DE2438588A1 - METHOD OF DEPOSITING AN EPITACTIC LAYER - Google Patents

Description

Process for depositing an epitaxial layer.

The invention relates to a method for depositing an epitaxial layer on a Surface of a preferably monocrystalline substrate, in which the epitaxial layer is one of that of the Substrate is given different composition; The invention further relates to a device which contains an epitaxial layer which, with the aid of this procedure is dejected.

The deposition of epitaxial layers on substrates is used, for example, in the manufacture of semiconductor devices applied"

In this production, e.g. in and on the epitaxial layer with the help of photomecha-

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nischer techniques circuit elements formed. When using photo-mechanical techniques, it is important to that - the surface of the layer to be treated is smooth, because - unevenness on the surface inaccuracies Alignment of masks can bring about.

For other applications the with the help

the above-mentioned method produced epitaxial Layer, e.g. in a transmission photocathode in an image intensifier tube, is a smooth surface the layer is necessary because parts of the image intensifier are very close to the epitaxial layer must be attached.

A substrate on which an epitaxial

The layer that is deposited is often a thin slice obtained, for example, from a rod by sawing is produced in a conventional mounting process.

The discs are then subjected to treatments designed to make a surface of the disc, on which the epitaxial layer is to be deposited, completely smooth.

In the case of procedures of the type mentioned above,

where the substrate and the epitaxial layer have different compositions is the deposition an epitaxial layer in general not simply because with the difference in composition often also a not insignificant difference in the lattice spacing between the epitaxial layer and the substrate

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goes hand in hand.

If the relative difference in the grid spacing is, for example, a few percent, it turns out that the formed monocrystalline epitaxial layer consists of grains which with respect to the orientation have a mutual deviation of about 0.1 ° and through areas with a high density of lattice defects, like dislocations, are separated from each other, in which the difference in lattice spacing is neutralized. Such grains can be identified with the X-ray reflection topography prove. With the formation of these grains is related that the surface of the epitaxial Layer often has unevenness, which are larger, the larger these grains and the difference in the grid spacing between the epitaxial layer and the substrate. It is also under conditions under which Grains are formed, often difficult to obtain layers without cracks.

An increase in temperature at which

the epitaxial 'layer is deposited is often favorable with regard to the grain size in the layer and the flatness of the layer. In general, however from other considerations tried high precipitation temperatures to avoid.

The invention aims, inter alia, at behaving low temperature epitaxial layers

knock down on a flat surface with no cracks

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exhibit. Experiments that have led to the invention have shown that epitaxial layers with a smooth surface often cannot be obtained if from a substrate with a smooth surface, but it can if a substrate with a rough surface is assumed.

The method mentioned at the beginning is characterized according to the invention in that, before the epitaxial layer is deposited, said substrate surface is subjected to a roughening treatment will.

Under a roughening treatment it κη to adjust that the surface of the substrate is rougher after the treatment than before the treatment, ie that during this treatment more unevenness per surface unit and / or deeper unevenness is formed on the substrate surface,

On with the help of the invention: s cn

Process-pretreated substrates become epitaxial Layering at a lower temperature, with a lower one . Korngiö; » se and a more level surface than on untreated substrates are knocked down. Also can the usual costly buffing treatments of the substrate can be omitted and the resulting rejects are lower due to the higher quality of the epitaxial layer.

The method according to the invention is preferably used when the relative difference

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BATH ORIGINAL

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in the lattice spacing between the substrate and the epitaxial layer is more than 0.3 $, e.g. 3 to k $>, and this method is therefore of greater importance, e.g. when depositing gallium arsenide phosphide on gallium arsenide or gallium arsenide or gallium aluminum arsenide on gallium phosphide / where the said relative difference can be 4 ^ b than when depositing gallium aluminum arsenide on gallium arsenide, the said relative difference being about 0.3 '$> .

It is known in the case of heteroepitaxy

Crystal lattice of the substrate and the epitaxial layer mutually adapt by making the composition of the phase from which the epitaxial layer is deposited is changed so that an intermediate layer is formed between the substrate and the epitaxial layer whose composition gradually changes from the substrate to the epitaxial layer. The change the composition of the phase that makes up the epitaxial Layer is deposited, can often be found in practice with epitaxy from the liquid phase more difficult to perform in a reproducible manner than with epitaxy from the gas phase. Hence the procedure Preferably used according to the invention when the epitaxial layer is deposited from the liquid phase will.

It has been found that in this preferred embodiment of the invention

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Method the difference in grid spacing over a very short distance bridged in the epitaxial layer and an epitaxial layer having a smooth surface can be obtained.

As a roughening treatment of the substrate surface a lapping treatment is preferably carried out.

Preferably, the roughening treatment results in a substrate surface having a middle Roughness from 0.3 to 2 / do, e.g. 0.5 to 1 / entertain.

Below the mean roughness of a substrate (R) is the mean distance between a r Piofil line, i.e. the profile of the surface of a rough Substrate in a section perpendicular to this surface, and the zero line, i.e. the straight line, which in the called cut the surface of a flat substrate .ni fc indicates the same content as the rough substrate to understand.

Furthermore, as a roughening treatment,

chemical etching treatments can be applied. This must include the composition and concentrations of a chemical Etching bath is often adapted to the composition of the substrate and the orientation of the substrate surface will.

For (111) A-areas of GaP and GaAs (areas occupied with CaHium atoms, in contrast to (1 1 1) B-areas occupied ^{with phosphorus 1 - or arsena toines)}

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BATH

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are suitable: 1 Vo 1. $ bromine ethanol mixtures, chloromethanol mixtures, H_SO. -H ₂ 0_-H "0 mixtures in a volume ratio of 3: 1: 1 and HpO_-HF-H" O mixtures with a volume ratio of 1: 1: 2.

Thermal treatments can also be used as the roughening treatment.

The invention is explained in more detail below with the aid of a few examples. Example I.

In a boat the one in the German one

Palontan report P Zh 18 830.5 described type comparatively the two following almost identical pre-unions are carried out.

In the first attempt, an undoped, monocrystalline gallium phosphide disk is used as the substrate a (111) A-face is used. Before knocking down the epitaxial layer is the surface of the disc, which has an R value of 0.05 / µm, a roughening

treated by leaving the disc for 3 minutes immersed in a known chloromethanol etching bath for a long time will. By this treatment the (1 1 1) A-r.lSclie, on which the epitaxial layer must be deposited, rougher. The R value is now 0.5 / µm. Then it will be

^a /

a homogenized at 900 ⁰ C solution of 7,6k g gallium, Ο, 2ό7 g # gallium arsenide with respect (3.5 $ wt. with respect to the gallium) and 0.030 g of aluminum (0, ^ g wt., ν.Γ the gallium) with a saturation temperature of about 86O ° C brought into contact with the substrate, which is at 83S ⁰ C

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is held.

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For a contact of a few minutes, the solution is first cooled slowly at a rate of 0.3 ° C / min and then at a rate of 1.5 ⁰ C / min until the temperature reaches a value of 760 ⁰ C.

At this temperature the disc is separated from the first solution and 'it turns out that there is a 25 / µm thick layer of gallium aluminum arsenide 'which has a relative difference in lattice constant to the substrate of $ 3.7 »

After that, the deposited epitak-

diagram layer with a homogenized also at 900 ⁰ C solution of 7.5k g gallium, 0.264 g of gallium arsenide (3.5 wt. ήα with respect to the gallium) and 0.226 g of germanium (3 wt. $ * with respect to the gallium) brought in contact. The solution has a saturation temperature of about 765 ⁰ C. The deposited layer only remains in contact with the solution for a short time (about 2 minutes, which corresponds to a temperature range of 3 ° C), and it turns out that a 2 / µm thick gallium arsenide layer is deposited, which has a relative difference in lattice constant to the gallium aluminum arsenide layer of 0.3 i ° .

The R value of the surface of the gallium arsenide layer is practically immeasurable and in any case smaller than 0.02 / µm. The maximum asperity (θ, 5 / µm) is considerably smaller than that of the roughened substrate

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OfUGJNAL INSPECTED

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surface. The flatness of the deposited gallium aluminum arsenide layer is practically the same as that of the gallium arsenide layer. The pane with the two knocked down epitaxial layers is after activation as a transmission photocathode in an image intensifier tube usable.

The second attempt is carried out in the same way as the first attempt, only with the difference: that the gallium phosphide disk is not undoped, but with the help of a suitable dopant ρ has been made conductive. Incidentally, under constant Etching conditions becomes the substrate surface

(Η ^ 0.05 / µm) now less strong than in the previous ^a /.

Experiment roughened} the R value is ^ 0.1 / µm. In

the attached layers are now bumps (3 / um) which are much larger than that of the substrate surface, " whereby the substrate with the attached epitaxial layers is not suitable for use as a transmission photocathode suitable. If, under the same conditions, this second attempt on gallium phosphide substrates with (111) B- or (100) surfaces (roughness of the etched surface

R \ 0, O5. / Um), rough gallium ^a /

aluminum arsenide layers formed with pits and even holes.

Example II '

A surface of a (100) -oriented Gallium phosphide disk is given a lapping treatment

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Subjected to carborundum powder No. 500, whereby the R -

Vert of the surface increases from \ 0.05 / µm to 0.8 / µm.

After a brief cleaning etching treatment, the R value is still more than 0.6 / um,

^a /

The roughened surface is brought into contact with solutions 1 and 2 below, one after the other brought·

'Solution 1 has a composition of

7.66 g of gallium, Ο, 46θ g gallium arsenide, germanium, and 0.230 g _t O on o46 g of aluminum and a saturation temperature of 910 ° C.

Solution 2 has a composition of 7000 g gallium, 0.474 g gallium arsenide and 0.237 g Germanium and a saturation temperature of 815 ° C.

After the disk has been brought into contact with solution 1 at 908 ° C., an immediately occurs programmed cooling at a rate of 1.5 ° C / min. At a temperature of 813 ° C, the Disc with the deposited 25 µm thick gallium aluminum lumar arsenide layer in contact with solution 2 for 1 minute brought, with a 2 / µm thick gallium arsenide * layer is knocked down. The layers have an R value that is immeasurably small and with that of a good one homoepitaxial layer on a flat substrate is comparable.

Without the lapping treatment of the disc surface are under the conditions of this example only

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ORIGINAL INSPECTED

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get rough and discontinuous layers.

The invention is not restricted to the examples described above. It is obvious that within the scope of the invention, many variations are possible for those skilled in the art. -

This is how heteroepitaxy is transformed from the Plüssig-

phase e.g. when depositing magnetic materials on insulating substrates. Also can, if on the epitaxial layer a second epitaxial layer with one of the first epitaxial Layer deposited significantly different lattice constant must be the surface of the first epitaxial before the deposition of the second epitaxial layer Layer of roughening sbehandlting: subjected

will. '.

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Claims (1)

.- 12 PATENT CLAIMS. 1. Method of depositing an epitaxial layer on a surface of a preferably a crystalline substrate in which the epitaxial layer has a different composition from that of the substrate is given, characterized in that before the deposition of the epitaxial layer said Surface is subjected to a roughening treatment. 2. The method according to claim 1, characterized in that the roughening treatment is a lapping treatment is applied. 3.. Method according to claim 1, characterized in that that a chemical etching treatment is used as the roughening treatment. H. Method according to one of the preceding Claims, characterized in that? by the roughening treatment a substrate surface with an average roughness of 0.3 to 2 / Uli is obtained. 5. The method according to claim h, characterized in that the average roughness is 0.5 to 1 / µm. 6. The method according to any one of the preceding claims, characterized in that the relative difference in the lattice spacing between the epitaxial layer and the substrate is more than '0.3 1' . 7. The method according to claim 6, characterized in that 509809/0831 PHN. 7049. - 13 - shows that the said relative difference is 3 to h <$> . 8. Method according to one of the preceding Claims, characterized in that the epitaxial layer is deposited from the liquid phase. 9 · Device with an epitaxial Layer deposited by the method of any preceding claim. 509809/0831