DD222046A1 - METHOD FOR THE THERMOELECTRIC PROCESS CONTROL OF SEMICONDUCTOR CRYSTAL ACCOMPANYING PROCESSES - Google Patents

Abstract

The invention relates to the field of controlled and automated growth of semiconductor single crystals from the melt or melt solution by the Zonenzuechtungstechnik, the crucible drawing technique, the normal solidification, the crystallization of melt solutions, such as. B. Fluessigphasenepitaxie and could find application in Kristallzuechtungseinrichtungen especially for the purposes of the semiconductor industry, micro and optoelectronics, chemistry, and Festkoerpergrundlageforschung. The object of the invention is to control and regulate the growth process of semiconductor crystal ingots or layers insitu and de-energized in such a way that no impairment of the growth parameters occurs and the temperature conditions within the breeding system are unaltered and detected analogously. In essence, the method consists in the measurement of thermoelectric motor force (seabed voltage) resulting from temperature differences at both ends of the growth arrangement melt crystal, melt dissolution crystal or crystal fusion zone polycrystal during the crystal growth process and optionally supply of this signal to a control loop.

Description

Process for thermoelectric process control of semiconductor crystal growth processes

Field of application of the invention

The invention relates to a method for the controlled production of semiconductor crystals from the melt and from melt solutions. It can be used as in-situ control method of the temperature, concentration and growth rate ratios in a breeding arrangement and thus as Regelbzw. Automation method of Haibeliterkristallzüchtungsprozessen application find. It is primarily designed for the growth of single crystals from a migrating / * melt or melt solution zone, but also applicable to Tiegelziehtechniken and normal solidification methods and is suitable

! address the needs of power, micro, optoelectronics,

Chemistry and Solid-State Grunglage Research.

Characteristic of the known technical solutions

It is known to control, regulate and if necessary to automate crystal growth processes of semiconductor substances for the purpose of high perfection and reproducibility of the material parameters and crystal dimensions during the crystal growth process (E.L.Lube in: Rost Kristallov, tom III, AN SSSR 1980). For the most commonly used crystal growth variants, such as the crucible pulling technique according to. Czochralski, Bridgman normalization, zone melting techniques or crystallization from molten solutions,

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such as. Liquid phase epitaxy, there are numerous known control and regulating methods which are used for automation of the breeding process (H.Blumberg, K.Th.Wilke Kristall and Technik 9 (1974) 447; DTJ Hurle, J. Crystal Growth 42 (1977) 473; K.Th.Wilke, Kristallzüchtung, VIg.der Wissensch. Berlin 1973; BRPamplin, Crystal Growth, Perg '., Press 1975; P. Rudolph, Profile Growth of Monocrystals, Ak. VTg., Berlin 1982, chapter 3, all volumes J. Crystal Growth 1969-1983, A. Ya.ITashels * ki; J, Tekhnologija poluprovodnikovykh materialov, Metallurgija, Moskva 1972). In these breeding techniques are used as a control element of a control loop in the majority of outside (outside the breeding container or the growing crystal) measuring detectors, either the temperature at the growing phase boundary (optical pyrometers, IR imaging systems) or the crystal diameter by means of from outside register the crystallizing phase boundary directed laser or X-rays. These types of detectors already require significant amounts of deviation and are therefore inaccurate, not analog or, in the case of a laser or X-ray measurement, extremely complicated, costly and thus uneconomical. Also in-use are system-internal detectors, which are either incorporated into the crystal growth system, e.g. Thermocouples and thereby affect the single crystal growth or the weight-weighing technique of crystal and melt, which is very complicated and complicated (W.Bardsley, D.T.J.Hurle, G.C.Joyce, J. Crystal Growth 40 (1977) 13 and 21). For zonal breeding techniques such intrinsic detectors are also being tested. By measuring the rotational moment of the growing crystal, the viscosity and thus the temperature of the melting zone is determined or the local position of the -phase boundaries by ultrasonic reflection parallel to the drawing axis geordet (E.L.Lube in: Rost Kristallov, torn XIII, AN SSSR 1980). Both methods are also technically complicated and require special measuring arrangements, which makes the breeding process costly.

Known is the exploitation of the Peltier effect on a "solid-liquid" phase boundary to make their macroscopic shape flat and the rate of crystallization

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(WGPfann, Zone Melting, J. Wiley and Sons, New York-London-Sydney 1966). In this case, a certain amount of heat at the phase boundary is generated or canceled by an axis-parallel flow of a direct current through the crystal and the melt, whence the contacting of a crystal growth system with two electrical contacts is known (See also: S.Vojdani, AFDabiri, H.Ashoorn, J. Crystal Growth 24/25 (1974) 374). This method is not suitable for measuring and controlling the growth process, since the axial DC injected current through electromigration affects and changes the growth process. Also known is the inverse thermoelectric Peltier effect, referred to as Seebeck effect (Grimsehl, Textbook of Physics, Bd.IV, BGTeubner Verlagsges Leipzig 1968, p.633), according to which in a semiconductor volume with imprinted temperature difference .DELTA.Τ a volume-Seebeckspannung between two crystal ends U _15,. = OC Δ Τ arises. At the same time arises -

SV S

a "solid-liquid" phase boundary of a semiconductor crystal to a metallic melt, a contact-seabed voltage U _e , = T ( _Ol'-0 ^ _n ), with Ot and O ^ _Ί as Seebeck coefficients

SJC SJ. SX

Crystalline Cs) and liquid (I) phases, and T as the absolute temperature (See, in more detail, AFIoffe, Poluprovodnikovye termoelementy, AN SSSR, Moskva-Leningrad 1960, LS Stil-bans, Fizika Poluprovodnikov, Sov. Radio, Moskva 1967). The size and temperature function of the Seebeck coefficients is known for the most common semiconductors and their melts (VM Glazov et al, Zhidkie Poluprovodniki, Nauka, Moskva 1967). The measurement of the volumetric and contact Seebeckspännungea is de-energized and was previously carried out only on finished crystalline investigation object, but not during a crystal growing process zum.Zwecke its control and possibly regulation. · \ For the growth of dissociating semiconductor compounds is lately increasingly the technology of a traveling Lbsungsmittelzone as THM (traveling heater method) referred practiced. For this crystal growth variant, no control and regulating method has hitherto been known (GA Wolff, AIMlavsky in: Crystal Growth, Vol.I, Ed. By CHL Goodman, Plenum Press 1974).

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Object of the invention

The aim of the invention is to breed perfect semiconductor single crystals and layers from the melt or melt solution, controlled primarily from a migrating solvent zone with little equipment and economic effort and, if necessary, to regulate.

Explanation of the essence of the invention

The invention has for its object to develop a method that allows, with little effort, the crystallization process of semiconductor crystals and layers from the melt or melt solution, primarily from a migrating solvent zone, in-situ, with high accuracy, without affecting the To control crystal growth process and possibly with little effort to regulate or automate. According to the invention, this object is achieved in that the thermoelectric motor force generated via a semiconductor crystal volume with an impressed temperature gradient and at a "solid-liquid" phase boundary (volume and contact seabed voltage) to measure during the breeding process and this size as Supply actual value of a controlled system, so as to exploit it for process control or design of a Halbleiterkristallzüchtungsvorganges.

This is achieved by bringing the crystal growing system, consisting of the growing crystal, a melt volume and possibly a polycrystalline spring bar, between the two measuring contacts of a currentless Potentiälmeßkreises. The realization is technically uncomplicated, since in the most common semiconductor growth systems, the crystal ingot and the melt volume are arranged coaxially and thus there is a "series connection" of the resulting sea-plane voltages. In zone melting techniques (e.g., floating zone technique or THM), the two off-zone free ends of the growing single crystal (seed) and polycrystalline swelling bar are contacted. In crucible pulling techniques (e.g., Czochralski, Kyropoulos, Stepanov, etc.), the upper cold end of the seed crystal (seed) and melt are contacted. In the normal solidification techniques from the melt or melt solution takes place

the contacting of the seed crystal and the melt by means of feedthroughs through the breeding container. In the case of layer growth from the melt solution, the substrate surface remote from the melt solution and the melt solution above or below are contacted. With the contacting the first procedural step is completed. The second process step consists in the measurement, evaluation and, if necessary, utilization of the seabed voltage which arises over the crystal growth system. With the setting of cultivation-related temperature differences arise in the volume of the seed crystal and in the polycrystalline spring ingot (zone breeding variants) volume seabed voltages, which are directed opposite, since the maximum temperature is in the melting zone center. The resulting Seebecksignal depends on the asymmetry of the axial Temperaturverlaufea and is at a symmetrical temperature field zero · Thus, the measured Seebeckspannung information about the location of the ring heater in the zone breeding techniques, as well as the already crystallized volume in the Tiegelzieh- and Normalälerstarrungsvarianten. At usual temperature differences between 10 and 100 K, the absolute values of the Seebecksignales in the mV Meßelbeelch, since the thermoelectric coefficient In semiconductors between 10 and 400yuV »K is. The measurement of the Seebeck voltage is best done with a y-t-recorder to register time functions and to use for a process control and regulation.

In zone growth from a constant melt solution zone (THM), the contact Seebeck stress, which arises at the two "solid-liquid" phase boundaries, is particularly useful for controlling the growth process. The growth from a melt solution zone differs from that from a native melt zone in that a significant temperature difference can arise between the crystallizing and dissolving phase boundary, since both boundaries are in different solution equilibria. This produces at both phase boundaries different sized contact seabed voltages, which result in the measuring circuit, similar to two differentially connected thermocouples, a differential contact signal. It should be noted,

that adds this difference voltage to the volume-Seebeckspannung. This results in standing and moving heater different sized measurement signals, the difference in size of the contact Seebeckspannungen.von the heater speed depends. The measurement signal on a crystal growth system provides information about temperature fluctuations that are present either in the culture system itself or in the heater since volume and contact contents are sensitive to the change in temperature differences across the growing crystal or absolute temperature at a phase boundary. Thus, a control of the crystallization kinetics and the control behavior of a temperature controller is possible.

If the resulting Seebeckspannung be exploited to control and automation of a crystal growing process, so the time function of the measuring signal is first to be determined by a calibration measurement and then to simulate this with a schedule setpoint generator. During the actual control process, both time functions are compared with each other and the deviations are fed to a controller with an actuator. The latter can be used to correct the temperature or heater speed.

embodiment

The invention will be explained below using an exemplary embodiment. As a breeding variant, the zone melting technique of semiconductor crystals is made of either a proprietary melt, e.g. in the production of germanium, silicon and A B single crystals or from a melt solution zone, e.g. for the dissociating · semiconductor compounds InP, AlSb, GaSb, CdTe or PbTe (hereinafter referred to as matrix component A) selected from an In, Sb, Ga or Te-melt solution (hereinafter referred to as solvent B). The cultivation can be carried out without a floating zone technique or in a chemically resistant container (quartz glass ampoule, tube). In the accompanying drawings: Figure 1 - Schematic diagram of the measuring method for determining the Seebeckspannung on a zone breeding system

and approximate temperature profile T over the location ζ

Figure 2 - Scheme to illustrate the control of the temperature difference and concentration differences between the two Zonenpliasengrenzen the THM process

The contacting of the cultivation arrangement takes place according to FIG. 1 with the electrical contacts 7 and 8 on the growing crystal 3 with the seed crystal 3a and on the polycrystalline swelling bar 4. Both sections include the melting zone 5, which is produced by means of a mobile ring heater 6. The zone boundaries are the crystallizing phase boundary 1 and the dissolving or reflowing phase boundary 2. The contacting of the measuring legs 7 and 8 can take place in many different ways. When contacting containerless variants, it is most sensible to use terminal contacts. If the cultivation system is located in a quartz glass tube, welding or pressure contacts can be used. Pressure contacts are particularly suitable when the risk of demolition between zone 5 and 4 swelling bar in a vertical arrangement by volume contraction during melting of the zone. In this case, the contact 8 is provided with a spring. The contact implementation in the breeding chamber or the container is carried out according to the methods of kon-. conventional vacuum technology. The measuring wires contacted in this way are connected for control purposes to a yt recorder with measuring range switching between o, 1 and 1000 mV and fed to automation targets a control loop. Contacting and wiring are simple and do not require complex technology or special electronics. According to Figure 1 consists in heated zone heaters, the measurement signal from the two oppositely directed volume Seebeck voltages in the crystal sections 3 and 4 according to the relationship U _sv = U ₃₃ - U ₃₄ - Ot ₉₃ (T ₁ - T ₇₎ - OD ₃₄ ( T ₃ -T ₀ ) and the two oppositely directed contact sea- _{plane voltages of} both phase boundaries 1 and 2 as well as contact points 7 and 8 according to the relationship U _sk = ( _{k k1 -U k2} ) + (7 7 _· q q)

/ (oc _s4 - 0C ₁₎ T ₂ - (OC ₃₃ -Oi ₁₎ T ₁ / + / (0C ₃₃ -Oi _n) T ₁ - (ot _e4 -

Ot ^) ¹ Zo / together, where OL ₀ -, the thermoelectric Koeffim ο sj χ

cient (s) and liquid (1) phases and OC _m

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mean thermoelectric coefficients of the metallic Meßdrahtmaterials. In addition, the various control and regulation options will be explained separately:

Control of the melting process of the zone In certain breeding arrangements a visual control of the melting process not ^{1 is} possible, since the zone is covered by resistance heaters and Fachheizer. During the heating up, ie when the heater is at a standstill near the germ, the seabed voltage runs with a specific time function, which depends on the temperature profile of the thermoelectric coefficient in the corresponding semiconductor material and the asymmetry of the axial temperature profile. At the moment of melting a volume segment, the measured value drops abruptly by a certain amount, which is determined by the jump of the thermoelectric coefficient between solid and liquid phases. The melting process is completed when the sea level signal remains constant over time. Thus, the homogenization process in melt solution zones is controllable.

Control and regulation of the movement speed of the zone heater

When the heater is moving, both oppositely directed volume seabed voltage components U ^ -2 and U * change as the volume of the growing crystal increases and that of the polycrystalline swelling bar decreases, as shown in FIG. ₁ , the temperature differences T ₁ -T, , and T ₂ - Tg change. This voltage-time function is first recorded via a calibration measurement. For control purposes, a corresponding desired value time function is simulated and compared with the actual value profile. The deviations during the breeding process are fed to a regulator for correcting the heater speed.

Control and regulation of the temperature of the zone heater The measuring signal depends sensitively on the absolute temperature of the heater, since this determines the temperature differences T ₁ - T ₇ and T ₂ - T ₃ (Fig.1). Changes in the absolute temperature of the heater can thus be detected accurately. At the same time, the relaxation behavior of a temperature controller can be controlled by simulating a disturbance variable on it and checking the time behavior of the seabed voltage

becomes. Thus, there is an in-situ control method of the control behavior of a temperature controller, since the actual temperature reaction is detected inside the culture system (crystal). If the heating process is to be automated, the voltage-time function is to be recorded, simulated with a schedule setpoint generator and fed to a temperature control loop.

Control of the growth kinetics at the crystallizing phase boundary,

For the basic research and the retraction of a crystal growth process, the temporal behavior of the growth rate at the crystallizing phase boundary is of interest. In a rhythmic law of growth, with each growth period, a certain subcooling builds up at the phase boundary, which produces a small temperature difference between the crystallizing and melting phase boundary 1 and 2, which is expressed in the contact Seebeckspannungssignal by a slight increase. When using a compensation circuit, the relative size of the temperature difference between the two phase boundaries and their rhythm is measurable.

Control of the temperature and concentration ratios in the THM breeding process

FIG. 2 schematically shows the temperature and concentration ratios over the location of a melt solution zone consisting of components A and B for a quiescent (continuous function) and a traveling heater (dotted function) with the aid of an AB solubility diagram. While both phase boundaries 1 and 2 have the same equilibrium tempera ture T ₁ = T ₂ when the heater is stationary, a temperature difference Δ T = T ₂ -T.sub .-- is established for a moving heater which determines the concentration difference ΔC a C required for material transport ₁₂ - C ₁₁ creates with respect to the component A to be crystallized. The size of Δ Τ and accordingly of Δ C is dependent on the heater speed. In the measuring signal, this difference is expressed in a resulting differential voltage of the contact sea-plane voltages at the phase boundaries 2 and 1. This value adds up to the volume difference.

Seebecksignal added and can be determined in case of sudden standstill of the heater, since this value then goes back to zero. The decay time is dependent on the diffusion rate in the zone and can be used to determine this.

All above-mentioned measuring examples are in-situ and have an analogous character. They therefore give a direct, unadulterated insight into the growth processes inside a crystal growth system without exerting a detrimental effect on the growth process.

Claims (1)

Invention claim ' Method for thermoelectric process control of semiconductor crystal growth processes by means of detection of the seabed voltage between two measuring contacts enclosing the growth system in the proprietary melt melting zone or a melt solution zone, crucible pulling technique, container normal solidification or crystallization from melt solutions, e.g. liquid phase epitaxy, characterized in that the Seebeckspannung resulting from züchtungsbedingter temperature differences, consisting of the volume fractions in the crystal material and the contact portions at one or more "solid-liquid" phase boundaries, during the crystal growing process measured without current, to control the melting process, the growth rate of the Temperaturregelverhaltens, the growth kinetics and heat or mass transport ratios used and, if necessary, as an in-situ Istwertignai for the purpose of automating the breeding process is fed to a control loop. For this Λ page drawings