US20010012677A1 - Semiconductor element forming process having a step of separating film structure from substrate - Google Patents

Abstract

The present invention is aimed at providing a process of forming a transistor of excellent properties and its circuit on a substrate of a low heat resistance in simple steps at a low treatment temperature and with high precision. According to an aspect of the invention, there is provided a process of forming a semiconductor device, comprising the steps of forming a separation layer on a support substrate, forming, on the separation layer, a film structure consisting of a single layer or plural layers, and separating the film structure from the support substrate by removing the separation layer. According to another aspect of the invention, there is provided a process of transferring a film structure which consists of a single layer or plural layers, comprising the steps of forming a separation layer on a first substrate, forming, on the separation layer, a film structure which consists of a single layer or plural layers, adhering a second substrate to the film structure, and separating the first substrate from the film structure. The film structure includes therein a semiconductor element such as a thin film transistor, a MOSFET, a bipolar transistor, a solar battery, etc., or an integrated circuit consisting of a plurality of such active elements. When air gaps are formed in the separation layer, the layer facilitates the separation of the first substrate from the film structure.

Description

BACKGROUND OF THE INVENTION
• This invention relates to a process of manufacturing a semiconductor device, and more particularly to a process of manufacturing a semiconductor element or circuit using a transfer technique.[0001]
• Bipolar transistors and MOS transistors formed on monocrystalline silicon surfaces show excellent electric characteristics and hence are used to constitute various types of electronic devices. Further, an SOI technique for forming a transistor on a thin silicon film, which film is formed on a silicon substrate with an insulating film interposed therebetween, has recently been developed to meet, for example, a demand for reduction of element size. In this technique, thermal oxidation, thermal diffusion, etc. are employed to form semiconductor elements. These heat treatments are usually performed at about 1000° C.[0002]
• On the other hand, semiconductor layers have come to be formed at a relatively low temperature by plasma CVD, laser crystallization, etc., on which layers are formed polycrystalline silicon thin film transistors or amorphous silicon thin film transistors.[0003]
• At the present stage, there is a demand for application of the thin film transistors to a driving circuit incorporated in a wide-screen direct viewing display. To meet this demand, it is necessary to establish a big-scale substrate treatment technique.[0004]
• The aforementioned process technique for forming silicon transistors is based on a heat treatment technique using a high temperature of about 1000° C. Therefore, a transistor of excellent electric characteristics, for example, cannot be formed on a semiconductor thin film provided on a substrate of a low heat resistance.[0005]
• Although reduction of the process temperature has been realized by new techniques such as plasma CVD, laser crystallization, etc., it is still necessary, even in the case of using the new techniques, to set the process temperature at 300° C. or more in order to form an element of excellent electric characteristics. Thus, it is difficult to directly form a transistor circuit on a non-heat-resistive substrate formed of, for example, plastic. In addition, in the case of directly forming transistor circuits on a large scale substrate, a large process apparatus is necessary, the precision of the process apparatus may well degrade, and produced transistor circuits will be expensive.[0006]
BRIEF SUMMARY OF THE INVENTION
• The present invention has been developed to solve the above problems, and is aimed at providing a process of forming a transistor circuit of excellent properties on a substrate of a low heat resistance, and realizing a large scale device.[0007]
• The aim can be attained by the step of separating a film structure which consists of a single layer or plural layers and is necessary to form a transistor circuit, from a substrate which supports the film structure. If necessary, the film structure is adhered to another substrate of a low heat resistance. To this end, the invention employs a separation layer interposed between the film structure and the substrate supporting it.[0008]
• In the process, according to the invention, of forming the film structure which consists of the single layer or plural layers and is necessary to form the transistor circuit, a separation layer is interposed beforehand between the substrate and the film structure. After a transistor circuit, for example, is formed in the film structure by a high temperature treatment, the separation layer is removed by etching to separate the film structure from the support substrate.[0009]
• In this case, the removal of the separation layer is more facilitated by forming air gaps in at least a portion of the layer.[0010]
• In addition, in the invention, the step of separating the film structure from the support substrate by removing the separation layer can be performed during or after the formation of a desired semiconductor device in the film structure.[0011]
• The semiconductor device circuit produced by the process of the invention is, for example, a circuit which consists of one or more thin film transistors, one or more MOSFETs, or one or more bipolar transistors, a circuit using a solar battery, or an integrated circuit consisting of a plurality of such active elements. It is a matter of course that the semiconductor device circuit is not limited to the above.[0012]
• Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.[0013]
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
• The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.[0014]
• FIGS.[0015]1A-1C are views, useful in explaining the basic idea of the invention that a film structure consisting of a single or plural layers is separated from a substrate;
• FIGS.[0016]2A-2C are views, useful in explaining a case where when a film structure consisting of a single or plural layers is separated from a substrate, another substrate for supporting the film structure is used;
• FIGS.[0017]3A-3C are views, showing a case where a metal oxide semiconductor (MOS) field effect transistor (FET) is transferred to another substrate;
• FIGS.[0018]4A-4C are views, useful in explaining process steps of forming a gate electrode, an insulating film, a silicon film, a doped layer and an interlayer insulating film, then performing a transfer according to the invention, and forming metal wires to provide a semiconductor device circuit;
• FIGS.[0019]5A-5C are views, useful in explaining a manner of forming an amorphous silicon TFT circuit and transferring the circuit;
• FIGS.[0020]6A-6C are views, useful in explaining a manner of forming a solar battery element and transferring the element;
• FIG. 7 is a view, showing a manner of forming wiring between TFTs after the transfer;[0021]
• FIG. 8 is a view, useful in explaining a manner of transferring a transistor circuit formed on a small substrate onto a larger substrate;[0022]
• FIG. 9 is a view, useful in explaining a manner of transferring a transistor circuit formed on a large substrate onto a smaller substrate;[0023]
• FIGS.[0024]10A-10F are views, useful in explaining a manner of forming a separation layer with gaps defined therein;
• FIG. 11 is a view, illustrating a manner of removing an organic material using a solvent;[0025]
• FIG. 12 is a view, illustrating a manner of introducing a sample into a vacuum container, exhausting air gaps formed in the sample using a vacuum force, and etching the resultant sample by an etching solvent; and[0026]
• FIG. 13 is a view, illustrating a manner of removing part of a film structure provided on a separation layer with air gaps, and then removing the separation layer.[0027]
DETAILED DESCRIPTION OF THE INVENTION
• The embodiments of the invention will be described with reference to the accompanying drawings.[0028]
• FIGS.[0029]1A-1C illustrate the basic idea of the invention. As shown in these figures, aseparation layer20 is formed on asubstrate10 made of a semiconductor material such as silicon, silicon nitride, quartz or ceramic, or of a heat resistive insulating material. Then, afilm structure30 is formed on theseparation layer20. Thefilm structure30 consists of a single or plural layers which include a semiconductor layer necessary for forming a predetermined circuit and made of silicon, or a II-VI group or III-V group compound semiconductor.
• Preferably, the separation layer is made of a material which is stable at a heat treatment temperature for forming a semiconductor element in the semiconductor layer, desirably at 1000-[0030]1100° C., and which will not adversely affect the semiconductor layer or the semiconductor element formed therein even at that temperature. Specifically, the separation layer is made of a metallic material such as chrome, nickel, tantalum, tungsten, etc. or of an insulating material such as alumina, silicon nitride, silicon dioxide, etc. or of InZnO.
• It is necessary to set the thickness of the separation layer at least 200 nm or more in light of etching of the separation layer performed layer. In view of the necessity to reduce the thermal strain between the[0031]substrate material10 and thefilm structure material30, or of the time necessary to form the separation layer, the thickness of the separation layer is desirably set at 20000 nm or less, and more desirable at about 1000-10000 nm. The separation layer is formed by vacuum deposition employed in a usual semiconductor manufacturing process, vapor phase epitaxy, sputtering, etc.
• After that, a semiconductor element such as a solar battery, a diode, a transistor, etc. is formed in the semiconductor layer of the[0032]film structure30 in a predetermined semiconductor treatment step such as a usual diffusion step or an ion implant step. Instead of the single semiconductor element, plural semi-conductor elements connected to each other by metal wires may be formed as an integrated circuit. At this stage, the step of forming the semiconductor element is not necessarily completed, but at least a high temperature treatment must be finished.
• Thereafter, the separation layer is removed by, for example, etching as shown in FIG. 1B, to thereby separate from the[0033]substrate10 thefilm structure30 consisting of a single or plural layers. The separation layer is etched using an etching solution containing phosphoric acid as a main component when the separation layer is made of alumina, silicon nitride, etc., using an etching solution containing fluoric acid when it is made of silicon dioxide, and using hydrochloric acid when it is made of InZnO.
• If the[0034]film structure30 consisting of a single or plural layers has a sufficient mechanical strength and does not need any other physical support, it can be used, after separation, as a separate semiconductor element or a circuit device including semiconductor elements.
• On the other hand, if the[0035]film structure30 is separated during the process step, a process step of forming a semiconductor element, a circuit device using the semiconductor element, or metallic wiring is carried out immediately after the first-mentioned step.
• Moreover, the[0036]substrate10 obtained after the separation of thefilm structure30 can be used again as a support substrate by forming thereon a single or plural layers necessary for forming a semiconductor element or circuit, as is shown in FIG. 1C.
• FIGS.[0037]2A-2C show another embodiment using asupport substrate40 which differs from thesubstrate10. As is shown in FIG. 2A, first, theseparation layer20 is formed on thesubstrate10, and then afilm structure30 consisting of a single or plural layers necessary for forming a predetermined semiconductor circuit is formed on theseparation layer20.
• After the formation of the predetermined semiconductor circuit, another[0038]substrate40 is adhered to thefilm structure30 by an appropriate adhesive. Different from thesubstrate10, thesubstrate40 does not require stability at a high temperature. Accordingly, thesubstrate40 can be made of a cheap organic material such as plastic.
• Referring to FIG. 2C, the[0039]separation layer20 is removed by e.g. etching, thereby to separate, from thesubstrate10, thefilm structure30 consisting of a single or plural layers. Thus, the step of transferring the film structure to thesubstrate40 is completed.
• FIGS.[0040]3A-3C are views, useful in explaining a specific example of transfer, in which a transistor element and an integrated circuit using the transistor element are transferred. More specifically, these figures show an example of transfer, in which a metal oxide semiconductor (MOS) field effect transistor (FET) is transferred.
• First, a[0041]separation layer20 is formed on asubstrate10. In the next MOSFET forming step, acrystalline silicon film50 is formed. Agate insulating film60 is formed on thefilm50. Thereafter, a mask with a predetermined pattern is formed, thereby forming source and drainregions70 and72, which consist of doped silicon layers, by ion implant, diffusion, etc. Then, interlayer insulatingfilms90 and92 are formed, and contact holes are formed therein, thereby forming source, gate and drainelectrodes80,82 and84. Further, anoxide film94 is provided for passivation. Preferably, thecrystalline silicon film50 has a thickness of 1000-5000 nm. The electrode metal has a thickness of 10-2000 nm, and desirably of 100-1000 nm. If necessary,metal wires100 and102 can be provided which connect transistors incorporated in the integrated circuit or connect the integrated circuit to an external circuit. FIG. 3A schematically shows that cross section of the substrate, which is obtained after theseparation layer20 and thecrystalline silicon film50 are formed on thesubstrate10, thereby finishing the step of forming a MOSFET, wiring therein, etc.
• High temperature treatments of 1000° C. are used to form the[0042]crystalline silicon film50 for forming a MOSFET, to form a gate insulating film, and to activate an impurity for forming a doped silicon region. These high temperature treatments can be performed by forming thesubstrate10 of a material, such as quartz, which can stand 1000° C. or more.
• Furthermore, in the above-described MOSFET manufacturing process, the properties of the[0043]crystalline silicon layer50 can be improved using laser crystallization, laser activation, etc., and the time required for the manufacture of the MOSFET can be reduced, as compared with the high temperature treatment, using a technique for performing a treatment at a relatively low temperature, such as plasma CVD.
• Then, as shown in FIG. 3B, the[0044]substrate40 is adhered to the structure in which the transistor circuit is formed. After that, theseparation layer20 is removed and the transistor circuit is transferred to thesubstrate40, as is shown in FIG. 3C.
• The[0045]substrate40 is used only to support the transistor circuit formed in the above step, and hence it is not necessary to consider the influence on it of the high temperature treatment performed during the manufacture of the transistor circuit. Accordingly, although a technique using a high treatment temperature is employed to manufacture the transistor, thesubstrate40 may be formed of a cheap material with a low heat resistance, e.g. a plastic material such as an epoxy resin, polyimide, polycarbonate, etc.
• The process of the invention enables the formation of a semiconductor element with excellent properties and its circuit, on a substrate formed of a cheap material with a relatively low heat resistance. The element and its circuit are produced by a high temperature process.[0046]
• FIGS.[0047]4A-4C show another embodiment. After aseparation layer20 and asilicon layer50 are formed on asubstrate10, agate insulating film60, dopedlayers70 and72, agate electrode82 and an insulatingfilm90 are formed as shown in FIG. 4A. Subsequently, anothersubstrate40 is adhered to the film structure as shown in FIG. 4B, thereby performing the transfer of the invention. After that, a necessary insulating film andmetal wires80,84,100 and102 may be formed as shown in FIG. 4C. In this case, the side walls of contact holes for connection to electrodes are insulated, if necessary. Also in the case of using an element other than the MOSFET, the transfer process of the invention can be used.
• FIGS.[0048]5A-5C show an embodiment in which an amorphous silicon TFT circuit is produced and transferred. A metal layer is formed by, for example, sputtering on aseparation layer210 provided on asubstrate200, and is patterned into agate electrode220 by, for example, etching. The metal electrode has a thickness of 10-2000 nm, and more preferably, 100-1000 nm. Subsequently, asilicon nitride film230 and anamorphous silicon film240 which serve as gate insulating films are formed by e.g. plasma CVD. The silicon nitride film has a thickness of 50-2000 nm, and more preferably, 100-1000 nm. The amorphous silicon film has a thickness of 10-1000 nm, and more preferably, 20-500 nm. After the formation of theamorphous silicon film240, an impurity-dopedamorphous silicon film250 with a thickness of 50-200 nm is formed by e.g. plasma CVD. After that, that portion of the impurity-doped layer which corresponds to a channel is removed by etching to thereby form source and drain regions.
• Thereafter, there are provided source and drain[0049]electrodes260 and270,interlayer insulating films280 and290, apassivation film291, andmetal wires292 and293 for connecting transistors to each other or connecting the transistors to an external circuit. FIG. 5A shows a state in which all the above-described steps are finished and the amorphous silicon TFT circuit is completed on thesubstrate200.
• As is shown in FIGS. 5B and 5C, the amorphous TFT and its circuit are transferred to a[0050]new substrate294 by removing the separation layer. Thesupport substrate200 used to produce a film structure which includes the to-be-separated semiconductor element can be used again as the next substrate.
• FIGS.[0051]6A-6C show another embodiment in which a solar battery element is formed. In this case, a solar battery element is formed on aseparation layer310 provided on asubstrate300. To form an amorphous silicon solar battery, alower electrode320 is formed by e.g. sputtering, with an appropriate electrode protectlayer315 provided on theseparation layer310, and then a semiconductor p-type impurity layer330 with a high concentration, a non-doped semiconductor layer340 and a semiconductor n-type impurity layer350 are formed in this order by e.g. plasma CVD. It is preferable that the p-type highly concentrated impurity layer, the non-doped semiconductor layer and the n-type impurity layer have thicknesses of 10-1000 nm, 100-5000 nm and 10-100 nm, respectively.
• After that, an[0052]upper electrode360 is formed, and a light receiving region is defined by removing, by e.g. etching, an outside area of the semiconductor layer of the solar battery element. Moreover, apassivation layer370 andmetal wires380 to be connected to an external circuit or other circuit elements (not shown) are formed to thereby constitute a circuit. Thus, an amorphous silicon solar battery element is provided.
• On the other hand, when a crystalline silicon solar battery is formed by the process of the invention, a three-layer structure solar battery is provided using, for example, a p-type highly concentrated impurity layer, a p-type semiconductor layer and an n-type impurity layer in place of the[0053]amorphous layers330,340 and350. Each semiconductor film is formed by e.g. plasma CVD, and then subjected to a necessary crystallization treatment. The p-type highly concentrated impurity layer is formed by solid phase crystallization or fusion hardening of a doped semiconductor film. Impurity thermal diffusion is also applicable to increase the impurity concentration. The p-type semiconductor layer is formed by solid phase crystallization or fusion hardening of a semiconductor film. The n-type impurity layer is formed by implanting ions into a semiconductor film or thermally diffusing impurity in the film. It is preferable that the p-type highly concentrated impurity layer, the p-type semiconductor layer and the n-type impurity layer have thicknesses of 10-100 nm, 1000-50000 nm and 10-100 nm, respectively.
• The solar battery and its circuit are adhered to a[0054]new substrate390 as shown in FIG. 6B, and then transferred thereto by removing the separation layer as shown in FIG. 6C.
• Since the structure of the element and its circuit transferred to a new substrate is inverted with respect to the original one, the original one must be designed in consideration of the inverted one. For example, if in the case of transferring the MOSFET shown in FIGS.[0055]3A-3C, a top-gate TFT is formed first, it becomes a bottom-gate TFT after the transfer. In light of this, if a top-gate TFT is necessary after the transfer, a bottom gate TFT as shown in FIGS.5A-5C is first manufactured and then transferred.
• To connect TFTs after the transfer, a[0056]contact portion400 for wiring is provided as shown in FIG. 7, thereby forming first a contact hole and then the wiring.
• Another embodiment of the invention is illustrated in FIG. 8. A[0057]film structure510 which includes a semiconductor layer provided with a transistor circuit is formed on asubstrate505 beforehand, with aseparation layer504 interposed therebetween. Thefilm structure510 is transferred to alarger substrate520. This process enables elimination of the conventional difficulty in very fine patterning on a large substrate. As a result, a fine semiconductor element with excellent properties and its circuit can be formed on a verylarge substrate520.
• Further, as is shown in FIG. 9, the invention enables simultaneous formation of fine semiconductor elements or circuits with excellent properties on multiple[0058]fine substrates540 by transferring, to thefine substrates540,layers530 including transistor circuits and formed on asubstrate531 with aseparation layer532 interposed therebetween.
• The semiconductor element forming process of the invention is not limited to the embodiments illustrated in FIGS.[0059]1A-9, but may be modified without departing from the technical scope of the invention.
• Although in the embodiment shown in FIGS.[0060]3A-3C, for example, the semiconductor element and its circuit are specifically a MOSFET and its circuit, the semiconductor can be an amorphous silicon TFT shown in FIGS.5A-5C, a solar battery element shown in FIGS.6A-6C, a bipolar element, an amorphous image sensor, etc.
• Although in the embodiments illustrated in FIGS.[0061]3A-7, transfer is performed after the completion of at least the transistor element, it can be performed even during the manufacture of the element.
• FIG. 1 illustrates a removal process using etching, as a process for removing the separation layer. In this case, a[0062]film structure30 consisting of a single layer or plural layers is separated from asubstrate10 by decomposing the separation layer using a solution or a gas for dissolving the separation layer.
• FIGS.[0063]10A-10F illustrate a process of forming a separation layer withair gaps635 using a lithography technique. As shown in FIG. 10A, first, afilm600 constituting the separation layer is formed on asubstrate610. Thefilm600 is formed of chrome in this embodiment, but is not limited to it. It may be made of any other material suitable for carrying out the invention, i.e. a metallic material such as nickel, tantalum, tungsten, etc., of an insulating material such as alumina, silicon nitride, silicon dioxide, etc. or of InZnO. Theseparation layer600 may be formed by CVD, sputtering, or any other optimal method.
• Next, portions of the[0064]film600 are removed by lithography or etching as shown in FIG. 10B. Then, the resultant structure is coated with a material620 which is highly soluble in an organic solvent such as a high polymer material, as is shown in FIGS. 10C and 10D. Thematerial620 is removed and flattened from its surface by dry etching or polishing until thefilm600 is exposed.
• Thereafter, as shown in FIG. 10E, a[0065]film630 for protecting the flattened surface is formed by a treatment of a low temperature such as ECR plasma CVD, sputtering, etc. Thefilm630 is formed of silicon oxide in this embodiment, but is not limited to it. It may be made of any other material suitable for carrying out the invention.
• After the formation of the[0066]film630, thematerial620 is removed using a solvent, thereby forming aseparation layer structure640 withair gaps635 as shown in FIG. 10F. To remove thematerial620 using the solvent, to soak the sample in asolvent solution650 is an easy method. Thematerial620 can be removed more effectively by heating the solvent solution to enhance its solvency power, or by evaporating the solvent into a highly reactive vapor.
• To remove the[0067]separation layer600, an etching solvent which can dissolve thelayer600 but not thefilm630 is used. Since theseparation layer600 has the air gaps, the etching solvent can easily enter thelayer600 to remove it.
• To cause the etching solution to effectively enter the separation layer so as to separate a[0068]film structure690, the sample is contained in avacuum container660, then air in the air gaps of the separation layer is exhausted byvacuum exhaustion670, and anetching solvent680 is introduced into thecontainer650, as is illustrated in FIG. 12. Since the pressure in the air gaps is reduced, the etching solvent quickly enters the air gaps, dissolves theseparation layer600, and separates, from thesubstrate610, the film structure consisting of a single layer or plural layers.
• To more effectively remove the separation layer, the[0069]film structure690 with the air gaps on the separation layer may be partially removed so that no semiconductor element or circuit will be influenced by the removal, thereby accelerating the function of the etching solvent for removing the separation layer.
• A technique for forming a film with air gaps using sputtering is known from, for example, J. Electrochem. Soc., 131(1984), pp. 2105-2109 written by T. Serikawa and T. Yachi. According to this publication, an SiO[0070]₂film with air gaps can be formed by sputtering in the atmosphere of Ar gas. Since this film can be etched at a very high speed, it can be used as the separation layer employed in the invention.
• Moreover, plasma chemical phase reaction or evaporation reaction enables formation of a film with[0071]air gaps635 by applying high gas pressure to at least portions of a film during its formation to enhance chemical phase reaction and contain fine particles in the film. The resultant film can be etched at a very high speed and hence be used as the separation layer of the invention.
• The process of forming a semiconductor element according to the invention can produce, in a simple manner, a device of a large area which includes semiconductor elements of excellent properties and their circuits. In addition, the process enables formation of a semiconductor element of excellent properties and its circuit on a substrate made of a material with a low heat resistance, such as glass, plastic, etc.[0072]
• Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.[0073]

Claims (20)

1. A process of forming a semiconductor element, comprising the steps of:

forming a separation layer on a support substrate;

forming, on the separation layer, a film structure consisting of a single layer or plural layers; and

separating the film structure from the support substrate by removing the separation layer.

2. A process according to

claim 1

, wherein the step of separating the film structure from the support substrate includes the step of removing the separation layer by etching.

3. A process according to

claim 1

, wherein the step of forming the film structure includes the step of forming a transistor in a portion of the film structure consisting of the single layer or the plural layers.

4. A process according to

claim 1

, wherein the step of forming the film structure includes the step of forming a solar battery in a portion of the film structure consisting of the single layer or the plural layers.

5. A process according to

claim 1

, wherein the step of forming the film structure includes the step of forming air gaps in at least part of the separation layer.

6. A process according to

claim 5

, wherein the step of forming air gaps includes the step of removing part of the separation layer by lithography and etching.

7. A process according to

claim 1

, wherein the step of forming the separation layer uses sputtering.

8. A process according to

claim 1

, wherein the step of forming the separation layer uses plasma chemical phase reaction.

9. A process according to

claim 1

, wherein the step of forming the separation layer uses evaporation.

10. A process according to

claim 1

, wherein after the film structure consisting of the single layer or plural layers is separated from the support substrate, the support substrate is reused to support another film structure consisting of a single layer or plural layers.

11. A process of transferring a film structure which consists of a single layer or plural layers, comprising the steps of:

forming a separation layer on a first substrate;

forming, on the separation layer, a film structure which consists of a single layer or plural layers;

adhering a second substrate to the film structure; and

separating the first substrate from the film structure.

12. A process according to

claim 11

, wherein the step of separating the first substrate from the film structure includes the step of removing the separation layer by etching.

13. A process according to

claim 11

, wherein the film structure consisting of the single layer or plural layers includes a semiconductor layer.

14. A process according to

claim 11

, wherein the step of forming the film structure includes the step of forming a transistor in the film structure.

15. A process according to

claim 11

, wherein the step of forming the film structure includes the step of forming a solar battery in the film structure.

16. A process according to

claim 11

, wherein the step of forming the film structure includes the step of forming, in the film structure, an integral circuit which includes plural transistors and internal wiring.

17. A process according to

claim 11

, wherein the step of forming the film structure includes the step of forming air gaps in at least part of the separation layer.

18. A process according to

claim 17

, wherein the step of forming air gaps includes the step of removing part of the separation layer by lithography and etching.

19. A process according to

claim 11

, wherein the step of forming the separation layer uses sputtering.

20. A process according to

claim 11

, wherein the step of forming the separation layer uses plasma chemical phase reaction.

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