CN106601593A - Method for reducing the polysilicon surface roughness - Google Patents

Abstract

The invention relates to a method for reducing the surface roughness of polysilicon, which comprises the following steps: i) O ₃ water is contacted with the surface of the polysilicon layer for oxidation treatment, and a surface oxide layer is formed on the surface of the polysilicon layer; ii) the surface of the polysilicon layer is oxidized The surface oxide layer formed on the surface is contacted with HF solution for etching treatment to obtain a polysilicon layer through oxidation treatment and etching treatment; iii) repeating the oxidation treatment of step i) and the etching treatment process of step ii) n times in sequence until the polysilicon interface The height of the protrusion is less than 30nm, wherein n is a positive integer. The method of the present invention utilizes O ₃ water to carry out oxidation treatment to the polysilicon layer surface, O ₃ has strong oxidizing property, greatly shortens the oxidation time; Then significantly improves the flatness of the polysilicon film surface through multiple oxidation treatment and etching treatment, to reduce thin film transistor Leakage current, optimize its electrical properties.

Description

Method for Reducing Surface Roughness of Polysilicon

technical field

The invention belongs to the technical field of liquid crystal panel manufacture, and in particular relates to a method for reducing the surface roughness of polysilicon in thin film transistors.

Background technique

A thin film transistor (TFT) of a liquid crystal display element is composed of a silicon film formed on an insulating substrate, and is used as a switching element provided in a pixel of a liquid crystal display element or a driving element formed in a peripheral circuit portion. As a silicon film constituting a TFT, an amorphous silicon film is mostly used, but in recent years, a polysilicon film having better characteristics has been increasingly used, and much development work is currently being carried out in this regard. The formation of polysilicon film needs to be carried out at high temperature, but because the heat resistance of the insulating substrate is low, it is easy to cause substrate deformation. Therefore, low temperature polysilicon thin film (Low Temperature Polysilicon Thin Film) is usually used when making the active layer of TFT .

Excimer laser annealing (abbreviated as ELA) method is generally used in the existing preparation of polysilicon film, which utilizes high-energy excimer laser to irradiate amorphous silicon film to make it absorb the energy of excimer laser, and make it The amorphous silicon film is in a melting state, and after cooling, it crystallizes to form a polysilicon film. The preparation process is generally carried out at a temperature of 400°C to 600°C, which can effectively prevent the deformation of the substrate. The pulse laser of the excimer laser generator is used to scan the amorphous silicon layer to form an irradiation area. After the pulse laser scanning is completed, it moves forward for a certain distance, so that the formed multiple irradiation areas overlap each other. Because the temperature of the overlapping part is relatively high The temperature of the non-overlapping part is high, and non-uniform nucleation occurs at the interface between the overlapping part and the non-overlapping part. Usually, the transverse temperature gradient generated between the overlapping part and other non-overlapping parts will lead to crystal nuclei along the direction of higher temperature, that is, from the non-overlapping part to The direction of the overlapping portion grows and eventually crystallizes into a low-temperature polysilicon film.

Excimer laser annealing process is a relatively complicated annealing process. For polysilicon thin films, the control of film surface flatness, grain size and grain uniformity has always been a research hotspot in the annealing process. At present, due to the non-uniform growth of polysilicon grains caused by the ordinary laser annealing process, the film roughness is very large, and the grain size of the polysilicon film is small and unevenly distributed.

The number and distribution uniformity of polysilicon grains covered by the channel region of the low temperature polysilicon thin film transistor, and the surface flatness (or surface roughness) of the polysilicon film will directly affect the electrical properties of the low temperature polysilicon thin film transistor, such as mobility Size, leakage current size, mobility and uniformity of threshold voltage, etc.

In the existing LTPS production process, a layer of SiO _x /SiN _x film will be plated between the polysilicon film and the gate film, and because the surface roughness of the polysilicon film is too high (the highest height at the grain boundary exceeds 40nm). It is easy to form parasitic capacitance and tip discharge, resulting in excessive leakage current of TFT, and it is easy to pierce the gate insulating film (GI). Therefore, in order to avoid suppressing these phenomena, the method of increasing the thickness of the GI film will be adopted during production. GI The increase of film thickness will inevitably increase the tact time of GI coating machine, and will also cause difficulties in subsequent IMP doping.

The publication number is: CN102655089, and the manufacturing method of the polysilicon thin film disclosed in the patent titled "A Method for Making a Low-Temperature Polysilicon Thin Film" is as follows: first, a buffer layer and an amorphous silicon layer are sequentially deposited on the substrate, and then the amorphous silicon layer is Heating at high temperature, and performing excimer laser annealing on the amorphous silicon layer to form a polysilicon layer, followed by oxidation and etching in sequence to obtain a polysilicon film. The oxidation process is to place the polysilicon layer formed after excimer laser annealing in a rapid thermal annealing device under an oxygen atmosphere at a temperature of 700°C for rapid thermal annealing, which can oxidize the uncrystallized amorphous silicon into silica. Another oxidation treatment method is to oxidize the polysilicon layer under the atmosphere of laughing gas plasma (N ₂ O plasma), and the specific process is carried out in PECVD vapor deposition equipment.

In the etching process, hydrofluoric acid solution is used to etch the oxidized polysilicon layer. Due to the chemical reaction between silicon dioxide and hydrofluoric acid, the silicon dioxide on the polysilicon layer will be separated from the polysilicon layer to form a polysilicon layer. film.

The oxidation process of the polysilicon layer in this patent is to perform rapid thermal annealing in a rapid thermal annealing device under an oxygen atmosphere at a temperature of 700° C., so that uncrystallized amorphous silicon is oxidized into silicon dioxide. However, the efficiency of oxidation treatment by oxygen is low, and the oxidation treatment time is relatively long.

Contents of the invention

The purpose of the present invention is to provide a method for reducing the surface roughness of polysilicon to solve the problem that the surface roughness of the polysilicon film obtained by the existing LTPS production process is too high, which is easy to form parasitic capacitance and cause excessive TFT leakage current.

The method for reducing the surface roughness of polysilicon in the present invention comprises the following steps:

i) O ₃ water is contacted with the surface of the polysilicon layer for oxidation treatment, forming a surface oxide layer on the surface of the polysilicon layer;

ii) contacting the surface oxide layer formed on the surface of the polysilicon layer with an HF solution for etching treatment to obtain an oxidized and etched polysilicon layer;

iii) repeating the oxidation treatment of step i) and the etching treatment of step ii) n times in sequence until the height of the protrusion at the polysilicon interface is less than 30 nm, wherein n is a positive integer.

The polysilicon layer described in step i) of the present invention can be obtained by methods such as plasma enhanced chemical reaction vapor deposition (PECVD), excimer laser crystallization (ELA) or low pressure vapor phase chemical vapor deposition (LPCVD).

In one embodiment, the polysilicon layer described in step i) is obtained on the quartz glass substrate by low-pressure gas-phase chemical vapor deposition. The LPCVD deposition method has the characteristics of fast growth, dense and uniform film formation, and large loading capacity. The polysilicon film can be directly deposited on the substrate by LPCVD using silane gas, and the deposition parameters are generally controlled as follows: silane pressure is 13.3-26.6Pa, deposition temperature Td=580-650°C, and growth rate is 5-10nm/min.

The polysilicon thin film grown by LPCVD method has a preferred orientation of grains, a "V" shape, contains high-density micro-twin crystal defects, and the grain size is small, and the carrier mobility is not large enough to make it suitable for use in devices. subject to certain restrictions. Although reducing the silane pressure helps to increase the grain size, it is often accompanied by an increase in surface roughness, which adversely affects the mobility of carriers and the electrical stability of TFT devices.

In another embodiment, the polysilicon layer described in step i) is deposited on the surface of amorphous silicon by plasma enhanced chemical reaction vapor deposition (PECVD). The PECVD method uses glow discharge electrons to activate the chemical vapor deposition reaction at the same time as low-pressure chemical vapor deposition. During the deposition process of polysilicon film, silane is decomposed by radio frequency glow discharge method (Radio Frequency Glow Discharge). Under the action of radio frequency power, silane gas is decomposed into a variety of new particles: atoms, free radicals and various ions Wait for the plasma. These new particles are deposited after a series of complex processes such as migration and dehydrogenation. On the whole, the deposition process of polysilicon film can be divided into two steps: the decomposition of SiH ₄ gas and the deposition of groups. The deposition temperature required by this method is relatively low, and polysilicon can be obtained at about 300-450°C. However, the polysilicon grain size prepared by the CVD method is small, generally not exceeding 50nm, and there are many defects in the grain and many grain boundaries, so follow-up is required. oxidation and etching treatments.

In a preferred embodiment, the polysilicon layer described in step i) is deposited on the surface of amorphous silicon by excimer laser crystallization (ELA). In the excimer laser crystallization method, the melting and crystallization process of the amorphous silicon film is very short, and the thermal impact on the substrate is very small, and cheap glass or even plastic substrates that are not resistant to high temperatures can be used, which greatly reduces the cost of making large-area displays .

Excimer laser crystallization is to use the high energy generated by the instantaneous laser pulse to be incident on the surface of the amorphous silicon film, and only generate a thermal effect at a depth of about 100nm thick on the surface of the film, so that the a-Si film can reach about 1000°C in an instant, thereby realizing a -Si to p-Si transformation. During this process, the instantaneous (15-50ns) energy of the laser pulse is absorbed by the a-Si film and converted into phase transition energy. Therefore, there will not be too much thermal energy conducted to the film substrate, and the wavelength and power of the laser should be selected reasonably , using laser heating can make the a-Si film reach the melting temperature and ensure that the temperature of the substrate is lower than 500 ° C, which can meet the requirements of LCD and OEL for transparent substrates. Its main advantage is that the pulse width is short (15-50ns), and the substrate generates less heat. Mixed crystallization can also be obtained by selection, that is, a mixture of polycrystalline silicon and amorphous silicon.

The mechanism of excimer laser annealing and crystallization: the laser irradiates the surface of a-Si, so that the surface reaches the crystallization threshold energy density Ec when the temperature reaches the melting point. a-Si absorbs energy under laser radiation, excites unbalanced electron-hole pairs, increases the conduction energy of free electrons, and heat electron-hole pairs recombine their own energy by non-radiative recombination within the thermalization time. Passed to the crystal lattice, resulting in an extremely rapid temperature rise near the surface. Since the amorphous silicon material has a large number of gap states and deep energy levels, the non-radiative transition is the main recombination process, so it has a high photothermal conversion efficiency. If the laser When the energy density reaches the threshold energy density Ec, that is, the semiconductor is heated to the melting point temperature, the surface of the film will melt, and the melting front will penetrate into the material at a speed of about 10m/s. After laser irradiation, the film forms a certain depth of melting layer. After stopping the irradiation, the molten layer starts to cool at a speed of 108-1010K/s, and the interface between the solid phase and the liquid phase returns to the surface at a speed of 1-2m/s. After cooling, the thin film crystallizes into polycrystalline, and then As the laser energy density increases, the grain size increases. When the amorphous film is completely melted, the film crystallizes into microcrystalline or polycrystalline. If the laser energy density is less than the threshold energy density Ec, the absorbed energy is insufficient. In order to raise the surface temperature to the melting point, the film does not crystallize.

It is generally believed that the polysilicon film prepared by the ELA method has large grains, good space selectivity, high doping efficiency, relatively few intragranular defects, good electrical properties, and a mobility as high as 400cm ² /vs, which is the best comprehensive performance at present. Low temperature polysilicon thin film. The process maturity is high, and there are large-scale production line equipment, but there is a deficiency that the grain size is sensitive to the laser power.

Specifically, the process of preparing the polysilicon layer by using the excimer laser crystallization (ELA) method is as follows:

S1, sequentially depositing a buffer layer (buffer layer) and an amorphous silicon layer (amorphous silicon layer) on the glass substrate by CVD;

S2, performing high-temperature heating treatment and excimer laser annealing treatment on the amorphous silicon layer described in step S1 to form a polysilicon layer.

In the process of preparing the polysilicon layer by adopting the excimer laser crystallization method, before depositing the buffer layer and the amorphous silicon layer, the substrate can also be cleaned in advance to keep the substrate clean.

The method for depositing the buffer layer and the amorphous silicon layer on the substrate in the step S1 can be sputtering, vacuum evaporation or decompression CVD.

In one embodiment, the buffer layer is composed of a silicon nitride layer (SiN _x ) and a silicon dioxide layer (SiO ₂ ), and the buffer layer can prevent impurities in the substrate from diffusing into the polysilicon during subsequent heating. layer. A silicon nitride layer is firstly deposited with a thickness controlled at 50-150 nm, and then a silicon dioxide layer is deposited with a thickness controlled at 100-300 nm.

The method for forming the above-mentioned composite buffer layer on the substrate can be:

A layer of _SiNx is deposited on the substrate by PECVD (Plasma Enhanced Chemical Vapor Deposition) or other deposition methods; then a layer of SiO ₂ is deposited by PECVD or other deposition methods, so that A composite buffer layer is formed on the substrate.

In another embodiment, the buffer layer can also be a SiO ₂ buffer layer. At this time, the method for forming the SiO ₂ buffer layer on the substrate may be: deposit a 100-350 nm thick SiO ₂ layer on the substrate as the SiO ₂ buffer layer by using PECVD or other deposition methods.

In one embodiment, the amorphous silicon layer is deposited by PECVD, and the thickness of the amorphous silicon layer is preferably 30-150 nm.

Wherein, the high-temperature heating process described in step S2 is generally at a temperature of 400° C. to 600° C. for 0.5 to 3 hours.

The excimer laser annealing treatment in the S2 step adopts a xenon chloride excimer laser, and can select an excimer that performs one, two or more times on the amorphous silicon layer according to the characteristics such as the material and thickness of the amorphous silicon layer. Laser annealing and setting process parameters for each excimer laser annealing.

In addition, excimer lasers such as krypton fluoride (KrF) and argon fluoride (ArF) can also be used. The output wavelengths of ArF, KrF and XeCl excimer lasers are 193nm, 248nm and 308nm respectively, and the pulse width is between 10 and 50ns.

In one embodiment, an excimer laser annealing treatment is performed once, the laser energy density is controlled to be 300-500 mJ/cm ² , the laser pulse frequency may be 300 Hz, and the preferred overlap rate is 92%-98%.

In another embodiment, the amorphous silicon layer is subjected to excimer laser annealing twice, wherein the process parameters of the first excimer laser annealing are: the laser pulse frequency is 300 Hz, the overlap ratio is 92% to 98%, and the laser energy The density is 300-500mJ/cm ² ; the technological parameters of the second excimer laser annealing are: the laser pulse frequency is 300Hz, the overlap rate is 5%-10%, and the laser energy density is 50-150mJ/cm ² .

After excimer laser annealing, the polysilicon layer is formed, and uncrystallized amorphous silicon protrusions will appear on the surface, and there are relatively obvious grain boundaries, resulting in uneven surface of the film and increased roughness.

Therefore, step i) of the present invention first utilizes O ₃ water to contact the surface of the polysilicon layer for oxidation treatment, and oxidizes the surface of the polysilicon layer by O ₃ water to form a surface oxide layer, and adjust the oxide layer by controlling the time of oxidation treatment thickness of.

In one embodiment, the thickness of the oxide layer is 1-8 nm, and the oxidation treatment time is 3-100 seconds, preferably, the oxidation treatment time is 10-30 seconds.

Since O ₃ water also has a cleaning effect, the use of O ₃ water to oxidize can also play a role in cleaning the polysilicon layer, removing surface pollutants, and transforming amorphous silicon into silicon dioxide after oxidation treatment.

In step ii) of the present invention, the oxidized polysilicon layer is etched by HF solution, the concentration of the HF solution is 0.5wt% to 10wt%, and the preferred concentration is 1wt% to 5wt%, so that silicon dioxide and polysilicon For detachment, in one embodiment, the (mass) concentration of the HF solution is 1 wt% to 3 wt%, and the etching treatment time is preferably 10 to 80 seconds.

The multiple oxidation/etching treatments in step iii) of the present invention can significantly reduce the roughness of the surface of the polysilicon layer, but the polycrystalline film is generally under the _SiOx film, which is similar to the substance after grain boundary oxidation, and is easily etched away by the etchant to form cavities , so the surface oxidation and etching processes cannot be performed too much.

In step iii) of the present invention, the oxidation treatment and etching treatment are repeated 1 to 5 times in sequence, preferably, the oxidation treatment and etching treatment are repeated 1 to 3 times in sequence, and the etching thickness is precisely controlled.

The _O3 water described in step i) of the present invention is obtained by dissolving ozone into water, and the dissolved concentration of ozone in _O3 water is generally in the range of 5 mg/L to 20 mg/L, and the preferred concentration is controlled at 8 mg/L to 15 mg /L, the oxidation treatment time is short. O ₃ water oxidation treatment can form an oxide layer with a uniform thickness on the surface of the polysilicon layer without causing adverse effects on the underlying polysilicon layer. The method solves the problems of low oxidation efficiency and long time in the existing method of oxidation by thermal annealing in a high-temperature oxygen atmosphere.

In step ii) of the present invention, due to the chemical reaction between silicon dioxide and hydrofluoric acid, the silicon dioxide on the polysilicon layer will separate from the polysilicon layer, thereby forming a polysilicon film. Then, the surface roughness of the polysilicon layer can be significantly reduced by multiple oxidation/etching treatments, but the polycrystalline film is generally under the SiO _x film, which is similar to the substance after grain boundary oxidation, and is easily etched away by the etchant to form voids, so it cannot Excessive surface oxidation and etching processes are performed, and the etching thickness needs to be precisely controlled.

The low-temperature polysilicon thin film obtained by adopting the method for reducing the surface roughness of polysilicon provided by the present invention has uniform distribution of crystal grains and a very low surface roughness, thereby solving the problem of low mobility when applied to the backplane of a low-temperature polysilicon display. Thin film transistors have large leakage current, mobility and threshold voltage non-uniformity, and reduce the process time of subsequent GI coating machines and IMP machines, increasing production capacity.

The low-temperature polysilicon film prepared by the method for reducing the surface roughness of polysilicon provided by the invention can be used as the active layer of a low-temperature polysilicon thin-film transistor, and is applicable to an active matrix organic light-emitting diode display (AMOLED) and a low-temperature polysilicon thin-film transistor liquid crystal display (LTPS TFT) -LCD) etc. production.

Compared with the prior art, the beneficial effect of the present invention is: the present invention uses O ₃ water to oxidize the surface of the polysilicon layer, and due to the strong oxidizing property of O ₃ , the oxidation time can be greatly shortened. Subsequent oxidation/etching treatments can significantly reduce the surface roughness of the polysilicon film to reduce the leakage current of the thin film transistor (TFT device), optimize its electrical properties, and reduce the subsequent GI (gate insulating layer) coating machine and IMP The operating process time (tact time) of the machine increases the production capacity.

Description of drawings

The present invention will be described in further detail below in conjunction with the accompanying drawings.

1 is a schematic diagram of the surface roughness of a polysilicon layer without oxidation treatment and etching treatment in Example 2 of the present invention;

2 is a schematic diagram of the surface roughness of the polysilicon layer after one oxidation treatment and etching treatment in Example 2 of the present invention;

3 is a schematic diagram of the surface roughness of the polysilicon layer after n times of oxidation treatment and etching treatment in Example 2 of the present invention, wherein n≥2 and n is a positive integer.

detailed description

The implementation of the present invention will be described in detail below in conjunction with the drawings and examples, so as to fully understand and implement the process of how to apply technical means to solve technical problems and achieve technical effects in the present invention. It should be noted that, as long as there is no conflict, each feature in each embodiment of the present invention can be combined with each other, and the formed technical solutions are all within the protection scope of the present invention.

Example

Example 1

The method for reducing the surface roughness of polysilicon in this embodiment comprises the following steps:

1. Use _O3 water with a concentration of 5 mg/L to contact the surface of the polysilicon layer for oxidation treatment for 15 seconds, thereby forming a surface oxide layer;

2. Contacting the surface oxide layer formed on the surface of the polysilicon layer with an HF solution with a concentration of 1 wt% for 40 seconds to obtain an oxidized and etched polysilicon layer;

3. Repeat the oxidation treatment of step 1 and the etching treatment of step 2 three times in sequence, thereby reducing the surface roughness of the polysilicon.

In this embodiment, the concentration of _O3 water is controlled to be low, so that the thickness of the surface oxide layer after each oxidation treatment is also relatively thin, and subsequent use of a lower concentration of HF solution to etch the polysilicon with an oxide layer on the surface, due to the oxidation Silicon and hydrofluoric acid react chemically, so the silicon dioxide on the polysilicon layer is separated from the polysilicon layer, and the time of oxidation treatment and etching treatment is controlled to make the grain boundary reach saturated oxidation and etching, but due to the oxidation of each oxidation treatment The thickness of the layer is relatively thin, so step 3 is repeated more times, so as to achieve the effect of reducing the surface roughness of the polysilicon.

The _O3 water and HF solution selected in this embodiment will not affect the electrical properties of the thin film transistor, and the more optimized _O3 water concentration, HF solution concentration and oxidation/etching treatment time are to make the grain boundary reach saturated oxidation and etch.

Example 2

The method for reducing the surface roughness of polysilicon in this embodiment is realized in the following steps:

1. The buffer layer and the amorphous silicon layer are sequentially deposited on the glass substrate by PECVD method;

2. Heat the amorphous silicon layer described in step 1 at 500° C. for 1.5 hours, and then carry out an excimer laser annealing treatment to the amorphous silicon layer to form a polysilicon layer;

_3. Oxidation treatment is carried out for 15 seconds in contact with the surface of the polysilicon layer formed in step 2 by using concentration of 10 mg/L of O water to form a surface oxide layer;

4. Contact the surface oxide layer formed on the surface of the polysilicon layer with a concentration of 2wt% HF solution for etching for 50 seconds to obtain a polysilicon layer that has been oxidized and etched;

Fifth, repeating the oxidation treatment of step three and the etching treatment process of step four n (n is a positive integer) times in sequence, thereby reducing the surface roughness of the polysilicon.

In this embodiment, the concentration of HF solution of _O3 water is preferred, and the time of oxidation treatment and etching treatment is optimized, so that the surface of the finally obtained polysilicon is smooth, and the highest height at the grain boundary is less than 25nm, which significantly reduces the roughness of the surface, thereby reducing the device leakage current.

Step 5 of this embodiment repeats the process of oxidation treatment and etching treatment, as shown in conjunction with accompanying drawings 1 to 3, in Figure 1, L represents the polysilicon layer, a represents the substrate, b represents the buffer layer, d ₀ represents no oxidation treatment and etching treatment The height of the amorphous silicon protrusions, d ₁ in Figure 2 represents the height of the amorphous silicon protrusions after one oxidation treatment and etching treatment, and by analogy, d _n in Figure 3 represents the amorphous silicon protrusions after n times of oxidation treatment and etching treatment It can be seen that the surface of the polysilicon can be made smoother after multiple oxidation treatments and etching treatments, the leakage current of the thin film transistor can be reduced, and the electrical properties of the thin film transistor can be optimized. However, under the polycrystalline film is a SiO _x film, which is similar to the substance after grain boundary oxidation. It is easy to be etched away by etchant, forming cavities, and difficult to dry. In the embodiment, it is preferable to repeat the oxidation treatment and the etching treatment in Step 4 once more, that is, perform the oxidation treatment and the etching treatment twice in total.

In this embodiment, a lithographic etching process is performed on the obtained polysilicon layer (film) after the roughness is reduced, and the polysilicon film layer is patterned through a photoresist pattern to form a polysilicon island to be used as an N-TFT and a P-TFT , and then deposit a gate insulating layer.

In this embodiment, after the patterning of the polysilicon film layer is completed, a gate insulating layer (GI) is deposited on the surface of the polysilicon by plasma CVD. , the second dielectric layer and the third dielectric layer, and the first dielectric layer is SiO ₂ , the second dielectric layer is SiON, and the third dielectric layer is SiN _x . Since the surface of the polysilicon layer is sufficiently flat at this time, the thickness of the subsequent gate insulating film can be relatively thin, which shortens the operating process time (tact time) of the subsequent GI coating machine and IMP machine, increases its production capacity, and can also directly Use the hydrogen fluoride cleaning machine before laser annealing in the existing production line for processing.

It should be noted that the above-mentioned embodiments are only used to explain the present invention, and do not constitute any limitation to the present invention. The invention has been described with reference to typical embodiments, but the words which have been used therein are words of description and explanation rather than words of limitation. The present invention can be modified within the scope of the claims of the present invention as prescribed, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the invention described therein refers to specific methods, materials and examples, it is not intended that the invention be limited to the specific examples disclosed therein, but rather, the invention extends to all other methods and applications having the same function.

Claims (10)

1. it is a kind of reduce polysilicon surface roughness method, which comprises the steps：

I) by O₃Water is contacted with the surface of polysilicon layer and carries out oxidation processes, forms surface oxide layer on the surface of polysilicon layer；

Ii) surface oxide layer formed on the surface of polysilicon layer is contacted with HF solution and is etched process, obtain oxidized Process the polysilicon layer with etch processes；

Iii the oxidation processes and step ii of step i)) are repeated in) etching treatment procedure n time, until convex at polysilicon interface The height for rising is less than 30nm, and wherein n is positive integer.

2. it is according to claim 1 reduce polysilicon surface roughness method, it is characterised in that O described in step i)₃ O in water₃Concentration be 5mg/L～20mg/L.

3. it is according to claim 1 reduce polysilicon surface roughness method, it is characterised in that oxygen described in step i) The time for changing process is 3～30 seconds.

4. it is according to claim 1 reduce polysilicon surface roughness method, it is characterised in that the surface oxide layer Thickness be 1～8nm.

5. it is according to claim 1 reduce polysilicon surface roughness method, it is characterised in that the HF solution it is dense Spend for 0.5wt%～10wt%.

6. according to any one in claim 1-5 reduction polysilicon surface roughness method, it is characterised in that according to The oxidation processes and step ii of secondary repeat step i)) etching treatment procedure 1～3 time.

7. it is according to claim 1 reduce polysilicon surface roughness method, it is characterised in that described in step i) The preparation method of polysilicon layer comprises the steps：

S1, is sequentially depositing cushion and amorphous silicon layer on substrate；

S2, carries out high-temperature heating treatment to the amorphous silicon layer described in step S1 and quasi-molecule laser annealing is processed, and is formed many Crystal silicon layer.

8. it is according to claim 7 reduce polysilicon surface roughness method, it is characterised in that described in step S1 Cushion is made up of silicon nitride layer and silicon dioxide layer.

9. it is according to claim 7 reduce polysilicon surface roughness method, it is characterised in that described in step S1 The thickness of amorphous silicon layer is 30～150nm.

10. according to any one in claim 7-9 reduction polysilicon surface roughness method, it is characterised in that High-temperature heating treatment described in step S2 is to process 0.5～3 hour at a temperature of 400 DEG C～600 DEG C.