DD154108A1 - METHOD FOR DOTING SEMICONDUCTOR STAFFS IN LOCK-FREE ZONES - Google Patents

Abstract

The invention relates to the production of doped Halbleiterstaebe or crystals for their use in power and microelectronics. The aim of the invention is the production of doped dislocation-free or polycrystalline Halbleiterstaebe, in particular Siliziumstaebe with diameters> equal to 50 mm by lowering d. Discharge Committee to make economic. The object is to influence the process of introducing the doping from the gas phase so that the melting zone on reaching the cylindrical rod portion has the dopant concentration corresponding to the stationary state, without the zone melting process being interrupted by a waiting time t down w. According to the invention, this is achieved by virtue of the fact that, with the transition to the cylindrical rod part, the steady state dopant concentration N below L is at least reached or exceeded by <10%, then reduced and kept constant until the end of the zone melting process (see curve C).

Description

5 022 -'-

Method for doping semi-precious rods in crucible-free zone melting

Field of application of the invention

The invention relates to the production of doped semiconductor rods or crystals for their application in power electronics and microelectronics.

Characteristic of the known technical solutions

In the doping of semiconductor rods, but in particular of polycrystalline and monocrystalline, dislocation-free silicon rods by the method of crucible-free zone melting (FZ method) has, especially for rods with diameters> 50 mm, the method of doping from the gas phase prevailed.

The function of the method is based on the assumption that, given the stabilization of all growth parameters, there is a stable relationship between the dopant concentrations in the crystallizing semiconductor and the surrounding gas phase.

This ratio ^, the absolute size of which depends on the geometric and thermal parameters of the plant, is defined as follows:

⁰ G

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2 where η. the dopant incorporation rate of the crystal.

Semiconductors ÜAtome},

n_ the dopant addition rate into the gas phase [atoms], Vg- the growth rate of the semiconductor

[cm.min] J C is the dopant concentration in the crystal. Semiconductors [[Atoms - cm "" ^ J

Έ the crystallization area of the semiconductor ["cm JC _G the dopant concentration in the gas phase

[Atoms · cm ** - ^ J and

r °> -Λ-ι V " the gas flow rate [_cm ^ min J

represent. However, the ratio σ E becomes stable only when the dopant concentration Oj corresponding to the intended dopant concentration C is reached in the liquid melt zone

 CL. is after the condition

⁰ L ^{= C} s (2)

depending on the segregation coefficient k of the dopant used.

In order to set Οχ, a number of IL dopant atoms dependent on the volume Έh of the liquid zone is required:

H - 0 _B · '· ^h (3)

TE

In order to achieve the "steady state", ie an equilibrium, in which the same number of doping atoms / unit time are incorporated at the solidification phase boundary in the solid phase, keeping constant all breeding parameters and the ratio n./n in the migration of the melt zone, as per unit time arrive from the gas phase into the liquid phase, it is necessary before the start of migration zone, ¹¹ or saturated FINISH s ze it t, a concentration in the zone are built up during a "waiting which corresponds to the equilibrium state.

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The required waiting time is calculated from

This condition is obsolete in breeding technologies seed crystal diameter ratios close to 1: 1 ZM meet easily with formation of dislocations during the growth process.

However, in growing dislocation-free, large diameter crystals using very thin seeds, the condition presents a major obstacle in the application of the gas phase doping during the crystal growth pass. The doping is therefore usually performed in an additional zone pass preceding the crystal growth process greater expenditure of time, energy and semiconductor material is required.

But even with the doping of the polycrystalline semiconductor material during the preparatory zonal passage difficulties with respect to the maintenance of the waiting time, t grows with increasing zone height h and decreasing crystallization rate Y _rx and z. B. in the doping of silicon with phosphorus 10 ... 30 ™ i ⁿ amount. It is very complicated to keep the melting zone stable at V ₁₇ - = 0 over such a period of time.

Dispensing with t would, while keeping all parameters constant, in the transition cone and in a considerable part of the cylindrical rod part, cause a deviation from the target dopant concentration to be set (curve A, FIG. 1) similar to the curve B (FIG. 1). This concentration profile, which is due to the constant increase in the diameter of the crystallization phase boundary (curve D, Fig. 2) and the height and the volume of the Schmelazone (curve E, Fig. 2), leads to an unacceptable decrease in the Dotierausbeute.

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Object of the invention

The aim of the invention is to make the production of doped dislocation-free or polycrystalline semiconductor rods, in particular silicon rods, with diameters ^ 50 mm by reducing the doping Committee more economical.

Explanation of the essence of the invention

The invention has for its object to influence the process of introducing the doping from the gas phase so that the melting zone has reached the stationary state corresponding dopant concentration on reaching the cylindrical rod portion without the zone melting process is interrupted by the waiting time t.

According ^to the invention, in a process for doping gaseous-phase semiconductor rods ^of diameter 50 nra, during crucible-free zone melting in inert gas or vacuum, in which a melt zone is passed through a transition cone and a subsequent cylindrical rod member, using a nozzle arrangement for inflating the in the melt zone, without observing a waiting time t at the growth rate of the crystal Vg. = 0, during the migration of the melting zone through the transition cone in that the dopant concentration C 1 in the doping gas stream is increased in proportion to the geometric conditions prevailing in the transition cone so that, with the transition into the cylindrical rod portion, the doping center corresponding to the stationary state l concentration Nt reaches the melting zone or up to 10 % is exceeded and the O ^ reduced after this condition to the stationary state corresponding dopant concentration and kept constant until the end of the zone melting process.

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The continuous change of the dopant concentration C _G can be computer-controlled via automatic control. The Rege! Characteristic of the dopant concentration in Dotiergasstrom it determines from the position-related values of the actual and intended dopant concentrations at certain portions of the cone area and the cylindrical portion of the semiconductor rod as well as the determined by electrical measurements dopant concentrations in the cone area for tests without dose of _C.

The particular advantage of the method according to the invention is that the zone melting without interruption

(Waiting time t) can be carried out and thereby the Entw

avoidance of dislocations during the breeding process.

embodiment

The invention will be explained in more detail with reference to an example.

FIG. 1 shows the dopant concentration C in FIG

Initial part of the rod as a function of rod length.

Figure 2 shows the rod diameter-zone volume relations in the cone area

3 shows a longitudinal section through the crystal and the inductor after the beginning of zone pulling in the critical cone area

and the figure shows a small longitudinal section through the crystal after the inductor has reached the cylindrical area.

In general, the cultivation process is performed so that the height h, (Figure 3) of the transition cone between germ and zy-

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cylindrical rod part approximately equal to the diameter d

of the cylindrical rod part. In the range h ^. the diameters d ,, and do of the lower or upper phase boundary, the height h, - of the melting zone and thus their volume V ,, increase, until above d_ a stable zone

I Z

Height hp (Fig. 4-) and a stable zone volume V _{2 are achieved} on the assumption that the diameter d ^ of the growing and d ^ of the melting rod portion are the same and constant. In order for the stationary state to take effect in this area without a preparatory waiting time t

can, with the attainment of d ", also have to

ten zone volume V ₂ corresponding number. Ή-r dopant atoms may be contained in the zone.

This is achieved by keeping the dopant concentration Cq in the dopant gas flow constant while maintaining all other parameters, in the range h, in such a way that, on the one hand, the setting of H ₁ . without waiting time and on the other hand the constantly changing geometrical conditions of the melting zone are taken into account.

In practice, Cq is continuously increased variably ^ ^m - ⁵⁰¹ ^ i ^{00 n} v and lowered to the stationary value Cq _s -fc _a -fci _{on r} when d _{z is} reached.

The control characteristic for Cq. variable ⁱⁿ relation h ^ can be determined in various ways. The simplest way is to calculate them from the position-related values C_ (Fig. 1), which can be found by doping without t and without varying Cq, and the apparatus-constant <£. Prerequisite for a reproducible application of the control characteristic for Cq variably "*" ^s ^ ^ ^{e re} P ^r ° izable increase of d ,. and V, - in the range h,. The best case is for both sizes a linear dependence according to curve F (Fig. 2), which, however, can not be achieved without expensive tools.

Therefore, one can control the increase of d ^ and V ^) in the range h ^ by means of a computer and / or changes of d, -, d ₂ and h ,. capture a video system and use for the control of variable Cq ^ ^{m exp} AEB & th sense.

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Since with doping elements with k close to 1 supersaturations> N, - of the zone after setting C ^ stationary, ^s ^ ^{lr v} ^ ^e l are compensated faster than subsaturations /. Nt, it is advantageous Cq _var i _a t, ^{so to re} S ^e l ⁿ > äaß ^ ₈ shortly before reaching d_ by a small amount above the stationary setpoint C ₀ is (curve C, Fig. 1).

Without these supersaturations, waiving t,

When all parameters are kept constant, in the transition cone and in a large part of the cylindrical rod part, a deviation from the desired doping agent concentration to be set, shown in curve A, FIG. 1, is produced, similar to the curve B, FIG.

This concentration profile, which is due to the constant increase in the diameter of the crystallization phase boundary, shown in the curve D, Fig. 2, as well as the height and the volume of the melt zone shown in curve E, Fig. 2, leads to an unacceptable decrease in the Dotierausbeute ,

Claims (1)

225 022 β Claim of invention. ^: Method of doping semiconductor rods with diameters> 50 mm from the gaseous phase during crucible-free zone melting in inert gas or in vacuum, in which a melt zone is passed through a transition cone and a subsequent cylindrical rod part, using a nozzle arrangement for blowing the separate doping gas on the liquid semiconductor melt zone characterized in that the adjustment of the stationary state corresponding AusgangsdotiermitteI concentration N _T in the melting zone, without adherence to a waiting time t Xi W with the growth rate of the crystal V. = 0, during the change of the melting zone by the transition cone by the dopant concentration C ^ in the doping gas is increased proportional to the geometrical relationships in the transition cone so far that with the transition into the cylindrical rod part of the stationary State corresponding dopant concentration Nj- reaches the melting zone or up to 10 % is exceeded and that Cq is reduced after fulfillment of this condition to the steady state corresponding dopant concentration and kept constant until the end of the zone melting process. For this purpose, rent drawings