KR101057147B1 - Manufacturing method for thin film of poly-crystalline silicon - Google Patents

Abstract

PURPOSE: A poly-crystal silicon membrane manufacturing method is provided to manufacture a poly-crystal silicon membrane using an induced metal crystallization method, thereby enabling to crystallize in low temperature and precisely measuring an amount of a catalyst metal. CONSTITUTION: A poly-crystal silicon membrane manufacturing method is comprised of following seven steps. A metal layer formation step(S1) in which a metal layer is formed on an insulating substrate. A first silicon layer formation step(S2) in which a silicon layer is laminated on the metal layer formed in the metal layer formation step. An oxidation layer formation step(S3) in which an oxidation layer is formed on the silicon layer formed in the first silicon layer formation step. A first thermal processing step(S4) in which a metal-sili oxide layer is formed by thermal processing the oxidation layer and laminated silicon layer from the first silicon layer formation step. A second silicon layer formation step(S6) in which an amorphous silicon layer is laminated on the metal-sili oxide layer. A crystallization stage(S7) which is thermal processing in order to create crystalline silicon on the amorphous silicon layer by using a particle in the metal-sili oxide layer as a medium.

Description

Manufacturing method for thin film of poly-crystalline silicon}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a polycrystalline silicon thin film for use in a solar cell, and more particularly, to a method for effectively producing a polycrystalline silicon thin film of an amorphous silicon thin film by metal induction crystallization.

In general, most problems arising in the production of poly-silicon (poly-Si) are due to the use of glass substrates that are vulnerable at high temperatures, and the process temperature cannot be raised sufficiently to the temperature at which the amorphous silicon (a-Si) thin film is crystallized.

The process requiring high temperature heat treatment in the production of poly-Si is a crystallization heat treatment (Crystallization) that converts the amorphous silicon (a-Si) thin film to a crystalline silicon thin film and an activation heat treatment (Dopant) that is electrically activated after doping Activation).

At present, a variety of processes (LTPS: Low Temperature poly-Si) have been proposed for forming a polycrystalline silicon thin film in a short time at a low temperature that the glass substrate allows. Representative methods for forming a polycrystalline silicon thin film include solid phase crystallization (SPC), excimer laser annealing (ELA), and metal induced crystallization (MIC).

Solid Phase Crystallization (SPC) is the most direct and long used method of obtaining polycrystalline silicon (poly-Si) thin films from amorphous silicon (a-Si). SPC is a method of obtaining a polycrystalline silicon thin film having a grain size of about several micro by heat-treating the amorphous silicon thin film at a temperature of 600 ℃ or more for several tens of hours. The polycrystalline silicon thin film obtained by this method has a disadvantage in that it is difficult to use a glass substrate because of high defect density in crystal grains and a high heat treatment temperature, and a long process time due to long heat treatment.

Excimer Laser Annealing (ELA) is a method of instantaneously irradiating an excimer laser to a amorphous silicon thin film for nanoseconds to melt and recrystallize the amorphous silicon thin film without damaging the glass substrate.

However, ELA is known to have significant problems in mass production processes. ELA has a very non-uniform grain structure of polycrystalline silicon (poly-Si) thin film according to the laser irradiation amount. ELA has a problem that it is difficult to manufacture a uniform crystalline silicon thin film because of the narrow process range. In addition, the surface of the polycrystalline silicon thin film is rough, which adversely affects the characteristics of the device. This problem is more serious in the application of organic light emitting diodes (OLEDs) in which the uniformity of thin film transistors (TFTs) is important.

To overcome this problem, the proposed method is Metal Induced Crystallization (MIC). MIC is a method of inducing crystallization of silicon by applying a metal catalyst to amorphous silicon by sputtering or spin coating, followed by heat treatment at low temperature. As the metal catalyst, various metals such as nickel (Ni), copper (Cu), aluminum (Al), and palladium (Pd) may be used. In general, nickel (Ni) is used as a metal catalyst in MIC, in which reaction control is easy and large grains are obtained. MIC can be crystallized at a lower temperature of less than 450 ° C., but there are significant problems in the actual production process. This problem is that a significant amount of metal diffused in the active region in the TFT causes typical metal contamination, increasing leakage current, one of the TFT characteristics.

The development of Low Temperature Poly-Si (LTPS) has been carried out for the purpose of application to liquid crystal display devices. In addition, the need for development is increasing.

Inexpensive, high-productivity poly-Si fabrication methods will compete with amorphous silicon thin-film transistor liquid crystal displays (a-Si TFT LCDs) in the display family with many active organic light emitting diodes (AMOLEDs) in the market. It is important in that it is. The method of manufacturing polycrystalline silicon is also important in that active organic light emitting diodes (AMOLEDs) will compete with crystalline wafer forms in solar cells. Therefore, the production cost and market competitiveness of the product can be stably polycrystalline at a low price compared to an amorphous silicon thin film transistor liquid crystal display (a-Si TFT LCD) and a crystalline wafer type solar cell in which the production technology has reached a stabilization stage. It depends on whether you can make silicon.

1 schematically shows a manufacturing process for obtaining a polycrystalline silicon thin film from amorphous silicon by a metal induction crystallization method. Referring to FIG. 1, in the conventional process, a buffer layer 2 made of silicon oxide (SiO ₂ ) is formed on a substrate 1 such as glass, and an amorphous silicon layer 3 is formed on the buffer layer 2 by plasma chemical vapor deposition (PECVD). After forming by Plasma Enhanced Chemical Vapor Deposition, sputtering and coating a metal such as nickel (Ni) on the amorphous silicon layer (3) and then heat-treated by RTA (Rapid Thermal Annealing) at about 700 ℃ The crystalline silicon 4 is formed from the silicon layer 3. However, according to the conventional method, since it is difficult to precisely control the amount of the metal applied to the upper portion of the amorphous silicon layer 3, there is an inconvenience that it is necessary to remove the excessively applied metal. This process not only increases manufacturing costs but also adversely affects the quality of the crystallized silicon.

An object of the present invention is to solve the above problems, in the method of manufacturing a polycrystalline silicon thin film using the metal induction crystallization method, precisely control the amount of catalyst metal and enable crystallization at low temperature By providing an efficient method for producing a polycrystalline silicon thin film.

In order to achieve the above object, a method of manufacturing a polycrystalline silicon thin film according to the present invention includes: forming a metal layer on an insulating substrate;

A first silicon layer forming step of laminating a silicon layer on the metal layer formed in the metal layer forming step;

An oxide film forming step of forming an oxide film on the silicon layer formed in the first silicon layer forming step;

A first heat treatment step of forming a metal silicon oxide layer by heat-treating the silicon layer and the oxide layer stacked in the metal layer, the first silicon layer forming step;

A second silicon layer forming step of laminating an amorphous silicon layer on the metal silicon oxide layer; And

And a crystallization step of heat-treating the crystalline silicon in the amorphous silicon layer through the particles of the metal silicide oxide layer.

The substrate preferably includes a buffer layer made of silicon nitride (SiN) or silicon oxide (SiO ₂ ) between the metal layer and the metal layer.

The thickness of the metal layer is 5 kPa to 1500 kPa, the thickness of the oxide film is 1 kPa to 300 kPa, the thickness of the first silicon layer is 5 kPa to 1500 kPa, and the ratio of the thickness of the metal layer and the thickness of the first silicon layer is 1: It is preferable that it is 0.5-1: 6.

Performing an auxiliary heat treatment step of stacking and heat treating an auxiliary silicon layer on the metal silicide oxide layer after the first heat treatment step to reinforce the metal silicide oxide layer.

A second silicon layer forming step of laminating an amorphous silicon layer on the metal silicon oxide layer subjected to the auxiliary heat treatment step; And

And a crystallization step of heat-treating the crystalline silicon in the amorphous silicon layer through the particles of the metal silicide oxide layer.

The heat treatment temperature in the oxide film forming step is 400 ℃ to 1000 ℃, the heat treatment temperature in the first heat treatment step is preferably 300 ℃ to 1000 ℃.

After the metal layer forming step, the first silicon layer forming step may be performed after the patterning step of removing a portion of the metal layer by a photolithography method.

The method for producing a polycrystalline silicon thin film according to the present invention is effective to produce an effective polycrystalline silicon crystallized thin film by precisely controlling the amount of a metal catalyst diffused into the amorphous silicon layer and acting as a nucleus of silicon crystallization in the amorphous silicon layer. There is. In addition, the manufacturing method of the polycrystalline silicon thin film according to the present invention has an advantage that can be crystallized at a lower temperature than the conventional manufacturing method.

1 is a view for explaining a conventional method for producing a polycrystalline silicon thin film by a metal induction crystallization method.
2 is a view showing a manufacturing process according to a preferred embodiment of the invention.
3 is a cross-sectional view after the oxide film forming step illustrated in FIG. 2.
4 is a view showing a cross section after the first heat treatment step shown in FIG.
FIG. 5 is a view illustrating a state in which a silicon layer is stacked on a metal silicide oxide layer during the auxiliary heat treatment step shown in FIG. 2.
FIG. 6 is a view illustrating a cross section after the second silicon layer forming step illustrated in FIG. 2.
FIG. 7 is a cross-sectional view schematically showing the formation of polycrystalline silicon on a substrate after the crystallization step shown in FIG. 2.
8 is a photograph of the surface of amorphous silicon as viewed under an optical microscope.
FIG. 9 is a graph analyzing the wave number of the amorphous silicon illustrated in FIG. 8.
10 is a photograph of the surface of a crystalline silicon wafer viewed with an optical microscope.
FIG. 11 is a graph analyzing the wave number of the silicon wafer illustrated in FIG. 10.
12 is a photograph of a surface of a polycrystalline silicon thin film manufactured by a conventional metal induction crystallization method viewed with an optical microscope.
FIG. 13 is a graph analyzing the wave number of the polycrystalline silicon thin film illustrated in FIG. 12.
14 is a photograph of the surface of the polycrystalline silicon thin film prepared according to the present invention under an optical microscope.
FIG. 15 is a graph analyzing the wave number of the polycrystalline silicon thin film illustrated in FIG. 14.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a view showing a manufacturing process according to a preferred embodiment of the invention. 3 is a cross-sectional view after the oxide film forming step illustrated in FIG. 2. 4 is a view showing a cross section after the first heat treatment step shown in FIG. FIG. 5 is a view showing a state in which a silicon layer is stacked on a metal silicide oxide layer during the auxiliary heat treatment step shown in FIG. 2. FIG. 6 is a view illustrating a cross section after the second silicon layer forming step illustrated in FIG. 2. FIG. 7 is a cross-sectional view schematically showing the formation of polycrystalline silicon on a substrate after the crystallization step shown in FIG. 2.

2 to 7, a method of manufacturing a polycrystalline silicon thin film (hereinafter, referred to as a “manufacturing method”) according to a preferred embodiment of the present invention includes a metal layer forming step S1 and a first silicon layer forming step S2. And an oxide film forming step (S3), a first heat treatment step (S4), an auxiliary heat treatment step (S5), a second silicon layer forming step (S6), and a crystallization step (S7).

In the metal layer forming step S1, a metal layer 30 such as nickel (Ni) is formed on an insulating substrate 10 such as glass. The substrate 10 includes a buffer layer 20 made of a material such as silicon nitride (SiN) or silicon oxide (SiO ₂ ). The buffer layer 20 is provided to serve as an insulation function. In addition, the buffer layer 20 may have impurities in the first silicon layer 40 or the second silicon layer 60 described later from the substrate 10 in the first heat treatment step S4 or the crystallization step S7 described later. Diffusion is provided to prevent impurities from being contaminated in the first silicon layer 40 or the second silicon layer 60. The metal layer 30 may be performed by a known method such as sputtering or plasma chemical vapor deposition (PECVD). It is preferable that the thickness of the said metal layer 30 is 5 kPa-1500 kPa. If the thickness of the metal layer 30 is less than 5Å, the thickness of the metal layer 30 is so thin that the process reproducibility deteriorates, and the problem of deterioration in uniformity of the metal layer 30 when deposited in a large area. have. On the other hand, when the thickness of the metal layer 30 exceeds 1500 kPa, too much metal penetrates into the second silicon layer 60, which will be described later, so that a problem of metal contamination occurs. There is a problem of degrading the characteristics of a device containing silicon. After the metal layer forming step S1, a patterning step of removing a portion of the metal layer 30 by a photolithography method may be performed. If necessary, the patterning step can be omitted. The patterning step is to uniformly distribute the growth nucleus of the crystalline silicon.

In the first silicon layer forming step (S2), an amorphous first silicon layer 40 is formed on the metal layer 30 using a known means such as plasma chemical vapor deposition. It is preferable that the thickness of the said 1st silicon layer 40 is 5 kPa-1500 kPa. When the thickness of the first silicon layer 40 is less than 5Å, the thickness of the first silicon layer 40 is so thin that the process reproducibility deteriorates and the uniformity of the first silicon layer 40 when deposited in a large area. There is a problem of poor uniformity. On the other hand, when the thickness of the first silicon layer 40 exceeds 1500 kPa, the chemistry that is not necessary for the first silicon layer 40 to form the metal silicon oxide layer 55 in combination with the metal layer 30 There is a problem that a join is created. In addition, the ratio of the thickness of the metal layer 30 and the thickness of the first silicon layer 40 is preferably 1: 0.5 to 1: 6. When the ratio of the thickness of the metal layer 30 and the thickness of the first silicon layer 40 is out of the above range, as described above, there is a problem in that chemical bonds that are not necessary to form the metal silicide oxide layer 55 are generated. have. In other words, a chemical bond of a composition other than the metal silicide composition required for metal inductive bonding is formed, which hinders inductive crystallization.

In the oxide film forming step (S3), the metal oxide film 50 is deposited on the first silicon layer 40 to form the metal oxide film 50. The heat treatment temperature for forming the oxide film 50 is preferably 400 ℃ to 1000 ℃. When the heat treatment temperature of the oxide film forming step is less than 400 ° C., an oxide of nickel (Ni) may not be formed well. On the other hand, when the heat treatment temperature of the oxide film forming step exceeds 1000 ° C, the substrate 10 made of glass deforms or breaks due to thermal shock. The heat treatment method of the oxide film forming step (S3) may be a high temperature furnace, a metal heat treatment (RTA), an ultraviolet (UV) heating method, or the like. The oxide film 50 serves to lower the activation energy during diffusion of the catalyst metal in the process of forming the metal silicide oxide layer 55 in the first heat treatment step S4 described later.

In the first heat treatment step S4, catalytic metal atoms, such as nickel (Ni), move from the metal layer 30 to the first silicon layer 40 to combine with oxygen transferred from the oxide layer 40 to form a metal silicide oxide. Heat treatment is performed to form the layer 55 (NiSiO). The heat treatment performed in the first heat treatment step S4 may be performed by a high temperature furnace, rapid heat treatment (RTA), ultraviolet (UV) heating, or the like. The metal silicide oxide layer 55 formed in the first heat treatment step S4 serves as a nucleus for crystallizing amorphous silicon (a-Si) in the crystallization step S7 described later.

In the auxiliary heat treatment step S5, after the first heat treatment step S4, the auxiliary silicon layer 57 is laminated on the metal silicide oxide layer 55 and heat treated to enhance the metal silicide oxide layer 55.

In the second silicon layer forming step (S6), the second silicon layer 60 is formed by stacking amorphous silicon on the metal silicon oxide layer 55. The method of forming the second silicon layer 60 may be performed using a method such as a known plasma chemical vapor deposition method.

In the crystallization step S7, heat treatment is performed such that crystalline silicon 70 is generated in the amorphous second silicon layer 60 through the metal particles of the metal silicon oxide layer 55. The heat treatment in the crystallization step (S7) is performed at 630 ° C using Rapid Thermal Annealing (RTA) equipment.

In order to analyze the crystallization state of the polycrystalline silicon thin film manufactured by such a manufacturing method, the size of the crystal grains was observed by using an optical microscope and Raman Spectroscopy, and the wave number having the maximum intensity was analyzed.

8 is a photograph of the surface of amorphous silicon as viewed under an optical microscope. FIG. 9 is a graph analyzing the wave number of the amorphous silicon illustrated in FIG. 8. 10 is a photograph of the surface of a crystalline silicon wafer viewed with an optical microscope. FIG. 11 is a graph analyzing the wave number of the silicon wafer illustrated in FIG. 10. 12 is a photograph of a surface of a polycrystalline silicon thin film manufactured by a conventional metal induction crystallization method viewed with an optical microscope. FIG. 13 is a graph analyzing the wave number of the polycrystalline silicon thin film illustrated in FIG. 12. 14 is a photograph of the surface of the polycrystalline silicon thin film prepared according to the present invention under an optical microscope. FIG. 15 is a graph analyzing the wave number of the polycrystalline silicon thin film illustrated in FIG. 14.

8 and 9, the second silicon layer 60, which is amorphous silicon, exhibits maximum intensity at a wavenumber of 480 cm ⁻¹ . In FIG. 9, the horizontal axis represents a wave number (cm ⁻¹ ) and corresponds to a frequency. A wave number is a unit of frequency that represents the number of waves in a unit distance by dividing the frequency of light by the speed of light in atomic, molecular, and nuclear spectroscopy. In other words, the frequency of a wave is represented by the Greek letter ν (nu), which is equal to the luminous flux c divided by the wavelength λ. That is, ν〓c / λ. In the visible region of the spectrum, a typical spectral line is a wavelength of 5.8 × 10 −5 cm and corresponds to a frequency of 5.17 × 10 14 kHz. However, because such a frequency has a value that is too large, it is convenient to divide the number by the speed of light to reduce the size. The frequency divided by the speed of light is ν / c, which is 1 / λ in the above equation. When the wavelength is measured in m, 1 / λ represents the number of waves found within 1m. The wavenumber is usually measured in units of 1 / m, i.e. m ^{- 1} and 1 / cm, i.e. cm- ¹ .

In FIG. 9, the vertical axis is a sum of waves measured per unit time and corresponds to intensity (CPS, Count Per Second). The units of the horizontal axis and the vertical axis of FIGS. 11, 13, and 15 are the same as those of FIG. 9. In contrast, silicon wafers, which are typical crystalline silicon, exhibit maximum strength at a wavenumber of 520 cm ⁻¹ , as shown in FIGS. 10 and 11. 12 and 13 show surface photographs and wave number analysis graphs of a polycrystalline silicon thin film manufactured by a conventional metal induction crystallization method. 12 and 13, the maximum strength is shown at a similar frequency compared to the crystalline silicon wafers shown in FIGS. 10 and 11. By the way, it can be seen that the optical micrograph of the surface of the silicon thin film shown in FIG. 12 is enlarged by 1000 times and the size of the crystal grains is relatively small.

Meanwhile, optical micrographs and wave number analysis graphs of the polycrystalline silicon thin film manufactured by the present invention are shown in FIGS. 14 and 15, respectively. Referring to FIG. 15, it can be seen that the wave number representing the maximum strength in the polycrystalline silicon thin film manufactured by the present invention is well represented as in the crystalline silicon wafer shown in FIG. 11. In addition, Figure 14 is an optical micrograph 1000 times magnified, compared with Figure 14 and Figure 12, the crystal grains of the polycrystalline silicon thin film produced by the present invention is much larger than the grains of the polycrystalline silicon thin film prepared by the conventional method Able to know. From the experimental results, it can be seen that the manufacturing method of the polycrystalline silicon thin film according to the present invention is superior to the conventional manufacturing method. In addition, the manufacturing method of the polycrystalline silicon thin film according to the present invention has the advantage that it can be crystallized at a lower temperature than the conventional manufacturing method. In the method for producing a polycrystalline silicon thin film according to the present invention, by precisely controlling the amount of the catalyst metal in advance by disposing the catalyst metal, which is a nucleus of the reaction that is transformed from amorphous silicon into crystalline silicon, under the amorphous silicon layer, it is then diffused into the amorphous silicon layer. By doing so, there is an advantage of preventing the inflow of impurities and lowering the activation energy.

In a preferred embodiment of the present invention, it is described that the first silicon layer forming step is performed after the patterning step of removing a portion of the metal layer by a photolithography method after the metal layer forming step, but the patterning step may be omitted as necessary. .

In a preferred embodiment of the present invention, after the first heat treatment step, an auxiliary heat treatment step of stacking an auxiliary silicon layer on the metal silicide oxide layer and heat treatment to augment the metal silicide oxide layer; and the metal subjected to the auxiliary heat treatment step A second silicon layer forming step of depositing an amorphous silicon layer on the silicide layer; And a crystallization step of heat treating the crystalline silicon in the amorphous silicon layer through the particles of the metal silicide oxide layer. However, the auxiliary heat treatment step may be omitted as necessary.

The present invention has been described above with reference to preferred embodiments, but the present invention is not limited to the above examples, and various forms of embodiments may be embodied without departing from the technical spirit of the present invention.

10 substrate 20 buffer layer
30 ... metal layer 40 ... first silicon layer
50 oxide film 55 silicon oxide layer
57 ... Secondary Silicon Layer 60 ... Second Silicon Layer
70 ... crystalline silicon S1 ... metal layer forming step
S2 ... first silicon layer forming step S3 ... oxide film forming step
S4 ... First heat treatment step S5 ... Secondary heat treatment step
S6 ... second silicon layer forming step S7 ... crystallization step

Claims (6)

A metal layer forming step of forming a metal layer on the insulating substrate;
A first silicon layer forming step of laminating a silicon layer on the metal layer formed in the metal layer forming step;
An oxide film forming step of forming an oxide film on the silicon layer formed in the first silicon layer forming step;
A first heat treatment step of forming a metal silicon oxide layer by heat-treating the silicon layer and the oxide layer stacked in the metal layer, the first silicon layer forming step;
A second silicon layer forming step of laminating an amorphous silicon layer on the metal silicon oxide layer; And
And a crystallization step of heat-treating the crystalline silicon in the amorphous silicon layer through the particles of the metal silicide oxide layer. The method of claim 1,
The substrate is a method of manufacturing a polycrystalline silicon thin film, characterized in that it comprises a buffer layer made of silicon nitride (SiN) or silicon oxide (SiO ₂ ) between the metal layer. The method of claim 1,
The thickness of the metal layer is 5 kPa to 1500 kPa, the thickness of the oxide film is 1 kPa to 300 kPa, the thickness of the first silicon layer is 5 kPa to 1500 kPa, and the ratio of the thickness of the metal layer and the thickness of the first silicon layer is 1: Method for producing a polycrystalline silicon thin film, characterized in that 0.5 to 1: 6. The method of claim 1,
Performing an auxiliary heat treatment step of stacking and heat treating an auxiliary silicon layer on the metal silicide oxide layer after the first heat treatment step to reinforce the metal silicide oxide layer.
A second silicon layer forming step of laminating an amorphous silicon layer on the metal silicon oxide layer subjected to the auxiliary heat treatment step; And
And a crystallization step of heat-treating the crystalline silicon in the amorphous silicon layer through the particles of the metal silicide oxide layer. The method according to claim 3 or 4,
The heat treatment temperature in the oxide film forming step is 400 ℃ to 1000 ℃, the heat treatment temperature in the first heat treatment step is a manufacturing method of a polycrystalline silicon thin film, characterized in that 300 ℃ to 1000 ℃. The method of claim 1,
And a first silicon layer forming step after the patterning step of removing a portion of the metal layer by a photolithography method after the metal layer forming step.

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