A method of obtaining a uniformly-doped silicon

 

(57) Abstract:

The invention relates to the field of production of semiconductor material. Growing lead by the Czochralski method from a melt containing phosphorus. Spend recharge melt compensating admixture of boron on the program to reflect changes in phosphorus concentrations in the melt. Given a mathematical expression to calculate this change. 3 C.p. f-crystals, 1 table.

The invention relates to the field of production of semiconductor materials and can be used to obtain a semiconductor silicon electronic conductivity type with a given resistivity, doped with phosphorus in the process of crystallization by pulling from the melt (Choralschola).

A method of obtaining doped silicon ingots with a given resistivity in the process of crystallization by pulling from the melt [1] . How is that in the crucible together with the load placed a portion of the ligature (alloy source material with alloying impurity). Then spend the meltdown download with ligature, seeding and pulling the alloy ingot.

The disadvantage of this method is the large neodermata heterogeneity associated with the in the ingot enters the lower concentration of impurities with the allocation ratio < 1, than its concentration in the melt (the distribution coefficient of phosphorus in silicon TOabout= 0,35). In addition, the amount of melt in the crucible continuously decreases as the pulling of the ingot. All this leads to a continuous increase in the concentration of impurities in the melt, and hence in the ingot during solidification.

Under these conditions, the accumulation of excess compared with the specified amount of impurities, without regard to its evaporation takes place in accordance with the analytical dependence:

C = KeffCo[(1 - g)KEF-1- 1], (1) where is the excess concentration of impurities in the ingot;

WITHaboutthe concentration of impurities in the melt;

g - crystallized portion of the melt;

TOeff- effective coefficient distribution,

Keff= , where CSLthe concentration of impurities in the ingot.

The table below shows the change in the excess phosphorus concentrations along the length of the ingot during pulling. The initial concentration in the melt WITHabout= 6,76x1014cm-3; in the bar WITHSL= 2,51014and TOeff= 0,37.

You can see that getting ingot deviation of Kohn and deviation of 20% - not greater than 0.25 part of it.

A method of obtaining a uniformly doped along the length of the bars is based on the change ratio of the impurity distribution when programming in a wide range rate of withdrawal and rotation of the ingot, and the rotation speed of the crucible with the melt. However, a significant drawback of this method of production is the emergence in the semiconductor crystal structural defects due to violations of the optimal conditions for crystallization. This increases the overall heterogeneity of the material, leading to the impossibility of its use.

A known method of reducing the concentration of accumulated impurities in the melt during the pulling of the ingot by evaporation from the melt. This is achieved by selection of the rate of withdrawal that influence the evaporation [1]. However, phosphorus is a non-volatile silicon, especially during crystallization in a protective gas atmosphere. In this regard, such a method of obtaining a uniformly doped material is unsuitable.

The closest in technical essence to offer are ways to maintain the desired concentration of dopant in the melt, based on the use of continuous processes which can be carried out by feeding to the melt as a solid, and liquid material. In the first case, the feed material in the form of pure or doped with the same impurity as that of the melt, a silicon rod is fixed in the holder of the additional rod, located inside the working chamber crystallization setup. When extruding the ingot simultaneously dipped into the melt feed rod with a speed dependent on the speed of extrusion, the ratio of the diameters kristallicheskogo ingot and feed rod, the density of the feed rod and his staff. Also fueling the fuel rod and rotate. In a known embodiment, the method of feeding the rod is pre-melted in an intermediate tank, from which the melt flows into the crucible. The main disadvantage of these methods of recharge melt is a significant complication of the apparatus registration process of crystallization, leading to more expensive equipment, making it less reliable and more complex management process. The supply terminals must be constant line length, cylindrical and of constant diameter. Their introduction into the melt complicates the selection and maintenance of the necessary thermal conditions of crystallization, which has a negative effect

Because of the additional operations (mounting supply terminal and the organization of its additional heating) performance of the process of crystallization is reduced. Due to the low profitability of the process method has not found practical application.

Another group of methods of recharge melt based on the continuous supply of material in the molten state. While no requirements to the stability of the composition along the length of the supply terminals, the constancy of their diameter and cylindricity.

For the implementation of such methods of recharge material placed in the crucible feeder and lead to melting. The feeder can be remote or in the form of a crucible with a clear melt, which feature the working crucible with alloyed molten silicon. In all cases, the recharge is based on the principle of communicating vessels. The disadvantage of this group of methods is a significant complication and appreciation of the process of obtaining doped semiconductor silicon due to the need for additional expensive synthetic quartz crucibles and communications for filing of the melt, as well as nodes for heating of the feeder and communications, to secure pitalo process. In addition, significantly complicated the selection and maintenance of the necessary thermal conditions, and the probability of accidents of the crystallization process due to breakage of quartz products increases. In these conditions increase the profitability of the process of obtaining the doped material is small (a few percent). This resulted in very limited ways.

The aim of the invention is to increase the yield of silicon and increase the profitability of the process.

The objective is achieved by feeding the melt to produce a compensating admixture of boron in amounts corresponding excessive concentrations of phosphorus in it with respect to its nominal value. The proposed method of producing homogeneously doped silicon-based automatic control according to a given program distribution of impurities from the beginning of the crystallization process. Moreover, this program takes into account the nonlinear nature of the change of the impurity concentration in the melt in accordance with well-known and well-proven dependence.

According to this widely known, the main dependence of the impurity distribution along the length of the ingot (excluding evaporation) by pulling it from the situation impurities in the ingot;

WITHabout- the initial concentration of impurities in the melt;

TOeff- effective distribution coefficient of an impurity;

g - share zakristallizuetsya melt.

g = f(t), where t is the current time.

Then, the excess amount of impurities in the ingot relative to nominal concentrations will vary along its length according to a ratioCL.houses= KeffWITHabout(1 - g)KEF-1- KeffWITHabout=KeffWITHabout[(1 - g)KEF-1- 1].

Share zakristallizuetsya melt corresponding to the maximum permissible concentration of impurities after the last compensation can be evaluated analytically considering the fact thatandSLZB.= KeffWITHabout. Then in the limit

TOeffWITHabout[(1 - g)KEF-1- 1] = KeffWITHabout, where is the value of the permissible deviation of the concentration of the dopant with respect to its nominal value.

For values of the nominal concentration of impurities in the ingot WITHnom.SL= 2,5 1014cm-3value = 3,71013cm-3and TOeff= 0,37. Then (1 - g)KEF-1- 1 = . Where g1= 1 - ( + 1)1/KEF-1. From this it follows, Thu is ncentratio phosphor with respect to its nominal value, in accordance with the dependency WITHwt.R= Cabout[(1 - g)KEF-1- 1].

It is possible to feed molten silicon with boron from the gas phase volatile and biodegradable compounds, for example, applying to the surface of the melt vapor isopropylaminocarbonyl. With this technical solution is not disturbed selected optimal mode of crystallization and simplified instrumentation of the recharge process of the melt, since the nodes recharge is simple and reliable. The admixture of boron does not accumulate in the melt, as it is the distribution coefficient 1 (Keff= 0,9).

Examples:

P R I m e R 1. The apparatus for pulling the ingot from the melt of the type "Subject 10 receive a monocrystalline ingot of silicon electronic conductivity type with a diameter of 80 mm and a resistivity of 20 MSM and valid by the deviation in relation to a specified nominal value of 15%, which corresponds to the impurity concentration in the ingot on 3,71013cm-3.

To do this in a quartz crucible with a diameter of 200 mm load 5 kg source polysilicon brand CP1 with the level of cleanliness boron impurities >3000 MSM and donor impurities 400 Ohm cm (1,31013cm-3MSM containing phosphorus equal to 51018cm-3.

To create the necessary concentration of impurities in the melt a portion of the ligature Pldetermine the ratio

Pl= PpWITHSL/[1 -)effWITHl], where Rp- the weight of the melt;

WITHSLthe concentration of phosphorus in the ingot corresponding to specified nominal resistivity;

WITHlthe concentration of phosphorus in the sample ligatures;

fields impurities ligatures, disappearing due to oxidation and evaporation.

Pp= 500 grams; CSL= 2,5 1014cm-3;l= 5 x 1018cm-3; = 0,1. Then Rl= 0,76,

Then work the camera crystallization setup pumped to a residual pressure of 5 10-4mm RT.article and heat the crucible to melt it contains silicon and ligatures. Afterwards inside the working chamber let purified argon and create its duct with a speed of 350 l/h To melt down the seed crystal, produce seeding, patience and begin pulling of the single crystal at a speed of 2 mm/min while rotating the crystal with a speed of 20 rpm and the crucible at a speed of 8 rpm

In accordance with the table. the maximum concentration of impurities FD is at a diameter of 80 mm, which corresponds to 86 mm of its length.

To obtain a uniformly doped material after crystal pulling length 84 mm, i.e., after 42 min in the melt shed ligature boron. Thus compensate 71013cm-3/Keffphosphorus in the melt, which reduces the concentration in the crystal to the upper level, a deviation of resistivity (up to 22-23 OSM), as introduced into the melt 2 TOeffBora.

Calculation of sample ligatures boron is carried out taking into account the fact that at the time of her discharge weight of the melt is equal to 4 kg. I.e., Rp= 4000 g; Cl= 1018cm-3;SL= 7 1013cm-3;eff= 0,37 and = 0, since boron is a non-volatile silicon. TOeff- phosphorus (Pacem). Then

Pl= = 0,76 g Next reset ligatures weight of 0.58 g (taking into account the weight of the melt by the time of discharge) in accordance with table.1 is performed after pulling 0,41 part of the melt, when the ingot reaches a length of 164 mm through 42 min after the previous reset. The third reset ligatures weight of 0.43 g is performed after the extrusion of 0.55 part of the melt through 31 min after the last reset. Active concentration of phosphorus in the melt will remain in zadannymi pulling 0,66 part of the melt (75%). This corresponds to an increase in the extraction of suitable goods for one process more than 3 times. This recharge of boron melt stop, because at the end of the melt excessive amount of impurities increases very rapidly with further recharge quickly increases the degree of compensation of phosphorus. The fourth dropping ligatures boron makes it possible to get only 250 g of material with a given resistivity, but with the degree of compensation, up to 50%, which may be undesirable.

P R I m m e R 2. Get a monocrystalline silicon ingot with a diameter of 80 mm under the same conditions and with properties as in example 1. Melt alloyed mounted a ligature phosphorus weight 0,76, Compensation accumulated impurities of phosphorus begin immediately after razresevanja ingot to a specified diameter and hold it continuously during the whole crystallization process to a given level of compensation. To do this continuously fed into the melt powder doped with boron silicon to a concentration of 11018cm-3. A continuous supply of powder is produced by a screw feeder (feeder). When pulling up to 0.2 parts melt the powder ligatures served in the melt in the number 0,76 g for 42 min, or 18 mg is 14 mg per minute. In the future, this rate constant support. Filing ligatures stop after extrusion ingot length 30 cm, feed Rate ligatures set by selecting the corresponding speed of rotation of the auger dosing.

P R I m e R 3. Get an ingot of monocrystalline silicon, as in example 2. Compensation is accumulating excessive amounts of phosphorus in silicon is conducted continuously during the whole crystallization process to the specified compensation level of phosphorus with a rod of doped boron silicon 11018cm-3with a diameter of 4 mm, which is continuously lowered into the crucible with the melt. The lowering is performed with the help of additional stock, is introduced into the working chamber. The holder rod is fixed by a rod of silicon. The speed of lowering of the rod shall establish and maintain with the help of special gear.

When pulling up to 0.2 of a melt doped with boron silicon served in the melt with the speed of 0.32 g for 42 minutes, This corresponds to lowering it into the melt with a speed of 0.25 mm / min.

Upon further pulling of the melt from 0.2 to 0.41 part by crystallization doped with phosphorus and silicon in the melt lower legs is with the speed of 0.19 mm/min In the future, this rate constant support until the termination of the feeding of the melt, i.e., prior to extrusion ingot length 30 cm

P R I m e R 4. In the same conditions and with the same properties as in examples 2 and 3, receive a monocrystalline silicon ingot with a diameter of 80 mm, doped with phosphorus. Accumulated in the melt excess phosphorus compensate for the continuous feeding of the melt boron from the gas phase of isopropylaminocarbonyl.

Intake of boron in the molten silicon occurs in the decomposition of vapors of isopropylaminocarbonyl, recovery of boron from boron carbide in contact with the surface of the molten silicon and its subsequent diffusion into the melt.

For carrying out the process of doping use remote metering device to the evaporator and orifice. Isopropylaminocarbonyl placed in the evaporator and the flow conditions necessary impurity concentration set by selecting the diameter of the bore holes of the evaporator or evaporation temperature of the alloying compounds. A pair of alloying compounds delivered to the surface of the melt using analiziruyuschei tube and a current of argon passing through the evaporator. To maintain the required concentration of the crystallization process with the rate of introduction into the melt 71013/Keffatoms per cm3boron for 32 min, or 6,751013cm-3boron within 15 minutes the concentration chosen by doping pure silicon melt within 15 min when the hole diameter of 2 mm and at two different temperatures evaporation of alloying substances. Then from the graphical dependence of impurity concentration in the melt, the temperature of the evaporation of alloying compounds find the desired evaporation temperature in the conditions of the crystallization process for the introduction of 6,751013cm-315 minutes After crystallization of 0.2 part of the melt feed rate vapor alloying compounds decrease in the ratio of 0.58/0,76 or 0.76 times. I.e. achieve the introduction into the melt for 15 minutes 5,11013cm-3Bora. This value is determined from the dependences of impurity concentration in the melt from evaporation temperature, and then adjust.

In the future, this mode of doping to maintain a constant pulling of the ingot length 30 cm, after which the boron doping stop. The required concentrations of impurities in the doping from the gas phase can be done by using the dependence of impurity concentration in the melt (or crystal) from diameter bore others SILICON electronic conductivity type with the specified resistivity by crystallization from the melt, including the meltdown download with alloys containing phosphorus, seeding, endurance and pulling the ingot from the recharging of the melt, characterized in that, to increase the yield of silicon and profitability of the process, feeding the melt to produce a compensating admixture of boron in an amount corresponding to the excess concentration of phosphorus in silicon with respect to its nominal value, in accordance with addiction

CRandZB= Co[(1-g)-1],

where chousesp- excessive concentration of phosphorus in the melt;

C0- initial concentration of phosphorus in the melt;

g - share zakristallizuetsya melt;

Keff- effective distribution coefficient of phosphorus in silicon.

2. The method according to p. 1, characterized in that the feeding of molten silicon with boron is produced periodically by hanging the ligatures.

3. The method according to p. 1, characterized in that the feeding of molten silicon with boron produces a continuous supply of molten powder or a thin rod of doped boron silicon.

4. The method according to p. 1, characterized in that the feeding of molten silicon with boron is produced from the gas phase volatile and biodegradable compounds,

 

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1 ex, 2 dwg

FIELD: technological processes.

SUBSTANCE: method of production of regular systems of nano-size silicon whiskers includes preparation of silicon plate by masking of its surface with photoresist, making holes in it, electrochemical deposition of metal islets into photoresist holes from electrolyte solution, and installation of prepared plate into growth furnace with further growing of silicon whiskers on it, at that cylindrical openings in photoresist are created with diameter of less than 250 nm by means of imprint-lithography, metal islets are deposited with thickness of less than 12.5 nm, after that photoresist is removed in 5% solution of hydrofluoric acid.

EFFECT: method makes it possible to considerably facilitate creation of nano-technological instruments on nano-crystals.

4 ex

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