DE2337238A1 - Epitaxial layer growth process - by sliding plates holding molten soln over recesses for substrate and saturation crystal - Google Patents

Abstract

Two crystalline layers are epitaxially grown on a mono-crystalline substrate from the liquid phase by using a device made of high-purity graphite. The base part has two recesses, one for a substrate, and a second for a saturation crystal. The middle parts have recesses to accept layer material. This material consists of a suitable semiconductor material, a metallic solvent for it and the required amount of dopant. In subsequent process stages, small amounts of the solution which has melted at high temps, are displaced in steps.

Description

IICEITIA

Patent-Verwaltungs-GmbH

5000 Frankfurt (Main) 70, Theodor-Stern-Eai 1

Ulic (Danube), July 20, 1S "3 pIDL / B / rü HL 73/73

"Method and device for the epitaxial -Λ" _ ^ - fermentation of crystallized layers. on a monocrystalline substrate made of aineia material ir. liquid additive

The invention "relates to a method of epitairy deposition crystallized layers on a single crystalline Substrate made of a material in the liquid state ^ "οei den set the substrate and the material in a jig, which is heated by an oven, the material being formed out of contact with the substrate in a liquid state is, after which the liquid material to its saturation rait a Ealbleiterstück from appropriate material in contact is brought, whereby after saturation Ealble-

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piece and liquid material are separated from each other, after which the saturated liquid material is epitaxial Layer to be coated substrate surface in contact is brought, then by cooling the liquid material on the substrate surface an epitaxial Layer is deposited.

The invention also relates to a device for epitaxial Deposition of crystallized layers on a monocrystalline substrate made of a material in the liquid state.

Certain semiconductor components, especially those made from semiconductor materials from Groups III and V of the Periodic System of the elements and their alloys are composed, can advantageously be according to a method the liquid phase epitaxy. Under liquid phase epitaxy one understands a method for depositing an epitaxial layer of a single crystal semiconductor on a substrate, where "at a surface of the substrate with a solution of a semiconductor material in a molten metal solvent and the solution is then cooled so that part of the semiconductor material is precipitated from the solution and is on the substrate as

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epitaxial layer is deposited.

In a liquid phase epitaxy method, it is "special." important, an exactly saturated separation solution "with a to maintain the optimum temperature for the separation. Because on the one hand contains a reading oversaturated with semiconductor material already solid semiconductor crystals, which are a terisT; alline Aust can prevent the formation of the layer to be deposited · on the other hand the substrate material itself dissolves in the solution if it is in an unsaturated state with the substrate material is brought into contact.

When using liquid phase epitaxy, in particular in the successive deposition of a plurality of epitaxial layers of different composition » which, for example, have a so-called double heterostructure composed, there is another problem d ^ rii, the intermingling those belonging to different work steps Solutions to prevent. Only then can precisely defined epitaxial layers of a multilayer structure be produced, whereby the individual layers are often only slightly different different concentration of a dopant from each other · differ.

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It is already a liquid phase epitaxy process known (DOS 2 215 355), in which the first-mentioned problem of the exact saturation of a separation solution is solved by that the deposition solution or the deposition solutions for the purpose of saturation initially with a suitable semiconductor crystal be brought into contact before the deposition solution is brought into contact with the substrate · For the deposition of very thin and uniform epitaxial layers of good surface quality of the final layer, it is advantageous if the deposition takes place from very narrow, closed quantities of melt. In an already known method this Art (J.M. Woodall, J. Cryst. Growth, 12, 32 (1972)), however can not be prevented, especially in the production of many epitaxial layers in succession, the material from a solution from which an epitaxial layer has just been deposited into a solution that is wildly carried over the deposition of a subsequent epitaxial layer is provided.

The invention is based on the object of a method for the epitaxial deposition of crystallized layers on a specify single-crystalline substrate made of a material in the liquid state, in particular in the case of the deposition of many epitaxial layers successively prevented that material of a previously deposited epitaxial layer in the often differently doped melt solutions subsequently

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epitaxial layers to be separated are carried away · With such a method, the surface of the last deposited epitaxial layer of such a good quality, that is as smooth and even as possible., so ate no further polishing steps are necessary.

The invention is also based on the object of specifying devices for carrying out the method according to the invention.

According to the invention, this object is achieved in that, in a method for epitaxial deposition, crystallized material Layers on a single crystalline substrate made of material liquid state of the type mentioned, the liquid material before the saturation or separation step only in a small amount from a larger storage volume of the liquid Material is separated, and that, after the deposition of the last epitaxial layer, possibly still present Remnants of the liquid material from which the last epitaxial layer was deposited, still at high temperatures be completely separated from the substrate.

Advantages of the method according to the invention can be seen in that with an epitaxial multilayer structure, in which there are many epitaxial layers one after the other on the same substrate are to be applied, is prevented that liquid material

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a pre-deposited epitaxial layer in the epitaxial layers to be deposited subsequently to the liquid material is abducted. As a result, however, the deposition of epitaxial layers is of a precisely defined composition possible. This is of great importance "in multi-layer structures, such as B. the so-called double heterostructure semiconductor lasers, which consist of a large number of epitaxial layers "consist of each other only by low doping additions differ, but the concentration of these doping substances must be adhered to as precisely as possible.

Another advantage of the method according to the invention is that to see that the surface of the last epitaxial layer deposited on the substrate with such a good Surface quality is produced that there are further process steps for treating this surface, in particular thus also polishing processes are superfluous. Such polishing processes for treating a surface have always been in particular required when there is intimate contact with a heat sink should be established. It is known that such additional polishing steps are always very expensive and the price of the components produced do not increase insignificantly. Under certain circumstances, however, such a polishing

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gang is associated with a reduction in the quality of the component itself, which is associated with the impairment of the crystal structure of the multilayer structure could be explained by the polishing process. As a result of the method according to the invention, the surface of the component is now immediately produced in a quality that makes further post-treatment of the component unnecessary and thus of the IT disadvantages associated with such work steps from the outset avoids.

The invention is intended below in connection with devices which are suitable for carrying out the method according to the invention are to be explained. In the accompanying drawing show:

Figure 1 shows a first embodiment for the deposition of two epitaxial layers one after the other,

Figure 2 shows a further embodiment for deposition of two epitaxial layers,

Figure 3 ei & embodiment of a device for Deposition of four epitaxial layers one after the other on a substrate,

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FIG. 4 shows an embodiment of a device for deposition of four epitaxial layers,

A first embodiment of a suitable device for carrying out the method according to the invention is shown in the figures la his If. Using this device, individual steps of the method according to the invention are explained at the same time. The _{exemplary embodiments of the device according to the invention depicted in FIGS. 1 1} 2 explain by way of example the implementation of the method according to the invention in the deposition of two epitaxial layers one after the other. There are no difficulties in configuring these devices in such a way that a plurality of epitaxial layers can be deposited one after the other.

A suitable for carrying out the method according to the invention

te device is designated as a whole with 100 (Figure la). This device is advantageously made of an in ^ active material, such as made from very fine graphite. It stands out in detail from a lower part 11 two middle parts 12 and 13 as well as a cover 14. The lower part has a first recess 16 in which -

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a substrate 15 can be arranged during the process, on which the epitaxial layers are to be deposited. The external shape of such a substrate 15 "and the shape of the Wells 16 are matched to one another as precisely as possible. That

17 lower part 11 of the device has a further Vertie fungus; on, in which a saturation crystal 18 can be arranged. This saturation crystal 18 saturates the liquid solution in each case before an epitaxial layer is deposited on the substrate 15. The middle parts 12 and 13 differ in their different thicknesses. Both middle parts in the illustrated embodiment each contain 2 recesses designated by 19, which are the same in both middle parts! Are spaced from each other. In the process step shown in FIG. 1 a, the central parts 12 and 13 are in such a position with respect to one another that the recesses in the thicker central part 13 are exactly opposite the recesses in the thinner central part 12. Bounded by the lower part 11 and the cover 14, these recesses 19 thus form two storage spaces for receiving the layer material. As already mentioned, this device is suitable for the deposition of two epitaxial layers one after the other. A device for the deposition of several epitaxial layers one after the other on the same substrate would correspond to the number of epitaxial layers to be deposited

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Layers several such recesses 19 ΪΏ- the two middle parts 12 "or 13 included. The distance between the Ausnetanuigen from each other is slightly larger than -the width of the recesses itself and corresponds exactly to the distance between the recess 16 for receiving the substrate and the recess 1? to the Taking up a saturation crystal in the lower part 11 of the device. The device 10OC is constructed such that 3egelunterteil 11 and crucible middle parts 12 and 13 relative to each other are movable. In this schematic representation of the device for carrying out the inventive Procedures are displacement or movement devices as well as devices for temperature control of the simplicity omitted for the sake of At the beginning of the method according to the invention, which is explained by Figure la is located in the through the recesses in the central parts of the device 12 and 13 formed reservoirs for the deposition The material 110 or 111 required for the epitaxial layers on the substrate. According to the desired type of material to be deposited Epitaxial layers, this material consists of a suitable semiconductor material ^ a metallic solvent for this semiconductor material as well as the required amount of IT extraneous or dopants. A substrate is in the recess 16 of the lower part 13y. a saturation crystal in recess 17.

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To carry out the method, the device shown in Figure 1 is arranged in a furnace, not shown in the drawing, in which such a temperature can be generated that the material in the storage rooms intended for deposition can be brought to a temperature at which the semiconductor material including the foreign or dopants are completely dissolved in the solvent. Eei the semiconductor substances used for the production of semiconductor lasers, such as gallium aluminum arsenide and gallium arsenide, this temperature is in the order of about 800 ^° C. to about 950 ^° C. This high temperature is maintained for a long time in a protective gas atmosphere, for example in hydrogen gas in order to achieve a homogenization of the materials in the storage rooms. When this homogenization has been achieved, the device must be cooled in order to reach the lower temperature required for the epitaxy. The epitaxial temperature is selected, inter alia, so that the solvent is unsaturated with respect to the semiconductor material. Shortly before the optimum epitaxial temperature is reached, the thinner central part 12 is displaced in the direction of the arrow shown in FIG. La. As a result, as shown in FIG. 1b, relatively small amounts 120 and 130 of Schrr.el solution for the two epitaxial layers to be applied one after the other are separated from the stock material 110 or 111 of FIG. 1a. In a further step, with the central parts 12 and 13 held, the lower part 11 of the device is moved in the direction of that shown in FIG

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Arrow "moved that the one containing the saturation crystal18 Deepening of the lower part 11 under the first melt solution

to the
which is located in the thin central part 12 which is not "moved" in this step. A part of the saturation crystal 18 lc.-t rises and falls in the molten solution 120. A further displacement of the lower part 11 of the device in the direction of the in Figure 1d now brings the substrate located in the recess ... 6 of the lower part 11 under the previously saturated melt solution 120. If certain temperature gradients and cooling speeds are observed, a first epitaxial layer of the desired composition, doping and layer thickness is then deposited on the substrate 15 Simultaneously with the last shifting step of the lower part 11 of the device, the depression 7 of the lower part 11 containing the saturation crystal 18 was brought under the melt volume 130 separated from the store 110 (FIG further shift sc When the lower part 11 of the device sifting through the salvation shown in FIG. 1e, the substrate with a first epitaxial layer on it passes under this now saturated melt solution I30, so that the second epitaxial layer can also be deposited. By a last shifting step of the lower part 11 of the front

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direction, the result of which is shown in Figure If after the desired second epitaxial layer has been deposited, the substrate now provided with two epitaxial layers 15 Completely also separated from the melt solution 130. These Separation takes place at high temperatures and has the consequence that, after cooling, the surface of the epitaxial structure produced is perfectly smooth and of almost optical quality. In particular, no further polishing processes are required, to enable good contact with any heat sink that may be provided.

FIG. 2 shows a further exemplary embodiment - a device shown for performing the method according to the invention. This device, designated 200, in turn consists of a lower part 21i, a thinner middle part 22, a thicker one Middle part 23 and a cover 24, In the lower part 21 are in turn Recesses 26 and 27 are provided, which are used to receive a substrate 25 or a saturation crystal 28.

Recesses 29 in the two middle parts 22 and 23 are again located in the process step shown in FIG. 2a exactly opposite and form storage rooms for receiving the Semiconductor materials from which the epitaxial solutions are created when heated. This device shown in FIG agrees completely with the one in Figure 1

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shown device match, so that in itself a no further description is required. Differences to the method steps explained with reference to FIG. 1 result only because the small enamel solutions from which the epitalctic layers are deposited should be separated from the stock solutions in a slightly different way will. Starting from the situation shown in FIG. 2a, only the thicker middle part is initially now 23 moved in the direction of the arrow shown. This simultaneously becomes the one in the recesses of the thicker one The central part 23 contains a larger amount of the stock solutions 210 and 211 from those in the thinner central part 22

remaining smaller amounts of melt 212 and 213 separated. In a further step, in which at the same time cover 24, Middle part 23 and middle part 22 in sight of the in Figure 2b The melt solution 212, as shown in FIG. 2c, first passes through the arrow shown Saturation crystal 28. After another: equilateral shifting the three named parts of the device in the same direction, the situation shown in Figure 2d arises, in which the first molten solution 212 is now above the sub-

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strat 25 "is located, and with the second melt solution 213 over the saturation crystal 28 stands. In Figure 2e it is again shown how the second melt solution over the substrate is brought to deposit the second epitaxial layer there. Finally, FIG. 2f again shows how after the deposition of the second epitaxial layer, if necessary residues still present; the second melt solution 213 from the substrate removed. This was done at relatively high temperatures in order to achieve the smoothest possible surface of the last to achieve deposited epitaxial layer.

FIG. 3 shows a further exemplary embodiment for carrying out the method according to the invention. The method steps already explained with reference to FIG. 1 can be carried out with this device, but four epitaxial layers can be deposited one after the other. The movable parts of the apparatus lower part 311 thin central portion 32 and thick Kittel part 3 ³ are led 34 in a U-shaped guide member can be introduced into the thermocouples for temperature control. To carry out the displacement movements of the parts of the device required for carrying out the method according to the invention, it is sufficient in this embodiment.

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example-.all alone the movement of the lower part 31 ^ i * the substrate 35 "and the saturation crystal 38 via one from the outside operable, leading into the interior of the furnace. You disconnect Quartz. By moving the sub-area 31 to the left in the first step of the method, over a stop at the Koppelstal ·. at the same time the thin smock part 32 to the left mitger.om.aen, while the thicker upper Middle part 33 secured against displacement by a / quartz pin is. After the process of separating the cutting solutions as shown in FIG. 1b, this quartz pencil continues to fall into a hole which is located in the lower thinner smock part 32, whereby this is also anetiert. By then subsequent displacement steps of the lower part 31 according to on the right, the growth process of the epitaxial layers can take place in accordance with FIGS. 1c to If.

So far, embodiments of devices for carrying out the method according to the invention have been explained, in which the required relative movements of the device parts could be carried out as sliding movements. the necessary for carrying out the method according to the invention However, relative movements can also be implemented by rotating the various parts of the device will. Figure 4 shows the embodiment of a rotary rod, with which the method steps explained with reference to FIG. 2 can now, however, be carried out by means of rotary movements.

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The rotatable parts of the device lower part 41, middle part 42 and thicker upper part 43 are in a cup-shaped housing 46 led. 40 is a cover that closes this cup-shaped housing 46. Through a leading to the outside of the furnace Connection, the thicker upper part 43 can be rotated in the desired direction. In this embodiment one Device for carrying out the fiction s according to he. Procedure contain the thicker upper part 43 and the lower thin middle part 42 each have four recesses 49, which for receiving four different melting solutions are suitable. Kit of this embodiment of a device is therefore particular the creation of a four-layer epitaxial structure on a substrate is possible. By turning the thicker top 43 from the outside and with the aid of a stop between the lower part 41 of the device and the middle part 42 will correspond to FIG. 2b shows the small amounts of melt solution from the storage solutions intended for the deposition of the epitaxial layers separated. After this working step, a graphite pin 47 movably arranged in the cover 40 of the device can be inserted through in the parts 42 and 43 located holes 50 fall down and thereby the two parts 42 and 43 against each other lock so that a further relative movement of these two parts is no longer possible. Go berserk-

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of the externally operable upper part 43 in ma tipi or the opposite The deposition of the epitaxial layers explained with reference to FIGS. 2c ″ to 2f can then take place in the direction completed on a substrate 45 arranged in the lower part 4-1 will. There is a slight difference to the method steps explained in FIG. that a saturation crystal 48 in the lower part 41 of the device only to saturate the melt solutions two, three and four provided Ic .-.,. The first epitaxial layer on the substrate 45 is deposited without prior saturation of the first melt solution.

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Claims (6)

- 19 - UL 73/73 Patent claims 1 Process for the epitaxial deposition of crystallized layers on a monocrystalline substrate from a material in the liquid state, in which the substrate and the material are placed in a device which is heated by an oven, the material being out of contact with the substrate in the liquid state is formed, after which the liquid material is brought to its saturation with a semiconductor piece of appropriate material in contact, wherein after saturation semiconductor piece and liquid material are separated from each other, after which the saturated liquid material is brought into contact with the substrate surface to be coated with an epitaxial layer is, then by cooling the liquid material, an epitaxial layer is deposited on the substrate surface, characterized in that the liquid material before the saturation or deposition step in small amounts from a larger supply volume of the flü ssigen material is separated, and that after the last epitaxial layer has been deposited, any residues of the liquid material from which the last epitaxial layer was deposited are still completely separated from the substrate at high temperatures. 409885/0808 - 20 - - 20 - UL 73/73 2. The method according to claim 1, characterized in that the separation of the small amount of material takes place in such a way that When several layers are deposited, the separated amount of material is carried over to other material stocks, which serve to deposit further layers, is avoided. 3. Device for carrying out the method according to claim 1, characterized by a cover (30) that can be covered, Guide part (34) having a substantially U-shaped cross section and in which can be displaced relative to one another a lower part (31), a first thin central part (32) and a further thicker central part (33) are arranged one above the other, which lower part (31) contains two spaced apart recesses for receiving a substrate (35) and a saturation crystal (38), and which central parts (33, 32) in contain the same number of equally spaced recesses (39), the distance between these recesses (39) being the distance the depressions arranged in the lower part (31) for receiving a substrate (35) or saturation crystal (38). 4. Apparatus for performing the method according to claim characterized by a cover (40) which can be covered, cup-shaped housing (46), in which relative to one another - 21 409885/0808 - 21 - UL 73/73 rotatably one above the other a lower part (41), a thin middle part (42) and a thicker upper part (43) are arranged, which parts have the shape of circular disks, the lower part: (41) two spaced depressions for receiving a saturation crystal CS} or a substrate (45), the thin Ml; _w älteil (42) and the thicker upper part (43) contain the same Λ, 2 number of evenly spaced recesses (49) which can be brought to cover by a relative rotation of the middle part (42) and upper part (43). 5. Apparatus according to claim 4, characterized in that the upper part (43) is rotatable by means of a device leading to the outside. 6. Device according to claims 4 and 5, characterized in that that after a rotary movement of the upper part (43), a separation of the standing one above the other before this rotary movement Recesses (49) in the upper part (43) and middle part result in the upper part (43) and middle part (42) by means of a graphite pencil (47), which then engages one below the other in bores (50) of the parts (43) and (42), locked against each other are. 409885/0808