KR100943426B1 - Method and apparatus for depositing thin film - Google Patents

Abstract

The thin film is deposited on the substrate loaded in the chamber by chemical vapor deposition (CVD). A source gas including a silicon-based gas and a nitrogen-based gas is supplied into the chamber, and polycrystalline silicon is deposited on the substrate through the source gas. In this case, the mixing ratio of the nitrogen-based gas to the silicon-based gas may be 0.05 or less except 0, and when the mixing ratio of the nitrogen-based gas is excessive, silicon nitride (Si) containing a large amount of silicon on the substrate is used. _x N _y ) is deposited. The silicon-based gas may be silane (SiH ₄ ) or disilane (disilane: Si ₂ H ₆ ), and the nitrogen-based gas may be ammonia (NH ₃ ). Through this, it is possible to deposit polycrystalline polysilicon having an extremely small size, and to improve the uniformity of the electrical characteristics to prevent the characteristics from being lowered.

Chemical vapor deposition, process temperature, process pressure, ultrafine grain

Description

Thin film deposition method and thin film deposition apparatus {method and apparatus for depositing thin film}

1A and 1B are photographs showing a polycrystalline silicon film according to a conventional deposition method.

2 is a diagram illustrating a deposition apparatus in which a deposition process is performed according to an embodiment of the present invention.

3 is a graph showing refractive indexes of thin films deposited according to pressure and temperature conditions.

4A to 5B are photographs showing the crystal structure of a thin film deposited according to an embodiment of the present invention.

6 is a photograph showing a crystal structure of a thin film deposited according to another embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

11 chamber 12 introduction part

13: shower head 14: heater

16: heater support 17: vacuum port

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

The semiconductor device has many layers on a silicon wafer, and these layers are deposited on the substrate through a deposition process. The deposition process is generally divided into two categories, one is chemical vapor deposition (CVD) and the other is physical vapor deposition (PVD). In each case, the wafer is placed in a deposition chamber and the components of the thin film are supplied to the surface of the wafer to form the thin film in gaseous form. In the case of chemical vapor deposition, the reaction gases are introduced into the deposition chamber, and a thin film is formed on the surface of the wafer through chemical reaction between the reaction gases.

Among various thin films, a method of depositing polycrystalline silicon used as a gate electrode is as follows. First, after loading the wafer into the deposition chamber, a source gas is supplied into the chamber to deposit a thin film on the wafer. In this case, the source gas supplied into the chamber includes silane (SiH ₄ ), and a thin film is deposited on the wafer by the source gas supplied into the chamber. At this time, a polycrystalline deposition is deposited on the wafer through pyrolysis of silane (SiH ₄ ).

However, in such a deposition process, it is very difficult to deposit a polycrystalline silicon film having a thin silicon crystal structure (about 400 GPa or less), and it is difficult to deposit a uniform polycrystalline silicon film. Therefore, when it is used as a floating gate electrode such as a semiconductor flash memory, the uniformity, durability, and reliability aspects due to the threshold voltage shift of the device due to problems such as over erase of the manufactured device In this case, the uniformity of the threshold voltage (Vt) uniformity of the device is very uneven, which causes problems such as deterioration of device characteristics.

In more detail, first, amorphous silicon that is not crystalline by using silane (SiH ₄ ) or disilane (Si ₂ H ₆ ) at a constant process temperature (typically 550 ° C. or lower) is used. After the process of growing the thin film and the process of crystallizing the thin film grown by a subsequent constant heat treatment process (for example, 650 ℃ to 900 ℃), as a result shown in Figures 1a and 1b Get the result. 1A and 1B are photographs of a polycrystalline silicon film according to a conventional deposition method with a transmission electron microscope (TEM).

When the gate electrode of a device such as a flash memory is formed using such a process, the grain size of the crystallized crystal grains of the thin film is very irregular, and crystal grains having a size of several tens of nanometers to several hundred nm are formed and are used as transistors. In the region where the electrons move in the transistor having a large grain, one or two grain boundaries are formed, whereas in a region where the grains are very small, many grain boundaries are formed. As a result, the lower tunnel tunnel region where the grain meets the grains forms an area called an oxide valley. The lower grain boundary between the larger grains forms a larger oxide valley, which causes more phosphorus in the subsequent formation of the phosphorus poly process. concentration to reduce the local barrier height, resulting in an over erase point when driving the device, Or electron trap formation site caused by phosphorus, which greatly reduces the reliability of the device. This means that the movement of electrons is very different in the driving ability of several transistors included in the chip when the device is operated after the transistor is formed. Then there was a problem that the device characteristics are very poor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for depositing a thin film having a crystal structure having a very fine crystal structure.

Other objects of the present invention will become more apparent from the following detailed description and the accompanying drawings.

According to an embodiment of the present invention, a method of depositing a thin film on a substrate may include depositing the thin film by supplying a source gas into a chamber loaded with the substrate, wherein the source gas is a silicon-based gas and It is characterized by containing a nitrogen-based (nitrogen-based) gas.

The mixing ratio of the nitrogen-based gas to the silicon-based gas may be 0.05 or less except for zero. In addition, the nitrogen in the thin film may be less than 10 at% (atomic percentage).

On the other hand, when the temperature of the deposition process is 580 ℃ to 650 ℃ the pressure of the deposition process may be 100torr to 300torr. In addition, when the temperature of the deposition process is 650 ℃ to 750 ℃ the pressure of the deposition process may be 5torr to 100torr.

The method may further comprise a heat treatment process for the thin film deposited on the substrate. The thin film may be polycrystalline silicon. The silicon-based gas may be silane (SiH ₄ ) or disilane (Si ₂ H ₆ ). The nitrogen-based gas may be ammonia (NH ₃ ).

According to another embodiment of the present invention, a method of depositing a thin film on a substrate is to deposit the thin film by supplying a source gas in the chamber loaded with the substrate, the source gas is a silicon-based (silicon-based) gas When the temperature of the deposition process is 640 ° C. to 680 ° C., the pressure of the deposition process is 10 torr or less except for 0, and the columnar thin film is deposited.

According to another embodiment of the present invention, a method for depositing a thin film on a substrate is to deposit the thin film by supplying a source gas in the chamber loaded with the substrate, the source gas is a silicon-based (silicon-based) gas When the temperature of the deposition process is 640 ° C to 680 ° C, the pressure of the deposition process is 10 tortor to 50torr, characterized by depositing crystalline and amorphous thin films.

According to another embodiment of the present invention, a method for depositing a thin film on a substrate is to deposit the thin film by supplying a source gas in the chamber loaded with the substrate, the source gas is a silicon-based (silicon-based) gas When the deposition process is at a temperature of 640 ° C. to 680 ° C., the deposition process may have a pressure of 50 torr or more to deposit an amorphous thin film.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to FIGS. 2 to 6. Embodiment of the present invention may be modified in various forms, the scope of the present invention should not be construed as limited to the embodiments described below. This embodiment is provided to explain in detail the present invention to those skilled in the art. Accordingly, the shape of each element shown in the drawings may be exaggerated to emphasize a more clear description.

The present invention is a method of depositing a thin film having a columnar crystal form having a fine crystal structure in a semiconductor device by chemical vapor deposition using a single chamber as described above. In general, chemical vapor deposition is a process of forming a thin film on a semiconductor substrate by supplying a gaseous source gas to induce a chemical reaction with the substrate. The present invention to perform such chemical vapor deposition in a single chamber will be described with reference to FIG. 2. 2 is a diagram illustrating a deposition apparatus 10 in which a deposition process according to an embodiment of the present invention is performed.

The chamber 11 provides an internal space that is blocked from the outside, and an introduction portion 12 for introducing a source gas into the internal space is provided at the upper portion of the chamber 11. The introduction part 12 is connected to the main supply line 12a and the first supply line 18a and the second supply line 19a connected to the main supply line 12a. The first supply line 18a supplies the first source gas into the chamber 11, and the second supply line 18b supplies the second source gas into the chamber 11. The first source gas is a silicon-based gas including silane or disilane, and the second source gas is a nitrogen-based gas including ammonia. However, unlike this, only one source gas may be supplied into the chamber 11. In addition, a first flow controller 18b and a first valve 18c are installed on the first supply line 18a, and a second flow controller 19b and a second valve 19c are provided on the second supply line 19a. Is installed. On the other hand, the gas introduced by the introduction portion 12 is injected into the chamber 11 through the shower head (13). In addition, the wafer 15 to be deposited is placed on the heater 14, and the heater 14 is supported by the heater support 16.

When the deposition is completed, the unreacted gas and the reaction by-product inside the chamber 11 are discharged by the vacuum port 17. A discharge line 17a and a vacuum pump 17b are connected to the vacuum port 17 to forcibly discharge the unreacted gas and the reaction byproduct inside the chamber 11. In addition, the process pressure inside the chamber 11 may be adjusted using the discharge line 17a and the vacuum pump 17b. In this way, the source gas is supplied into the chamber 11 on the substrate, and a thin film is deposited on the substrate through the reaction gas decomposed by pyrolysis. On the other hand, the heater 14 for adjusting the process temperature, the vacuum pump 17b for adjusting the process pressure, and the first and second for adjusting the supply amount (or mixing ratio) of the first and second source gas The flow controllers 18b and 19b are controlled by the control unit 20.

3 is a graph showing refractive indexes of thin films deposited according to pressure and temperature conditions. As shown in Figure 3, the horizontal axis is the process temperature and the vertical axis shows the refractive index (R.I) value that can know the crystal properties of the deposited thin film. As the index of refraction is close to 4.5, the amorphous silicon thin film growth state is shown. As the value is close to 4.0, the crystalline structure of the crystal structure close to the crystallized polycrystalline silicon thin film is formed.

On the other hand, crystalline refers to a solid having three-dimensional periodicity in atomic arrangement, and a solid having no such periodicity is called an amorphous material (amorphous material). Amorphous silicon is mentioned as a semiconductor using the above-mentioned amorphous state. Such amorphous semiconductors are used for thin film transistors because they can be deposited at low temperatures.

As shown in FIG. 3, a change in refractive index measured according to pressure occurs in a temperature range of 640 ° C. to 685 ° C. As an example, in the case of 655 ° C., the process pressure is constant when the source gas is constant. It can be seen that below 10torr, the measured refractive index value is close to 4.0, and thus, polycrystalline silicon in the form of columnar form is formed. On the other hand, when the deposition process pressure is increased to 100 Torr or more, the measured refractive index approaches 4.5. Therefore, the deposited thin film can be seen that the amorphous silicon thin film is formed. As an example, when the source gas supplied is constant, the graph shows a form in which no amorphous silicon thin film can be formed even if the pressure is controlled below the pressure at the process temperature of 685 ° C or higher, that is, 10torr at the process temperature of 685 ° C. It can be seen that not only the polycrystalline silicon is formed at the pressure below, but the pressure is close to the value of 4.0 measured under the process conditions of 100 torr or more, which is the formation of the polycrystalline silicon.

Meanwhile, surface roughness is used as a coefficient for evaluating the performance of the deposited thin film. In the present invention, atomic force microscopy (AFM) is used, but a root mean square (RMS) is used for the calculation method. As a result, the case where surface roughness was 2 was the most preferable.

4A and 4B show the crystal structure of the deposition of crystalline silicon thin film at 685 ° C. process temperature and pressure of 10 Torr, and FIGS. 5A and 5B show the deposition of crystalline silicon thin film at 730 ° C. process temperature and pressure of 10 Torr. The crystal structure is shown.

As described above, although the silane is used as the source gas presented in the present invention by using the idea of the present invention, the idea of the present invention to be implemented in the present invention by using disilane as another source gas, constant temperature and constant Another embodiment of the invention is characterized by forming a columnar crystal grain under pressure, a crystal structure in which equiaxed crystal grains or an amorphous silicon thin film is mixed, or a thin film forming an amorphous silicon thin film.

Another embodiment of the present invention will be described with reference to FIG. 2 again.

As shown in FIG. 2, first, an introduction part 12 for introducing a source gas into the chamber 11 is formed. The gas introduced by the introduction part 12 is injected into the chamber 11 through the shower head 13. In addition, the wafer 15 to be deposited is placed on the heater 14, which is supported by the heater support 16. After the deposition is performed by this apparatus, it is discharged by the vacuum port 17. In this single wafer type chemical vapor deposition method, a silane (SiH4) gas is introduced into the chamber 11 on the substrate, and the reaction gas decomposed by thermal decomposition is moved through the surface movement on the silicon substrate disposed on the substrate. Will be deposited.

In this case, when ammonia is injected into the reaction chamber at the same time with the silane, silicon atoms of the pyrolyzed reaction gas do not proceed with silicon nucleation and grain growth due to nitrogen atoms decomposed from the ammonia. Even at a high temperature (above 650 ° C.), deposition is possible with polysilicon in an amorphous state. In this case, when the mixing ratio of the NH 3 / SiH 4 gas is maintained at a predetermined level or more, the mixing ratio of the two reaction gases is the most important factor in the present invention because it may be deposited with silicon nitride (Si _x N _y ). The following table shows the tendency of the Nitrogen concentration in atomic% and the grain size according to the gas mixing ratio of NH3 / SiH4.

<Table>

N concentration NH3 / SiH4 = 0.007 NH3 / SiH4 = 0.012 NH3 / SiH4 = 0.017 NH3 / SiH4 = 0.022 1E20atoms / cc 16.4 31.0 44.0 56.5 atomic% 2.93% 6.12% 8.82% 11.3% grain size 108.5Å 75.5Å 63Å 33Å

As can be seen from the table, it can be seen that when the ammonia is mixed, the grain size decreases, and as the mixing ratio of ammonia increases (to the right in the table), the grain size decreases. Therefore, by mixing ammonia, very fine and uniform crystal grains can be formed.

However, if the mixing ratio of ammonia is excessively increased, the thin film deposited on the wafer may be closer to silicon nitride (SixNy) rather than polycrystalline silicon. Therefore, the mixing ratio of the nitrogen-based gas to the silicon-based gas is preferably 0.05 or less, and the nitrogen in the thin film is preferably 10 at% (atomic percentage) or less. In order to form polycrystalline polysilicon having an ultrafine grain structure, a subsequent thermal process is performed at a predetermined temperature or more using a reaction chamber of Furnace or Single Wafer method. 7 is a cross-sectional TEM of a polycrystalline polysilicon thin film having an ultrafine grain structure deposited by the present invention.

As described above, although the SiH4 gas is used as the source gas presented in the present invention using the spirit of the present invention, the idea of the present invention to be implemented in the present invention using Si2H6 gas as another source gas, and the constant temperature and Another embodiment of the present invention is characterized by forming a thin film having a very fine grain structure by injecting the reaction chamber at a constant ratio of NH 3 / SiH 4 at a constant pressure.

In addition, although the present invention has been described in detail through preferred embodiments, other forms of embodiments are possible. Therefore, the spirit and scope of the claims set forth below are not limited to the preferred embodiments.

As described above, the present invention is a method capable of depositing a polycrystalline silicon thin film having an ultrafine grain structure using chemical vapor deposition using a single wafer chamber, and using SiH4 (silane) gas as a silicon source gas. As a process method for controlling grains, when depositing a thin film within a certain range of process temperature and process pressure, a gas containing Nitrogen, such as NH3, is mixed with SiH4 and injected at a predetermined ratio to form a microcrystalline polycrystalline polysilicon thin film. As a result, it is possible to form uniform crystal grains when used as a floating gate electrode of a flash memory in a semiconductor device, thereby ensuring durability and reliable device characteristics of the device. Can secure excellent device characteristics when manufacturing semiconductor devices using them. Here a yield and device characteristic improving effect.

Claims (17)

delete delete delete delete delete delete delete delete delete Supplying a source gas into the chamber loaded with a substrate to deposit a thin film of amorphous silicon on the substrate, The source gas includes a silicon-based gas and an ammonia (NH 3) gas, The silicon-based gas is SiH 4 (silane) or Si 2 H 6 (disilane), Nitrogen in the thin film is a thin film deposition method, characterized in that 16.4 to 50 (1E20 atoms / cc). delete The method of claim 10, Nitrogen in the thin film is a thin film deposition method, characterized in that 2.93 to 10 at% (atomic percentage). The method of claim 10, The method further includes a heat treatment process for the thin film, The thin film is a thin film deposition method characterized in that the heat treatment process is completed polycrystalline silicon (polycrystalline silicon). The method of claim 10, Thin film deposition method characterized in that the pressure of the chamber is 100torr to 300torr when the temperature of the chamber during deposition is 580 ℃ to 650 ℃. The method of claim 10, Thin film deposition method characterized in that the pressure of the chamber is 5torr to 100torr when the temperature of the chamber during deposition is 650 ℃ to 750 ℃. delete delete

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