CN1549313A - Method for converting amorphous silicon into polycrystalline silicon - Google Patents

Abstract

The present invention relates to a method for converting amorphous silicon into polycrystalline silicon, which mainly includes: providing an amorphous silicon substrate, and performing an inert gas atom doping process on the amorphous silicon substrate; and raising the temperature of the surface of the amorphous silicon substrate to perform a thermal process or a thermal program process.

Description

Method of Converting Amorphous Silicon to Polysilicon

technical field

The invention relates to a method for converting amorphous silicon (amorphous silicon) into polysilicon (poly-silicon).

Background technique

At present, semiconductor technology is mainly based on the processing of amorphous silicon, which has the advantages of relatively simple manufacturing process, suitable for large-scale manufacturing, and low cost. However, the semiconductor element made of amorphous silicon has a slow electron movement rate, which gradually cannot meet the high-speed electron movement rate required after the semiconductor element is miniaturized. Therefore, a new technology "Low Temperature Polysilicon" (LTPS, Low Temperature PolySilicon) came into being. At present, the more significant application is in the TFT-LCD industry.

The biggest difference from the original a-Si TFT-LCD is that the transistors of LTPS TFT-LCD need to be further subjected to the process steps of excimer laser annealing (ELA, excimer laser annealing) to convert the amorphous silicon film into a polysilicon film layer. Such a transformation makes LTPSTFT-LCD more orderly in the silicon crystal structure than a-Si TFT-LCD, and can increase the electron conduction rate by more than 100 times that of a-Si TFT-LCD, reaching 200cm ² /V-sec ; Therefore, the TFT element can be made smaller but responds faster. Compared with a-Si TFT-LCD, the TFT element can be reduced by more than 50%; and the aperture ratio (aperture ratio) can be improved. -Compared with LCD, LTPS TFT-LCD can produce higher resolution and lower power consumption; and because of its faster electron conduction speed, part of the driver IC can be integrated into the glass substrate to reduce material costs, At the same time, it can avoid product damage caused by assembly in the later stage of module assembly process, thereby improving yield rate and reducing manufacturing cost; and adopting a simple P-type circuit structure, compared with traditional CMOS circuit structure, it can save more masks. In addition, due to the integration of part of the Driver IC, in addition to reducing the weight of the IC, it can also reduce other materials required for subsequent assembly, and the overall weight will be greatly reduced.

However, the a-Si precursor material plated by chemical vapor deposition (CVD, Chemical Vapor Deposition) generally has a narrow application range (process window) (10-20mJ/cm ² ) when undergoing ELA (Excimer Laser Annealing). ), however, the a-Si precursor is very sensitive to the stability of the laser, as long as the laser stability is not good, the quality uniformity of the polysilicon will be poor, which will affect or reduce the yield of the semiconductor device produced.

Contents of the invention

The main purpose of the present invention is to provide a method for converting amorphous silicon into polysilicon, so as to reduce the sensitivity of a-Si precursor to laser instability and increase its application range.

Another object of the present invention is to provide a method for converting amorphous silicon into polysilicon, so as to reduce the energy density required for excimer laser annealing, thereby increasing the overall yield.

In order to achieve the above object, a method for converting amorphous silicon into polysilicon according to the present invention mainly includes: providing an amorphous silicon substrate, and performing an inert gas atom doping (doping) process on the amorphous silicon substrate; and A thermal process or a thermal program process is performed by raising the temperature of the surface of the amorphous silicon substrate.

In detail, the method of the present invention is mainly to perform an inert gas doping process before the excimer laser annealing process converts a-Si into poly-Si, and an inert gas molecule such as helium, neon, argon Gas etc. are doped into the a-Si precursor to reduce the conversion energy density (Eth) and optimal energy density (Ec) in the silicon crystal, thereby increasing the process window.

In the method for converting amorphous silicon into polysilicon of the present invention, the inert gas atom is preferably at least one selected from a group consisting of nitrogen, helium, neon, argon, krypton, xenon and radon. Group, that is, the inert gas can be a single inert gas or a mixture of inert gases, wherein the inert gas is preferably argon; in the method of the present invention, the ratio of the inert gas atoms to the amorphous silicon substrate is not limited, more Preferably, the inert gas atoms account for 1-0.001 atomic percent of the amorphous silicon substrate; in the method of the present invention, there is no limit to the way to achieve the inert gas atom doping process, preferably by plasma doping , chemical vapor deposition, dry etching and other methods to achieve. The functional element in the method of the present invention can be an existing functional element, preferably the functional switching element is a thin film transistor. The polysilicon substrate in the method of the present invention can be an existing polysilicon substrate for various purposes, preferably the polysilicon substrate is a panel for a flat panel display, most preferably a panel for a liquid crystal display. The working energy range of the excimer laser in the method of the present invention can be any existing working energy range of the excimer laser, preferably the working energy range of the excimer laser is between 300 and 450 mJ/cm ² .

Description of drawings

In order to allow examiners to better understand the technical content of the present invention, a preferred specific embodiment is given as follows, wherein:

Fig. 1 is a graph showing the change of electron movement rate versus applied energy density in an embodiment of the present invention.

Fig. 2 is a graph showing the variation of grain size versus energy density in an embodiment of the present invention.

Fig. 3 is a graph showing the variation of energy density reduction value versus doping energy in an embodiment of the present invention.

Fig. 4 is a schematic diagram of a known excimer laser.

Detailed ways

Example: Argon Doping of Amorphous Silicon Substrates

In this embodiment, an argon doping process is performed on an amorphous silicon substrate before excimer laser conversion into polysilicon.

The top gate structure of N-type and P-type metal-oxide-semiconductor field-effect transistors (MOSFETs) is fabricated on a glass substrate. At 430°C, a layer of a-Si with a thickness of 2000A was deposited as a buffer layer by plasma-assisted chemical vapor deposition (PECVD), and then a layer of a-Si with a thickness of 500A was deposited for excimer laser annealing (ELA).

Prior to ELA, a dehydrogenation reaction was performed at 480° C. for 10 minutes under nitrogen flow (nitrogen now) to generate native oxides. Argon atom doping (Argon implantation) was performed on the a-Si precursor with a pulse duration of 30 ns and a scan overlap of 95%. In addition to using the first photomask to pattern the polysilicon layer, ion implantation is also used to form source, drain and LDD (thickness 1mm) regions. SiO ₂ was deposited to a thickness of 1000 Å as a gate insulating layer (gate insulator) by PECVD method at 430° C. The next steps are gate metal deposition, patterning and ILD deposition. After via hole etching, Ti/Al/Ti as a second layer metal is then deposited and etched. At the same time, the hydrogenation reaction (hydrogenation) is also carried out at high temperature. A SiNx capping layer is also included in this structure.

The results of this example are shown in FIG. 1 , FIG. 2 and FIG. 3 . Please refer to FIG. 1 first, which is a diagram of the variation of the electron movement rate versus the applied energy density in this embodiment. Four different experimental conditions are listed in this figure, namely N-STD (N-mos standard state), N-Ar (N-mos added with argon atom doping), P-STD (P-mos standard state ), and P-Ar (P-mos is doped with argon atoms). Figure 1 represents two meanings, one is that the polysilicon substrate doped with argon atoms has a higher electron mobility (mobility) stability; A range of values, for example, from 120 to 130, it can be seen that in this range, the slope after doping with argon atoms is lower than that of undoped argon atoms, so the polysilicon substrate doped with argon atoms is an excimer The working energy range of the laser (390-410mJ/cm ² ), which is larger than the working energy range (390-400mJ/cm ² ) of the polysilicon substrate not doped with argon atoms, means that the laser energy change that the process can tolerate is larger, or It means that the electron movement rate is affected by the instability of the laser or the sensitivity to the instability of the laser is reduced, and the instability of the laser has little effect on the uniformity, thereby improving the uniformity of the product and the production yield . On the other hand, the electron mobility rate of the polysilicon substrate doped with argon atoms is generally lower than that of the polysilicon substrate not doped with argon atoms. It is indeed slightly lower than that of doped argon atoms, but the reduction is not obvious. Taking 410mJ/cm ² as an example, the reduction is about 15%, and the electron movement rate of P-mos is no matter whether it is doped with argon atoms or not. , without much change.

Next, please refer to FIG. 2 , which is a graph showing the variation of grain size versus energy density in this embodiment. It can be seen from this figure that the process window of the silicon substrate with argon atom doping step is significantly larger than that of the silicon substrate without argon atom doping. Taking the grain size range of 2500-3000A as an example, the laser scanning range of silicon substrates not doped with argon atoms can only be allowed to be between about 373-378mJ/cm ² , but the silicon substrates doped with argon atoms can work The range is greatly expanded to about 360-380mJ/ ^cm2 , and the allowable laser scanning energy error value is increased by about four times, which proves that the present invention can increase the working range of the excimer laser annealing process and reduce the error caused by situation, improve the yield of the product.

Next, please refer to FIG. 3 , which is a graph showing the variation of the energy density reduction value with respect to the doping energy in this embodiment. It can be seen in this figure that the higher the doping percentage of argon atoms is used, the more the energy density can be reduced, which represents the optimal energy density (Ec, optimal energy density) does not need to use the high energy of the original doping, the excess energy can be used to widen the width of the scanning laser, thereby reducing the time required for laser scanning for each substrate, improving productivity and saving production cost.

Finally, please refer to FIG. 4 , which is a schematic diagram of a known excimer laser. The excimer laser mainly includes an excimer laser emitting element 2 , a substrate support 3 and a substrate 1 . The excimer laser emitting element 2 is connected to a support arm (not shown in the figure), and can scan the surface of the substrate 1 one by one according to the scheduled method, and complete the annealing process by heating to transform the surface of the amorphous silicon substrate. for polysilicon.

Based on the above examples, it can be found that adding an argon atom doping step before annealing the general a-Si layer can increase the working range of laser annealing and reduce the Ec required for laser annealing. , and can convert the excess energy output by the original machine into a wider scanning laser width, reduce the scanning time of each substrate, and improve the process efficiency on the production line.

The above-mentioned embodiments are only examples for convenience of description, and the scope of rights claimed by the present invention should be based on the scope of the patent application, rather than limited to the above-mentioned embodiments.

Claims (10)

1. one kind is converted to the method for polysilicon with amorphous silicon, it is characterized in that, mainly comprises:

One amorphous silicon substrate is provided, and this amorphous silicon substrate is carried out an intert-gas atoms dopping process; And

Carry the surface of this amorphous silicon substrate heating up and carry out a hot processing procedure or hot program processing procedure.

2. as claimed in claim 1 amorphous silicon is converted to the method for polysilicon, it is characterized in that, wherein, at least one intert-gas atoms is to be selected from a group that is made up of helium, neon, argon gas, krypton gas, xenon and radon gas.

3. as claimed in claim 2 amorphous silicon is converted to the method for polysilicon, it is characterized in that wherein this intert-gas atoms is to be argon gas.

4. as claimed in claim 1 amorphous silicon is converted to the method for polysilicon, it is characterized in that wherein this intert-gas atoms is the 1-0.001 atomic percent that accounts for this amorphous silicon substrate.

5. as claimed in claim 1 amorphous silicon is converted to the method for polysilicon, it is characterized in that wherein this intert-gas atoms dopping process is to reach with electricity slurry doping way.

6. as claimed in claim 1 amorphous silicon is converted to the method for polysilicon, it is characterized in that wherein this intert-gas atoms dopping process is to reach in the chemical vapour deposition (CVD) mode.

7. as claimed in claim 1 amorphous silicon is converted to the method for polysilicon, it is characterized in that wherein this intert-gas atoms dopping process is to reach in the dry ecthing mode.

8. as claimed in claim 1 amorphous silicon is converted to the method for polysilicon, it is characterized in that wherein this amorphous silicon substrate is the LCD panel.

9. as claimed in claim 1 amorphous silicon is converted to the method for polysilicon, it is characterized in that wherein this hot processing procedure is to be an excimer laser annealing process.

10. as claimed in claim 9 amorphous silicon is converted to the method for polysilicon, it is characterized in that wherein this excimer laser work capacity scope is to 450mJ/cm between 300 ²Between.

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