KR100997110B1 - Process for Preparation of Thin Layered Structure - Google Patents

Abstract

The present invention is a method for producing a thin film structure based on the PCC method.

The present invention is characterized in that a thin film is formed on a substrate using at least two different plasma frequencies in a thin film manufacturing method based on a plasma-enhanced chemical vapor deposition (PECVD) process.

Description

Process for Preparation of Thin Layered Structure

The present invention relates to a method for producing a thin film structure based on the PCC method.

The present invention relates to a method for manufacturing a thin film structure based on PECVD method.

Recently, with increasing interest in environmental problems and energy depletion, there is a growing interest in solar cells as an alternative energy with abundant energy resources, no problems with environmental pollution, and high energy efficiency.

Solar cells can be divided into solar cells that generate steam required to rotate a turbine using solar heat, and solar cells that convert photons into electrical energy using properties of semiconductors. Among them, researches on solar cells that convert light energy into electrical energy by absorbing light to generate electrons and holes have been actively conducted.

In photovoltaic cells, it is important to reduce the reflectance of absorbed light because the photoelectric conversion efficiency is adjusted according to the amount of light absorbed. Therefore, an anti-reflection film is used to reduce the reflectance of light, or a method of minimizing the area covering sunlight when forming electrode terminals is used. Among them, various researches on anti-reflection film that can realize high reflectance have been conducted and are still in progress.

As such an antireflection film, a silicon nitride film having a multilayer structure is generally known to be preferable. That is, when an additional low refractive index second silicon nitride film is further formed on the relatively high refractive index first silicon nitride film, a high radiation prevention rate is obtained.

Since the silicon nitride film is mainly formed by PECVD, in order to form a silicon nitride film having a multi-layer structure, deposition is performed by varying the ratio of the mixed gas of plasma. However, in order to change the ratio of the mixed gas, it is necessary to completely change the atmosphere of the PECVD reaction chamber, which inevitably consumes time, has a disadvantage in that the loss of raw materials is large and the composition uniformity of the thin film is inferior.

Therefore, in the present invention, as a method to fundamentally solve this problem, when forming a thin film structure consisting of two or more thin films made of the same components, but different compositions, such as the anti-reflection film of the solar cell, the reaction chamber We propose a technique that can innovatively shorten the manufacturing process by changing the plasma frequency only while maintaining the gas atmosphere.

While some prior art methods have been proposed in some prior arts to alter the plasma frequency in a PECVD process, they do not teach or imply application to the method of forming a multilayer thin film structure as in the present invention.

Accordingly, the method of manufacturing a multilayer thin film structure according to the present invention is a method of manufacturing a multilayer thin film structure having different physical properties on a substrate by a plasma-enhanced chemical vapor deposition (PECVD) process, and mixing for plasma generation. And a step of sequentially forming a thin film corresponding to the plasma composition at the plasma frequency by changing the applied plasma frequency (frequency) without changing the proportion of the gas.

That is, the manufacturing method of the present invention changes only the plasma frequency in consideration of the fact that the ionization ratio of the mixed gas is changed even if the plasma frequency is different even if the mixed gas for generating plasma is the same. Thin films of different compositions are grown sequentially on the base material.

Therefore, according to the present invention, it is possible to easily manufacture a multilayer thin film structure of a desired physical property by selectively changing only the plasma frequency without changing the proportion of the mixed gas for plasma generation, and thus, a chamber atmosphere for forming such a multilayer thin film structure. Compared with the prior art, which has to be renewed, the manufacturing process can be greatly shortened and the loss of raw materials can be minimized.

Changing the plasma frequency in the PECVD reaction chamber can be implemented in a variety of ways. In one preferred example, the PECVD apparatus includes two or more generators that provide different frequencies and the plasma frequency can be changed by the selective operation of these generators. In some cases, the plasma composition may be determined by changing the plasma frequency application time in a predetermined cycle.

As described above, according to the present invention, in the manufacture of a multilayer thin film structure having the same components but having different compositions, the multilayer structure can be formed by a continuous process by changing only the plasma frequency, thereby reducing the overall process time. And the loss of raw materials can be reduced to reduce the manufacturing cost, it is possible to manufacture a multilayer thin film structure of excellent physical properties with high uniformity.

Although FIG. 1 shows a schematic diagram of a showerhead type flat electrode PECVD apparatus according to an embodiment of the present invention, the scope of the present invention is not limited thereto.

Referring to FIG. 1, the reaction chamber 100 having an open top is covered by a chamber cover 200, and a reaction space is blocked from the outside. In the reaction space, a susceptor 300 capable of vertically transporting and electrically grounded is installed, and the substrate 400 is seated on the susceptor 300, and the substrate 400 is disposed inside the susceptor 300. It is equipped with a heater for heating the.

In the reaction space above the susceptor 300, a showerhead type flat electrode 700 connected to two different external RF generators 500 and 600 is installed. That is, the first RF generator 500 provides a relatively high frequency, and the second RF generator 600 provides a relatively low frequency. The plate electrode 700 is hollow and the gas injection tube 800 is in communication with the inside of the plate electrode 700. Small diameter injection holes 720 are formed on the bottom of the plate electrode 700, and the plate electrode 700 made of metal is anodized to prevent arc generation by plasma.

The mixed gas for plasma formation injected from the gas injection tube 800 is ionized by the plate electrode 700 to perform a predetermined deposition on the substrate 400 and is then exhausted through the gas exhaust pipe 820. In this ionization process, the thin film deposited due to the mixed gas ionized by the high frequency first RF generator 500 operates and the thin film deposited due to the mixed gas ionized by the low frequency second RF generator 600 operates different from each other. It will have a composition. The operation of the RF generators 500 and 600 may be performed sequentially, or may be repeatedly operated at regular time intervals.

The side wall of the reaction chamber 100 is provided with a slot valve (900) for determining the communication between the load lock portion (not shown) and the reaction space, the substrate 500 from the load lock portion on the susceptor 300 The slot valve 900 is opened at the time of conveyance.

In the present invention, the substrate is not particularly limited as long as the substrate is required to form a multilayer thin film by a PECVD process. Examples thereof include a silicon wafer for semiconductor manufacture, a glass substrate for TFT manufacture, a silicon wafer for solar cell manufacture, and the like. have. In some cases, one or more thin films may be already formed on such a substrate, or may be in a state where activation is partially or entirely performed by injection of a predetermined dopant.

The thin films manufactured by the above method are thin films made of the same components and varying in composition, for example, a multilayer silicon nitride film used as an antireflection film of a solar cell, but is not limited thereto. The silicon nitride film as the antireflection film has a structure in which a lower thin film having a high refractive index and an upper thin film having a low refractive index are sequentially stacked on a silicon wafer. Here, the lower thin film and the upper thin film are made of Si and N as constituents, respectively, but are manufactured from thin films having different refractive indices (physical properties) by changing their component ratios (compositions).

Thus, in one preferred embodiment, the substrate is a silicon wafer for solar cell manufacturing, the multilayer thin film may be an antireflection film of a multilayer structure consisting of different refractive indices.

When forming a silicon nitride film on a silicon wafer by a PECVD process, a mixed gas containing, for example, SiH ₄ and NH ₃ as a reaction gas may be supplied to a reaction chamber of a PECVD apparatus as in FIG. 1 to perform chemical vapor deposition. . In general, the PECVD reaction chamber is filled with an inert gas as an atmosphere gas, and examples of the inert gas include N ₂ and Ar.

In one preferred embodiment, the PECVD chamber forming the multilayer silicon nitride film is provided with a 5 to 50 MHz generator as a high frequency generator and a 10 to 500 kHz generator as a low frequency generator, and sequentially operates the high frequency generator and the low frequency generator. By doing so, a multilayer antireflection film of different refractive index can be produced. In some cases, the refractive index of the thin film may be adjusted by alternately operating the high frequency generator and the low frequency generator at a time interval of 1 to 60 seconds.

The present invention also provides an electronic device comprising a multilayer thin film structure manufactured by the above method. Representative examples of such devices include a solar cell module including an antireflection film having a multilayer thin film structure.

The construction of a solar cell module including an antireflection film as a multilayer thin film structure and a method of manufacturing such a solar cell module are well known in the art, and a description thereof will be omitted herein.

Hereinafter, the content of the present invention will be described in detail with reference to Examples, but the scope of the present invention is not limited thereto.

First, a 13.56 MHz high frequency generator was installed as the first RF generator and a low frequency generator 10 ~ 500 kHz was installed as the second RF generator in the PECVD apparatus as shown in FIG. 1. In this experiment, the applied frequency of the second RF generator was set to about 450 kHz. In addition, in order to deposit a multilayer silicon nitride on a silicon wafer, the process conditions shown in Table 1 were set.

TABLE 1

Example 1

While only the first RF generator is operated and 13.56 MHz is applied, the silicon on the silicon wafer is changed while the composition ratio (NH ₃ / SiH ₄ ) of SiH ₄ and NH ₃ , which are reaction gases (mixed gases), is changed within a range of 0.6 to 2.0. Nitride films were deposited, and the refractive indices of such silicon nitride films were measured, respectively.

In addition, the silicon nitride film was deposited in the same manner as described above with 450 kHz applied to only the second RF generator, and the refractive indices were measured.

In addition, the first and second RF generators were alternately operated at intervals of about 10 seconds, and silicon nitride films were deposited in the same manner as described above with 13.56 MHz and 450 kHz alternately applied, and the refractive indices were measured, respectively.

The measurement results are shown in FIG. 2. As shown in FIG. 2, it can be seen that silicon nitride films having different refractive indices are obtained according to the composition ratio of the reaction gas as well as the applied plasma frequency. For example, at a reaction gas composition ratio (NH ₃ / SiH ₄ ) of 1.0, the silicon nitride film having a refractive index of 2.07 is obtained by the operation of the first RF generator, and the silicon nitride film having a refractive index of 1.96 is obtained by the operation of the second RF generator. The alternating operation of the first RF generator and the second RF generator yields a silicon nitride film having a refractive index of 1.99.

[Example 2]

In order to form an antireflection film in which a low refractive index silicon nitride film is laminated on a high refractive index silicon nitride film on a silicon wafer, the composition ratio (NH ₃ / SiH ₄ ) of the reaction gas is set to 1.0 under the process conditions as shown in Table 1 above. The first RF generator was operated for 90 seconds to deposit a silicon nitride film having a refractive index of 2.07 at a thickness of 40 nm, and after a break of 1 to 2 seconds, the second RF generator was operated for 98 seconds to make a silicon nitride film having a refractive index of 1.96 at a thickness of 40 nm. By depositing at nm, an antireflection film having a multilayer structure was prepared.

Comparative Example 1

In order to form an antireflection film in which a low refractive index silicon nitride film is laminated on a high refractive index silicon nitride film on a silicon wafer, first, a process ratio of the reaction gas (NH ₃ / SiH ₄ ) is set to 1.0 under the process conditions as shown in Table 1 above. The first RF generator was operated for 90 seconds to deposit a silicon nitride film having a refractive index of 2.07 with a thickness of 40 nm. Then, the atmosphere of the chamber was renewed by injecting only the atmospheric gas for 60 seconds while stopping the injection of the reaction gas. Again, the composition ratio (NH ₃ / SiH ₄ ) of the reaction gas was adjusted to 1.5, injected into the chamber, the first RF generator was operated for 98 seconds, and a silicon nitride film having a refractive index of 1.96 was deposited to a thickness of 40 nm, thereby forming a multilayer antireflection film. Was prepared.

[Result analysis]

As shown in Example 2 and Comparative Example 1, in manufacturing an antireflection film having the same multilayer structure on a silicon wafer, in Example 2 according to the present invention, only about 1 to 2 seconds in the process of changing the applied frequency On the contrary, in Comparative Example 1, at least 1 minute to 2 minutes or more are required for renewal of the chamber atmosphere and redeposition of the thin film, so that a large difference occurs in the overall process time.

In addition, in the case of Comparative Example 1, the loss of a large amount of reaction gas in the process of renewal of the chamber atmosphere was inevitable, it was confirmed that the uniformity of the refractive index in the low refractive index silicon nitride film is lower than the multilayer thin film structure prepared in Example 1 .

Although the present invention has been described in detail with reference to specific examples, it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention, and such variations and modifications belong to the appended claims. .

1 is a schematic diagram of a showerhead type flat electrode PECVD apparatus according to an embodiment of the present invention;

2 is a graph showing the experimental results in Example 1 of the present invention.

Claims (14)

delete delete delete delete delete delete delete delete In the method of manufacturing a multilayer structure anti-reflection film of a solar cell based on the plasma-enhanced chemical vapor deposition (PECVD) process, Forming a first anti-reflection film in a state where only a high frequency plasma frequency is applied; And And forming a second anti-reflection film having a refractive index lower than that of the first anti-reflection film while applying only a low frequency plasma frequency. The high frequency plasma frequency ranges from 5 MHz to 50 MHz, and the low frequency plasma frequency ranges from 10 kHz to 500 kHz. The high frequency plasma frequency and the low frequency plasma frequency are applied to the same electrode of the plasma enhanced chemical vapor deposition apparatus, In the forming of the first anti-reflection film and the forming of the second anti-reflection film, the reaction chamber in which the first anti-reflection film is formed and the reaction chamber in which the second anti-reflection film is formed are the same, and the plasma strengthening is performed. A method for manufacturing a multilayer antireflection film having the same plasma generating power supplied to a chemical vapor deposition apparatus. The method of claim 9, The plasma frequency of the high frequency is 13.56 MHz, the plasma frequency of the low frequency is 450 kHz manufacturing method of a multilayer structure anti-reflection film. The method of claim 9, And the electrode to which the plasma frequency of the high frequency and the plasma frequency of the low frequency are applied are a showerhead type flat plate electrode. The method of claim 9, Forming the first anti-reflection film and forming the second anti-reflection film, the deposition temperature and the deposition pressure is a multi-layer structure anti-reflection film manufacturing method equal to each other. The method of claim 9, The method of claim 1, wherein the forming of the first anti-reflection film and the forming of the second anti-reflection film include the same ratio of the mixed gas for plasma generation supplied to the plasma enhanced chemical vapor deposition apparatus. The method of claim 9, The first anti-reflection film and the second anti-reflection film are silicon nitride film manufacturing method of a multilayer structure anti-reflection film.

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