DE2242138A1 - METHOD OF GROWING EPITAXIAL LAYERS FROM THE LIQUID PHASE - Google Patents

Description

oe-fr

August 24, 1972

Applicant: International Business Machines

Corporation , Armonk, If.Y. 10504

Aratl. File number: Neuarameldurag

Applicant's file number: YO 97i 005

Process for growing epitaxial layers from the liquid phase -

The invention relates to a method iEiim growth of epitaxial layers on kristallinenr & loto®.einheitlich tempered at Qfoenrf substrates from the liquid phase, wsfeai the LSI transferred the liquid phase aufzuwachsende material pushed to grow over the substrate tsa & d ffi & sfefo "r wlmä @ g% refgeschoben is .

Gesaaant the growth of epitaxial layers of liquid phase is below EFP * let a useful Värfaiire!% _R w s B * Halbleiteracfeichten uad feaaat "mi krittallo ^ r ^ hlsGh related substrates zuwache · !! <> Itseäji «eoRd« is · * siad with dtoaesi method llcht * aittier <iEida Dloäesi old d «r Höefeetoea an earlier quant * ßauab« at *

With the most popular SFP-ferfs & s ^ i »-al * sS H. among others in the Applied Physics Letter»? 11, §i CätSTi ^ XJ. Liad »n in Infrared Physics, 10, 141 {1§7Q \, tmä Sa Sauii ud. .! *. '■ "Journal of Applied Physics ket & ers, IS, 22 $ {lW9l iMsehreilMn, it is difficult, however, to produce layers« l & issitLiG & er thickness and »with a smooth surface reproducible, since in the known processes a deposition of skin is not only on the substrate takes place, with the result that only a small amount of the added material is incorporated into the epitaxial layer, and it is necessary during 1 of the growth to avoid it

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Adding material to an impoverishment quickly makes it even more difficult »Layers with a desired composition and thickness can be reproducibly produced.

Although M.B. Panish et al, as in J. Phys. Chen. Solids, Vol. 30, page 129 ff., And J.M. Blum et al, as described in IBM Technical Disclosure Bulletin, Vol. 13, page 3221, a smooth surface of the grown layer can be achieved by leaving residues of the Aisle to be wiped off before cooling. Also in that cited article by J.M. Blum stated that the uniformity of the layer thickness can be improved by the substrate is uniformly tempered when growing up. However, the other difficulties described are eliminated by these improvements not eliminated and, as said, the uniformity of the layer thickness is only improved.

Bs is the task for invention, smooth with the BFP process Layers of uniform thickness have a uniform degree of concentration of lentane perpendicular to the surface of the substrate and as much as possible between the hens of the grown-up of the s * fl * Mt.st »n data sheet in a reproducible manner.

Dl · ·· ftisjffmj »· is erflftduagsgmaäs btl AtM Verfahr« * 4 »r eUfanf · fsnisnfr "n Art dadurc" solved, because by placing the cover plates, the lines are made uniformly high under pressure become *, so that the distance becomes a substrate and from * * * * fcfanelsenob «rflieh« kislasx fmight as the diffusion layer of all ••• part of the enamel, and that perpendicular to the substrate surface, the temperature gradient is maintained at an increasing distance from the substrate surface.

Since the liquid phase is uniformly thick, dl · «, assuming a uniform substrate temperature, also applies to the grown layer. The diffusion length is understood to be the average distance that the constituents of the melt travel to

vo, ₇₁₀₀₅ 3098 10 / 10.7 _{AL | NSPECTED}

put back before the crystallization and thus the precipitation begins. The term is comparable to the mean free path of an atom in a dilute gas. Since the temperature in the melt decreases upwards and because of the favorable ratio of diffusion length to height of the melt, a separation takes place only take place on the substrate surface. This keeps the cost of materials low. As the temperatures, the dimensions the melt and the necessary amount of material are under control, it is possible to reproducibly produce the desired thickness and Composition of the layer to produce.

As it is to achieve good adhesion of the epitaxial layer on It is advantageous for the substrate to first slightly dissolve the substrate with the melt, on the other hand this dissolving must take place in a controlled manner, it is advantageous if the temperature of the liquid Phase is lowered until saturation occurs, that the liquid phase is then pushed over the substrate, then the temperature of the liquid phase is briefly increased and finally is slowly lowered as you wake up.

It is advantageous to equip the growing device so that the constituents of the liquid phase can be added and withdrawn continuously.

With this configuration it is possible to have layers of the same composition on many substrates or on one substrate several discrete layers of different composition to grow up.

The described. The method has proven to be advantageous when a substrate made of GaAs is used and an epitaxial layer made of Ga Al _1- As is grown, a melt with GaAs and AlAs as components being used as the liquid phase and being grown at 900 to 1000 ° C.

The invention is illustrated by the drawings explained by

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- 4 ~
examples of management described. Show it:

Fig. 1 in longitudinal section the apparatus in which the method described is carried out,

FIG. 2 shows the apparatus in cross section along the line in FIG

Fig. 1 with 2-2 designated line,

Figs. 3A and 3B graphically show the temperature profiles in the melt in the horizontal and vertical directions Direction,

Fig. 4 shows the layer thickness distribution in one after

described method produced epitaxial layer,

Fig. 5 shows another version of the apparatus for the through

implementation of the procedure described,

Fig. 6 shows an embodiment of the apparatus for the continuous implementation of the described Procedure and

Figs. 7A and 7B further possible configurations of the substrate chamber of the apparatus shown in Fig. 1, in the case grown on several substrates at the same time shall be.

Fig. 1 shows an apparatus such as that used for the process described is used. The apparatus includes a conventional diffusion furnace comprising a quartz tube surrounded by a heating source 12 10 contains. The controlled heating source 12 can for example consist of a heating coil. The heating source heats the quartz tube 10 over its entire scope and thus also the actual waxing device 14, which is located in the tube 10.

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24

To the growing device 14 is a boat 16, which with two movable plates 18 and 20 is equipped »These plates, as well as the boat 16, are independent of one another, e.g. with the pull rods 22 movable. The boat 16 rests on the platform 24, which in turn rests on the guide rods 26 “The platform 24 can be opened to the waxing device 14 to be transported along the quartz tube 10 »· Inside From boat 16 there is a chamber 28 in which the substrate 30 lies. The chamber 28 is deeper than the substrate 30 is. Therefore, within the chamber 28, melt can be layered on the substrate. The thickness of the grown epitaxial Layer is determined by the difference 29 between the chamber depth and the substrate thickness.

In the boat 16 there is also the recess 32, which is the starting material 34 for the melt contains. The sliding plate 18 has a hole 36 that is completely flush with the melt 38 is filled, and the cross section of which is approximately the same as that of the substrate 30. Since the sliding plate 20 is also present, the melt 38 is enclosed on all sides »The weight of the plate 20 exerts a pressure on the melt that is just about sufficient to bring about the aforementioned complete filling of the hole 36 with melt. The pressure also prevents the Melt forms an upwardly curved meniscus due to surface tension. The lard contains the ingredients that to be grown on the substrate 30 »In general the melt contains 1 to 2 g of the material that has grown

should be, per cm of the substrate. The small volume favors a uniform composition of the melt.

The movable plate 20 contains numerous openings 40A, 40B, 4OC and 4OD, through which different dopants or other materials for selective growth into the melt. 38 can be introduced. The openings 40A to 40D are covered with the movable plates 42A to 42D in order to protect the openings 4OA to 4OD to be covered individually.

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A gas stream, indicated in the figure by the arrow 44, flows through the open quartz tube 10 during the epitaxial growth. This gas can consist of forming gas (90% N , 10% H 2) or other known gases such as argon. The gas flow creates either an inert or a reducing atmosphere in the system. A reducing atmosphere is beneficial to remove any oxides that may form at the melt-substrate interface.

Fig. 2 shows the apparatus shown in Fig. 1 in cross section along the line 2-2 marked in FIG. 1. The one composed of the boat 16 and the two movable plates 18 and 20 Apparatus 14 for the EFP, the platform 24 and the guide rods 26 can be seen.

From Fig. 2 it can be seen that the melt 38 is above the axis of tube 10 is located. Boot 16 lies between the melt 38 and the heating source 12. This arrangement causes the temperature of the upper surface of the melt is higher than that of the lower surface. I.e. the temperature of the melt increases nnch to the top. The fact that the melt is coldest at the interface with the substrate ensures that a deposition occurs of constituents of the melt 38 will take place on the substrate.

The FIGS. 3A and 3B show temperature profiles in the melt, measured perpendicular to the substrate surface (y) or parallel to the substrate surface (x) or, which means the same thing, parallel to the Axis of the tube 10. It can be seen from Fig. 3A that the temperature Tl at the upper surface of the melt is greater than the temperature T2 at the lower surface of the melt contacting the substrate. Fig. 3B shows that the temperature, temperature of the melt in the x-direction is constant. That the melt is at the interface between substrate and melt Located at a constant temperature is desirable in order to have a uniform growth rate throughout

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ca » " Ί eta

To ensure substrate surface «

The materials from which the "growth apparatus will be built 14 must be selected so that they react with the constituents of the melt under the Aufwachsbedingungen'nicht = Many semiconductor materials react Zob. Not with graphite, quartz or nitrides. Quartz is but for" B An unsuitable material if aluminum is part of the melt, since aluminum "reacts with quartz" When growing garnet films epitaxially *, it is beneficial if the parts of the growing device with which the melt comes into contact are made of platinum.

In general, it can be said that all materials can be grown epitaxially with the method described and the growth device described, in which this is possible from the liquid phase. Either the liquid phase contains the material to be grown in dissolved form? 'F © m _F or there is a liquid phase from the material that a "£ should be grown *% u the materials -. With the. The methods described can be grown on, include, for example, semiconductors, oils aus.Elementen of the fourth group, composed of compounds of elements of the third and fifth groups and of alloys, garnets, metals and oxides.

The composition of the melt depends on the material that is to be grown. If sB, Ga ₁ Al As is grown, the melt contains GaAs and

The selection of the substrate 30 is not critical. Normal catfish a material is used whose lattice constant is compatible with the lattice constant of the material to be grown on is. For example, Al Ga, As epitaxial layers can be formed on a

χ χ — χ

GaAs substrate can be grown.

Before discussing other arrangements for implementation

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of the method described, it may be helpful to consider the individual steps of the epitaxial growth. This is supposed to
based on FIGS. 1 and 2 happen. The substrate 30 is in the
Chamber 28 is placed and the starting material for the melt is

brought into the recess 32. The starting material is sufficient (

long enough and heated to a temperature of 38 in )

the hole 36 and in the recess 32 to produce. To be sure- I

make sure that the melt is saturated, the temperature is now>

lowered. A saturated melt is not switch the substrate \

dissolve when brought into contact with the substrate. The {

The melt and the substrate are then in contact with one another j

placed, for example, characterized in that the plate 18 is displaced so that ·

the melt is brought into a position above the substrate 30. j

The temperature is now increased slightly to achieve a full level

to effect wetting of the substrate. The wetting of the substrate ί

improves the adhesion of the epitaxially grown layer. j

Subsequently, the epitaxial layer is grown by the j swath to a temperature which is not higher is generally \, cooled than the temperature of the saturated melt. In
at this stage the melt is wiped off the substrate surface by moving the plate 18 back to its original position
will. The epitaxial layer treated in this way has a smooth surface which is free from all excess constituents of the melt. ί

Although it was found above that the epitaxial growth [

is already caused by the fact that the melt and the sub \ strat are brought into contact with each other, but are obtained
better grown layers when the others described
Process steps are inserted.

When using the method described, it was recognized that
that it is very important to keep the heat losses in the melt in such a way
to regulate that it covers the entire upper surface of the melt
are uniform. For this reason it is ensured that the

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The surface of the melt does not have a curved meniscus like him is typical of the known methods such as shown in the figures in U.S. Patent 3,565,702 and in the publication by M.B. Pänish et al in the journal JN Phys. Chem. Solids, Pergamon Press, Vol. 30, page 129 ff (1969). The. The control of the heat losses described results in a uniform Temperature at the interface between substrate and melt. ■

The pressure exerted on the melt by the plate 20 causes it to fill ^{the entire volume of the hole 36%.} This ensures that the melt when it is brought into contact with the substrate 30 is of a uniform height.

The advantages of the method described will be explained in more detail using the example of the growth of Al Ga ₁ As on a substrate, such as GaAs. Aluminum gallium arsehid has a tendency to precipitate out of solution. In the known processes it was therefore necessary to add additional material in order to compensate for the loss caused by the precipitation. It was then difficult to determine and control the final thickness of the Äl ^ Gaj ^ As layer in advance. When using the method described, the necessary amount of material can be controlled reproducibly and therefore the grown epitaxial layer has a uniform thickness and composition «

Since the height of the melt is low * a precipitation of Ga occurs. _Χ Α1 _χ Αβ only on the substrate, which means an additional efficiency; the method causes .. The low level of the melt does not affect the temperature at the »substrate surface.

The upper limit of the permitted level of the melt is determined by the diffusion length of the constituents in the melt. The diffusion lengths of all components are longer than the melt is high. Therefore no spontaneous crystallization takes place in the _; Solution, but only crystallization on the substrate surface

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instead of. The diffusion lengths are a function of the abilities of the constituents in the melt, the temperature, the · ^; ~ Environment in which the components are located and the concentration of the components. Typical diffusion lengths for materials used for light emitting diodes are on the order of 1 cm. Therefore, heights of the melt between about 0.5 and 6 mm can be used. If the melt is too high, the difficulties of the known processes arise, namely inefficient growth and spontaneous crystallization.

The height of the melt, however, must not be arbitrarily small, because otherwise there is the risk that not enough material is available to grow a layer of the desired thickness.

2 In general, the ratio of the substrate surface (in cm) to the height of the melt (in cm) is large; in the case of Al Ga ₁ _ As growth, this ratio is about 10.

The properties of the epitaxial layers grown according to the method described can be reproduced. the Layers have a uniform thickness with fluctuations that lie within a few percent, while the thicknesses with The layers grown according to the known method vary in the range between 100 and 200%. It also adds that the yield in good layers when using the method described is significantly higher than when using the known methods, In the known processes it is customary to grow thick layers and then lap them until the desired final thickness is reached. However, the lip procedure worsens “The yield of usable films is rather strong.

JueEtalich to the uniform thickness, the layers grown using the methods described are smooth and without «Further preparation suitable for photolithographic processes.

Fig. 4 shows the thickness distribution of a on a plate layer grown according to the method described.

from «» 309t! 0 /! 0t7

In this particular case, the epitaxial layer consisted of . The epitaxial layer had an area of 0.8 1.8 cm *

The growth took place in a temperature range between 900 and 955 ° C. The cooling rate was 0.4 ° C / min. The thickness distribution shown shows that substantially uniform thicknesses are achieved over the entire epitaxial layer could. The uniform thickness achieved is also reproducible. When comparing layers from different batches, the Reproducibility of the layer thickness within + 4%. -

FIG. 5 shows an EFP growing device 46 which, in contrast to the growing device shown in FIG. 1, is located in a vertical furnace system and in which the melt is displaced by a rotary movement. The EFP growing device 46 includes a boat ¹ 48 which has a recess 50 in which the substrate 52 lies. The movable container 54 with the two chambers 56A and 56B is seated above the boat 50. The melts 58A and 58B are enclosed in these chambers. The cover plates 6OA or 6OB enclose the melts under pressure, the pressure being exerted either by the tightened screws 62A or 62B or by a weight. *

The container 54 is rotatably arranged so that both the melt 58a and the melt 58B are in contact with the substrate 52 to be able to bring. The container 54 is rotated by means of the screw mechanism 64. However, not shown in the figure Heating sources similar to those in FIG. 1, tuned to heat the melt * - b "e>», surround the EFP growing device 46 ■: »ν

There is practically a constant temperature over the entire substrate surface and by turning the melt excess material is wiped away on the substrate surface, whereby a smooth surface is achieved. It ist.auchi mög, _{lich>;! I,} convert -the growing apparatus so that it can be grown on several substrates, or that on a substrate a plurality of ^ *! s ^ j differently composed epitaxial layers applied ^ yiei ^ n:; - © can. For example, melts 58A and 58B are different

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assembled, the EFP growing device 46 can do so are used, epitaxial layers of different composition simply manufactured by sliding chambers 56A and 56B over substrate 52 in succession.

Fig. 6 shows one suitable for continuous EFP growth Design of the growing device shown in FIG. 1. The quartz tube 10 and the heating sources 12 are shown in FIG Fig. 6 not drawn separately. With the EFP waxing device 66, melt can be refilled when it is used up, or the melt can be removed from the chamber 76 when a melt with a different composition is introduced target.

The boat 68 with the chambers 70A and 70B incorporated therein belongs to the EFP growing-up device 66. Lying in these chambers the substrates 72A and 72B, respectively. On the boat 68 is a first movable plate 74 which contains the hole 76 in which the Melt 78 is located. At the beginning, the melt 78 is located above the recess 80 let into the boat 68. The recess 80 contains the starting material 82 for the melt.

The second movable plate 84 is formed in the same way as that Plate 20 in FIG. 1. To simplify the figure, the chambers 40A to 40D shown in FIG. 1 are in the plate 84 omitted.

The EFP growing device 66 differs from that in FIG Fig. 1 depicted growth device 14 in that the arrangement 88 is present with which the melt 78 in the chamber 76 can be refilled or removed from this. In the simplest case, the arrangement 88 includes a storage container 90, in which the constituents of the melt are kept under pressure by means of the cover plate 92. If this is desired, A plurality of storage containers 90 can be provided in order to successively enter new constituents of the melt into the hole 76

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permit. The valve Vl connects the hole 76 via the pipe 94 on the one hand with the storage container 90, and on the other hand with the open ending pipe socket 96, through which the system can be ventilated. From the hole 76 goes down from a pipe 98, which when open Valve V2 connects hole 76 to the vacuum system.

In order to remove melt from the hole 76, the valve V2 opened to the vacuum, while valve Vl in the ventilation position is rotated. In order to refill components of the melt into the hole 76, valve V2 is first closed, and then the connection to reservoir 90 is established with valve V1. In this way, epitaxial layers from the repeatedly refilled can be applied to a large number of substrates 72A, 72B, etc. Melt 78 grow up. This is achieved in that the movable plate 68 is shifted so that the substrates under the refilled melt 78 come to rest.

The Pign. 7A and 7B show two designs of a boat 100 with Wells for holding substrates. The boat 16 in the FIG. 1 and the boat 68 in FIG. 6 can be equipped in this way. In FIG. 7A, the boat 100 has depressions 102A and 102B for receiving the substrates 104A and 1Q4B, respectively. One boat can have several Have depressions 102 so that it is possible with the same Melt many layers to grow.

The boat in Fig. 7B has two recesses 102A and 102b which are in the external dimensions are similar to those in Fig. 7A. However let the construction in Fig. 7B be used so that simultaneously multiple substrates can be placed in each well. The wells have, for example, three partitions 103 so that four substrates 104A can be placed in recess 102A and four substrates 104B can be placed in recess 102B. Additions to this Art can still be refined in order to improve in this way Versions of all waxing * shown in the drawings fixtures to come. If so, you can several melts are used so that for each one substrate

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containing recess a melt is present. The different Melts can also be used so that over Several uniform epitaxial layers that differ in their composition are grown on the same substrate will.

example

The following example is intended to explain the method described in more detail.

For applying a layer of Al _Q 35Ga _{0 65} As on a GaAs substrate, the Aufwachsapparatur heated 14 to about 930 ⁰ C 1/2 to 1 hour to obtain a saturated melt, wherein the starting material contains GaAs and AlAs. The melt is then cooled for about 5 hours, during which its temperature drops by 5 to 10 ° C. This ensures that the melt is saturated. The melt is then moved into a position above the substrate and then the temperature is slightly heated for 1 to 5 minutes, ie approximately to the starting temperature, in order to wet the substrate. Then the temperature is increased at a rate between 0.1 and 2 ° C / min. lowered until the desired thickness of the grown layer is reached. In general, the temperature between 20 and 50 ⁰ C is lowered. Finally, the melt is wiped from the substrate surface by retracting the movable plate 18 to its original position. The epitaxial layer produced in this way has a smooth surface and is completely free of gallium.

In summary, it can be said that with the method described a smooth, uniformly thick and uniformly composed epitaxial layer can be produced. This is mainly because of this achieves that the melt is made uniformly high by applying pressure over the entire substrate surface that only the lowest possible level of the melt is allowed, which on the one hand ensures that the diffusion length of each individual

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ORIGINAL INSPECTED

of the constituents in the melt is greater than the amount of Prevents melt and thus crystallization within the melt, and on the other hand the crystallization of the constituents in the melt only takes place on the substrate, as a result of which the melt is only slowly depleted of its constituents, and that finally No temperature gradient is permitted along the substrate surface, but the temperature profile perpendicular to the substrate is set in this way will * that there is a minimum on the substrate.

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Claims (14)

PATENT CLAIMS 1. Method for growing epitaxial layers crystalline, uniformly tempered substrates from the liquid phase on the surface, with the in the liquid phase transferred, material to be grown pushed over the substrate to grow and then again is pushed away, characterized in that the liquid Phases (38 or 58A, 58B) are made uniformly high under pressure that the distance between substrate and the upper melt surface is made smaller than the diffusion lengths of all constituents of the melt and that perpendicular to the substrate surface an increasing distance from the substrate surface increases Temperature gradient is maintained. 2. The method according to claim 1, characterized in that 1 to 2 g of flüs:
be brought. 2
1 to 2 g liquid phase / cm substrate surface applied 3. The method according to claim 1, characterized in that the growing device (14) localized to the heater (12) is that the substrate (30) is further away from the heater (12) than the liquid phase (38). 4. The method according to one or more of claims 1 to 3, characterized in that the temperature of the liquid Phase is lowered until saturation occurs, so that the liquid phase is then pushed over the substrate, then the temperature of the liquid phase is increased briefly and is finally decreased slowly during the growth. 5. The method according to claim 1, characterized in that rt.-ß the cover plates (60A) and ((> 0P) through the screw ™ 971 005 3 0 9810/1017 BATH ORIGINAL Exercise (62A) and (62B) or a weight on the liquid Phases (58A) and 58B) are pressed. 6. The method according to one or more of claims 1 to 4 ,. characterized in that the growing device (66) is equipped so that the constituents of the liquid phase are continuously added and withdrawn can. 7. The method according to one or more of claims 1 to 6, characterized in that a melt is taken as the liquid phase. 8. The method according to one or more of claims 1 to 7, characterized in that a semiconducting epitaxial layer is grown on a semiconductor crystal. 9. The method according to claim 8, characterized in that the melt is applied between about 0.5 and 6 mm thick will. 10. The method according to claim 8, characterized in that a substrate made of GaAs is used, and an epitaxial layer made of Ga Al ₁ As is grown. 11. The method according to claim 10, characterized in that GaAs and AlAs are used as constituents of the melt will. 12. The method according to claim 10, characterized in that the ratio of the substrate surface (in cm). to the height the melt (in cm) is made about .10. 13. The method according to claim 10, characterized in that at 900 to 1000 ⁰ C is grown. YO 9 71 005 3 0 9 8 10/1017 14. The method according to one or more of claims 1 to 7, characterized in that an insulator is used as the substrate and a garnet layer is epitaxially grown will. YO 971 OO5 3098 10/1017 λ * Blank page