DE2346399A1 - PROCESS FOR GROWING EPITAXIAL LAYERS - Google Patents

Description

DR-INC. DIPL.-INQ. M. SC. DIPL.-PHYS. DB. OIF> i ..- PH \ S.

HÖGER - LEGAL RIGHT-GRIESSBACH - HAiZCKER

PATENT LAWYERS IN STUTTGART

A 40 349 m

a - 149

Sep 12, 1973

Massachusetts Institute of Technology

Cambridge, Mass. 02139 / USA

Process for growing epitaxial layers

The invention relates to a method for growing epitaxial layers from a solution in a solution / substrate system.

The essay "Modulation of Dopant Segregation by Electric Currents in Czochralski-Type Crystal Growth "on pages 1013 to 1015 of the journal J. Electrochem. Soc .: SOLID STATE SCIENCE, dated June 1971, which goes back to the authors of the present invention, a discussion relating to "the separation of" dopants in tellurium-doped indium-antimonide single crystals can be found refers, with the growth limit

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layer during the crystal growth of the Czochralski type electrical Currents are applied. Very short pulsed electrical current pulses are used to mark a time to achieve during the crystal growth what the observation of growth rates under different growth conditions enables.

In another article, which is here for information only Reference is made, entitled "Current-Controlled Growth and Dopant Modulation in Liquid Phase Epitaxy", the also goes back to the authors of the present invention and was published in the April 1973 issue on the Pages 583-584 of J. Electrochem. Soc., SOLID STATE SCIENCE, is a work related to crystal growth described, whereby a solution / substrate system of the im the type described below is indicated, in which a thermal equilibrium of the system is established.

Most of the semiconductor devices used are junction or boundary layer systems. Most of these arrangements are made using diffusion techniques. Such techniques lead to boundary layers, transitions or barriers, which are usually not abrupt, i.e. have a slope; this fact has a strong influence on the operation of such semiconductor devices. There are abrupt boundary layers or transitions particularly important in light emitting diodes (for example GaP), in solar cells (for example GaAs) and the like.

The object of the present invention is therefore to provide a method

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for growing epitaxial layers in semiconductors, with a doping profile of the boundary layer or the junction is achieved, which can be made very steep.

To solve this problem, the invention is based on the above named method and according to the invention consists in that materials are used for the system, which at the Boundary layer between solution and substrate have a Peltier effect that a substrate is in contact with a conductive solution is brought, which contains one or more of the materials to be deposited on the substrate, that solution and substrate on brought and maintained a temperature at which the solution is saturated or is close to its saturation point, that by the solution / substrate system in the An electric current is conducted in such a way that cooling is effected at the interface between the solution and the substrate, the cooling only during the time when the electrical current flows over the "boundary layer" and only in the area of the boundary layer occurs and that the remainder of the solution / substrate system, with the exception of the boundary layer, is maintained at temperature that existed before the passage of the electric current.

The invention consists in the fact that by suitable action during the breeding or growth process a very steep Doping profile can be achieved at the boundary, with the growth of the semiconductor itself much faster than in previously known methods. To do this, the procedure is that for a solution / substrate system, an electrical conductive solution is used, which is one or more of the on the

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Substrate contains materials to be deposited and those in contact is brought with the substrate. It is essential that the temperature of the system is maintained and adjusted at a level that brings the solution close to its saturation or keep it at the saturation point. An electric current is then passed across the interface between Solution and substrate, the direction and magnitude of the current being selected so that it is only at the boundary layer alone gives a cooling effect, but the "residual system" is maintained at the equilibrium temperature.

In this way, a controlled distribution of the dopant and thus more uniform properties are achieved of the semiconductor achieved.

Furthermore, it is using the method according to the invention possible controlled changes in the structure and to achieve the miffihung.

According to the method, epitaxial layers are made to grow from a solution / substrate system, the entire As already mentioned, the system is kept close to or at the saturation point of the solution, but the temperature is at the limit or Interlayer between solution and substrate is controlled by a current passed through. To achieve the the desired growth is then brought into contact with an electrically conductive substrate or a seed, which contains the materials to be deposited on the substrate.

For this purpose a device is used which is made of a quartz

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tube consists of a generating the desired temperature Oven is surrounded. Electrodes made of graphite are arranged in the quartz tube, one electrode the solution and the other electrode is associated with the substrate in a conductive connection. In the electrodes or electrodes associated there are thermocouples for regulating and monitoring the necessary temperatures, the electrodes are connected to a direct current source, which can carry a base current and which is further adjustable so that Current pulses can be superimposed on this base current in selected form. The electrode associated with the solution and the The electrodes assigned to the substrate or the nucleus are electrically insulated from one another, for example by layers made of boron nitride, a layer called a slider is so movable and adjustable that a connection between Substrate and solution can be prepared.

In the following, the method according to the invention and the structure and mode of operation of a device for implementation detailed this procedure, showing:

Fig. 1 in a schematic representation of a device which is designed so that with her the inventive method carried out and at the interface between liquid and Solid can v / ground an electric current to cause epitaxial growth,

Fig. 2 is a photomicrograph of an epitaxial layer of InSb formed using the method according to the invention has been grown,

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Fig. 3 shows in the form of a diagram the dependence of the growth thickness of the epitaxial layer as Function of time and current density across the boundary layer, the layer being the composition of Example 3 to be described, while

4 shows, in the form of a diagram, the relationship between the growth rate as a function of the current density over the interface of Example 3 shows.

The following is a brief explanation of the in Fig. 1 given with the reference numeral 101, the device for growing or for pulling semiconductor layers from solution in a solution / substrate system. Epitaxial layers of the following in more detail descriptive type were in an area 1 controlled atmosphere (e.g. hydrogen) within a Quartz tube 2 brought to growth or pulled (grown). The quartz tube used in the illustrative embodiment The device is located within an electric furnace 3, which has a controllable and controllable ambient temperature generated. In order to generate the Peltier effect, which will be explained in more detail below, electrodes are used 4 and 5 are supplied with electric power from a direct current source (not shown).

In a cavity in an upper graphite element 8 is a Solution 6 contain one or more of the on one

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Substrate 7 (or a seed) contains materials to be deposited. The substrate 7 is held by a lower graphite element 9, which is also in electrical contact with it. The lower and upper graphite lines are against each other insulated, by means of an insulating slider 10, which is placed horizontally between insulating elements and 12 is slidable. In the illustrated position of the slider 10, the solution and the germ are electrically relative to one another isolated. To initiate the pulling or growth process, the slider 10 is moved to the left so that the opening provided with the reference number 13 is aligned with the germ and the solution. At this point and this time In place, the temperature of the working parts of the device is such that the solution is saturated or close to it Saturation is located.

If the solution and the substrate are in contact with each other, then An electric current is passed across the boundary layer between the two in such a way that cooling is achieved at the boundary layer is effected. The direction of the current flow causing such a cooling depends on the or to be deposited materials to be precipitated. For the In-Sb system described below, the electrical flow occurs Current from the substrate 7 to the solution 6. The rate of deposition depends on the current density at the boundary layer and is directly proportional to this.

From the explanation so far it can be seen that the cooling due to the electric current is located at the interface area between the solution 6 and the substrate 7, that such a cooling only during the

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Flow of the electric current occurs and that the Remainder of the solution / substrate system with the exception of this boundary layer is maintained at or near the original temperature. It is also understood that according to a Feature of the invention developed the seed solution by reducing the temperature of a region of the liquid solution can be formed, thereby molding a substrate of the base material; the epitaxial layers are then in the still to bred descriptive way. On the other hand, any conductive material is solid in contact with the solution able to perform the functions required. In this context, care must be taken to ensure that the the surface heating due to the Peltier effect to keep the electrical contact between the substrate 7 and the electrode contact on this small.

In game 1

The epitaxially grown InSb material 'of Fig. 2 was made from an indium solution containing 60 atomic percent indium and 40 atomic percent antimonide. The solution contained Tellurium as a dopant (dopant) to mark growth marks in accordance with the explanations in the aforementioned Publication of June 1971 to be provided. The InSb layer was grown on an InSb substrate. The solution / substrate system was set and maintained at a temperature of 47O ° C, at which temperature the solution is for this particular mixture is at or near saturation. At this temperature there can be a slight Proportion of the substrate to be dissolved in the solution and it

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a flat boundary layer forms between the solution and the substrate. The three growth regions B 1, B ₂ and B ₃ in FIG. 2 were achieved by using direct current with 0, 5.5 and

1 ampere / cm each through the growth boundary layer or growth boundary layer passed through. In all three areas, streaking or streaking rates (as in the article discussed in June 1971) introduced by the fact that

current pulses of 0.1 second duration (100 amps / cm) with a repetition rate of 0.01, 0.02 and 0.02 seconds, respectively, were superimposed.

The irregularities in growth at the transition from areas B ₂ and B ₃ (with a change in the boundary layer morphology) have not yet been fully clarified and are subject to further investigations.

It can be seen from FIG. 2 that in the first growth region (B ₁ ), to which only intermittent pulses were supplied, but no "base current" was passed through, the growth process was only very limited. Over a period of 5000 seconds, an epitaxial layer with a total thickness of 25 ^ m could be formed intermittently (due to the cooling caused by the pulses) with a net growth rate of 3 10 µm / minute, a base current of 5.5 Amps / cm for a period of 1200 seconds (middle range) results in a layer (B ₂ ) with a total thickness of 1.25 pn with an average growth rate of about 6 µm / minute. It should be pointed out here that in this area of the growth rate this was about 4000 ^ in / minute during the superimposition of each pulse (as can be seen by determining the width of the streak rates, the

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the pulses with a duration of 0.1 sec. were assigned) / i.e. the growth rate was about 670 times greater than the average growth rate. With

epitaxial layer obtained at a base current density of 1 ampere / cm (Bo in Fig. 2) grew with an average Rate of 3 µm / minute; during the superposition of the impulses the growth rate was approximately 1,500 pounds per minute.

In the area made to grow with a base current of 5.5 amps / cm, the pulse attributable to the pulses appeared Stripes or streaks appear as bands rather than lines. This result reflects a high of the rate of growth induced by the base current, this rate of growth was increased still further by a factor close to 700 for the duration of each pulse producing a high current density. The sudden increase in the growth rate leads to a substantial increase in the concentration of the dopant, which then in turn over the duration of the pulse is attenuated or weakened due to the boundary layer depletion. Such separation behavior actually became while working with the help of edging properties of the bands observed, which show a pronounced increase in concentration at their lower edges (beginning of the pulse) and showed a gradual transition at their upper edges (end of pulse). In this way one achieves a controlled modulation of the chemical composition by suitable selection of pulse shape and pulse duration.

In example 1, the matrix material is indium antimonide and the dopant is tellurium. The matrix material has a Solidification point, which is determined by the percentage

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Distribution of indium and antimony, for any given particular mixture, the rate of precipitation or deposition of the matrix material and the dopant can be changed upwards or downwards, in each case by the electrical Current density at the boundary layer is increased or decreased. In addition, all used Data areas and in all work carried out so far, both the rate of crystal growth and also the concentration of the incorporated dopant in direct relation to the current density, as approximated linear functions that have differences in their increases or slopes. So z. B. change the concentration or the concentrations of the dopant, for example to form a boundary layer or transition layer. In addition, change the rates of deposition or deposition of the dopant when two or more dopants are introduced into the solution are each as a function of the current density, so that the ratio of the concentrations of dopants can be modified in the layer. In this context it should be noted that the percentage of tellurium in the deposited layer increases with increasing current density, in the case of other dopants however, the concentration of the dopant in the layer increases or decreases, depending on from the special dopant; this change can be determined beforehand.

Example 2

The epitaxial growth of crystals of In-Sb was also observed

reached from an antimony solution at an oven temperature of 510 ⁰ C;

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the solution consisted of 68 atomic percent .Antimony, 32 atomic percent Indium and small amounts of tellurium to enable growth marking. The growth rates corresponded to the rates which have already been determined with reference to Example 1.

Example 3

The epitaxial growth of crystals of In-Sb was further achieved from an indium solution at an oven temperature of 46O ° C; the solution consisted of 75 atomic percent indium, 25 atomic percent Antimonide and small amounts of tellurium as doping smit te 1 for displaying streak or streak rates as already mentioned above. The direction of flow of the Direct current again ran from the substrate to the solution and there were direct current pulses of 0.5 sec duration and one Current density of 105 amperes / cm superimposed to achieve the stripes or streaks. In Fig. 3 are material thicknesses, which have grown as a function of the current density through the boundary layer between liquid and solid, for the materials of Example 3, FIG. 4 shows the growth rate as a function of the current density.

In the systems described so far, the obtained solid forms a semiconductor of the η-type, which can be converted into a semiconductor of the η -type by modifying the tellurium concentration, which results in an nn ⁺ "structure The concentration of tellurium is increased by increasing the current density over the boundary layer and vice versa

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Formed current density. Boundary layers or transitions from p-n types can be formed by providing a matrix material with two or more dopants; the The concentration of the constituents of the matrix, the selected dopants and the relative concentration of the dopants are such that the concentration of the dopant in the solid can be influenced by changes in the current density at the liquid-solid interface undertakes. The present method is particularly useful for matrix compositions consisting of systems of Groups III-V and consisting of dopants from group IV of the element table (e.g. germanium and silicon), Some of these matrix materials, such as a linen matrix, change from η to ρ based on the concentration a single dopant. It is thus possible to use a single element matrix and a single learning dopant in a p-n junction by the present technique by changing the current density at the liquid-solid interface abruptly. Pierzu is GaAs as Given example.

In the previous discussion, the stream was referred to as only in assumed to flow in one direction, i.e. a direct current was used. The electricity can be used for a period or for rise for a time and then fall for a time or vice versa, in order to achieve a particular growth profile and / or a particular dopant concentration, it flows but always in one direction. Changes in current density can be at a uniform rate or at a non-uniform rate Rate, if desired, to be carried out.

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Claims (18)

Claims 1. A method for growing epitaxial layers from a solution in a solution / substrate system, characterized in that that materials are used for the system, which are at the interface between solution and substrate have a Peltier effect that a substrate is brought into contact with a conductive solution, the one or more of the materials to be deposited on the substrate contains that solution and substrate are brought to a temperature and held on that at which the solution is saturated or near its saturation point is that an electric current is passed through the solution / substrate system in such a way that at the Boundary layer between solution and substrate a cooling is effected, the cooling only during the time of the electric current flow across the boundary layer and only occurs in the area of the boundary layer and that the remainder of the solution / substrate system with the exception of the boundary layer is maintained at the temperature that existed before the passage of the electric current. 2. The method according to claim 1, characterized in that the conductive solution is a single material to be deposited as an element or as a stoichiometric compound and that the density of the electric current at the boundary layer is controlled so that a desired deposition or growth rate of the material is achieved. AÜ9383 / Ü765 3. The method according to claim 1 or 2, characterized in that that the current density at the boundary layer is changed to change the growth rate. 4. The method according to claim 1-3, characterized in that the current density to achieve a predetermined Change in growth rate is changed at a uniform unidirectional rate. 5. The method according to any one of claims 1-4, characterized in that that at a given point in time during growth to form a transition or boundary layer the current density is changed abruptly. 6. The method according to any one of claims 1-5, characterized marked indicates that the conductive solution contains a plurality of materials to be deposited together and that the Current density at the interface is controlled so that a desired deposition rate is made for each material the variety of materials is achieved. 7. The method according to one or more of claims 1-6, characterized in that one of the materials in the Solution is a dopant (impurity) and another of the materials is a matrix or base material and that the dopant and the matrix material are co-deposited on the substrate and the rate of common deposition is set by regulating the current density at the boundary layer. 8. The method according to one or more of claims 1-7, 409883/0765 characterized in that the solution contains a plurality of dopants and that the current density at the Boundary layer to regulate the rate of deposition of each dopant and to regulate the deposition of the matrix material is set. 9. The method according to claim 8, characterized in that the concentration of the dopants in the solution so is selected so that appropriate current density changes occur at any point during growth such that, in terms of rate of deposition, one of the dopants will dominate. 10. The method according to one or more of claims 1-9, characterized in that a semiconductor Epitajcialschi cht is grown from the solution by bringing a seed into contact with the conductive solution. 11. The method according to one or more of claims 1-10, characterized in that the temperature is substantially is maintained at the saturation temperature for the particular mixture of the solution that the temperature in an area of the solution is lowered to a level at which solidification occurs and that through the boundary layer an electric current is passed in one direction between the solution and the solid formed in this way, to cause a cooling of the boundary layer area that the cooling only during the passage of current and only occurs in the region of the boundary layer and that the rest of the system formed, with the exception of the boundary layer, is essentially is kept at the saturation temperature. 409883/0765 12. The method according to claim 11, characterized in that the mixture contains materials that upon solidification form a semiconductor. 13. The method according to one or more of claims 1-12, characterized in that the electrical current is a direct current and the current level at a predetermined time is changed abruptly to form a semiconductor junction or a semiconductor junction. 14. The method according to any one of claims 1-13, characterized in, that "indium and antimonide are used as materials to form the matrix material, which furthermore contains tellurium as a dopant and that between the n- and the n + -region of the semiconductor transition or a barrier layer is formed. 15. The method according to one or more of claims 1-14, characterized in that the forming the matrix material Components correspond to groups III-V and that at least one element from group IV is used as a dopant. 16. The method according to one or more of claims 1-15, characterized in that the matrix material and dopants can be set to form either a p- or η-type semiconductor, namely in Depending on the concentration of the dopant in the pesticide and that the proportions of the material * components in the solution are selected and the current densities are set so that a semiconductor in 4 0 9 8 8: W U 7 6 5 the shape of a p-n junction is formed. 17. The method according to claim 16, characterized in that the Group IV dopant is either germanium or silicon. 18. The method according to claim 16, characterized in that the matrix material is gallium and the dopant is arsenic and that a GaAs junction is formed. ύ 0 8 8 M U 7 6 5 ■ fs Blank page