CN101942701A - Heat treatment method of solar-grade silicon crystal - Google Patents
Heat treatment method of solar-grade silicon crystal Download PDFInfo
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- CN101942701A CN101942701A CN 201010271861 CN201010271861A CN101942701A CN 101942701 A CN101942701 A CN 101942701A CN 201010271861 CN201010271861 CN 201010271861 CN 201010271861 A CN201010271861 A CN 201010271861A CN 101942701 A CN101942701 A CN 101942701A
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Abstract
The invention discloses a heat treatment method of a solar-grade silicon crystal, which comprises the steps of placing the silicon crystal into a vacuum heating furnace, introducing protective gas into the vacuum heating furnace and leading the protective gas to flow through the surface of the silicon crystal during the heat treatment process of the silicon crystal, wherein the protective gas is a) gas containing hydrogen atoms; or b) mixture of the gas containing the hydrogen atoms and inert gas. The adoption of the method for carrying out heat treatment on the silicon crystal can significantly prolong the minority carrier lifetime of the silicon crystal, simultaneously regulate the distribution uniformity of radial resistivity of the silicon crystal and lead the resistivity of the silicon crystal to be more uniform on the radius direction of the crystal due to the roles of passivation, impurity absorption and the like of H to impurities and defects in the silicon crystal. The method is simple to operate and easy to carry out industrial production, and can significantly improve the quality of a product.
Description
Technical field
The present invention relates to a kind of heat treating method of silicon crystal, relate in particular to the heat treating method of the silicon crystal that is used for the high conversion efficiency solar cell.
Background technology
The used raw silicon crystal of preparation crystal silicon solar energy battery is divided into silicon single-crystal or policrystalline silicon.In the silicon crystal preparation process, difference because of raw materials used or the course of processing, there are metallic impurity, oxygen carbon impurity, crystal boundary, dislocation in silicon materials inside, space defectives such as (point defects), these impurity and defective often form numerous unsaturated dangling bonds, form electric activity center, and become the trap and the deathnium of minority carrier (few son).These traps and deathnium have reduced minority diffusion length, influence the performance of photovoltaic device.Be in particular in that the silicon chip minority carrier life time made from above-mentioned silicon single-crystal and policrystalline silicon is on the low side, and finally influence the photoelectric transformation efficiency and the life-span of the crystal-silicon solar cell of manufacturing.
In addition, owing to silicon crystal preparation technology's reason (has used main component to be SiO in preparation process
2Thermal field component), tend to contain higher oxygen level at crystals.Be subjected to the difference of the thermal history that silicon crystal experienced in manufacturing processed, the oxygen precipitate has all kinds.Longer in low temperature (400 ℃＜T＜550 ℃) residence time when silicon crystal, the oxidation precipitate is SiO
4, and having stronger hot alms giver (thermal donor) performance, this will change the conductivity of silicon crystal.When the silicon crystal temperature between 550～700 ℃ during thermal treatment, hot alms giver's characteristic of oxidation precipitate will disappear, thereby eliminate the change of oxygen precipitate to the original conductivity of silicon crystal.When silicon crystal when 700～900 ℃ temperature province stops for a long time, lepidiod oxygen precipitate will appear, this class precipitate also has hot alms giver's performance, and such oxygen precipitate will become the oxygen precipitate of octahedral structure between 900～1100 ℃, and its hot alms giver's performance is weakened.For these reasons, the thermal treatment of carrying out proper temperature can change the conductivity of silicon crystal, thereby changes the resistivity and the resistivity distribution of the silicon crystal that is used for the photovoltaic industry, improves the efficient of solar cell.
Heat treating method commonly used in the industry is that silicon crystal is placed in the atmospheric pressure kiln; and adopt protection of inert gas such as nitrogen in the stove; by heating silicon crystal is placed in the suitable temperature range, thereby improve the conductivity of the silicon crystal relevant with the oxygen precipitate.
Summary of the invention
The invention provides a kind of heat treating method of silicon crystal, the silicon crystal that obtains after the thermal treatment can also prepare the more solar cell of high conversion efficiency on the basis of the resistivity of improving silicon crystal and resistivity distribution.
A kind of heat treating method of solar-grade silicon crystals is inserted silicon crystal in the vacuum furnace, in the heat treatment process of silicon crystal, feeds shielding gas in the vacuum furnace and the silicon crystal surface of flowing through, and described shielding gas is:
A) gas of hydrogen atoms;
Or b) mixture of the gas of hydrogen atoms and rare gas element.
From security consideration, described thermal treatment unit is a vacuum furnace, and described heat-processed is carried out under the low pressure of 0.1～5000Pa.
The gas of hydrogen atoms and rare gas element; must with silicon and the material of making vacuum furnace at high temperature (400-1000 ℃) do not react or quantitative response seldom just, the shielding gas that is used to simultaneously reduce the resistivity range of variation of silicon crystal and/or improve the silicon crystal minority carrier life time must not influence the product performance of silicon crystal as the photovoltaic application material.
The gas of hydrogen atoms can be selected H for use
2Or SiH
4In at least a, can be arbitrary proportion during multiple using with, both can be pre-mixed, also can be feed respectively the back in reactor, mix.Consider from economic angle, preferentially select hydrogen (H for use
2).
Rare gas element can be selected at least a in argon gas or the nitrogen for use.Can be arbitrary proportion during multiple using with, both can be pre-mixed, also can be to feed the back respectively to mix in reactor.
When the gas of hydrogen atoms and rare gas element feed simultaneously, both can be pre-mixed, also can be to feed the back respectively to mix in reactor.
Silicon crystal of the present invention can be silicon single crystal crystal bar, polycrystalline silicon bar, silicon single crystal ingot casting or polycrystalline silicon ingot casting.
Heat treatment process of the present invention is divided into intensification, insulation, temperature-fall period, and described holding stage temperature is a thermal treatment temp.The thermal treatment temp of silicon crystal of the present invention when shielding gas feeds is 400～1000 ℃, preferred 500～700 ℃, and most preferably 600 ℃.
In the heat treatment process of silicon crystal, when the hydrogen atom in the gas of hydrogen atoms contacted with the silicon crystal surface, because the temperature of silicon crystal is higher, hydrogen was diffused into silicon crystal inside with the form of lewis' acid attitude.Because when the temperature of silicon crystal was high more, the velocity of diffusion of H atom was fast more.For example at normal temperatures, silicon in the atmosphere of H half an hour H diffusion depth have only 4.1 μ m, and in the time of 1000 ℃, silicon can spread about 4700 μ m under similarity condition.For the speed that guarantees to spread, the temperature of silicon crystal in hydrogen-containing gas should be more than 400 ℃.This process is not brought too much extra-expense for the silicon crystal thermal treatment process of carrying out in order to suppress hot alms giver.Because in the inventive method, the silicon crystal thermal treatment of carrying out in order to suppress hot alms giver is preferably carried out about 600 ℃, feed hydrogen-containing gas in this course,, also realized the diffusion of hydrogen atom to silicon crystal reaching the purpose while of realizing the hot alms giver of inhibition and regulating resistivity.
Because the hot alms giver (thermal donor) that the oxygen doping causes in the silicon crystal has very big influence to silicon crystal resistivity, therefore, in the methods of the invention, carries out silicon crystal thermal treatment at a certain temperature, to suppress hot alms giver's formation.Because (the hot alms giver of this moment is called old thermal donor) generally appears in hot alms giver about 450 ℃ when low temperature, be suppressed in temperature higher (about 600 ℃) time, (the hot alms giver of this moment is called new thermal donor) appears about 800 ℃ once more in a large number, therefore, consider from the angle of the formation that suppresses hot alms giver, the low-temperature heat treatment temperature of silicon crystal is preferably 600 ℃, can suppress old thermal donor to the full extent and avoid the appearance of new thermal donor.Simultaneously, based on above consideration, the time of the temperature that thermal treatment process of the present invention requires silicon crystal when being 450 ℃ and 800 ℃ of left and right sides is short as far as possible.
After in hydrogen atom enters into silicon crystal, hydrogen atom is finished diffusion and passivating process in silicon.When hydrogen entered in the silicon with molecular state, hydrogen molecule was decomposed into hydrogen atom or directly and { H-V} is right in conjunction with formation in the room.Be in the H+ of gap digit and { H-V} is at the silicon internal diffusion.During low temperature so that { H-V} is diffused as master with H+ to being diffused as the master during high temperature.When low temperature (＜500 ℃), H exists in silicon usually in the following manner at last:
1, be draped on the defective locations of silicon key constraint forms the Si-H key of multiplicity.
2, at electroactive impurity (for example metallic impurity such as Fe, Cr) on every side, combine, form the H key with unsaturated dangling bonds.
3, with stable H
2Form, occupy the tetrahedral center of silicon, at this moment the electricity of H and optical property are all more stable.
4, occupy the interstitial site of silicon with the form of hydrogen atom.
Can learn that by above analysis H may improve performance as the silicon crystal of solar energy photovoltaic utilization raw material in following three kinds of modes:
1, the trap and the deathnium of the minority carrier (few son) that causes because of point defect (empty fall into and between fall into impurity), dislocation and crystal boundary etc. of passivation.
2, combine with the unsaturation dangling bonds that oxygen, carbon, nitrogen, metallic impurity cause, the minority carrier life time of silicon crystal is improved in trap and deathnium that passivation causes because of impurity, and avoid/reduce photo attenuation (LID) to effect of material performance.
3, hydrogen atom accumulates in gettering (gettering) space of harmful metal impurity such as forming Fe, Cr together in silicon, and harmful metal impurity such as Fe, Cr are reunited, and improves the performance of silicon materials as the photovoltaic application material.
Consider that from cost and actual effect in the silicon crystal heat treatment process, the flow of the shielding gas of the silicon crystal surface-area of flowing through is at 2.5～100slpm/m
2Proper between (slpm refers to standard liter per minute, i.e. standard liters per minute).
When furnace pressure need maintain certain force value because of thermal treatment process, feed rare gas element and can play the effect of regulating pressure.Simultaneously, the adding of rare gas element can reduce the concentration of hydrogen, improves the security of system.
Adopt vacuum furnace, the purpose that heating is under low pressure carried out is, needs lower furnace pressure to guarantee the security of producing when hydrogen atoms gas feeds.Show that after deliberation when furnace pressure during less than 5000Pa, the absolute mass of actual hydrogen-containing gas has seldom guaranteed economy and security in the heating under vacuum furnace inner space.Therefore, the pressure of the hydrogeneous shielding gas in the feeding stove should be fixed between 0.1Pa～5000Pa.
On effect, furnace pressure is higher than 5000Pa does not influence above-mentioned thermal treatment result, even to improving the better effects if of silicon crystal minority carrier life time.But consider from security standpoint, need the assurance system definitely not have leakage, improved the cost of device fabrication cost and outfit safe-guard system.Among the present invention, under hydrogeneous shielding gas, silicon crystal is heat-treated, to effects such as the passivation of impurity in the silicon crystal and defective and getterings, the minority carrier life time of silicon crystal is obviously improved, and improved the photoelectric transformation efficiency of the battery sheet of follow-up manufacturing by H; And, adjust hot alms giver's concentration by heat-treating at a certain temperature, improve the homogeneity of the resistivity of silicon crystal at crystals.
The inventive method is simple to operate, and is safe, is easy to suitability for industrialized production, and can obviously improve the quality of product.The resistivity of the silicon crystal that obtains after the thermal treatment and resistivity distribution have obtained effective improvement, can be used for the more solar cell of high conversion efficiency.Used shielding gas is easy to handle in reacted product among the present invention, can not pollute environment.
Description of drawings
Fig. 1 is for adopting the average minority carrier lifetime distribution plan of silicon crystal on radial direction of the inventive method thermal treatment front and back;
The average resistivity distribution plan of silicon chip on radial direction that obtains after the silicon crystal section of Fig. 2 for employing the inventive method thermal treatment front and back.
Embodiment
Embodiment 1
Adopt 6.5 inches solar level gallium doped monocrystaline silicon crystal of Czochralski method preparation general in the sun power industry.
Get long one section of single crystal silicon head (lifting out the part of crucible at first) 200mm, wherein the resistivity distribution of upper surface (part of solidifying at first) is shown in curve before handling among Fig. 2, and minority carrier life time distributes shown in curve before handling among Fig. 1.Above-mentioned single crystal silicon is put into vacuum furnace.After being evacuated down to below the 5Pa in the stove, feeding volume ratio is 1: 1 the argon gas and the mixed gas of hydrogen, and the flow of the shielding gas by the silicon crystal surface-area is at 2.5～100slpm/m
2, make that the vacuum tightness in the stove is issued to about 1000Pa in the effect of bleeding of vacuum pump, and with body of heater by resistive heater heats about 600 ℃ of medial temperatures in the body of heater.Keep said temperature after 4 hours, progressively move back temperature to room temperature.Before taking out single crystal silicon, the argon gas of feeding 100% is to normal pressure in stove.The resistivity distribution of the single crystal silicon upper surface of the above-mentioned heat treatment process of process is as handling among Fig. 2 shown in the curve of back, and minority carrier life time distributes shown in curve after handling among Fig. 1.Can analyze from Fig. 1 and 2 and learn, above-mentioned heat treatment process has improved the homogeneity of the radially resistivity distribution of single crystal silicon, has improved the minority carrier life time of silicon crystal simultaneously.
Adopt the flow processing silicon crystal of embodiment 1, difference is that shielding gas is 100% hydrogen, suitably regulates the flow of shielding gas and the suction performance of vacuum pump furnace pressure is controlled at about 500Pa.
Embodiment 3
Adopt the flow processing silicon crystal of embodiment 1, difference is that this silicon crystal is the silicon single crystal ingot casting that adopts directional solidification method (Directional Solidification) growth.
Claims (9)
1. the heat treating method of a solar-grade silicon crystals is inserted silicon crystal in the vacuum furnace, in the heat treatment process of silicon crystal, feeds shielding gas in the vacuum furnace and the silicon crystal surface of flowing through, and described shielding gas is:
A) gas of hydrogen atoms;
Or b) mixture of the gas of hydrogen atoms and rare gas element.
2. heat treating method as claimed in claim 1 is characterized in that: the gas of described hydrogen atoms is H
2Or SiH
4In at least a.
3. heat treating method as claimed in claim 1 is characterized in that: described rare gas element is at least a in argon gas or the nitrogen.
4. as the arbitrary described heat treating method of claim 1～3, it is characterized in that: described shielding gas formed pressure around silicon crystal is 0.1Pa～5000Pa.
5. as the arbitrary described heat treating method of claim 1～3, it is characterized in that: the thermal treatment temp of described silicon crystal when shielding gas feeds is 400～1000 ℃.
6. heat treating method as claimed in claim 5 is characterized in that: the thermal treatment temp of described silicon crystal when shielding gas feeds is 500～700 ℃.
7. heat treating method as claimed in claim 6 is characterized in that: the thermal treatment temp of described silicon crystal when shielding gas feeds is 600 ℃.
8. as the arbitrary described heat treating method of claim 1～3, it is characterized in that: in the described silicon crystal heat treatment process, the flow of the shielding gas of the silicon crystal surface-area of flowing through is at 2.5～100slpm/m
2
9. heat treating method as claimed in claim 1 is characterized in that: described silicon crystal is silicon single crystal crystal bar, polycrystalline silicon bar, silicon single crystal ingot casting or polycrystalline silicon ingot casting.
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102286784A (en) * | 2011-08-19 | 2011-12-21 | 江西旭阳雷迪高科技股份有限公司 | Treatment method for solar polysilicon chips with abnormal resistivity |
| CN102304764A (en) * | 2011-09-19 | 2012-01-04 | 江西旭阳雷迪高科技股份有限公司 | Treatment method capable of reducing resistance value of monocrystalline silicon wafers |
| CN103173867A (en) * | 2013-04-16 | 2013-06-26 | 江西豪安能源科技有限公司 | Method for eliminating resistance distortion caused by heat donor at head part of solar single crystal |
| CN103194802A (en) * | 2012-01-05 | 2013-07-10 | 昆山中辰矽晶有限公司 | Tempering method of crystal bar surface, and crystal bar |
| CN104651946A (en) * | 2015-03-19 | 2015-05-27 | 太原理工大学 | Silicon waveguide surface smoothing process based on silicon hydrogen bond current density method |
| CN105332061A (en) * | 2015-11-17 | 2016-02-17 | 阳光能源（青海）有限公司 | Thermal treatment process for eliminating influences of oxygen donor effect of monocrystalline rods on electrical resistivity |
| CN108546990A (en) * | 2018-06-28 | 2018-09-18 | 晶科能源有限公司 | A kind of method and apparatus improving polysilicon grain boundary defect |
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| CN101238557A (en) * | 2005-07-27 | 2008-08-06 | 胜高股份有限公司 | Silicon wafer and method for producing same |
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Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102286784A (en) * | 2011-08-19 | 2011-12-21 | 江西旭阳雷迪高科技股份有限公司 | Treatment method for solar polysilicon chips with abnormal resistivity |
| CN102304764A (en) * | 2011-09-19 | 2012-01-04 | 江西旭阳雷迪高科技股份有限公司 | Treatment method capable of reducing resistance value of monocrystalline silicon wafers |
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| CN103173867A (en) * | 2013-04-16 | 2013-06-26 | 江西豪安能源科技有限公司 | Method for eliminating resistance distortion caused by heat donor at head part of solar single crystal |
| CN104651946A (en) * | 2015-03-19 | 2015-05-27 | 太原理工大学 | Silicon waveguide surface smoothing process based on silicon hydrogen bond current density method |
| CN105332061A (en) * | 2015-11-17 | 2016-02-17 | 阳光能源（青海）有限公司 | Thermal treatment process for eliminating influences of oxygen donor effect of monocrystalline rods on electrical resistivity |
| CN108546990A (en) * | 2018-06-28 | 2018-09-18 | 晶科能源有限公司 | A kind of method and apparatus improving polysilicon grain boundary defect |
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Application publication date: 20110112 |