, it can be considered that the polycrystalline silicon thin film is formed.

[37] Surface roughness is used as a coefficient for evaluating performance of the deposited thin film. In the present invention, the surface roughness was measured by using an AFM (Atomic Force Microscopy) and RMS (Root Mean Square) calculation method. As a result, the case having the roughness of "2" was most desirable.

[38] FIGS. 5 and 6 show crystalline structures of crystalline silicon thin films deposited under a process temperature of 685⁰C and pressure of lOtorr, and FIGS. 7 and 8 show crystalline structures of crystalline silicon thin films deposited under a process temperature of 73O⁰C and pressure of lOtorr.

[39] In the above embodiment, silane was used as the source gas. However, columnar crystalline grains, crystalline structure including isometric grains or amorphous silicon thin film, or amorphous silicon thin film may be formed by using disilane as other source gas under constant temperature and pressure without departing from the spirit and scope of the present invention.

[40] Referring to FIG. 3, another embodiment of the present invention will be explained below.

[41] First, the introducing unit 12 is formed in the chamber 11 to supply the source gas.

Gas supplied through the introducing unit 12 is ejected into the chamber 11 through the shower head 13. In addition, the wafer 15 for deposition is placed on the heater 14 supported by the heater support 16. After the deposition is completed by the device, the gas is discharged through the vacuum port 17. By the chemical vapor deposition method using the single wafer, silane (SiH₄) gas is supplied to the substrate in the chamber. Then, reaction gas decomposed by thermal decomposition is deposited on a silicone substrate provided on the substrate through movement on the surface.

[42] In this time, when ammonia is injected into the chamber at a predetermined ratio simultaneously with silane, nucleation and grain growth of silicon atoms of thermally decomposed reaction gas do not occur due to nitrogen atoms decomposed from ammonia. Accordingly, amorphous polysilicon can be deposited even at a high temperature more than 65O⁰C. In this time, when a mixing ratio of NH₃/SiH₄ is kept more than a predetermined level, silicon nitride (Si_xN_y) may be deposited. Accordingly, the mixing ratio of the two gases is the most important factor in the present invention. Concentrations (at%) and grain sizes of nitrogen in a table below show tendency according to the mixing ratio of NH₃/SiH₄.

[43] Table 1 [Table 1] [Table ]

[44] As shown in the table, the grain size is decreased when ammonia is mixed. In other words, the grain size is decreased according to increase of the mixing ratio of ammonia (the mixing ratio gradually increases toward the right direction in the table). Thus, very fine and uniform grains can be formed by mixing ammonia.

[45] However, when the mixing ratio of ammonia is excessively increased, the thin film deposited on the wafer may become not polysilicon thin film but silicon nitride (SixNy). Accordingly, it is desirable that the mixing ratio of the nitrogen-based gas to the silicon-based gas is less than 0.05, and the content of nitrogen in the thin film is less than 10at%. Polycrystalline polysilicon thin film having a very fine grain structure is formed through a subsequent heating process at a temperature higher than a predetermined temperature by using a furnace or a single wafer type reaction chamber. FIG. 9 is a TEM photograph illustrating the polycrystalline polysilicon thin film having the very fine grain structure deposited according to the embodiment.

[46] In the above embodiment, silane was used as the source gas. However, the polycrystalline polysilicon thin film having the very fine grain structure may be formed by using disilane (Si₂H₆) gas as other source gas and injecting a predetermined mixing ratio of NH₃/SiH₄ into the reaction chamber under constant temperature and pressure. Industrial Applicability

[47] The polycrystalline silicon thin film can be used in DRAM, SRAM or LOGIC device. Yield and characteristics of the semiconductor device manufactured by using the polycrystalline silicon thin film are improved due to excellent device characteristics thereof.

Claims

[I] A method of depositing a thin film on a substrate, comprising: depositing a thin film by supplying source gas in a chamber loaded with the substrate, where the source gas includes silicon-based gas and nitrogen-based gas.

[2] The thin film deposition method of claim 1, wherein a mixing ratio of the nitrogen-based gas to the silicon-based gas is less than 0.05.

[3] The thin film deposition method of claim 1, wherein a content of the nitrogen in the thin film is less than 10at% (atomic percentage).

[4] The thin film deposition method of claim 1, wherein pressure of the deposition process is 100 to 300torr when a temperature of the deposition process is 580 to 65O⁰C.

[5] The thin film deposition method of claim 1, wherein the pressure of the deposition process is 5 to lOOtorr when the temperature of the deposition process is 650 to 75O⁰C.

[6] The thin film deposition method of claim 1, further comprising a heat treatment process for the thin film deposited on the substrate.

[7] The thin film deposition method of claim 1, wherein the thin film is poly- crystalline silicon.

[8] The thin film deposition method of claim 1, wherein the silicon-based gas is silane (SiH₄) or disilane (Si₂H₆).

[9] The thin film deposition method of claim 1, wherein the nitrogen-based gas is ammonia (NH₃).

[10] A method of depositing a thin film on a substrate, comprising: depositing a columnar thin film by supplying source gas in a chamber loaded with the substrate, where the source gas is silicon-based gas and pressure of the deposition process is less than lOtorr when a temperature of the deposition process is 640 to 68O⁰C.

[I I] A method of depositing a thin film on a substrate, comprising: depositing crystalline and amorphous thin film by supplying source gas in a chamber loaded with the substrate, where the source gas is silicon-based gas and pressure of the deposition process is 10 to 50torr when a temperature of the deposition process is 640 to 68O⁰C.

[12] A method of depositing a thin film on a substrate, comprising: depositing an amorphous thin film by supplying source gas in a chamber loaded with the substrate, where the source gas is silicon-based gas and pressure of the deposition process is more than 50torr when a temperature of the deposition process is 640 to 68O⁰C.

[13] The thin film deposition method of any one of claims 10 to 12, wherein the silicon-based gas is silane (SiH₄) or disilane (Si₂H₆).

[14] The thin film deposition method of any one of claims 10 to 12, wherein the thin film is polycrystalline silicon.

[15] A thin film deposition apparatus, comprising: a chamber providing an internal space where processes are performed on a substrate; a substrate support unit provided in the chamber to support the substrate; first and second supply units, connected to an introducing unit formed at one side of the chamber, supplying first and second source gases into the chamber respectively through the introducing unit; first and second flow rate controllers controlling flow rates of the first and second source gases supplied respectively from the first and second supply units; and a controller controlling a supply ratio of the first and second source gases by controlling the first and second flow rate controllers.

[16] The thin film deposition apparatus of claim 15, further comprising a heater controlling a process temperature inside the chamber, where the heater is controlled by the controller.

[17] The thin film deposition apparatus of claim 15, further comprising a discharge unit connected to a vacuum port formed in the chamber to gas in the chamber forcibly, where the discharge unit is controlled by the controller.