DE1444526A1 - Process for the thermal deposition of silicon or another semiconducting element - Google Patents

Description

24AUGt 1H2

Siemens & Halsice Munich 2, den

Aktiengesellschaft Wittelsbacherplatz 2

Act.Z «

Method of, thermal _ ^. Bseheiden_ of. Silicon or a ^ ^ nderen it semiconducting Ele mente s

A known process for the production of monocrystalline silicon is based on a heated, monocrystalline rod-shaped carrier body held only at its ends, which is heated to such an extent by a reaction gas consisting of hydrogen and silicon halide that free silicon is deposited on the carrier body and becomes monocrystalline there grows up. This gives the monocrystalline

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Carrier body has a jacket made of monocrystalline silicon, which in principle can be brought to any thickness. Since the carrier body, e.g. by means of the brackets The electrical current supplied can be heated to a high uniform temperature, stands for the deposition With the exception of the ends of the carrier located in the holders, the entire carrier surface is available, so that the silicon content of the reaction gas can be used well. Prerequisite for a trouble-free single crystalline Growing up is above all that the melting temperature of the The carrier on the carrier surface is not exceeded, otherwise the melted silicon will agglomerate to form drops and thus the uniformity required for monocrystalline growth on a semiconductor surface Deposition would be impossible. But even if one avoids melting the carrier, a monocrystalline face Deposition of silicon and other semiconducting elements from the gas phase. Considerable difficulties opposite. - ..

In order to overcome these difficulties, various methods have already been given. Such a method is described in German Patent 1,048,638.

This refers to a process for the production of

Semiconductor single crystals for semiconductor arrangements by means of deposits voji purest, with or without doping additives

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provided semiconductor material on a heated, monocrystalline consisting of the same semiconductor material Carrier body through thermal decomposition or reduction. She suggests that to avoid growth irregularities the exposed surface structure of the monocrystalline carrier body is heated to a temperature, which is below the temperature at which the maximum separation of the semiconductor material in the selected reaction

takes place on the support body that further the reaction gas flows around the surface of the support body and turbulent that the deposition rate taking place at the selected working temperature and the selected reaction in • is set in a manner known per se so that the carrier is oversaturated with the resulting semiconductor material is avoided.

In this patent only embodiments are described in which the carrier by direct passage of an electrical Stromes is heated. But it is also known to heat the rod-shaped carrier in an inductive manner. To this Purpose, the carrier is arranged in the axis of an induction pub that surrounds it concentrically and is supplied with alternating current, in particular High frequency current is fed. The length of the coil is preferably dimensioned in such a way that it covers the upper, flat,! ; it is intended for the deposition, at as uniform a temperature as possible by inductive means

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heated. Such a method is described in German patent application S 650 059 VI / 48 Td and is used for illustration of "particularly pure silicon applied =

The invention "relates to a method for the thermal deposition of elementary silicon or another semiconducting element from a reaction gas containing the semiconductor element in a bonded state and free from the semiconductor undesirably contaminating. Reaction gas on a single crystal from the semiconductor in question existing rod-shaped support body, which in the flowing reaction gas to such a high temperature, but below the melting point of the semiconductor, "that the semiconducting element released from the reaction gas is deposited in a monocrystalline state on the surface of the support body which furthermore generates the high temperature of the carrier surface required to convert the reaction gas by direct induction of an electromagnetic, in particular high-frequency alternating field which acts as uniformly as possible on the carrier. and is characterized by the fact that the composition of the reaction gas is adjusted during the entire deposition process so that the deposition rate of the semiconducting element is below the deposition temperature T _{n used} on the carrier surface.

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Temperature T has its maximum value and in a temperature range above this temperature T ₀ and containing the selected deposition _{temperature T a of} the support surface decreases monotonically with increasing temperature, so that the actually set deposition rate

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becomes noticeably smaller than the deposition rate present at the low / at temperature T _Q.

Because that growth of the carrier as a result of the deposition in radial Direction takes place, the carrier surface approaches the induction coil more and more in the course of the deposition process, so that the coupling between induction coil and carrier surface increases during the deposition process. As a result, if the power is kept constant, the temperature of the carrier surface also increases. In the same In addition, the skin effect of the eddy currents induced on the surface of the carrier and heating it has an effect the end. Projecting parts of the support surface, e.g. warts or knuckled elevations, are therefore necessarily hotter as a normal support surface or even depressions in the same. So the situation is exactly the opposite of what * ßie when the carrier is heated by an electrode fed Alternating current or direct current are given.

If that reaction gas in accordance with the invention Gauge is chosen so that there is a -

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The deposition temperature set when this temperature is increased leads to a reduction in the deposition, when it drops Temperature, on the other hand, must lead to a strengthening of the deposition, so occurs at protruding and therefore hotter Place the support surface a diminished one at deeper and therefore cooler parts of the support surface increased deposition instead. Since there is increased deposition at cold spots on the carrier surface, if the reaction gas is set according to the teaching of the invention, these points after some time over the Level of the normal carrier surface, become hotter than this and then receive a reduced deposition » Conversely, areas of the support surface that grow more slowly become ultimately colder than the normal carrier surface and thus in turn receive increased deposition. The teaching of the invention thus has the effect that as a result of the use of induction heating of the carrier, an automatic Compensation for irregularities in the growth rate takes place, which is essential for the production of single-crystal silicon b2w. other semiconducting elements is essential. With Aus. ' would take the demand in the increasing branch of the dependent on the deposition rate curve shown to work the carrier temperature, the remaining in the German Patent specification 1 048 638 measures described with advantage applied. This applies in particular to the necessary cleanliness of the surface of the carrier and to the use of a den

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ÜDräger body turbulent flow around reaction gas.

Since these are work steps that are known per se, you can refer to the German Patent specification 1 048 638 should be referred to. As in the process according to the invention, the semiconducting compound is used in strong dilution with hydrogen and In addition, the deposition takes place either at normal pressure or at reduced pressure, is a supersaturation of the Support with presented semiconductor material is generally not to be feared.

In the interests of the purity of the semiconductor material to be produced, undoped semiconductors may be produced if undoped should, the reaction gas contain only halogen and hydrogen in addition to the semiconducting element to be represented. In the production of doped semiconductor elements, the reaction gas contains, if the dopant is used during the Manufacture of the semiconductor wants to build in this, the doping element to be used either in the pure or in on Halogen or hydrogen bonded state. Since the proportion of dopant in the reaction gas is generally very low must be set, v / ird the course of the deposition curveG of the semiconducting element from the reaction gas noticeably not influenced.

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Whether the curve of the depending on the carrier temperature T applied deposition rates that in the Pig. 1 shown for the proposed according to the invention Process has the necessary behavior, depends crucially on the composition of the reaction gas. Unusable is e.g. a compound based on silanes Reaction gas. Since it is semiconducting when using silanes or other pure gaseous hydrogen compounds Elements that decompose with increasing temperature to an increasing extent to form the semiconducting element, there is no occurrence of a falling area of the deposition curve when a reaction gas consisting of silanes is used. On the other hand, using Silicon halogen compounds produce a reaction gas exhibiting the necessary behavior. -. ■ ■ »

! If, for example, a reaction gas consisting of 5 Mo1 $ SiHCl ^ and 95 · Ιίο1 # hydrogen, the deposition at a substrate temperature will, """- 1400 ⁰ C maximum.

Max

The amount of silicon produced, however, still depends on the pressure of this gas and is about _<f , x2 _{ii at normal pressure;} mg silicon per minute and per cm of the surface of the support. If the carrier temperature is increased above HOO ⁰ C, the deposition rate decreases again. The position of the temperature T _max depends to a large extent on the hydrogen content of the reaction gas. If, for example, one uses a molar ratio of 7 '| .. »M0156 SiHCl, and 93 Mole ^ hydrogen, the temperature is

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T the maximum deposition rate already well above the melting point of silicon. Conversely, a Reaktionsgaa consisting of 2 moles of $ S SiHCl. * And 98 MoljS hydrogen, a maximum rate of deposition will develop at about 1100 ⁰ C, so that the deposition temperature T "in

et

Range from about 1150 ⁰ C to the melting point of the carrier can be set. If the compound SiCl is used instead of SiHCl ^, analogous temperature and composition ratios apply, only the amount of silicon accumulating in the unit of time at the same gas pressure and the same carrier temperature is less than that obtained when using SiHCl * under otherwise identical conditions.

If a SiHCl or SiCl. and hydrogen existing reaction gas is used, the SiHCl, - or the SiCl. -Content of the reaction gas at most 5 mol $ be. If, on the other hand, SiHCIp or SiH ^ Cl are used, then the result is Experience has shown that the values differ slightly.

In the pig. 1 a diagram of a deposition curve is shown, as must have a reaction gas suitable for carrying out the invention. The abscissa is the temperature the support surface, the ordinate is the amount m of the

Minute per cm of silicon amount deposited on the carrier surface. The flow rate of the reaction gas through the separation vessel is recorded. The deposition begins at a temperature threshold T _Q

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to become noticeable on silicon and _{initially increases up to a temperature 2L ax} , only to decrease again as the temperature continues to rise. The working temperature of the carrier surface T at which the deposition is carried out should be greater than the temperature T "". But she should be different

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lower than the melting temperature T _{e of} the carrier, i.e. lower than 1415 ° C. in the example of silicon.

Look the Pig. 2 the implementation of the method according to the invention is to be described in more detail in the form of an example. In a cylindrical separating vessel 1 made of quartz, a rod-shaped support body 3 made of high-purity silicon is held in a vertical position by means of quartz holders 2, 2 '. The reaction vessel has an inlet opening 4 and an outlet opening 5 for the reaction gas flowing through. A long, tightly wound induction coil 6, which is arranged outside the treatment vessel and concentrically to the carrier and which is fed by high-frequency Viechselstrom supplied by a high-frequency generator 7, is used to heat the carrier. The reaction gas consists of 2 moles of SiHCl ₅ and 98 mol% of H ₂ ; it is generated by passing a hydrogen stream through an _{evaporator vessel 8 filled with liquid SiHCl 5} , the temperature of which is kept constant by a temperature bath 10, the hydrogen used and the SiHCl _{5 used} are in a highly pure state. _ 11

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To determine the amount of in the reaction vessel in the The unit of time entering reaction gas is the gas flow rate meter 9 provided. In addition, as shown in “Pig provided so that the gas coming from the evaporator after If required, it can be further diluted with pure hydrogen.

By the temperature of the evaporation vessel and the flow rate of the flowing through the evaporator vessel Hydrogen gas, the amount of SiHCl * that gets into the reaction gas in the unit of time is determined. By variation The SiHCl content of the reaction gas can therefore be adjusted to these parameters. Of course, this salary also depends of the, size and shape of the evaporation vessel, so that Information on the temperature in the evaporator vessel and flow velocities, which are valid for all arrangements, are not can be made. With the help of one of the entire hydrogen flow measuring gas flow meter can measure the amount of hydrogen used in a certain time and can be adjusted at will by regulating the hydrogen flow. If you switch to the determination of the The parameters of the evaporator temperature to be set during operation and the flow rate of the hydrogen gas in preliminary tests Instead of the separation vessel, a cold trap in which all of the SiHCl entrained by the hydrogen stream, is made to freeze out, the content of the! Dräger-

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gases, which "at a" certain evaporator temperature a certain flow rate of the hydrogen gas is taken up by this, easily determined v / ground. Because of some preliminary tests carried out with different flow rates and / or evaporator temperatures On the basis of the results obtained, a combination of to achieve a reaction gas with a Content of 2 mol $ SoHCl, and 98 mol # hydrogen necessary Values for the carrier gas velocity and the temperature of the evaporator determine which then, during the actual Deposition process, used.

To compare the deposition process with that in 3? Ig. 2 shown

If necessary, after preheating to the desired deposition temperature, the carrier is heated to the desired deposition temperature by switching on the induction field of the coil 6 and bringing it to the strength required to heat the carrier to the desired annealing temperature. For the separation, it is advisable to set a temperature T of about 125O ⁰ C in the example, since the falling branch of the separation curve according to Hg. 1 then runs particularly steeply with the selected composition of the reaction gas. The deposition temperature is monitored in a known manner and kept constant. Before starting the actual deposition process, it is advisable to glow the carrier in a hydrogen stream for some time.

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composition determined by preliminary tests, - into the Reaction vessel initiated. .

The onset of a falling area of the temperature separation curve is likely to be related to formation composed of sub-halogenids, the formation of which is so favored with increasing temperature that the subhalide formation above a certain, already above the formation threshold, of free silicon from the Reaction gas lying temperature threshold in comparison to the formation of free silicon more in the foreground pushes. Of course there are also other reactions, e.g. disproportionation or dissolution of what has already formed Silicon into consideration, a region of falling course of the temperature deposition curve in the sense of Pig. I evoke.

4 claims
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Claims (4)

PA 9/495/384 Claims . Process for the thermal deposition of elementary silicon or another semiconducting element from a reaction gas containing the semiconductor element in a bonded state and free from the semiconductor undesirably contaminating accompanying substances on a monocrystalline rod-shaped carrier body consisting of the semiconductor in question, which is contained in the flowing reaction gas is heated to such a high temperature, but below the melting point of the semiconductor, that the semiconducting element freezing from the reaction gas is deposited in a monocrystalline state on the surface of the support body, at which the high temperature of the support surface required to convert the reaction gas is generated by direct induction of an electromagnetic, in particular high-frequency alternating field acting as uniformly as possible on the carrier, characterized in that the composition of the reaction gas during the entire Deposition process is set so that the deposition rate of the semiconducting element at a temperature below the deposition temperature used (Tj ^ ian the support surface temperature (GLAJpiren) has a maximum value and, at a temperature above this temperature (T _Q ), the selected deposition _{temperature (T a} ) the temperature range containing the support surface ■ -15- 809803/0395 -.15 - PA 9/493/384 decreases monotonically with increasing temperature, so that the actually set © Deposition rate noticeably lower than that at the low carrier temperature (T) present deposition rate v / ird. 2. The method according to claim 1, characterized in that a mixture of pure hydrogen and as the reaction gas a pure - optionally hydrogen-containing halogen compound of the semiconducting element to be represented is used, whereby the ratio between water * ■■■■■■ The hydrogen and halogen compounds are adjusted in such a way that at the deposition temperature T to be used the Deposition rate with an increase in the carrier temperature decrease, would increase with a decrease in the carrier temperature. 3. The method according to claim 1 or 2 for the preparation of silicon, characterized in that when using SiGl. or SiHCl, as a silicon-yielding gaseous compound the content of the reaction gas in SiCl. or SiHCl, not higher than 5 mol # SiCl. or SiHCl, is set. 4. The method according to any one of claims 1 to 3, characterized in that that the reaction gas from 98 mol $ water .4f ■ \ 809803/0395 - 16 PA 9/493/384 substance and 2-MoISi SiCl, bar /. SiHCl, "and is the deposition temperature T _a to the substrate surface to a ⁰ above 1100 C, in particular above 1150 ⁰ C, lying value -vorzugsv / else is set at 125O ⁰ C. 809803/0395 originally inspected