# Patent

## Title
Methods of forming an amorphous silicon thin film

## Abstract

A method for forming an amorphous silicon thin film is disclosed. In some embodiments, a method includes loading a substrate into a reaction chamber; and conducting a plurality of deposition cycles on the substrate. Each of at least two of the cycles includes: supplying a silicon precursor to the reaction chamber during a first time period; applying radio frequency power to the reaction chamber at least partly during the first time period; stopping supplying of the silicon precursor and applying of the radio frequency power during a second time period between the first time period and an immediately subsequent deposition cycle; and supplying hydrogen plasma to the reaction chamber during a third time period between the second time period and the immediately subsequent deposition cycle. The method allows formation of an amorphous silicon film having an excellent step-coverage and a low roughness at a relatively low deposition temperature.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to and the benefit of Korean Patent Application No. 10-2008-0042367 filed in the Korean Intellectual Property Office on May 7, 2008, the entire contents of which are incorporated herein by reference.
BACKGROUND
1. Field of the Invention
The present invention relates to a method for forming a thin film. More particularly, the present invention relates to a method of forming an amorphous silicon thin film.
2. Description of the Related Art
In manufacturing semiconductor devices, various apparatuses and processes have been developed to provide a high quality thin film on a substrate. Several methods have been used to form thin films, employing surface reaction of a semiconductor substrate. The methods include vacuum evaporation deposition, Physical Vapor Deposition (PVD), Molecular Beam Epitaxy (MBE), different variants of Chemical Vapor Deposition (CVD) (including low-pressure and organometallic CVD and plasma-enhanced CVD), and Atomic Layer Epitaxy (ALE). ALE was studied extensively for semiconductor deposition and electroluminescent display applications, and has been more recently referred to as Atomic Layer Deposition (ALD) for the deposition of a variety of materials.
An exemplary physical vapor deposition method is sputtering. However, sputtering tends to exhibit a poor step-coverage. Thus, sputtering may not be used for forming a film having a uniform thickness on a surface with protrusions and depressions, particularly in high aspect ratio applications like DRAM capacitors.
In a chemical vapor deposition process, two or more reactant gases are reacted with one another over a surface of a substrate. One or more resulting compounds that are produced by the gas phase reaction are deposited on the surface of the substrate. Chemical vapor deposition typically provides a film having a good step-coverage, but has a dependency on temperature and gas supply uniformity. In addition, chemical vapor deposition causes less damage to a substrate than physical vapor deposition. Chemical vapor deposition can also be used in mass production of thin films at a relatively low cost.
Generally, ALD involves sequential introduction of separate pulses of at least two reactants until a layer of a desired thickness is deposited through self-limiting adsorption of monolayers of materials on a substrate surface. For example, in forming a thin film including an AB material, a cycle of four sequential steps of: (1) a first reactant gas A supply; (2) an inert purge gas supply; (3) a second reactant gas B supply; and (4) an inert purge gas supply is repeated. An atomic layer deposition (ALD) method can be performed at a low temperature, for example, a temperature lower than 400° C.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form prior art already known in this country to a person of ordinary skill in the art.
SUMMARY
In one embodiment, a method for forming an amorphous silicon thin film on a substrate includes: loading a substrate into a reaction chamber; and conducting a plurality of deposition cycles on the substrate. Each of at least two of the cycles includes: supplying a silicon precursor to the reaction chamber during a first time period; supplying hydrogen plasma to the reaction chamber at least partly during the first time period; and stopping supplying of the silicon precursor and the hydrogen plasma to the reaction chamber during a second time period between the first time period and an immediately subsequent deposition cycle.
In another embodiment, a method for forming an amorphous silicon thin film on a substrate includes: loading a substrate into a reaction chamber; and conducting a plurality of deposition cycles on the substrate. Each of at least two of the cycles includes: supplying a silicon precursor to the reaction chamber during a first time period; applying radio frequency power to the reaction chamber at least partly during the first time period; stopping supplying of the silicon precursor and applying of the radio frequency power during a second time period between the first time period and an immediately subsequent deposition cycle; and supplying hydrogen plasma to the reaction chamber during a third time period between the second time period and the immediately subsequent deposition cycle.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a timing diagram illustrating a method for forming an amorphous silicon thin film according to one embodiment.
FIG. 2 is a timing diagram illustrating a method for forming an amorphous silicon thin film according to another embodiment.
FIG. 3 is a timing diagram illustrating a method for forming an amorphous silicon thin film according to yet another embodiment.
FIG. 4A is a graph illustrating atomic concentrations of a film resulting from Example 1 using the method of FIG. 1.
FIG. 4B is a graph illustrating atomic concentrations of a film resulting from Example 2 using the method of FIG. 2.
FIG. 4C is a graph illustrating atomic concentrations of a film resulting from Example 3 using the method of FIG. 3.
FIGS. 5A-5E illustrate a method of making an integrated circuit device according to one embodiment.



DETAILED DESCRIPTION OF THE EMBODIMENTS
The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.
Various CVD methods can be used for depositing an amorphous silicon thin film. If a low pressure chemical vapor deposition (LPCVD) method is used with a silicon precursor, polysilicon, rather than amorphous silicon, tends to be formed. A resulting thin film tends to have a surface having a relatively high roughness. If a plasma CVD process is used, deposition may be carried out at a relatively low temperature (for example, about 350° C. to about 500° C.), and an amorphous silicon thin film may be formed. However, such an amorphous thin film may not provide a good step-coverage over fine features having a high aspect ratio.
If a plasma enhanced atomic layer deposition (PEALD) process is used, a deposition process may be carried out at a relatively low temperature. In a PEALD process, however, if a precursor is not well-adsorbed on a surface of a substrate, it is difficult to deposit a film at a commercially acceptable deposition rate.
In certain embodiments, an undoped amorphous silicon film is formed on a substrate in a reaction chamber by a cyclical deposition process using a silicon precursor and hydrogen plasma. During the deposition process, the hydrogen plasma reacts with the silicon precursor by either or both of a surface reaction and a gas phase reaction, and removes ligands from the silicon precursor. In different embodiments, the hydrogen plasma can be supplied in pulses simultaneously with and/or subsequent to the supply of the silicon precursor. In either cases, the supplies of the reactants are pulsed while plasma power is applied to the reaction chamber.
In some embodiments, a method includes conducting a plurality of deposition cycles. At least one of the cycles includes steps of: supplying a silicon precursor to a reaction chamber during a first time period; supplying hydrogen plasma to the reaction chamber at least partly during the first time period; and supplying a purge gas to the reaction chamber during a second time period subsequent to the first time period. In another embodiment, the at least one of the cycles may further include a step of supplying hydrogen plasma to the reaction chamber during a third time period subsequent to the second time period. In yet another embodiment, the at least one of the cycles may further include a step of supplying a purge gas to the reaction chamber during a fourth time period subsequent to the third time period.
In other embodiments, a method includes conducting a plurality of deposition cycles. At least one of the cycles includes steps of supplying a silicon precursor to the reaction chamber without supplying hydrogen gas during a first time period; applying radio frequency power to the reaction chamber at least partly during the first time period; supplying a purge gas to the reaction chamber during a second time period subsequent to the first time period; and supplying hydrogen plasma to the reaction chamber during a third time period subsequent to the first time period.
In the illustrated embodiments, the time periods are separated by pauses in the supplies of reactants. During the pauses, a purge gas may be supplied to the reaction chamber to remove excess reactants and any by-products from the reaction chamber.
Referring to FIG. 1, a method for forming an amorphous silicon thin film on a substrate according to one embodiment will be described below. The substrate may be formed of silicon, and may also include features or structures formed thereon. The features or structures may include a metal, a semiconductor, and/or an insulator.
First, the substrate is loaded into a reaction chamber of a reactor. In one embodiment, the reactor may be a single wafer CVD reactor, such as EPSILONTM from ASM America, Inc. of Phoenix, Ariz., or a single wafer ALD reactor, such as a GENI CM-2000 reactor commercially available from ASM Genitech Korea of Cheonan-si, Chungcheongnam-do, Republic of Korea. In other embodiments, the reactor may be a single wafer ALD reactor with a showerhead, for example, a StellarTM reactor commercially available from ASM Japan K.K., Tokyo, Japan. In certain embodiments, a lateral flow reactor, such as the reactor disclosed by U.S. Pat. No. 6,539,891, the disclosure of which is incorporated herein by reference. A skilled artisan will appreciate that any suitable type of reactor can be used for the method. A surface of the substrate is exposed to the reaction space.
The illustrated method includes a plurality of deposition cycles. Although only first to fourth cycles are illustrated in FIG. 1, the method may include any selected number of cycles, depending on the thickness of a film to be deposited on the substrate.
During a first time period t1, a silicon (Si) precursor pulse is supplied to the reaction chamber. The silicon precursor may include one or more silicon atoms and one or more ligands (e.g., atoms or functional groups) bonded to the silicon atoms. In some embodiments, the silicon precursor may be a silane compound, such as silanes, disilanes, trisilanes, chlorosilanes, and derivatives thereof. Examples of silane compounds include, but are not limited to, monosilane (SiH4), disilane (Si2H6), chlorosilane (SiH3Cl), dichlorosilane (DCS or SiH2Cl2), trichlorosilane (TCS or SiHCl3), hexachlorodisilane (HCDS or Si2H6), and silicon tetrachloride (SiCl4). Examples of chlorosilanes include, but are not limited to, chlorosilane (SiH3Cl), dichlorosilane (DCS or SiH2Cl2), trichlorosilane (TCS or SiHCl3), hexachlorodisilane (HCDS or Si2H6), and silicon tetrachloride (SiCl4). In other embodiments, any suitable silicon-containing compound may be used as a silicon precursor.
The silicon precursor may be supplied with a carrier gas (such as Ar, He, or N2) at a flow rate of, for example, about 50 sccm to about 500 sccm, and optionally about 100 sccm to about 300 sccm. In one embodiment where the silicon precursor is in a liquid form, a bubbling method may be used to provide the precursor to the reaction chamber in a gaseous form. In such an embodiment, the carrier gas may be supplied through a silicon precursor container. In other embodiments, a liquid delivery system (LDS) may be used to vaporize a silicon precursor, which is then drawn from over the liquid and entrained in the carrier gas flow. A skilled artisan will appreciate that various other methods can be used for providing the silicon precursor to the reaction chamber in a gaseous form. The duration of the first time period t1 can be between about 0.1 seconds and about 3.0 seconds, and optionally between about 0.5 seconds and about 1.5 seconds.
During the first time period t1, a hydrogen (H2) gas pulse is also simultaneously or overlappingly supplied to the reaction chamber. In addition, radio frequency (RF) power is applied to the reaction chamber, generating hydrogen plasma in situ. The hydrogen gas may be supplied at a flow rate of, for example, about 50 sccm to about 500 sccm, and optionally about 100 sccm to about 300 sccm. The RF power may range from about 50 W to about 800 W at a frequency of about 5.0 MHz to about 30.0 MHz. In other embodiments, remotely generated hydrogen plasma may be supplied in pulses to the reaction chamber, instead of generating hydrogen plasma in situ.
During the first time period t1, both a gas phase reaction and a surface reaction occur over the substrate. At least a portion of the silicon precursor is adsorbed physically or chemically on the exposed surface of the substrate while excess silicon precursor may remain unadsorbed (in the gas phase) within the reaction chamber. Part of the excess silicon precursor may react with the hydrogen plasma by the gas phase reaction. The hydrogen plasma may remove at least some of the ligands from the excess silicon precursor in the gas phase, thereby depositing a silicon-containing layer on the surface of the substrate. For example, in an embodiment where the silicon precursor is hexachlorodisilane (HCDS), HCDS and H2 plasma react with each other, forming amorphous silicon while producing HCl as a by-product.
In addition, the silicon precursor adsorbed on the surface of the substrate may also react with the hydrogen plasma. The silicon precursor adsorbed on the surface may include molecules, each of which includes one or more silicon atoms and one or more ligands. The hydrogen plasma may remove the ligands from the silicon precursor adsorbed on the substrate surface by the surface reaction, thereby leaving silicon atoms on the substrate surface. The silicon atoms may form part of the silicon-containing layer. The silicon-containing layer may be undoped amorphous silicon.
During a second time period t2, a purge gas is supplied to the reaction chamber to remove any unreacted precursor and by-products. Examples of purge gases include, but are not limited to, relatively inert gases, such as argon (Ar), nitrogen (N2), and/or helium (He). The duration of the second time period t2 can be between about 0.1 seconds and about 3.0 seconds, and optionally between about 0.5 seconds and about 1.5 seconds. During the second time period t2, the purge gas may also remove ligands bonded via a dangling bond to silicon atoms adsorbed on the substrate. The term “dangling bond” generally refers to a chemical bond associated with an atom in the surface layer of a solid that does not join the atom with a second atom but extends in the direction of the solid's exterior.
The first and second time periods t1, t2 form a deposition cycle. The deposition cycle may be repeated at least twice until a thin film having a desired thickness is formed. For example, during a third time period t3, the silicon precursor may be supplied to the reaction chamber along with hydrogen gas activated by RF power. During a fourth time period t4, the purge gas may be supplied to the reaction chamber. In one embodiment, the deposition method may be performed at a reaction chamber temperature of about 300° C. or lower.
In the method described above, after the first time period t1 in each deposition cycle, a substantial portion of the silicon-containing layer formed on the surface of the substrate may include silicon atoms without ligands. However, at least some portion of the silicon-containing layer may include ligands bonded to the silicon atoms via a dangling bond. During the second time period t2, such ligands are at least partly removed from the silicon-containing layer by the purge gas, thus clearing the top surface of the silicon-containing layer. This allows more effective deposition of the silicon precursor during the next deposition cycle. Thus, the layer resulting from the method can have a uniform thickness and a good step coverage compared to a layer formed by a conventional CVD process.
Referring to FIG. 2, a method for forming an amorphous silicon thin film on a substrate according to another embodiment will be described below. First, the substrate is loaded into a reaction chamber. The details of the reaction chamber and the substrate can be as described above with respect to FIG. 1.
The illustrated method includes a plurality of deposition cycles. Although only first and second cycles are illustrated in FIG. 2, the method may include any selected number of cycles, depending on the thickness of a film to be deposited on the substrate.
During a first time period t1, a silicon (Si) precursor gas pulse is supplied to the reaction chamber. Details of the silicon precursor can be as described above with respect to those of the silicon precursor in FIG. 1. The precursor gas may be supplied with a carrier gas (such as Ar, He, or N2) at a flow rate of, for example, about 50 sccm to about 500 sccm, and optionally about 100 sccm to about 300 sccm. The duration of the first time period t1 can be between about 0.1 seconds and about 3.0 seconds, and optionally between about 0.5 seconds and about 1.5 seconds.
During the first time period t1, a hydrogen (H2) gas pulse is also provided to the reaction chamber, and radio frequency (RF) power is applied to the reaction chamber, generating hydrogen plasma in situ. The hydrogen gas may be supplied at a flow rate of, for example, about 50 sccm to about 500 sccm, and optionally about 100 sccm to about 300 sccm. The RF power may range from about 50 W to about 800 W at a frequency of about 5.0 MHz to about 30.0 MHz. In other embodiments, remotely generated hydrogen plasma may be supplied to the reaction chamber in pulses, instead of generating hydrogen plasma in situ.
During the first time period t1, both a gas phase reaction and a surface reaction occur over the substrate. At least a portion of the silicon precursor is adsorbed physically or chemically on the exposed surface of the substrate while excess silicon precursor may remain unadsorbed (in the gas phase) within the reaction chamber. Part of the excess silicon precursor may react with the hydrogen plasma by the gas phase reaction. The hydrogen plasma may remove at least some of the ligands from the excess silicon precursor in the gas phase, thereby depositing a silicon-containing layer on the surface of the substrate. For example, in an embodiment where the silicon precursor is hexachlorodisilane (HCDS), HCDS and H2 plasma react with each other, forming amorphous silicon while producing HCl as a by-product.
In addition, the silicon precursor adsorbed on the surface of the substrate may also react with the hydrogen plasma. The silicon precursor adsorbed on the surface may include molecules, each of which includes one or more silicon atoms and one or more ligands. The hydrogen plasma may remove the ligands from the silicon precursor adsorbed on the substrate surface by the surface reaction, thereby leaving silicon atoms on the substrate surface. The silicon atoms may form part of the silicon-containing layer. The silicon-containing layer may be undoped amorphous silicon.
During a second time period t2, a purge gas is supplied to the reaction chamber to remove any unreacted precursor and by-products. Examples of purge gases include, but are not limited to, relatively inert gases, such as argon (Ar), nitrogen (N2), and/or helium (He). The duration of the second time period t2 can be between about 0.1 seconds and about 3.0 seconds, and optionally between about 0.5 seconds and about 1.5 seconds. In certain embodiments, this step may be omitted.
During a third time period t3, another hydrogen gas (H2) pulse is supplied to the reaction chamber, and radio frequency (RF) power is applied to the reaction chamber to activate the hydrogen gas, thereby generating hydrogen plasma in the absence of silicon precursor supply. The hydrogen gas may be supplied at a flow rate of, for example, about 50 sccm to about 500 sccm, and optionally about 100 sccm to about 300 sccm. The RF power may range from about 50 W to about 800 W at a frequency of about 5.0 MHz to about 30.0 MHz. In other embodiments, remotely generated hydrogen plasma may be supplied to the reaction chamber, instead of generating hydrogen plasma in situ. The duration of the third time period t3 can be between about 0.1 seconds and about 3.0 seconds, and optionally between about 0.5 seconds and about 1.5 seconds.
At least a portion of the precursor adsorbed on the substrate during the first time period t1 may still have ligands remaining after the first time period t1. The hydrogen plasma supplied during the third time period t3 may remove the remaining ligands from the silicon precursor adsorbed on the substrate surface, thereby forming amorphous silicon. In an embodiment where the silicon precursor is hexachlorodisilane (HCDS), HCDS and hydrogen plasma may react with each other, leaving only silicon atoms on the substrate surface while producing HCl as a by-product.
In the method of FIG. 2, after the first time period t1 in each deposition cycle, a substantial portion of the silicon-containing layer formed on the surface of the substrate may include silicon atoms without ligands. However, at least some portion of the silicon-containing layer may include ligands bonded via a dangling bond to the silicon atoms. During the second time period t2, such ligands are at least partly removed from the silicon-containing layer by the purge gas, thus clearing the top surface of the silicon-containing layer. Further, during the third time period t3, any remaining ligands bonded to silicon atoms in the silicon-containing layer may be more effectively removed by the hydrogen plasma. This allows more effective deposition of the silicon precursor during the next deposition cycle. Thus, the layer resulting from the method can have a uniform thickness and a good step coverage compared to a layer formed by a conventional CVD process.
During a fourth time period t4, a purge gas is supplied to the reaction chamber to remove any unreacted precursor and/or by-products. Examples of purge gases include, but are not limited to, argon (Ar), nitrogen (N2), and helium (He). The duration of the fourth time period t4 can be between about 0.1 seconds and about 3.0 seconds, and optionally between about 0.5 seconds and about 1.5 seconds. In certain embodiments, this step may be omitted.
The first to fourth time periods t1-t4 form a deposition cycle. The deposition cycle may be repeated at least twice until a thin film having a desired thickness is formed. For example, during a fifth time period t5, the silicon precursor may be supplied to the reaction chamber along with hydrogen gas activated by RF power. During a sixth time period t6, a purge gas may be supplied to the reaction chamber. During a seventh time period t7, hydrogen gas may be supplied to the reaction chamber while RF power is applied to the reaction chamber. Subsequently, during an eighth time period t8, a purge gas may be supplied to the reaction chamber. The fifth to the eighth time periods t5-t8 form another deposition cycle. It will be understood that cycles can have arbitrarily defined starting and stopping points (e.g., t2-t5 can be considered a cycle). In one embodiment, the method may be carried out at a reaction chamber temperature of about 300° C. or lower.
Referring to FIG. 3, a method for forming an amorphous silicon thin film on a substrate according to another embodiment will be described below. First, the substrate is loaded into a reaction chamber. The details of the reaction chamber and the substrate can be as described above with respect to FIG. 1.
The illustrated method includes a plurality of deposition cycles. Although only first and second cycles are illustrated in FIG. 3, the method may include any selected number of cycles, depending on the thickness of a film to be deposited on the substrate.
During a first time period t1, a silicon (Si) precursor gas pulse is supplied to the reaction chamber in the absence of hydrogen supply. Details of the silicon precursor can be as described above with respect to those of the silicon precursor in FIG. 1. The precursor gas may be supplied with a carrier gas (such as Ar, He, or N2) at a flow rate of, for example, about 50 sccm to about 500 sccm, and optionally about 100 sccm to about 300 sccm. The duration of the first time period t1 can be between about 0.1 seconds and about 3.0 seconds, and optionally between about 0.5 seconds and about 1.5 seconds.
During the first time period t1, radio frequency (RF) power is also applied to the reaction chamber, but no hydrogen gas is supplied to the reaction chamber. The RF power may range from about 50 W to about 800 W at a frequency of about 5.0 MHz to about 30.0 MHz.
During the first time period t1, the silicon precursor is physically or chemically adsorbed on the substrate surface, forming a layer. The layer includes precursor molecules, each of which includes one or more silicon atoms and ligands.
During a second time period t2, a purge gas is supplied to the reaction chamber to remove any unreacted precursor and by-products. Examples of purge gases include, but are not limited to, inert gases, such as argon (Ar), nitrogen (N2), and/or helium (He). The duration of the second time period t2 can be between about 0.1 seconds and about 3.0 seconds, and optionally between about 0.5 seconds and about 1.5 seconds. In certain embodiments, this step may be omitted.
During a third time period t3, a hydrogen (H2) gas pulse is supplied to the reaction chamber, and radio frequency (RF) power is applied to the reaction chamber to activate the hydrogen gas, thereby generating hydrogen plasma in the absence of silicon precursor supply. The hydrogen gas may be supplied at a flow rate of, for example, about 50 sccm to about 500 sccm, and optionally about 100 sccm to about 300 sccm. The RF power may range from about 50 W to about 800 W at a frequency of about 5.0 MHz to about 30.0 MHz. In other embodiments, remotely generated hydrogen plasma may be supplied in pulses to the reaction chamber, instead of generating hydrogen plasma in situ. The duration of the third time period t3 can be between about 0.1 seconds and about 3.0 seconds, and optionally between about 0.5 seconds and about 1.5 seconds.
The hydrogen plasma removes the ligands from the silicon precursor adsorbed on the substrate, thereby forming amorphous silicon. In an embodiment where the silicon precursor is hexachlorodisilane (HCDS), HCDS and H2 react with each other, leaving only silicon atoms on the substrate while producing HCl as a by-product.
During a fourth time period t4, a purge gas is supplied to the reaction chamber to remove any unreacted precursor and/or by-products. Examples of purge gases include, but are not limited to, inert gases, such as argon (Ar), nitrogen (N2), and/or helium (He). The duration of the fourth time period t4 can be between about 0.1 seconds and about 3.0 seconds, and optionally between about 0.5 seconds and about 1.5 seconds. In certain embodiments, this step may be omitted.
The first to fourth time periods t1-t4 form a deposition cycle. The deposition cycle may be repeated at least twice until a thin film having a desired thickness is formed. For example, during a fifth time period t5, the silicon precursor may be supplied to the reaction chamber with RF power on. During a sixth time period t6, a purge gas may be supplied to the reaction chamber. During a seventh time period t7, hydrogen gas may be supplied to the reaction chamber while RF power is applied to the reaction chamber. Subsequently, during an eighth time period t8, a purge gas may be supplied to the reaction chamber. The fifth to the eighth time periods t5-t8 form another deposition cycle. It will be understood that beginning and end points for a cycle can be arbitrarily chosen (e.g., t2-t5 or t3-t6 can also be considered cycles). In one embodiment, the method may be carried out at a reaction chamber temperature of about 300° C. or lower.
In the method described above, during the first time period t1 in each deposition cycle, the silicon precursor is activated by plasma, and at least a portion of the silicon precursor is decomposed to silicon atoms without ligands. At least some of the silicon atoms are deposited on the substrate. However, other portions of the silicon precursor may still include one or more ligands. Such other portions of the silicon precursor may be adsorbed on the substrate. Thus, at least a portion of the silicon-containing layer may include ligands bonded to the silicon atoms in the layer. During the second time period t2, the purge gas may at least partially remove by-products and/or ligands bonded via a dangling bond to the silicon atoms. During the third time period t3, remaining ligands bonded to silicon atoms in the silicon-containing layer may be more effectively removed by the hydrogen plasma. This allows more effective deposition of the silicon precursor during the next deposition cycle. Thus, the layer resulting from the method can have a uniform thickness and a good step coverage compared to a layer formed by a conventional CVD process.
In the embodiments described above, amorphous silicon films can be deposited at a relatively low temperature, for example, about 300° C. or lower, compared to a conventional CVD process. The resulting films have better step-coverage and uniformity than films resulting from the conventional CVD process while having a smaller roughness than films resulting from the conventional CVD process.
EXAMPLES
An amorphous silicon (Si) film was deposited on a substrate in the reaction chamber of a StellarTM reactor having a showerhead available from ASM Japan K.K., Tokyo, Japan. The substrate was placed on a susceptor within the reaction chamber. The substrate had a surface covered with a silicon dioxide layer, and the amorphous silicon film was deposited on the silicon dioxide layer.
In Examples 1-3 described below, the temperature of the substrate was maintained at 200° C. to 300° C. during deposition. The temperature of the susceptor was maintained between 250° C. and 350° C. The temperature of the substrate was about 50 degrees lower than that of the susceptor. It is believed that the temperature difference was due to a loss of heat when the susceptor heats the substrate. The pressure of the reaction chamber during deposition was maintained at 3.0 torr.
Example 1
In Example 1, a deposition process was conducted repeating a cycle which includes two steps, as shown in FIG. 1. The cycle includes steps of: (1) supplying a silicon precursor (hexachlorodisilane) with a carrier gas (argon (Ar) gas) and hydrogen gas (H2) into the reaction chamber for 1 second; and (2) purging the reaction chamber with argon gas for 1 second. During the step (1), the carrier gas was supplied through a silicon precursor container at a flow rate of 100 sccm. In addition, the hydrogen gas was supplied at a flow rate of 100 sccm. During the step (1), 600 W of RF power was applied to the reaction chamber to generate in-situ hydrogen plasma. Steps (1) and (2) were repeated 500 times.
Example 2
In Example 2, a deposition process was conducted repeating a cycle which includes four steps, as shown in FIG. 2. The cycle includes steps of: (1) supplying a silicon precursor (hexachlorodisilane) with a carrier gas (argon (Ar) gas) and hydrogen gas (H2) into the reaction chamber for 1 second; (2) purging the reaction chamber with argon gas for 2 seconds; (3) supplying hydrogen gas (H2) into the reaction chamber for 1 second; and (4) purging the reaction chamber with argon gas for 2 seconds. During the step (1), the carrier gas was supplied through a silicon precursor container at a flow rate of 100 sccm. In addition, the hydrogen gas was supplied at a flow rate of 100 sccm. During the step (3), the hydrogen gas was supplied at a flow rate of 100 sccm. During the steps (1) and (3), 600 W of RF power was applied to the reaction chamber to generate in-situ hydrogen plasma. Steps (1) to (4) were repeated 500 times.
Example 3
In Example 3, a deposition process was conducted repeating a cycle which includes four steps, as shown in FIG. 3. The cycle includes steps of: (1) supplying a silicon precursor (hexachlorodisilane) with a carrier gas (argon (Ar) gas) into the reaction chamber for 1 second; (2) purging the reaction chamber with argon gas for 2 seconds; (3) supplying hydrogen gas (H2) into the reaction chamber for 1 second; and (4) purging the reaction chamber with argon gas for 2 seconds. During the step (1), the carrier gas was supplied through a silicon precursor container at a flow rate of 100 sccm, and 600 W of RF power was applied to the reaction chamber. During the step (3), the hydrogen gas was supplied at a flow rate of 100 sccm, and 600 W of RF power was applied to the reaction chamber to generate in-situ hydrogen plasma. Steps (1) to (4) were repeated 500 times.
Films Resulting From Examples 1-3
The atomic concentrations of the films resulting from Examples 1-3 are shown in FIGS. 4A-4C. In Examples 1-3, the substrates were cooled to room temperature, and then the substrates were exposed to air. The atomic concentrations of the films were measured by Auger electron spectroscopy (AES) analysis. In the AES analysis, a beam of electrons was sputtered onto a top surface of each of the resulting silicon films. Electrons emitted from the surface were collected for use in analysis of the composition of the film.
In FIGS. 4A-4C, the horizontal axis represents the duration of sputtering the beam of electrons, thus also representing the depth into the film, and the vertical axis represents atomic concentrations of elements in the films. C represents the atomic concentration of carbon atoms; O represents the atomic concentration of oxygen atoms; Si represents the atomic concentration of silicon atoms; and Cl represents the atomic concentration of chlorine atoms.
It is believed that oxygen atoms found in the films were from atmospheric oxygen gas that has diffused into the films after the deposition processes. Such diffusion of oxygen gas is at least partly attributable to a loose morphological structure of amorphous silicon resulting from the deposition processes, which is not typically found in crystalline silicon. Thus, the presence of oxygen atoms in the films indicates that the silicon films were at least partly in amorphous state.
In addition, the greater the concentration of oxygen atoms is, the more loose the morphological structure of the silicon film is. FIG. 4A shows a relatively greater concentration of oxygen atoms, compared to those of FIGS. 4B and 4C. FIG. 4B shows a relatively greater concentration of oxygen atoms compared to those of FIG. 4C. Thus, it is believed that the silicon film resulting from Example 1 has more loose morphological structure than the silicon film resulting from Example 2. In addition, it is believed that the silicon film resulting from Example 2 has more loose morphological structure than the silicon film resulting from Example 3.
The chlorine atoms in the films are residues of ligands that have not been removed from the films. Very low levels of chlorine indicate very effective scavenging of chlorine in all three processes.
Method of Making an Integrated Circuit Device
In manufacturing integrated circuit (IC) devices, a silicon oxide film may be used to electrically insulate circuit components from one another. However, if the density of a silicon oxide film is low, the film may not provide desired electrical insulation. Thus, there is a need for forming a dense silicon oxide film to provide desired electrical insulation.
Referring to FIGS. 5A-5E, a method of making an integrated circuit device including a silicon dioxide film according to one embodiment will be described below. First, a substrate 500 is provided, as shown in FIG. 5A. The substrate 500 includes a trench or via 502 on a surface 501 thereof. The trench 502 includes side surfaces 503 and a bottom surface 504. A lining layer 510 is formed conformally on the surface 501 of the substrate 500, and the surfaces 503, 504 of the trench 502. The lining layer 510 may be formed of Si3N4 and/or SiO2. SiO2 may be grown from the trench sidewalls to repair damage from the trench etch, and Si3N4 may be deposited as a barrier layer.
Subsequently, an amorphous silicon layer 520 is formed conformally on the lining layer 510, as shown in FIG. 5B. The amorphous silicon layer 520 may be formed by any of the methods described above in connection with FIGS. 1-3. The amorphous silicon layer 520 is undoped, and can have a good step-coverage, as described above.
Then, as shown in FIG. 5C, a silicon dioxide (SiO2) layer 530 is blanket deposited over the amorphous silicon layer 520, filling the trench 502. In the illustrated embodiment, a spin-on-glass (SOG) process may be performed to deposit the silicon dioxide layer 530.
Subsequently, a portion of the silicon dioxide layer 530 is removed, such as by polishing stop on the amorphous silicon layer 520, as shown in FIG. 5D, or on the underlying liner 510. In the illustrated embodiment, chemical mechanical planarization or polishing (CMP) may be used to remove the portion of the silicon dioxide layer 530.
The resulting structure is subjected to a heat treatment to densify the SOG SiO2 layer 530. The heat treatment may be performed at a temperature of about 600° C. to about 800° C., and optionally about 650° C. to about 750° C. The heat treatment may be performed in atmospheric gases, including oxygen gas. During the heat treatment, the oxide layer 530 densities and tends to shrink, which could cause voids. However, oxygen gas (O2) also diffuses into the amorphous silicon layer 520, and the amorphous silicon is converted into silicon dioxide, thereby changing the amorphous silicon layer 520 to a silicon oxide layer 525. During this conversion, the amorphous silicon layer 520 expands in the directions shown by the arrows in FIG. 5E. Such expansion of the amorphous silicon layer 520 compensates for shrinkage of the silicon oxide 530, and may further compress the silicon dioxide 530 in the trench 502, thereby making the layer 530 denser. As a result, a silicon dioxide layer having a high density can be formed. Such a silicon oxide layer can provide commercially acceptable electrical insulation.
Electronic Devices
The methods described above can be adapted for making various electronic devices. The electronic devices can include integrated circuits. Examples of electronic devices can include, but are not limited to, consumer electronic products, parts of the consumer electronic products, electronic test equipments, etc. Examples of the electronic devices can also include memory chips, memory modules, circuits of optical networks or other communication networks, and disk driver circuits. The consumer electronic products can include, but are not limited to, a mobile phone, a telephone, a television, a computer monitor, a computer, a hand-held computer, a personal digital assistant (PDA), a microwave, a refrigerator, a stereo system, a cassette recorder or player, a DVD player, a CD player, a VCR, an MP3 player, a radio, a camcorder, a camera, a digital camera, a portable memory chip, a washer, a dryer, a washer/dryer, a copier, a facsimile machine, a scanner, a multi functional peripheral device, a wrist watch, a clock, etc. Further, the electronic device can include unfinished products.
In at least some of the aforesaid embodiments, any element used in an embodiment can interchangeably be used in another embodiment unless such a replacement is not feasible. It will be appreciated by those skilled in the art that various other omissions, additions and modifications may be made to the methods and structures described above without departing from the scope of the invention. All such modifications and changes are intended to fall within the scope of the invention, as defined by the appended claims.

## Claims

1. A method for forming an amorphous silicon thin film on a substrate, the method comprising:
loading a substrate into a reaction chamber; and
conducting a plurality of deposition cycles on the substrate, at least two of the cycles, each comprising:
supplying a silicon precursor to the reaction chamber during a first time period;
supplying hydrogen plasma to the reaction chamber at least partly during the first time period; and
stopping supplying of the silicon precursor and the hydrogen plasma to the reaction chamber during a second time period between the first time period and an immediately subsequent deposition cycle.

2. The method of claim 1, wherein the at least two of the cycles further comprise supplying a purge gas to the reaction chamber at least partly during the second time period.

3. The method of claim 1, wherein the silicon precursor comprises a silane compound.

4. The method of claim 3, wherein the silane compound comprises a chlorosilane compound.

5. The method of claim 4, wherein the chlorosilane compound comprises chlorosilane (SiH3Cl), dichlorosilane (SiH2Cl2), trichlorosilane (SiHCl3), hexachlorodisilane (Si2H6), and silicon tetrachloride (SiCl4).

6. The method of claim 1, wherein supplying the hydrogen plasma comprises:
supplying hydrogen gas to the reaction chamber; and
applying radio frequency power to the reaction chamber while supplying the hydrogen gas, thereby generating hydrogen plasma in situ.

7. The method of claim 1, wherein supplying the hydrogen plasma comprises supplying remotely generated hydrogen plasma to the reaction chamber.

8. The method of claim 1, wherein the at least two of the cycles further comprise supplying hydrogen plasma to the reaction chamber during a third time period between the second time period and the immediately subsequent deposition cycle, wherein no silicon precursor is supplied to the reaction chamber during the third time period.

9. The method of claim 8, wherein supplying the hydrogen plasma during the third time period comprises:
supplying hydrogen gas to the reaction chamber; and
applying radio frequency power to the reaction chamber while supplying the hydrogen gas, thereby generating hydrogen plasma in situ.

10. The method of claim 8, wherein the at least two of the cycles further comprise stopping supplying of the hydrogen plasma to the reaction chamber during a fourth time period between the third time period and the immediately subsequent deposition cycle.

11. The method of claim 10, wherein the at least two of the cycles further comprise supplying a purge gas to the reaction chamber at least partly during the fourth time period.

12. The method of claim 1, wherein conducting the plurality of deposition cycles comprises conducting the at least one deposition cycle at a reaction chamber temperature of about 300° C. or lower.

13. A method of making an electronic device, the method comprising:
providing a substrate including a trench including surfaces;
depositing amorphous silicon on one or more of the surfaces of the trench of a substrate by the method of claim 1;
filling the trench with silicon dioxide; and
performing a heat treatment to convert the amorphous silicon to silicon oxide.

14. The method of claim 13, wherein filling the trench comprises performing a spin-on-glass process.

15. An electronic device comprising a silicon dioxide layer formed by the method of claim 13.

16. A method for forming an amorphous silicon thin film on a substrate, the method comprising:
loading a substrate into a reaction chamber; and
conducting a plurality of deposition cycles on the substrate, at least two of the cycles, each comprising
supplying a silicon precursor to the reaction chamber during a first time period;
applying radio frequency power to the reaction chamber at least partly during the first time period;
stopping supplying of the silicon precursor and applying of the radio frequency power during a second time period between the first time period and an immediately subsequent deposition cycle; and
supplying hydrogen plasma to the reaction chamber during a third time period between the second time period and the immediately subsequent deposition cycle.

17. The method of claim 16, wherein no silicon precursor is supplied to the reaction chamber during the third time period.

18. The method of claim 17, wherein no hydrogen gas is supplied to the reaction chamber during the first time period.

19. The method of claim 16, wherein the at least two of the cycles further comprise supplying a purge gas to the reaction chamber at least partly during the second time period.

20. The method of claim 16, wherein the silicon precursor comprises a chlorosilane compound.

21. The method of claim 20, wherein the chlorosilane compound comprises chlorosilane (SiH3Cl), dichlorosilane (SiH2Cl2), trichlorosilane (SiHCl3), hexachlorodisilane (Si2H6), and silicon tetrachloride (SiCl4).

22. The method of claim 16, wherein supplying the hydrogen plasma comprises:
supplying hydrogen gas to the reaction chamber; and
applying radio frequency power to the reaction chamber while supplying the hydrogen gas, thereby generating hydrogen plasma in situ.

23. The method of claim 16, wherein supplying the hydrogen plasma comprises supplying remotely generated hydrogen plasma to the reaction chamber.

24. The method of claim 16, wherein the at least two of the cycles further comprise supplying a purge gas to the reaction chamber during a fourth time period between the third time period and the immediately subsequent deposition cycle.

25. The method of claim 16, wherein conducting the plurality of deposition cycles comprises conducting the at least one deposition cycle at a reaction chamber temperature of about 300° C. or lower.

26. A method of making an electronic device, the method comprising:
providing a substrate including a trench including surfaces;
depositing amorphous silicon on one or more of the surfaces of the trench of a substrate by the method of claim 16;
filling the trench with silicon dioxide; and
performing a heat treatment to convert the amorphous silicon to silicon oxide.

27. The method of claim 26, wherein filling the trench comprises performing a spin-on-glass process.

28. An electronic device comprising: a silicon dioxide layer formed by the method of claim 26.