TWI407578B - Chemical vapor deposition process - Google Patents

Abstract

The present invention provides a chemical vapor deposition process. In particular, the process is provided to deposit and grow an amorphous silicon thin film containing microcrystalline silicon on a substrate under a controlled temperature of 25-250 DEG C by a hydrogen dilution ratio of 10-120, a deposition process at a pressure in the range 10-40 mtorr and a RF power 150-1200 W, so as to greatly improve the deposition rate of the amorphrous silicon thin film containing microcrystalline silicon, thereby manufacturing a high-efficiency silicon-based thin film solar cell with multiple energy levels.

Description

Chemical vapor deposition process

The present invention relates to a chemical vapor deposition process (CVD), and more particularly to a chemical vapor deposition process suitable for fabricating a germanium-based thin film solar cell.

There are many types of solar cells. Among them, bismuth-based solar cells are the most mature industrial manufacturing technology and the largest market share. Subdivided, 矽-based solar cells are divided into single-crystal 矽 solar cells and polycrystalline solar cells. There are three types of amorphous germanium (a-Si) thin film solar cells; however, in order to reduce process production and material costs, it is now mainly to actively develop amorphous germanium thin film solar cells.

Referring to FIG. 1, in order to maintain the output voltage, an amorphous germanium thin film solar cell having a "PiN" structure is preferably selected, comprising a substrate 11, an actuating film 12 deposited on the substrate 11, and a film The electrode unit 13 is in ohmic contact with the actuating film 12.

The substrate 11 is glass, and the actuating film 12 is made of amorphous germanium and generates electric energy by a photovoltaic effect when illuminated. More specifically, the actuating film 12 has a level difference by doping. a P-type (positive-type) semiconductor 121, an N-type (negative-type) semiconductor 123, and an intrinsic semiconductor 122 having an energy level between the energy levels of the P, N-type semiconductors 121, 123; In the above, the pure semiconductors 122 are located between the P and N-type semiconductors 121 and 123 in a layered manner. The electrode unit 13 has two electrodes 131 which are in ohmic contact with the P and N type semiconductors 121 and 123, respectively.

When the amorphous germanium thin film solar cell is illuminated, the P-type semiconductor 121, the N-type semiconductor 123, and the pure semiconductor 122 absorb photons to generate electron-hole pairs, and the electron-hole pairs form photocurrents due to self-built electric field separation. The two electrodes 131 of the electrode unit 13 apply the generated photocurrent to the outside.

The "PiN" structure of the amorphous germanium thin film solar cell can generate photocurrent during illumination and is applied at a stable voltage output; however, since the amorphous germanium contains a large number of defects and an unbonded dangling bond, The efficiency of the amorphous germanium film of the amorphous germanium thin film solar cell is rapidly attenuated (i.e., the Staebler-wronski effect) as the illumination time increases.

At present, the solution to the problem of photodegradation effect of moving film is generally to grow a so-called microcrystalline Si (μc-Si:H) having a grain size of more than 20 nm or a crystal grain size of less than 20 nm in a pure semiconductor. (nano crystalline Si, nc-Si: H), the carrier mobility of microcrystalline germanium and amorphous germanium is 1~2 orders of magnitude higher than amorphous tantalum, and the dark conductance is higher than amorphous.矽 3~4 orders of magnitude (about 10 ^-5 ~ 10 ^-7 (between S.cm ^-1 ), improving the practicality of amorphous yttrium thin film solar cells.

It is well known to those skilled in the art of amorphous germanium thin film solar cells that such amorphous germanium films are mainly formed by chemical vapor deposition processes, and chemical vapor deposition processes form amorphous germanium films, especially containing micro The difficulty of the amorphous germanium film of crystalline germanium or amorphous germanium structure lies in the hydrogen (H ₂ ) dilution ratio in the process (defined as the hydrogen flow rate and decane (SiH) in the chemical vapor deposition process introduced into the chemical vapor deposition system. ₄ ) The ratio of the flow rate), as the hydrogen dilution ratio increases, the degree of crystallization and the grain size increase, but the etching rate increases during the reaction due to a large amount of hydrogen. Therefore, the deposition rate is lowered. The current deposition rate is about 6 nm/min. In other words, although the power generation performance of the amorphous germanium thin film solar cell in which a microcrystalline germanium or an amorphous germanium structure is grown in a pure semiconductor is preferable. But it is impossible to actually mass produce.

Therefore, how to improve the chemical vapor deposition process, and the actual amount of amorphous germanium film with microcrystalline germanium or amorphous germanium structure has been one of the goals of the industry.

Accordingly, it is an object of the present invention to provide a chemical vapor deposition process for mass producing amorphous germanium films containing microcrystalline germanium.

Thus, a chemical vapor deposition process of the present invention is included in a chemical vapor deposition system, with a hydrogen dilution ratio of 10 to 120, a deposition process pressure of 10 to 40 mtorr, a deposition process temperature of 25 to 250 ° C, and 150~ The RF power of 1200 W is deposited on a substrate to grow an amorphous germanium film containing microcrystalline germanium.

The effect of the invention is to propose a method for controlling the hydrogen dilution ratio, deposition pressure and deposition temperature of the chemical vapor deposition process, depositing and growing an amorphous germanium film containing microcrystalline germanium, which is suitable for mass production. Amorphous germanium film of microcrystalline germanium.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments.

A preferred embodiment of the chemical vapor deposition process of the present invention is a process for controlling a process temperature of 25 to 250 ° C, a hydrogen dilution ratio of 10 to 40, an RF power of 150 to 1200 W, and a 10 ⁸ / The ion concentration of cm ³ ~10 ¹² /cm ³ , the microwave frequency of 40~80MHz, and the deposition process pressure of 10~40mtorr are controlled at a temperature of 25~250 °C on the glass substrate, 5~15 a high deposition rate of /sec deposits and grows a microcrystalline germanium-containing amorphous germanium film comprising a crystal portion and an amorphous portion defined as a hydrogen gas flow rate and a decane flow rate into the chemical vapor deposition system. The ratio is a high-performance amorphous "PiN" structure of amorphous germanium thin film solar cells.

Referring to FIG. 2, a high performance "PiN" structure amorphous germanium thin film solar cell mass produced by the preferred embodiment of the chemical vapor deposition process of the present invention is combined with the current "PiN" amorphous germanium thin film solar cell. There is no difference in view, comprising a substrate 21, an actuating film 22 deposited on the substrate 21 and generating electrical energy by a photovoltaic effect when illuminated, and an ohmic contact with the actuating film 21 to discharge electrical energy outward The electrode unit 23 is output.

The operating film 22 includes a P-type semiconductor 221 having an energy level difference doped, an N-type semiconductor 223, and a pure semiconductor having an energy level between the energy levels of the P, N-type semiconductors 221 and 223. 222.

In particular, the pure semiconductor 222 is an amorphous germanium film containing microcrystalline germanium prepared by the chemical vapor deposition process of the preferred embodiment of the present invention, having a crystal portion and a non-amorphous germanium. a crystal portion, and the crystal portion is composed of microcrystalline germanium having a crystal grain size of 2 to 40 nm; it is to be noted that when the crystal grain of the crystal germanium is less than 30 nm, a quantum confinement effect can be formed, and the energy gap can be adjusted by a size The change, when the electron is affected by the quantum confinement effect, causes the original continuous band structure to become a split energy level structure, and then the original indirect energy gap of the crucible becomes an energy band structure close to the direct energy gap. In addition, the quantum confinement effect can improve the electrical characteristics to increase the range of absorbable incident light energy spectrum. However, when the proportion of the crystal portion is too large, the leakage current of the intrinsic semiconductor 32 will increase; If the proportion of the part is too small, the carrier mobility will also decrease. Therefore, the crystal grain size of the crystal portion is between 10 and 30 nm, and the crystal ratio of the amorphous germanium film is 20 to 60%, and the crystal portion is located. The Si-H bond between 2070 and 2100 cm ^-1 accounts for 35 to 60% of the peak absorption ratio of the crystal portion.

Since 2070 bits representative of the absorption peaks between ^-1 ~ ^2100cm that the crystalline portion of the more dense and less defective Si-H bonds, and therefore, preferably, the crystalline portion located between the 2080 ~ 2090cm ^-1 The absorption peak accounts for 40 to 50% of the absorption peak ratio of the crystal portion.

That is to say, in addition to the amorphous tantalum thin film solar cell in which the "PiN" structure can be produced at a high deposition rate suitable for mass production, the chemical vapor deposition process of the present invention is a single-step surface. The multi-energy gap can increase the light absorption at different wavelengths and has higher luminous efficiency.

Hereinafter, the plasma enhanced chemical vapor deposition (PECVD) process, the inductively coupled chemical vapor deposition (ICP-CVD) process, and the electron cyclotron resonance chemical vapor deposition (ECR-CVD) process are specifically described.

<Micro plasma enhanced chemical vapor deposition process>

The plasma-enhanced chemical vapor deposition process has the greatest advantage of film deposition at "low temperature", so it is particularly suitable for growing amorphous germanium films containing microcrystalline germanium on glass or polymer substrates.

Specifically, in the preferred embodiment, the plasma enhanced chemical vapor deposition process controls the process temperature at 25 to 150 ° C, and the hydrogen dilution ratio of 10 to 40, and the RF power of 600 to 1200 W, 100. The bias voltage of ~300V and the deposition pressure of 10~40mtorr are deposited on a glass substrate with a temperature of 25~150 °C, and an amorphous germanium containing microcrystalline germanium is deposited and has a crystalline portion and an amorphous portion. Film; the amorphous germanium film containing microcrystalline germanium is 5~10 The deposition rate of /sec is increased, and the crystal grain size of the crystal portion is 10 to 30 nm and the ratio of the amorphous germanium film containing the microcrystalline crucible is 30 to 40%, and the amorphous portion is composed of amorphous germanium.

<Inductively coupled chemical vapor deposition process>

The inductively coupled chemical vapor deposition process is mainly a crystallization-inducing mechanism generated by etching of hydrogen, that is, during the growth process, hydrogen ions tend to react with the enthalpy of the unstable bond, and the weak bond is formed ( The weak bond of the ruthenium atom is carried away, leaving a stable ruthenium bond, so that an amorphous ruthenium film containing microcrystalline ruthenium can be grown at a temperature lower than that of the plasma enhanced chemical vapor deposition process.

Corresponding to the present invention, the process temperature of the inductively coupled chemical vapor deposition process is 150 to 250 ° C, and the hydrogen dilution ratio of 10 to 40, the RF power of 600 to 1200 W, the bias voltage of 100 to 300 V, and the 10 to 40 mtorr Under the deposition pressure, an amorphous germanium film containing microcrystalline germanium having a crystal portion and an amorphous portion is deposited on a glass substrate having a temperature controlled at 150 to 250 ° C; the amorphous crystal containing the microcrystalline germanium矽 film is 5~15 The deposition rate of /sec is increased, the crystal grain size of the crystal portion is 10 to 30 nm, and the ratio with respect to the amorphous germanium film is 30 to 40%, and the amorphous portion is composed of amorphous germanium.

<Electron Cyclotron Resonance Chemical Vapor Deposition Process>

The electron cyclotron resonance chemical vapor deposition process is characterized by a higher ability to excite or ionize gaseous molecules or ions than a plasma enhanced chemical vapor deposition process, and the ion concentration in the plasma can reach 10 ¹² /cm ³ , and The decomposition energy provided by electron cyclotron resonance can decompose gas at very low pressure (less than 10 ^-3 mbar). The amount of impurities in the plasma can be relatively reduced, and the life cycle of the reactants is also longer, so the reactants are in the cavity. The polymer in the body reacts less, the ion energy is also lower, and the damage to the surface of the film is relatively reduced.

Corresponding to the present invention, the process temperature of the electron cyclotron resonance chemical vapor deposition process is 150 to 250 ° C, and the hydrogen dilution ratio of 10 to 40, the RF power of 600 to 1200 W, the bias voltage of 100 to 300 V, and 10~ Under the deposition pressure of 40mtorr, an amorphous germanium film containing microcrystalline germanium having a crystal portion and an amorphous portion is deposited on a glass substrate controlled at a temperature of 150 to 250 ° C; the amorphous germanium film is 5 ~15 The deposition rate of /sec is increased, the crystal grain size of the crystal portion is 10 to 20 nm, and the ratio with respect to the amorphous germanium film is 30 to 40%, and the amorphous portion is composed of amorphous germanium.

The preferred embodiment of the chemical vapor deposition process of the present invention described above will be more clearly understood in conjunction with the description of the following two specific examples.

<Specific example 1>

In the inductively coupled chemical vapor deposition system (ICPCVD), the deposition pressure (cavity pressure) is controlled at 20mtorr, the deposition time is 30min, the process temperature is 150°C, and the glass substrate temperature is controlled at 150°C, with different RF power. The hydrogen dilution ratio is deposited to produce different amorphous germanium films containing microcrystalline germanium. The different RF power, hydrogen dilution ratio, deposition rate, and crystallinity of the amorphous germanium film containing microcrystalline germanium are prepared. Organized in Table 1.

<Specific example 2>

In the inductively coupled chemical vapor deposition system (ICPCVD), the deposition pressure (cavity pressure) is controlled at 20 mtorr, the RF power is controlled at 600 W, the deposition time is 30 min, the process temperature and the glass substrate temperature are controlled at 150 ° C, respectively. The amorphous germanium film containing microcrystalline germanium is deposited by different hydrogen dilution ratios, and the crystallinity of the amorphous germanium film containing the microcrystalline germanium is prepared by different hydrogen dilution ratio, substrate bias, and prepared microcrystalline germanium film. In Table 2.

Referring to FIG. 3, FIG. 3 is an FT-IR spectrum of the amorphous germanium film containing microcrystalline germanium prepared in the specific example 1 with a radio frequency power of 1200 W, a deposition pressure of 30 mtorr, and a hydrogen dilution ratio of R=30. Analysis results.

In Fig. 3, curve 1 is an FT-IR spectrum of the amorphous germanium film containing microcrystalline germanium, curves 2 and 3 are crystal portions of the amorphous germanium film containing microcrystalline germanium, and curves 4 and 5 are the non- In the crystal part, the absorption peak of the curve 4 represents the Si-H bond of the amorphous germanium (a-Si:H), and the absorption peak of the curve 5 is the process of depositing the amorphous germanium film containing the microcrystalline germanium. Methane (SiH ₄ ) is Si/H bond of agglomerate (SiH ₃ ) formed by incomplete or dissociation during the reaction, and curve 2 with absorption peak between 2070 and 2100 cm ^-1 represents the crystal part. The Si-H bond of the microcrystalline germanium and the amorphous germanium which are denser and less defective, and the absorption peak of the curve 3 indicates the Si-H bond with relatively loose crystal structure and many defects in the crystal portion. As a result of Si-H spectrum analysis of each zone, it was found that the Si-H bond between 2070 and 2100 cm ^-1 in this example accounted for about 56%.

In summary, since the amorphous germanium thin film solar cell with microcrystalline germanium is one of the solar cells with higher efficiency, the disadvantage is that the deposition growth rate is too slow, and the actual mass production cannot be achieved at all; By controlling the important process parameters of the chemical vapor deposition process such as hydrogen dilution ratio, RF power, and deposition process pressure, 5~15 on the substrate. The high deposition rate of /sec deposits an amorphous germanium film containing microcrystalline germanium, and can be used to mass-produce an amorphous germanium film having microcrystalline germanium, and the object of the present invention can be achieved.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

twenty one. . . Substrate

twenty two. . . Actuating membrane

221. . . P-type semiconductor

222. . . Pure semiconductor

223. . . N-type semiconductor

twenty three. . . Electrode unit

231. . . electrode

1 is a schematic view showing an amorphous germanium thin film solar cell of a general "P-i-N" structure;

Figure 2 is a schematic view showing an amorphous germanium thin film solar cell comprising microcrystalline germanium of the present invention;

Fig. 3 is a FT-IR spectrum chart showing the absorption peaks of different Si-H bonds obtained by the amorphous germanium film containing microcrystalline germanium produced by this specific example 1 of the present invention.

twenty one. . . Substrate

twenty two. . . Actuating membrane

221. . . P-type semiconductor

222. . . Pure semiconductor

223. . . N-type semiconductor

twenty three. . . Electrode unit

231. . . electrode

Claims (12)

A chemical vapor deposition process for forming an amorphous germanium film having microcrystalline germanium, wherein the amorphous germanium film having microcrystalline germanium comprises a crystal portion and an amorphous portion, and the crystal size of the crystal portion is 2~40nm, comprising: providing a substrate in a chemical vapor deposition system; controlling the chemical vapor deposition system to have a working pressure of 10 to 40 mtorr, an operating temperature of 25 to 250 ° C, and an RF power of 150 to 1200 W; A mixture of hydrogen and decane (SiH ₄ ) is introduced, and the dilution ratio of the hydrogen is 10 to 120. According to the chemical vapor deposition process of claim 1, wherein the ratio of the crystal portion to the amorphous germanium film containing microcrystalline germanium is 20 to 60%, and the crystal size is 10 to 30 nm. According to the chemical vapor deposition process of claim 1, wherein the hydrogen dilution ratio is 10-40. According to the chemical vapor deposition process of claim 1, wherein the amorphous germanium film containing the microcrystalline germanium is located at 2070-2100 cm ^{-1 and} the Si-H bond absorption peak accounts for the absorption peak ratio of the crystal portion. 35~60%. According to the chemical vapor deposition process of claim 3, wherein the amorphous germanium film containing microcrystalline germanium is located at a density of Si-H bond absorption peak at 2080 to 2090 cm ^-1 , which accounts for the peak absorption ratio of the crystal portion. 40~50%. According to the chemical vapor deposition process of claim 1, wherein the chemical vapor deposition system has an operating temperature of 150 to 250 ° C and a substrate temperature of 150 to 250 ° C. According to the chemical vapor deposition process of claim 1, the method further comprises the step of providing a bias of the substrate. According to the chemical vapor deposition process described in claim 7, wherein the bias voltage is 100 to 300V. The chemical vapor deposition process according to claim 1, wherein the chemical vapor deposition system has an ion concentration of 10 ⁸ /cm ³ to 10 ¹² /cm ³ . According to the chemical vapor deposition process of claim 1, wherein the deposition rate of the amorphous germanium film having microcrystalline germanium is 5 to 15 Å/sec. According to the chemical vapor deposition process of claim 1, wherein the chemical vapor deposition system has an operating temperature of 25 to 150 ° C and a substrate temperature of 25 to 150 ° C. According to the chemical vapor deposition process described in claim 1, wherein the chemical vapor deposition system has a radio frequency power of 600 to 1200 W.