Process for selective formation of III - V group compound film

Abstract: A process for selective formation of a III-V group compound film comprises applying a compound film forming treatment, in a gas phase including a starting material for supplying the group III atoms of Periodic Table and a starting material for supplying the group V atoms of Periodic Table, on a substrate having a non-­ nucleation surface (S NDS ) with small nucleation density and a nucleation surface (S NDL ) with a larger nucleation density (ND L ) than the nucleation density (ND S ) of said non-nucleation surface (S NDS ) and a large area sufficient for a number of nuclei to be formed, and forming selectlvely a III-V group compound film only on said nucleation surface (S NDL ).

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a process for selective formation of a deposited film, particularly to a selective formation process for forming a deposited film of a III - V group compound in a self-alignment fashion. The selective formation process of a deposited film according to the present invention is applicable for, for example, preparation of thin films to be used for semiconductor integrated circuits, optical integrated circuits, etc. Related Background Art Figs. 1A -1E illustrate the steps of the process for forming a thin film by photolithography according to the prior art. First, a substrate 1 comprising a material species with uniform composition as shown in Fig. 1A is washed, and then a thin film 2 is deposited on the whole surface of the substrate 1 according to various thin film depositing methods (vacuum vapor deposition method, sputtering method, plasma discharging method, MBE method, CVD method, etc.) (Fig. 1B). Subsequently, on the thin film 2 is applied a photoresist 3 (Fig. 1C), and the photoresist 3 is exposed to light by use of a photomask of a desired pattern and the photoresist 3 is removed partially by development (Fig. 1D). With the remaining photoresist 3 as the mask, the thin film 2 is etched to form a thin film 2 with a desired pattern (Fig. 1E). By repeating such photolithographic steps, thin films of desired patterns are laminated to constitute an integrated circuit. In that case, alignment between the thin films of the respective layers becomes an extremely important factor for the characteristics of the device. Particularly, in the case of ultra-LSI where precision of submicron is demanded, precision of the shape of thin films of the respective layers is also extremely important along with alignment. However, in the above process for forming a thin film of the prior art, it is difficult to effect necessary alignment of the photomasks with good precision, and also the precision of shape is insufficient, because thin films of desired patterns are formed by etching. Figs. 2A - 2D illustrate the steps of the process for forming a thin film by use of lift-off according to the prior art. First, a photoresist 4 is applied on a substrate 1 (Fig. 2A), and the photoresist 4 with a desired pattern is removed by photolithography (Fig. 2B). Subsequently, a thin film 5 is deposited according to a thin film deposition method (Fig. 2C), and the remaining photoresist 4 is dissolved away. By this operation, the thin film on the remaining photoresist 4 is removed at the same time, whereby a thin film 5 with a desired pattern is formed. By repeating the above steps, an integrated circuit is constituted. However, such a thin film forming process, because a thin film is formed on a photoresist, requires to perform deposition of a thin film at a temperature not higher than the resistant temperature of the photoresist, whereby the deposition method is greatly restricted. Also, in removing the photoresist, the shape of the remaining thin film is influenced thereby and therefore precision of the shape becomes insufficient. Also, there is also the problem that the side wall or the inner portion of the thin film may be highly probably contaminated with carbon, etc. which is the component of the photoresist, etc. Also, as the selective deposition method, there has been known the method in which a monocrystal substrate is covered partially with an amorphous thin film, and the same material as the substrate material is epitaxially grown selectively only at the exposed portion of the monocrystal substrate. For example, there are the selective epitaxial growth (SEG) method in which a silicon monocrystal substrate is partially covered with silicon oxide to effect selective growth of silicon (B.D. Joyce & J.A. Baldrey, Nature vol. 195, 485, 1962), the method in which a GaAs substrate is covered partially with an amorphous thin film such as SiO₂, Si₃N₄, etc. to effect selectively epitaxial growth of GaAs (P. Rai-Choudhury & D.K. Schroder, J. Electrochem. Soc., 118, 107, 1971), etc. However, these selective deposition methods, because of growing selectively the monocrystal semiconductor of the same kind from the exposed surface of a monocrystal substrate, are limited in the deposition surface for the base to monocrystalline semiconductors, and therefore not applicable to polycrystalline substrates, amorphous insulating substrates. Thus, the deposited film forming method of the prior art is limited in available substrates, and further there are involved problems also in shape of the pattern, dimensional precision of the deposited film formed. Mention is made of United States Patent No. 4,216,037 which concerns a method for manufacturing a heterojunction semiconductor device. In the specific example described a patterned layer of phosphorous is formed upon the surface of an n-type single-crystal substrate. A layer of gallium arsenide grown by a Zn-entrained Ga-PCl₃-H₂ vapour growth method is then produced. This layer is single-crystal and covers only that area formerly occupied by phosphorous. Similar results could not be obtained where phosphorous is diffused into the substrate surface and is not present as a layer during initial growth. SUMMARY OF THE INVENTION An object of the present invention is to solve such problems of the prior art and provide a process for forming a III-V group compound film with any desired shape in a self-alignment fashion at any desired portion of a substrate, irrespectively of crystallinity of the base substrate. A process for selective formation of a III-V group compound film according to the present invention, is defined in claim 1 of the claims appended. BRIEF DESCRIPTION OF THE DRAWINGS Figs.1A - 1E illustrates the steps showing a thin film forming process according to photolithography of the prior art. Figs. 2A - 2D illustrates the steps showing a thin film forming process by use of lift-off according to the prior art. Fig. 3 is a line diagram showing the relationship between the change ΔG in free energy G and the radius of nucleus. Figs. 4A - 4D illustrates schematically the process for selective formation of a deposited film according to the present invention. Figs 5A - 5E illustrates the steps showing an example of selective formation of a GaAs film. Figs. 6A - 6E illustrates the steps showing another example of selective formation of a GaAs film. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The III - V group compounds to be used in the present invention are not limited to 2-element compounds, but also include multi-element III - V group mixed crystal compounds of 3 elements or more. Generally, the deposited film formation process is considered as follows. When the substrate having a deposition surface is a material different in kind from the flying atoms, particularly an amorphous material, the flying atoms will be freely diffused on the substrate surface, or revaporized. And, as the result of collision mutually between the atoms, a nucleus is formed, and when the nucleus reaches the size rc where the change ΔG in its free general G becomes the maximum (stable nucleus) or more, ΔG is reduced and the nucleus continues to grow stably three-dimensionally and become shaped in an island. The change ΔG in free energy G created by formation of nucleus is represented as follows: G=4πf(ϑ)(σ o r² + 1/3·gv·r³) f(ϑ)=1/4(2 - 3 cosϑ + cos²ϑ) where r: radius of curvature of nucleus ϑ : contact angle of nucleus gv: free energy per unit volume σ o : surface energy between nucleus and vacuum. The manner in which ΔG is changed is shown in Fig. 3. In Fig. 3, the radius of curvature of the stable nucleus when ΔG is at the maximum value is rc. Thus, the nucleus grows to become shaped in an island, and further grows until contact mutually between islands proceeds to cover the substrate surface in shape of a network, finally covering completely the substrate surface as a continuous film. Through such process, a thin film is deposited on the substrate. In the deposition process as described above, the density of the nucleus formed per unit area of the substrate surface depends greatly on the interaction between the flying atoms and the substrate, and is also greatly influenced by the deposition conditions, typically the temperature. Accordingly, by selecting appropriately the kinds of the material for the deposited film and the substrate material, and setting appropriately the deposition conditions such as temperaure, pressure, gas species, etc., the nucleation density (or nucleation speed) can be determined. Therefore, when one kind of material to be deposited is used and deposit on a deposition surface comprising two or more kinds of surfaces differing greatly in the above nucleation density, the deposited film can be formed selectively depending on the difference of nucleation density. For example, it is formed selectively as described below. Figs. 4A - 4D illustrate schematically the process of forming a deposited film according to the present invention. First, the two kinds of materials constituting the deposition surface are called A and B, and the material to be deposited C, and the above materials A, B and C are selected so that the nucleation density of the material to be deposited C for the materials A and B may differ greatly, under certain deposition conditions. Here, it is supposed that the nucleation density for the material A is sufficiently great, and the nucleation density for the material B is negligibly small. In Fig. 4A, on a substrate 1 of a material resistant to high temparatures such as high-melting glass, quartz, alumina, ceramics, etc., a thin film 6 of the material B is deposited according to a thin film forming method, and ions for the material A are implanted with a desired pattern by use of the converging ion beam implantation technique thereon. By this process, as shown in Fig. 4B, a region 7 of the material A is formed with a desired pattern so as to have a large area sufficient for a number of nuclei for crystal growth to be generated on the thin film 6 of the material B. Thus, as the method for forming the region 7 constituted of the material A with a desired pattern on the deposition surface, as shown in Fig. 4C, a mask 8 may be formed with a desired pattern on the material B, and ions for the material A injected on the whole surface to provide the region 7, thereby forming a deposition surface as shown in Fig. 4B. Also, a thin film of the material A may be formed on the material B, and the thin film of the material A may be formed to a desired pattern by photolithography. As shown in Fig. 4B, on the deposition surface constituted of the material A and the material B to a desired pattern, the material C is deposited under predetermined conditions. At this time, no material C is deposited on the thin film 6 of the material B. This may be considered to be due to revaporization of the flying atoms of the material C before becoming stable nucleus, or due to formation of a substance with high vapour pressure through the reaction of C atoms with the material B, whereby the material B is etched. Thus, only on the region 7 of the material A, the material C is deposited, and consequently a deposited film 9 with same pattern as the pattern of the region 7 of the material A can be formed in a self-alignment fashion. The present invention is described in more detail below by referring to Examples along with the drawings. Example 1 Referring to Figs. 5A - 5E, the process for forming selectively a GaAs film is described as a first example of the present invention. First, on a substrate 1 resistant to high temperature comprising ceramics, a SiO₂ film 10 was deposited to about 100 nm (1000Å) by conventional CVD (chemical vapor deposition) by use of silane (SiH₄) and oxygen (O₂) [Fig. 5A]. The nucleation density (NDs) of GaAs on SiO₂ film is small, and the SiO₂ film 10 becomes the non-nucleation surface (S NDS ). Next, the surface of the SiO₂ film 10 was masked with a photoresist 11 to a desired pattern [Fig. 5B]. By use of an ion implanter, As ions 12 were implanted in an amount of 2.5 x 10¹⁶/cm². The As ions were implanted only on the surface exposed [Fig. 5C]. At the SiO₂ film surface 13 where no As ion is implanted, the nucleation density (NDs) of GaAs is small, and this portion becomes the non-nucleation surface (S NDS ) mentioned above. On the other hand, the region 14 where As ions are implanted has larger nucleation density (ND L ) than the non-nucleation surface (S NDS ), which portion becomes the nucleation surfaces (S NDL ). The size of the region 7 was made 1mm x 1mm square. After the photoresist 11 was peeled off, the substrate 1 was subjected to heat treatment in a H₂ atmosphere at about 900 °C for about 10 minutes to clean the surface [Fig. 5D]. Subsequently, while the substrate 1 was heated to 600 °C, trimethyl gallium (TMG) and arsine (AsH₃) at a molar ratio of 1:60 were flowed together with a carrier gas H₂ onto the substrate surface to grow a GaAs film according to the MOCVD (organometallic chemical vapor deposition) method. The reaction pressure was made 2.7x10² Pa (20 Torr). As shown in Fig. 5E, GaAs film 15 was formed only on the nucleation surface (S NDL ) 14 formed by implantation of As ions, and no GaAs film was formed on the non-nucleation surface (S NDS ), namely the SiO₂ film surface where no As was implanted. Accordingly, as understood from the above example, by implanting As ions with a desired pattern, a GaAs film with any desired shape and dimension can be selectively formed. Example 2 Figs. 6A- 6E are drawings for illustration of the film formation steps of another example of the present invention. First, similarly as in Example 1, on the surface of a substrate 1 resistant to high temperature comprising alumina, a SiO₂ film 10 was deposited to about 100 nm (1000 Å) according to the CVD method by use of SiH₄ and O₂ [Fig. 6A]. Next, by means of an arc discharge type ion plating device, on the SiO₂ film 10 was formed an Al₂O₃ film. After the device was internally evacuated to 10⁻³ Pa (10⁻⁵ Torr), O₂ gas was introduced to 4x10⁻²Pa (3x10⁻⁴ Torr), and an Al₂O₃ film 16 was deposited to about 30 nm (300 Å) on a substrate heated to 400 °C at an ionization voltage of 50 V, a substrate potential of -50 V and an output of 500 W [Fig. 6B]. With a photoresist 17 masked to a desired pattern on the Al₂O₃ film 16, the portion of the Al₂O₃ film exposed was etched with an etchant of H₃PO₄:HNO₃:CH₃COOH:H₂O=16:1:2:1 [Fig. 6C]. At this time, the substrate was heated to about 40 °C. After the photoresist 17 was peeled off, the substrate 1 was subjected to heat treatment in a H₂ atmosphere at about 900 °C for about 10 minutes to clean the surface [Fig. 6D]. On the surface of SiO₂ film 10, nucleation density (NDs) of GaAs is small, which portion becomes the non-nucleation surface (S NDS ). On the other hand, the surface of Al₂O₃ film 16 has larger nucleation density (ND L ) than the nonnucleation surface (S NDS ) 10, which portion becomes the nucleation surface (S NDL ) 16. The size of the remaining Al₂O₃ film 16 was made 1cm x 1cm square. Subsequently, while the substrate 1 was heated to 600 °C, trimethyl gallium (TMG) and arsine (AsH₃) at a molar ratio of 1:60 were flowed together with a carrier gas H₂ onto the substrate surface to grow a GaAs film according to the MOCVD (organometallic chemical vapor deposition) method. The reaction pressure was made 2.7x10⁻³ Pa (20 Torr). As shown in Fig. 6E, GaAs film 15 was formed only on the Al₂O₃ nucleation surface (S NDL ) 16, and no GaAs film was formed on the non-nucleation surface (S NDS ) 10, namely the SiO₂ film surface. Thus, also according to the process of this Example, a GaAs film of any desired shape and dimension can be formed selectively. The conditions of temperature and pressure may be broadened similarly as described in Example 1. Example 3 A GaAlAs mixed crystal III - V group compound film was selectively formed in the following manner. After deposition of SiO₂ film to about 100 nm (1000 Å) on the ceramic substrate 1 according to the CVD method by use of SiH₄ and O₂ in the same manner as in Example 1, with a photoresist masked to a desired pattern on the surface, As ions were implanted into the exposed SiO₂ film in an amount of 2.5 x 10¹⁶/cm² by use of an ion implanter. Next, the resist film was peeled off, and the substrate was subjected to heat treatment in a H₂ atmosphere at about 900 °C for about 10 minutes to clean the surface. Also for the GaAlAs mixed crystal, the SiO₂ portion implanted with no As ion has smaller nucleation density (NDs) to become the non-nucleation surface (S NDS ). On the other hand, the portion implanted with As ions has larger nucleation density (ND L ) to become the nucleation surface (S NDL ). Onto the substrate having a surface where the nucleation surface (S NDL ) and the non-nucleation surface (S NDS ) thus having a nucleation density difference (ΔND) were formed, by use of H₂ as the carrier gas, TMG, trimethylaluminum (TMAl) and AsH₃ were flowed at a ratio of (TMG+TMAl):AsH₃ of 1:15 (molar ratio). The substrate temperature was made 800 °C by heating, and the reaction pressure was made 2.7x10³ Pa (20 Torr). Similarly as shown in Fig. 5E, only on the nucleation surface (S NDL ) formed by implantation of As ions, the ternary mixed crystal III - V group compound GaAlAs film was formed selectively. The size of the nucleation surface (S NDL ) was made 1cm x 1cm square. The ratio of Ga and As in GaAlAs can be freely controlled by varying the ratio of the reactive gases TMG and TMAl. As shown above in Examples, according to the present invention, a nucleation surface (S NDL ) having large nucleation density (ND L ) can be formed to a desired pattern, and a III - V group compound semiconductor film following the pattern can be formed. In the above Examples, there are shown examples in which SiO₂ film is formed by the CVD method, but SiO₂ can be also formed according to the sputtering method. Further, quartz itself with its surface well flattened can be also used as the deposition surface. The ion species to be implanted for formation of the nucleation surface (S NDL ) is not limited to As ions, but ions of the group III elements, ions of other group V elements, ions of the group II elements and ions of the group VI elements also can be used. As the III - V compound, InP film can be selectively formed on an amorphous substrate by use of trimethyl indium In(CH₃)₃ and phosphine PH₃ as the reactive gases, and AlSb film by use of trimethylaluminum Al(CH₃)₃ and stibine SbH₃. According to combinations of the reactive gases as described above, films of GaP, GaSb, InAs, InSb, AlAs, AlP can be selectively grown, and further mixed crystal III-V group compound films according to any desired combination can be selectively grown. Also, the reactive gas of the group III element is not limited to compounds having methyl groups as described above, but compounds having ethyl groups, propyl groups, butyl groups, isobutyl groups such as triethylgallium Ga(C₂H₅)₃, tripropyl indium In(C₃H₇)₃, tributyl gallium Ga(C₄H₉)₃, triisobutylaluminum Al(CH₃)₂CHCH₂, etc. can be also used. The mixed crystal compound semiconductor can be selectively grown on the Al₂O₃ provided on SiO₂ similarly as in Example 2 as the nucleation surface (S NDL ), as a matter of course. Further, in the respective Examples as described above, there are shown examples in which the MOCVD method is used in the step of selective growth of GaAs and GaAlAs films, but selective growth of the III - V group compound film can be performed also according to the same principle by use of the MBE (molecular beam epitaxy) method, etc. As described in detail above, the process for selective formation of a III - V group compound film can form self-matchingly a deposited film of a desired pattern by utilizing the nucleation density difference (ΔND) depending on the kinds of the III - V group compound deposition surface materials, and therefore a deposited film with a desired pattern can be formed at high precision, which is advantageous particularly in constituting a highly integrated circuit. Further, the materials of the deposition surface are not required to be limited to only monocrystal but a III - V group compound deposited film can be formed at high precision also on an amorphous insulating material by selecting the material (M L ) for forming nucleation surface and the material (M S ) for forming non nucleation surface having nucleation density difference. Particularly, in the case of a compound semiconductor with large influence by chemical etching, a pattern can be formed without etching of the film itself, and therefore it becomes possible to maintain chemical stability of the film prepared at high level.

Claims: A process for selective formation of a film of a III-V group compound which process comprises the following steps: (a) providing a substrate which is quartz having a flattened surface, or a thin film of SiO₂ deposited on the surface of a substrate which is resistant to high temperature, said quartz or SiO₂ film providing a nonnucleation surface (S NDS ) for which the nucleation density (ND S ) of the III-V group compound is negligibly small then either: (b) implanting ions (12), which ions (12) are of a group II, III, V or VI element, in an area (7;14) of said quartz surface or said SiO₂ film (6;10), using a converging ion beam or a mask, to produce a nucleation surface (S NDL ) for which the nucleation density (ND L ) of the III-V group compound is comparatively great, said area (7;14) being large enough for forming a plurality of stable nuclei of the III-V group compound; or (c) forming on the quartz surface or the thin SiO₂ film a thin film (16) of Al₂O₃ and patterning said thin Al₂O₃ film (16) by photolithography to produce a nucleation surface (S NDL ) for which the nucleation density (ND L ) of the III-V group compound is comparatively large, the area of said nucleation surface (S NDL ) being large enough for forming a plurality of stable nuclei of the III-V group compound; then (d) depositing by gas phase deposition the film of III-V compound selectively on the nucleation surface (S NDL ) using as starting material a starting material for supplying the group III atoms and a starting material for supplying the group V atoms of the film of III-V group compound, and using a temperature and a pressure for which the nucleation density (ND S ) of the III-V compound is negligibly small for said non-nucleation surface (S NDS ) and for which the nucleation density (ND L ) of the III-V compound is comparatively large for said nucleation surface (S NDL ,) the mechanism of said gas phase deposition involving firstly forming a plurality of stable nuclei of the III-V group compound selectively on said nucleation surface (S NDL ), and secondly growing III-V group compound from said stable nuclei until islands of said III-V group compound mutually contact and form the III-V group compound film, this being self-aligned with said nucleation surface (S NDL ). A process as claimed in claim 1 wherein said film of III-V group compound is a film of a binary system III-V group compound. A process as claimed in claim 1 wherein said film of III-V group compound is a film of a mixed crystal III-V group compound, said starting materials including a respective starting material for supplying the atoms of each of the respective groups III and V constituents of the mixed crystal III-V group compound.

Inventors: TOKUNAGA HIROYUKI, YONEHARA TAKAO, TOKUNAGA, HIROYUKI, YONEHARA, TAKAO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: H01L21
IPC codes: C30B29, C30B25, H01L21