Process Of Manufacturing Semiconductor Devices

Abstract

A process of manufacturing semiconductor devices is described which comprises the steps of: Forming an insulating layer having a closed pattern on one surface of a semiconductor substrate, Forming a coating layer on the entire surface of the semiconductor substrate at least a portion of the coating layer deposited on the insulating layer being conductive, and then Carrying out electrolytic etching in such a manner that the portion of said coating layer on the insulating layer is connected as an anode whereby said portion of said coating layer on the insulating layer is removed and the portion of said coating layer encompassed by the insulating layer remains. The resulting semiconductor devices have a far more flattened surface.

Description

This invention relates to a process for preparing semiconductor devices, and more particularly to a process for preparing diffused planar semiconductor structures wherein three regions emitter, base and collector come to the same planar surface of the semiconductor device.

Semiconductor devices particularly those having large scale integrated circuits involve multilayer wirings for the interconnections to ensure highly densified circuits. In general, the multilayer wirings involve a silicon dioxide insulating layer formed on a silicon substrate. The insulating layer has one or more holes formed therein wherein wirings of the outer adjacent layer are formed. A metal layer used for such wiring usually includes an aluminium layer, or layers of chromium-copper-chromium combination, in view of the adhesion to silicon dioxide and the electric conductivity. Each of the metal layers and the silicon dioxide insulating layers usually has a thickness of approximately 1 micron.

However, semiconductor devices involving these multilayer wirings have some serious problems. When a conductive metal is deposited onto the semiconductor device by vacuum evaporation the resulting metal layer is thiner at the top edge of the sides of the holes formed in the silicon dioxide insulating layer than at the other portions. This is due to the altitude difference of approximately 1 micron between the bottom of hole and the outer surface of the insulating layer. Consequently, the metal layer tends to separate at the top edge of the sides of the hole. Further, when a silicon dioxide insulating layer having a thickness of approximately 1 micron is formed by chemical vapor deposition on the stripes of wiring having a thickness of approximately 1 micron, and then other stripes of wiring are formed on the silicon dioxide insulating layer in a direction intersecting with the embedded stripes of wiring, there is a fear that the two stripes of wiring will short-circuit each other at the points of intersection. This is because the intermediate silicon dioxide insulating layer is thiner at the edge of the embedded stripes of wiring than at other portions. To sum up, multilayer wirings involved in conventional semiconductor devices do not have a high degree of reliability.

In a planar transistor, the metal of the electrode is contacted with an emitter through a window formed in the oxidized layer. However, in the case where the emitter junction is shallow, the emitter junction tends to be destroyed by the sintering of the metal of electrode. In order to mitigate or avoid this defect, it has been proposed to build up a semiconductor material layer by a selective epitaxial growth process in the window to protect the emitter against migration phenomena of the metal of electrode. However, it has been very difficult to stably carry out the selective epitaxial growth because the limits of the condition at which semiconductor material is built up are severe.

Further, in the preparation of integrated circuits, a procedure has been employed wherein an oxide film is formed for dielectric isolation, i.e., to isolate islands of semiconductor. The formation of the oxide film is usually carried out by selective oxidation of a silicon substrate using a masking agent such as silicon nitride. Thus, a planar surface of the substrate is obtainable. This procedure is called an "isoplanar" process. In general, the isoplanar process is accompanied prior to oxidation, by the step of etching at least the surface portion of the silicon substrate which is to be oxidized, in order to result in a substantially planar surface. However, it has been very difficult to strictly control the amount of silicon etched away for producing a completely planar surface and the oxidizing of the entire depth of the epitaxial layer.

Therefore, it is an object of the present invention to provide semiconductor devices having a far more flattened conductor surface, over which metal wiring runs, as compared to those of conventional planar semiconductor structures.

It is another object to provide semiconductor devices involving metal wiring layers, with the layer on the semiconductor surface being at substantially the same level as the semiconductor surface.

It is still another object to provide semiconductor devices involving metal wiring layers which possess high degrees of reliability.

It is a further object to provide a process wherein planar semiconductor devices described above can be manufactured in a simple and easy way.

In accordance with the present invention, there is provided a process of manufacturing semiconductor devices which comprises the steps of:

forming an insulating layer having a closed pattern on one surface of a semiconductor substrate,

forming a coating layer on entire surface of the semiconductor substrate, at least a portion of the coating layer deposited on the insulating layer being conductive, and then

dipping the semiconductor substrate so treated into a bath of etching solution wherein electrolytic etching is effected in such a manner that the portion of said coating layer of conductive material deposited on the insulating layer is connected as an anode whereby said portion of said coating layer deposited on the insulating layer is removed and the portion of said coating layer encompassed by the insulating layer remains.

The term "insulating layer" used herein means a layer consisting of the material which exhibits a specific electric resistance of higher than 10.sup.2 times that of the conductive coating layer deposited on the insulating layer.

One preferred embodiment of the process of the present invention comprises the steps of:

a. forming a circuit element at one region on one surface of a semiconductor substrate,

covering the entire surface of the semiconductor substrate with a first insulating layer,

b. forming an opening in the first insulating layer to expose a portion of said one region,

c. forming a first wiring layer on the first insulating layer, the first wiring layer being electrically in contact with said circuit element,

d. covering the entire surface of the semiconductor substrate, so treated, with a second insulating layer,

e. forming a viahole in the second insulating layer to expose a portion of the first wiring layer for the interconnection between wiring layers,

f. forming a coating layer of metal on the entire surface of the semiconductor substrate, the portion of the coating layer of metal deposited on the viahole being at a lower level than the portion of the coating layer of metal deposited on the second insulating layer, and then

g. dipping the semiconductor substrate so treated into a bath of etching solution wherein electrolytic etching is effected in such a manner that a portion of said coating layer of metal deposited on the second insulating layer is connected as an anode whereby said portion of said coating layer deposited on the second insulating layer is removed and the portion of said coating layer deposited on the viahole layer remains: and further,

a'. covering the entire surface of said semiconductor structure, thus obtained, with a third insulating layer,

b'. forming a groove in the third insulating layer to expose at least a portion of the metal buried in the viahole,

c'. forming a coating layer of wiring metal on the entire surface of the semiconductor device, the portion of the coating layer of wiring metal deposited on the groove being at a lower level than the portion of the coating layer of wiring metal deposited on the third insulating layer, and then

d'. dipping the semiconductor structure so treated into a bath of etching solution wherein electrolytic etching is effected in such a manner that a portion of said coating layer of wiring deposited on the third insulating layer is connected as an anode whereby said portion of said coating layer deposited on the third insulating layer is removed and the portion of said coating layer deposited on the groove remains as a second wiring layer.

Another preferred embodiment of the process of the present invention comprises the steps of:

a. preparing a semiconductor substrate having an active region of a circuit element formed on one surface of the semiconductor substrate and an insulating layer, coated thereon, having window(s) for exposing a portion of said active region,

b. forming a semiconductor layer on the semiconductor substrate, the portion of the semiconductor layer deposited on the window(s) being at a lower level than the portion of the semiconductor layer deposited on the insulating layer,

c. dipping the semiconductor substrate so treated into a bath of etching solution wherein electrolytic etching is effected in such a manner that a portion of said semiconductor layer deposited on the insulating layer is connected as an anode whereby said portion of said semiconductor layer deposited on the insulating layer is removed and the portion of said coating layer deposited on the window(s) remains, and then

d. forming a wiring layer on the insulating layer, the wiring layer being electrically in contact with said semiconductor layer.

Still another embodiment of the process of the present invention comprises the steps of:

a. preparing a semiconductor substrate having a buried layer on one surface of said semiconductor substrate and an insulating layer of a closed pattern at an isolation region, said insulating layer having a closed pattern and encompassing said buried layer,

b. forming a semiconductor layer by epitaxial growth on the entire surface of the semiconductor substrate, the portion of the semiconductor layer deposited on said semiconductor substrate encompassed by the insulating layer being at a lower level than the portion of the semiconductor layer deposited on the insulating layer, the former portion consisting of monocrystalline and the latter portion consisting of polycrystalline,

c. dipping the semiconductor substrate so treated into a bath of etching solution wherein electrolytic etching is effected in such a manner that a portion of said semiconductor layer deposited on the insulating layer is connected as an anode whereby said portion of said semiconductor layer deposited on the insulating layer is removed and the portion of said semiconductor layer encompassed by the insulating layer remains to form islands, and then,

d. forming a circuit element on the island.

In the preferred embodiment last set forth, impurities may be diffused into the semiconductor layer, prior to the electrolytic etching.

Further, in the preferred embodiment last set forth, the insulating

a. forming on the entire surface of the semiconductor substrate a silicon oxide layer having substantially the same thickness as that of a semiconductor layer to be formed by epitaxial growth,

b. forming a silicon nitride layer on the entire surface of said silicon oxide layer,

c. patterning said silicon nitride layer in a manner such that said silicon nitride remains on said isolation region, and then

d. removing selectively said silicon oxide layer by using said silicon nitride layer as a mask.

The invention will now be illustrated by means of the following examples and by reference to the accompanying drawing.

IN THE ACCOMPANYING DRAWINGS,

FIG. 1 through FIG. 6 are cross sectional views illustrative of one embodiment of the process of the invention wherein a wiring metal is buried in an insulating layer,

FIG. 7 and FIG. 8 are cross sectional views illustrative of another embodiment of the process of the present invention wherein a semiconductor material is built up, after base diffusion, in a window for emitter diffusion, and

FIG. 9 through FIG. 15 are cross sectional views illustrative of still another embodiment of the process of the present invention wherein a semiconductor integrated circuit is prepared.

EXAMPLE 1

Examples 1 and 2 illustrate one embodiment of the process of the present invention wherein multilayer wiring is buried in an insulating layer which provides a planar surface. Example 1 relates to the first-half step wherein metal material is buried in a viahole formed in a second insulating layer over which viahole multilayer wiring passes.

In FIG. 1, a circuit element such as, for example, transistor is formed at one region one one surface of a semiconductor substrate 1 by preferably using a diffusion technique. A first insulating layer 2 is formed the entire surface of the semiconductor substrate 1. An opening is formed in the first insulating layer 2 to expose a portion of the region. The first insulating layer consists of, for example, silicon dioxide. Then, a first aluminium wiring layer 3 is formed on both the insulating layer 2 and the portion of the semiconductor substrate 1 not covered by the first insulating layer. Thus, the first insulating layer is electrically contact with the circuit element. The first aluminium wiring layer 3 is covered with a second insulating layer 4. This layer is, for example, phosphosilicate glass layer 4 having a thickness of 1 micron. Finally, a viahole 5, for connecting wiring layers, is formed by a photo-etching process.

In FIG. 2, aluminium is deposited by a vacuum evaporation process on the entire surface to form an aluminium coating layer 6 of a thickness of 1 to 1.5 micron. The portion of the aluminium coating layer 6 deposited on the viahole 5 is at a lower level than the portion deposited on the second insulating layer 4.

The semiconductor substrate so treated is dipped in a bath of aqueous phosphoric acid solution maintained at a temperature of approximately 30.degree.C, wherein electrolytic etching is carried out in the following manner. The coating layer of aluminium 6 is deposited on the second insulating layer 4 connected as an anode. A platinum plate located in said solution confronts said substrate at a distance maintained within the range from 10 to 100 cm. Thus, the platinum plate is connected as a cathode, and the electrolytic etching of the aluminium 6 is carried out with a direct current at a constant voltage of 1.2 volt.

In this example, aluminium 6 is etched away at a rate of 2,500 to 3,000 angstrom minute. In contrast, etching is carried out only at a rate of approximately 150 angstrom/minute, in chemical etching.

As the electrolytic etching proceeds, a part of the aluminium layer deposited in the viahole 5 is separated from the other part deposited on the second insulating layer 4, as shown in FIG. 3. After this separation, the part of the aluminium layer in the viahole 5 is not subjected to electrolytic etching but merely to chemical etching.

However, the electrolytic etching of the part of the aluminium layer 6 deposited on the second insulating layer 4 is continued. This electrolytic etching takes place so rapidly that the part of the aluminium layer 6 deposited on the second insulating layer 4 has entirely disappeared from the surface when a substantial part of the aluminium in the viahole 5 still remains therein. The electrolytic etching is continued until the etching current exhibits a sudden decrease which means the completion of the removal of the aluminium layer 6.

Aluminium, thus buried in the viahole 5, provides a substantially planar surface on which a second aluminium wiring layer is to be coated. This aluminium in the viahole 5 allows a second wiring layer to be firmly and effectively connected to the first wiring layer 3. The preparation of the second wiring layer will be illustrated in the succeeding example.

In this example, only aluminium is illustrated. However, other metals may also be buried in the viahole with satisfactory results.

EXAMPLE 2

This example illustrates a step succeeding the step described in Example 1. This step involves the flattening of a multilayer wiring layer wherein a metal for wiring is buried in a third insulating layer in such a manner that the surface of the metal buried is at substantially the same level as that of the third insulating layer.

In FIG. 4, after the aluminium 6 is buried in the viahole 5, the entire surface is covered with the third insulating layer 7 by chemical vapor deposition. This layer is, for example, a phosphosilicate glass layer having a thickness of 2 micron. In the third insulating layer 7 a groove 8, having a pattern corresponding to that of a second wiring layer to be formed, is formed as shown in FIG. 5. Thus, at least one portion of the metal buried in the viahole 5 is exposed.

Thereafter, aluminium is deposited by vacuum evaporation on the entire surface to form an aluminium coating layer (not shown in the figure) having a thickness of 2.0 to 2.5 micron. The portion of the aluminium coating layer deposited on the groove 8 is at a lower level than the portion deposited on the third insulating layer 7. Then, electrolytic etching of the aluminium layer is carried out in the same manner as described in Example 1 with reference to FIGS. 1 through 3. As etching proceeds, the portion of the aluminium deposited in the groove 8 is separated from the other portion deposited on the third insulating layer 7. After the separation, only the portion of the aluminium deposited on the third insulating layer 7 is rapidly etched and finally, completely removed. Thus, the portion of the aluminium remaining in the groove 8 provides the second aluminium wiring layer 9, the surface of which is substantially the same level as that of the third insulating layer 7, as shown in FIG. 6.

If the preparation of a third, a fourth or more succeeding wiring layers is required, the above procedure may be repeated. In other words, the following steps may be repeated. First, the semiconductor substrate is covered with an insulating layer, and then a viahole is formed at the position in the insulating layer in which interconnection between wiring layers is to be formed. The insulating layer is, for example, phosphosilicate glass layer. Secondly, aluminium is deposited onto the entire surface, and then the aluminium is etched away by an electrolytic etching procedure, except for the portion of aluminium deposited in the viahole. Thirdly, an insulating layer, for example, a phosphosilicate glass layer is again coated on the surface and then, a groove having a pattern corresponding to that of the succeeding wiring layer is formed. Finally, aluminium is buried in the groove in a similar manner as in the second step above.

EXAMPLE 3

This example illustrates another embodiment of the process of the present invention. After a base diffusion, semiconductor material is built up by expitaxial growth in window(s) formed in an oxidized surface layer for emitter diffusion so as to provide a planar surface ready for contact with a wiring metal.

In FIG. 7, a base 11 is formed in the silicon substrate 10 by a conventional selective diffusion procedure. Then a window 13 for emitter diffusion is opened in an insulating layer (oxidized surface layer) 12 at the position where the emitter is to be diffused into the base 11. A layer of semiconductor such as polycrystalline silicon 14 doped with a large amount of phosphorous is then formed on the whole surface. The portion of the semiconductor layer 14 deposited on the window 13 is at a lower level than the portion deposited on the insulating layer 12. This formation of the layer of polycrystalline silicon 14 is preferably effected by decomposing monosilane (SiH.sub.4) and phosphine (PH.sub.3 ) in a furnace at a temperature of 600.degree.C to 700.degree.C. The gaseous components so generated by such heat decomposition are condensed on the surface of the silicon substrate in the furnace to build up the polycrystalline silicon. In this step, a large amount of phosphorous can be doped into the polycrystalline silicon in excess of the solubility limit.

As a modification of this step, single crystals of silicon may be built up in the window 13 in substitution for the polycrystalline. This can be achieved by heating the furnace at a temperature of 1100.degree.C to 1200.degree.C. Through this step, polycrystalline silicon is built up on the oxidized layer 12.

Then, the silicon substrate so treated is dipped in a bath of etching solution wherein electrolytic etching is effected in such a manner that a portion of the polycrystalline silicon layer 14 deposited on the insulating layer 12 is connected as an anode. The etching solution is prepared for example, by mixing 8 percent by weight of aqueous phosphoric acid having a concentration of 85 percent or more; 2 percent by weight of aqueous hydrofluoric acid having a concentration of 47 percent or more; and, 90 percent by weight of water. Alternatively, the etching solution may be prepared by mixing 100 parts of 99 percent aqueous acetic acid, 10 parts of 62 percent aqueous nitric acid, and 1 part of 50 percent aqueous hydrofluoric acid all by weight. The temperature of the bath is preferably maintained at 35.degree.C.

The polycrystalline silicon 14 deposited on the insulating layer 12 is easily etched away at a rate of 1000 to 2000 angstrom/minute through electrolytic etching. However, as the electrolytic etching proceeds the polycrystalline silicon (or single crystals of silicon in the modified step) remaining in the window 13 is subjected to little or no etching after it is separated from the polycrystalline silicon deposited on the insulating layer 12. Thus, flattening is effected. This procedure is similar to that described in Example 1 with reference to FIGS. 1 through 3.

The silicon substrate so treated is then heated, whereby phosphorous in the polycrystalline silicon (or single crystals of silicon) remaining in the window 13 is diffused into the silicon substrate to form an emitter, as shown in FIG. 8. Thereafter, a metal 15 for wiring is deposited on the flattened surface.

In this planar semiconductor device, the polycrystalline silicon, or the single crystals, in the window 13 is interposed between the wiring metal 15 and the emitter junction, as an intermediate conductor which connects the wiring metal with the emitter. Therefore, the wiring metal 15 does not reach the emitter junction even though the wiring metal diffuses into the intermediate conductor.

The planar semiconductor structure illustrated above is particularly useful as semiconductor devices possessing shallow or narrow junctions, such as high frequency transistors.

EXAMPLE 4

This example illustrates a step of flattening a semiconductor surface of the semiconductor integrated circuit. This step is concerned with an improved "isoplanar process" wherein no selective oxidation is utilized.

In FIG. 9, a buried layer 17 of N-type is formed on one surface of a semiconductor substrate 16 of P-type by the diffusion of antimony at a high concentration.

In FIG. 10, an insulating layer, e.g. a silicon dioxide layer, 18 of a closed pattern is formed at an isolation region, for example, by a thermal oxidation technique. The thickness of the insulation layer is from 2 to 3 micron. It is apparent that the selective oxidation technique is not applied. For example, a layer of silicon dioxide having a thickness of 2.2 micron can be formed by heating the silicon semiconductor substrate in a furnace at a temperature of 1250.degree.C over a period of 310 minutes while steam of 100.degree.C is blown thereinto.

In FIG. 11, the insulating layer is subjected to photoetching in a way that a portion of the silicon dioxide remains only at the isolation region. The isolation region has a closed pattern.

In FIG. 12, then, a semiconductor 19 (e.g. N-type silicon layer having a thickness of 2.5 to 3.5 micron) is formed. A conventional epitaxial growth technique using monosilane may be applied to form the silicon layer. Single crystals 20 of silicon and polycrystalline silicon 21 are connected on the silicon substrate and on the insulating layer (silicon dioxide) 18, respectively, under ordinary conditions of the epitaxial growth.

In FIG. 13, an island of the single crystal 20 is separated from the many other islands 20 laid on a surface of the silicon substrate. This separation is realized by means of electrolytic etching of the present invention, wherein the polycrystalline 21 is etched away in the same manner as described in Example 3. It will be apparent from FIG. 13 that isolation of the single crystal 20 is ensured by both the silicon dioxide layer 18 of a closed pattern and the P.N. junction previously formed between the single crystal 20 and the semiconductor substrate.

In FIG. 14, the silicon semiconductor substrate so treated is then subjected to thermal oxidation to form a silicon dioxide layer 22 on each silicon single crystal layer 20. This silicon dioxide layer 22 is at substantially the level of the surface of the silicon dioxide layer 18. Thereafter, a circuit element is formed (not shown in FIG. 14) on each isolated single crystal island 20, wherein the silicon dioxide layer 22 described above is used as a mask against diffusion.

In this Example, the formation of the silicon dioxide layer 18 having a closed pattern as illustrated in FIG. 11 may also be carried out by etching, using a silicon nitride mask 23 as shown in FIG. 15. In accordance with this procedure, the succeeding separation of the silicon single crystal layer 20 by electrolytic etching may be easily carried out because of the silicon nitride layer 23 deposited on the top of the silicon dioxide layer 18 as shown in FIG. 15.

In this example, prior to the electrolytic etching illustrated in FIG. 12, impurities such as, for example, phosphorous may be diffused into the silicon semiconductor layer 19 at a high concentration. This pre-treatment has an advantage that the portion 21 of the silicon semiconductor layer 19 deposited on the insulating layer (silicon dioxide layer) 18, i.e., the portion comprising polycrystalline silicon, is etched away far more rapidly as compared to the portion 20 comprising single crystals of silicon deposited on the silicon semiconductor substrate 16, and therefore, separation of the single crystal layers 20 is readily achieved. This is because the diffusion velocity of phosphorous into the polycrystalline silicon 21 is twice or three times that into the single crystals 20. This pre-treatment is advantageously applied to the etching of the silicon layer particularly one having a high specific resistance, e.g., of several ohm-cm or more.

Although the invention has been illustrated with a high degree of particularity, it is understood that the disclosure has been made only by way of example and is not to be considered as limiting in any sense.

Claims

What we claim is:

1. A process of manufacturing semiconductor devices which comprises the steps of:

forming an insulating layer having a closed pattern on one surface of a semiconductor substrate,

forming a deposited layer on the entire surface of the semiconductor substrate, the deposited layer being thin in the proximity of the edges of the surface of the insulating layer, and at least the portion of the deposited layer located on the insulating layer being conductive, and,

dipping the semiconductor substrate so treated in a bath of an etching solution wherein electrolytic etching is effected in a manner such that said portion of the deposited layer of conductive material on the insulating layer is connected as an anode whereby said portion of the deposited layer on the insulating layer is removed and the portion of the deposited layer encompassed by the insulating layer remains substantially unchanged.

2. A process according to claim 1 wherein said insulating layer consists of silicon dioxide.

3. A process according to claim 1 wherein said insulating layer consists of phosphosilicate glass.

4. A process according to claim 1 wherein said deposited layer consists of metal.

5. A process according to claim 4 wherein said metal is aluminium.

6. A process according to claim 1 wherein said deposited layer consists of semiconductor.

7. A process according to claim 6 wherein said semiconductor is silicon semiconductor.

8. A process according to claim 6 wherein said semiconductor is polycrystalline silicon semiconductor.

9. A process according to claim 6 wherein said semiconductor is silicon semiconductor doped with impurities.

10. A process of manufacturing semiconductor devices which comprises the steps of:

forming a circuit element at one region on one surface of a semiconductor substrate,

covering the entire surface of the semiconductor substrate with a first insulating layer,

forming an opening in the first insulating layer to expose a portion of said one region,

forming a first wiring layer on the first insulating layer, the first wiring layer being electrically in contact with said circuit element,

covering the entire surface of the semiconductor substrate, so treated, with a second insulating layer,

forming a viahole in the second insulating layer to expose a portion of the first wiring layer for the interconnection between wiring layers,

forming a deposited layer of metal on the entire surface of the semiconductor substrate, the deposited layer being thin in the proximity of the edge of the surface of the second insulation layer, and the portion of the deposited layer of metal on the viahole being at a lower level than the portion of the deposited layer of metal on the second insulating layer, and,

dipping the semiconductor substrate so treated in a bath of an etching solution wherein electrolytic etching is effected in a manner such that said portion of the deposited layer of metal on the second insulating layer is connected as an anode whereby said portion of the deposited layer on the second insulating layer is removed and the portion of the deposited layer on the viahole layer remains substantially unchanged.

11. A process according to claim 10 wherein said semiconductor structure is further subjected to the steps of:

covering the entire surface of said semiconductor structure with a third insulating layer,

forming a groove in the third insulating layer to expose at least a portion of the metal buried in the viahole,

forming a deposited layer of wiring metal on the entire surface of the semiconductor device, the deposited layer being thin in the proximity of the edge of the surface of the third insulating layer, and the portion of the deposited layer of wiring metal on the groove being at a lower level than the portion of the deposited layer of wiring metal on the third insulating layer, and,

dipping the semiconductor structure so treated in a bath of an etching solution wherein electrolytic etching is effected in a manner such that said portion of the deposited layer of wiring metal on the third insulating layer is connected as an anode whereby said portion of the deposited layer on the third insulating layer is removed and the portion of the deposited layer on the groove remains substantially unchanged as a second wiring layer.

12. A process according to claim 10 wherein said circuit element is transistor.

13. A process according to claim 10 wherein said first insulating layer consists of silicon dioxide.

14. A process according to claim 10 wherein said second insulating layer consists of phosphosilicate glass.

15. A process according to claim 10 wherein said first wiring layer and said coating layer of metal consist of aluminium.

16. A process according to claim 10 wherein said deposited layer of metal consists of aluminium and said electrolytic etching is carried out in a bath of aqueous phosphoric acid solution.

17. A process according to claim 11 wherein said third insulating layer consists of phosphosilicate glass.

18. A process according to claim 11 wherein said second wiring layer consists of aluminium.

19. A process of manufacturing semiconductor devices which comprises the steps of:

preparing a semiconductor substrate having an active region of a circuit element formed on one surface of the semiconductor substrate and an insulating layer, coated thereon, having at least one window for exposing portion of said active region,

forming depositing a semiconductor layer on the semiconductor substrate, the semiconductor layer being thin in the proximity of the edge of the surface of the insulating layer, and the portion of the semiconductor layer deposited on the said window being at a lower level than the portion of the semiconductor layer deposited on the insulating layer,

dipping the semiconductor substrate so treated in a bath of an etching solution wherein electrolytic etching is effected in a manner such that said portion of the semiconductor layer deposited on the insulating layer is connected as an anode whereby said portion of said semiconductor layer deposited on the insulating layer is removed and the portion of the semiconductor layer deposited on the window remains substantially unchanged, and,

forming a wiring layer on the insulating layer, the wiring layer being electrically in contact with said semiconductor layer.

20. A process according to claim 19 wherein said semiconductor layer consists of polycrystalline.

21. A process according to claim 19 wherein said semiconductor layer consists of polycrystalline doped with impurities.

22. A process according to claim 19 wherein said active region consists of a base region in which emitter of transistor is formed by diffusing into said semiconductor substrate impurities doped in said semiconductor layer.

23. A process according to claim 19 wherein said wiring layer consists of aluminium.

24. A process of manufacturing semiconductor integrated circuits which comprises the steps of:

preparing a semiconductor substrate having a buried layer on one surface of said semiconductor substrate and an insulating layer of a closed pattern at an isolation region, said insulating layer encompassing said buried layer,

forming a semiconductor layer by epitaxial growth on the entire surface of the semiconductor substrate, the portion of the semiconductor layer deposited on said semiconductor substrate encompassed by the insulating layer being at a lower level than the portion of the semiconductor layer deposited on the insulating layer, the former portion consisting of monocrystalline and the latter portion consisting of polycrystalline,

dipping the semiconductor substrate so treated in a bath of an etching solution wherein electrolytic etching is effected in a manner such that the portion of said semiconductor layer deposited on the insulating layer is connected as an anode whereby said portion of said semiconductor layer deposited on the insulating layer is removed and the portion of said semiconductor layer encompassed by the insulating layer remains substantially unchanged to form islands, and

forming a circuit element on the island.

25. A process according to claim 24 wherein impurities are diffused into the semiconductor layer, prior to the electrolytic etching.

26. A process according to claim 24 wherein said insulating layer is formed by the steps of:

forming on the entire surface of the semiconductor substrate a silicon oxide layer having substantially the same thickness as that of a semiconductor layer to be formed by epitaxial growth,

forming a silicon nitride layer on the entire surface of said silicon oxide layer,

patterning said silicon nitride layer in a manner such that said silicon nitride remains on said isolation region, and then

removing selectively said silicon oxide layer by using said silicon nitride layer as a mask.