Semiconductor device

Abstract: A semiconductor device has an insulated gate transistor in which source and drain regions are provided in a single crystal semiconductor layer formed on an insulating layer with a channel region interposed between the source and drain regions. An insulating layers just below the source and drain regions are made thicker than an insulating layer just below the channel region.

Description: The present invention relates to a semiconductor device, more particularly a semiconductor device including an insulated gate transistor. In recent years, semiconductor devices have become key devices for increasing performance of imaging devices such as image sensors and image displays. As one example of semiconductor devices effective in improving a performance level, there is a transistor of the type that a semiconductor thin film on an insulating layer is used as an active region. Forming single crystal Si as a semiconductor thin film on an insulating layer is widely known as a Silicon-On-Insulator (SOI) technique. A lot of studies have been focused on the SOI technique because devices utilizing it have many superior points which cannot be attained by bulk Si substrates used to manufacture ordinary Si integrated circuits. The SOI technique is practiced by, for instance, a method of condensing and irradiating an energy beam, such as an electron ray and a laser beam, onto an amorphous or polycrystal Si layer and growing a single crystal layer on SiO 2 by recrystallization through melt, or a method of forming an SiO 2 layer in a single crystal Si substrate by ion implantation of oxygen (called a SIMOX (Separation by Ion Implanted Oxygen) process). Such a structure that a semiconductor thin film is formed on an insulating layer by using the SOI technique to suppress a short channel effect is proposed in, for instance, "Manufacture of very thin-film MOSFET/SIMOX with gate length of 0.15 µm and its characteristics", 1991 Autumn Congress of Japanese Electron Information Communication Society, SC-9-3. This paper describes that thinning the Si layer is effective in suppression of a short channel region effect and thinning a buried oxide film below the channel region is effective in suppression of a short channel effect upon the threshold voltage. It is also described that thinning the buried oxide film raises a problem of increasing parasitic capacity associated with source and drain regions. Furthermore, a double gate MOS has recently been also developed which includes a second gate on the side opposite to a semiconductor layer, where source and drain regions are formed, and a usual gate with insulating layer therebetween. Fig. 1 shows one example of such a double gate MOS. Denoted by reference numeral 61 is a substrate, 62 to 62" are insulating layers, 63 is a second gate, 64 is a source region, and 65 is a drain region. A source electrode 67 and a drain electrode 68 are connected to the source region 64 and the drain region 65, respectively. A portion 66 sandwiched between the source region 64 and the drain region 65 is a channel portion, and 69 denotes a first gate for controlling the channel portion. It is known that the double gate MOS have advantages of improving a short channel effect and increasing a current driving force. Apart from that, it is acknowledged that document JP-A-56 029 369 discloses an IGFET having an insulating layer, wherein a portion thereof under the source and drain region is thick and a portion under the channel between said regions is thin. Further, a thin gate insulating layer is deposited on these regions. Furthermore, document JP-A-61 125 163 discloses a semiconductor device in which an oxide film for isolating elements is formed in an element isolation region, and a lower layer MOS-transistor consisting of a gate oxide film, a gate electrode and source-drain regions is shaped in an element forming region. Also, an inter-layer insulating film is deposited on the whole surface and the surface is flattened. Moreover, document EP-A-0 063 915 discloses a metal insulator semiconductor (MIS) transistor which is built on an insulating layer being arranged with a thin portion under the channel region of the MIS-transistor and a thick portion under the remainder of the device. It is an object of the present invention to provide a semiconductor device having superior performance and high reliability. This object is solved according to what is defined by the appended independent claim. Fig. 1 is a schematic sectional view showing one example of a conventional semiconductor device. Fig. 2 is a sectional view for explaining the construction of an N-type MOS transistor according to a explanatory example. Fig. 3 is a view showing one of successive steps for manufacture of the N-type MOS transistor according to the explanatory example. Fig. 4 is a view showing one of successive steps for manufacture of the N-type MOS transistor according to the explanatory example. Fig. 5 is a view showing one of successive steps for manufacture of the N-type MOS transistor according to the explanatory example. Fig. 6 is a view showing one of successive steps for manufacture of the N-type MOS transistor according to the explanatory example. Fig. 7 is a view showing one of successive steps for manufacture of the N-type MOS transistor according to the explanatory example. Fig. 8 is a view showing one of successive steps for manufacture of the N-type MOS transistor according to the explanatory example. Fig. 9 is a view showing one of successive steps for manufacture of the N-type MOS transistor according to the explanatory example. Fig. 10 is a sectional view for explaining the construction of an N-type MOS transistor according to an embodiment of the present invention. Prior to describing semiconductor devices according to a preferred embodiment of the present invention, a description will first be given to a method of manufacturing a single crystal semiconductor thin film which is desirable to obtain those semiconductor devices, taking Si as an example. A single crystal Si layer is formed by using a porous Si substrate which is obtained by changing a single crystal Si substrate into porous Si. A transmission electron-microscopic observation shows that the porous Si substrate has micro-pores of about 60 µm (600 Å) in mean diameter.. Also, while the porous Si substrate has density less than a half that of the single crystal Si substrate, single crystallinity is still maintained and a single crystal Si layer can be formed on the porous layer through epitaxial growth. At a temperature not lower than 100°C, however, internal micro-pores are rearranged to impair a characteristic of enhanced etching. For this reason, a low-temperature method such as a molecular beam epitaxial growth process, plasma CVD process, thermal CVD process, optical CVD process, bias-sputtering process, crystal growth process, etc. is suitable for epitaxial growth of the Si layer. A description will now be given of a method of effecting epitaxial growth of a single crystal layer after changing P-type Si into porous Si. A single crystal Si substrate is prepared and then changed into porous Si by an anodization process using an HF solution. While single crystal Si has density of 2.33 g/cm 3 , the density of porous Si can be varied in the range of 0.6 to 1.1 g/cm 3 when the content of the HF solution is varied between 20 and 50 weight %. The porous Si layer tends to be easily formed on a P-type Si substrate from the following reason. Porous Si was discovered in the course of studies of electrolytic grinding of semiconductors. In a dissolving reaction of Si during anodization, holes are required for an anodic reaction of Si in an HF solution and the anodic reaction is expressed as follows; Si + 2HF + (2 - n)e + → SiF 2 + 2H + + ne - SiF 2 + 2HF → SiF 4 + H 2 SiF 4 + 2HF → H 2 SiF 6 or Si + 4HF + (4 - λ)e + → SiF 4 + 4H + + λe - SiF 4 + 2HF → H 2 SiF 6 where e + and e - respectively represent a hole and an electron, and n and λ each represent the number of holes necessary for one Si atom to dissolve. It is reported that porous Si is formed on condition of n > 2 or λ > 4. This means that P-type Si including holes is more easy to change into porous Si. It is, on the other hand, reported that high density N-type Si can also be changed into porous Si. Accordingly, single crystal Si can be changed into porous Si regardless of whether it is P-type or N-type. Further, a porous layer has a great number of voids formed therein and its density is as small as half or below that of the non-porous structure. As a result, the porous structure has a much increased surface area per unit volume and, therefore, a porous layer exhibits a much greater chemical etching rate than an ordinary single crystal layer. Porous Si is formed by anodization of single crystal Si under the following conditions. Note that the starting material of porous Si formed by anodization, however, is not limited to single crystal Si. Namely, it is possible to employ Si of other types of crystalline structures. Voltage applied 2.6 (V) Current density 30 (mA·cm -2 ) Anodizing solution HF : H 2 O : C 2 H 5 OH = 1 : 1 : 1 Time 2.4 (hours) Thickness of porous Si 300 (µm) Porosity 56 (%) A single crystal Si thin film is formed through epitaxial growth on the porous Si substrate formed by the above anodization. A thickness of the single crystal Si thin film is preferably not larger than 50 µm, more preferably not larger than 20 µm. Then, after oxidizing the surface of the single crystal Si thin film, a substrate which will become a substrate of the final device is prepared and the oxide film on the single crystal Si surface is bonded to the substrate. As an alternative, the surface of a single crystal Si substrate, newly prepared, is oxidized and then bonded to the single crystal Si layer on the porous Si substrate. The reason why the oxide film is provided between the substrate and the single crystal Si layer is below. In the case of using glass as a substrate, for instance, the interface level produced by the underlying interface of an Si active layer is lower for the glass interface than for the oxide film interface and, therefore, characteristics of an electronic device can be improved remarkably. As another alternative, it is also possible to etch away the porous Si substrate by selective etching later described, and bond only the remaining single crystal Si thin film to a new substrate. Just by contacting the single crystal Si thin film and the substrate room temperature after cleaning their surfaces, both the members adhere closely to each other by van der Waals' forces to such an extent that they cannot be easily separated. In addition, thereafter, both the members are completely bonded to each other by heat treatment under a nitrogen atmosphere at temperature in the range of 200 to 900°C, preferably 600 to 900°C. Subsequently, an Si 3 N 4 layer is deposited as an etching prevention layer all over the two substrates bonded to each other, followed by removing only the Si 3 N 4 layer which is located on the surface of the porous Si substrate. Apiezon wax may be used instead of the Si 3 N 4 layer. After that, the porous Si substrate is totally removed by etching or any other suitable means, thereby providing a semiconductor substrate with the thin film single crystal Si layer. A description will now be given to a selective etching process for removing only the porous Si substrate by non-electrolytic, wet etching. Preferable examples of an etchant, which has no etching action upon crystal Si but enables selective etching of porous Si alone, are hydrofluoric acid, buffered hydrofluoric acid such as ammonium fluoride (NH 4 F) or hydrogen fluoride (HF), a mixture of hydrofluoric acid or buffered hydrofluoric acid added with an aqueous solution of hydrogen peroxide, a mixture of hydrofluoric acid or buffered hydrofluoric acid added with alcohol, and a mixture of hydrofluoric acid or buffered hydrofluoric acid added with an aqueous solution of hydrogen peroxide and alcohol. Etching is made by immersing the bonded substrates in any of those solutions for etching. An etching rate depends on the content and the temperature of hydrofluoric acid, buffered hydrofluoric acid, and the aqueous solution of hydrogen peroxide. By virtue of adding the aqueous solution of hydrogen peroxide, the oxidation of Si can be accelerated so as to realize a greater reaction speed than the case where hydrogen peroxide is not added. Additionally, the reaction speed is controllable by varying the content of the aqueous solution of hydrogen peroxide. Also, by virtue of adding alcohol, voids of etching reaction product gases can be instantaneously removed from the etched surface without requiring agitation of the etchant, so that porous Si can be uniformly and efficiently etched. The HF content in the buffered hydrofluoric acid is set to be preferably in the range of 1 to 95 weight % for the etchant, more preferably 1 to 85 weight %, most preferably 1 to 70 weight %. The NH 4 F content in the buffered hydrofluoric acid is set to be preferably in the range of 1 to 95 weight % for the etchant, more preferably 5 to 90 weight %, most preferably 5 to 80 weight %. The HF content is set to be preferably in the range of 1 to 95 weight % for the etchant, more preferably 5 to 90 weight %, most preferably 5 to 80 weight %. The H 2 O 2 content is set to be preferably in the range of 1 to 95 weight % for the etchant, more preferably 5 to 90 weight %, most preferably 10 to 80 weight %, and also in the range where the effect of addition of hydrogen peroxide is maintained. The alcohol content is set to be preferably not larger than 80 weight % for the etchant, more preferably not larger than 60 weight %, most preferably not larger than 40 weight %, and also in the range where the effect of addition of alcohol is maintained. The temperature is set to be preferably in the range of 0 to 100°C, more preferably 5 to 80°C, most preferably 5 to 60°C. Alcohol used in the present process can be any suitable alcohol, such as ethylalcohol and isopropyl alcohol, which does not cause any problem from the view point of practical production process and with which the effect of addition of alcohol is expected. By making the single crystal Si thin film, obtained through the above process, subjected to ion implantation of O 2 or bonded to another Si wafer having an insulating film thereon, an insulating film can be obtained which has two single crystal Si thin films on both sides. In the case of the ion implantation process, the Si film thickness prior to the implantation is preferably in the range of 1 to 5 µm depending on purpose. O 2 ions are implanted with density of 5 x 10 17 to 5 x 10 18 cm -2 at acceleration energy of 200 keV, followed by heat treatment for several hours at temperature in the range of 1100 to 1200°C. As a result, there can be formed single crystal Si of 200 to 400 µm (2000 to 4000 Å) on the outermost surface and an SiO 2 layer of 100 to 500 µm (1000 to 5000 Å) therebelow. In the case of the bonding process, the insulating film is formed to be 50 to 1000 µm (500 to 10000 Å) thick and, after bonding, Si on the outermost surface can be thinned to be 200 µm (2000 Å) to several µm thick by grinding. The former ion implantation process is preferably used in the present invention. A manufacture method for a semiconductor device is as follows. Thick selective oxide films are formed just below those regions on a first single crystal substrate which become source and drain regions, the first single crystal substrate is flattened, and then an oxide film is formed on the flattened. substrate surface, thereby fabricating a first substrate in which thick oxide films are formed in those regions going to locate just below the source and drain regions, and a thin oxide film is formed in that region going to locate just below a channel region. On the other hand, a non-porous single crystal Si layer with good crystallinity is formed on a second single crystal Si substrate which has been changed into porous Si and has a high etching rate, or an insulating layer is further formed on the non-porous single crystal Si layer, thereby fabricating a second substrate. After bonding the first and second substrates to each other, the second single crystal Si substrate which has been changed into porous Si is removed by treatment including at least wet chemical etching. Thus, a thin single crystal Si layer with good crystallinity and uniform film thickness is formed on the bonded insulating layer by a simple process. The source and drain regions are formed on the thick selective oxide films. Also, by forming a gate electrode on the above single crystal semiconductor layer, forming a selective oxide film in the region around the gate electrode, and flattening the formed selective oxide film and an oxide film on the gate electrode, a wiring pattern or the like can be formed on the flattened oxide film surface. Further, by bonding the flattened selective oxide film and oxide film on the gate electrode to the surface of a non-porous single crystal layer on a third single crystal Si substrate which has been changed into porous Si, or to an oxide film formed on the non-porous single crystal layer, and removing the third single crystal Si substrate which has been changed into porous Si by treatment including at least wet chemical etching so as to form a single crystal Si on the bonded oxide film, a laminated semiconductor device can be obtained which has an insulated gate field effect transistor in the underlying layer. In the case of forming a double gate MOS transistor as the semiconductor device, , a first gate is preferably formed to have a film thickness not smaller than 50 µm (500 Å), more preferably not smaller than 200 µm (2000 Å). If the film thickness is smaller than 50 µm (500 Å), there would be a fear of undesirable increase in the gate resistance value. In a liquid crystal display of the present invention, a film thickness of the first gate is preferably in the range of 50 to 1000 µm (500 to 10000 Å), more preferably in the range of 200 to 600 µm (2000 to 6000 Å). If the film thickness is not larger than 50 µm (500 Å), there would be a feat of undesirable increase in the gate resistance value. On the other hand, if it is too thick, there would arise difficulties in making pixel portions completely transparent. Additionally, the area ratio between first and second gates is not particularly limited. Taking into account characteristics as a double gate device, however, when the first and second gates are used in one-to-one relation, the area ratio of second to first gate is preferably in the range of 1/1 to 10/1. If the first gate is too small or the second gate is too large, there would cause undesirable problems in connection and alignment between the first and second gates, etc., which would complicate the manufacture process and lead to the increased production cost. Further, it is also possible to make one second gate shared by all NMOS transistors and the other second gate shared by all PMOS transistors for controlling two groups of NMOS and PMOS transistors at the same time per group. In this case, the first and second gates are not connected and controlled independently of each other, and no particular limitations are imposed on the area ratio of second to first electrode. (Explanatory Example) Fig. 2 is a sectional view for explaining the construction of an N-type MOS transistor according to an explanatory example. In Fig. 2, denoted by reference numeral 1 is a single crystal Si substrate, 2, 3, 4 are respectively a source region, a channel region and a drain region, 5, 6, 7 are oxide films just below the source region 2, the channel region 3 and the drain region 4, and 8 is a gate electrode. The oxide films 5, 7 are selective oxide films made flattened and are formed to have a larger thickness than the oxide film 6. In the MOS transistor having such a structure, since the oxide films 5, 7 are formed to be thick, parasitic capacity associated with the source and drain regions (i.e., parasitic capacity between the substrate and the source region and between the substrate and the drain region) can be suppressed. Further, since the oxide film 6 is formed to be thin, a short channel effect can also be suppressed. It should be noted that while the LOCOS (Local Oxidation of Silicon) process is used to form the thick insulating layers just below the source and drain regions in this example, it is not limited to the use of the LOCOS process. Alternatively, it is also possible to etch bulk Si and then bury insulating layers of SiON or the like in place. A description will now be given of the manufacture process for the N-type MOS transistor having the above-mentioned structure. The manufacture method for the N-type MOS transistor having the above-mentioned structure comprises the steps of forming a single crystal Si layer on the flattened oxide films which are thick just below only the source and drain regions, and forming a MOS transistor on the single crystal Si layer. Thus, the method is practiced on the basis of an SOI technique adapted to form the single crystal Si layer on the flattened insulator surface. Although the N-type MOS transistor having the above-mentioned structure may be manufactured by using any of existing SOI techniques, for instance, a method of condensing and irradiating an energy beam such as a laser beam and growing a single crystal layer on SiO 2 by recrystallization through melt, the single crystal Si layer with uniform layer thickness and good crystallinity can be formed on the insulator surface by using the above-explained manufacture method with bonding. Figs. 3 to 9 are a series of views showing successive steps for manufacture of the N-type MOS transistor according to this example. First, as shown in Fig. 3, a single crystal Si substrate is anodized under the following conditions to form a porous Si substrate 10: Voltage applied 2.6 (V) Current density 30 (mA·cm -2 ) Anodizing solution HF : H 2 O : C 2 H 5 OH = 1 : 1 : 1 Porosity 56 (%) Then, a non-porous single crystal Si layer 9 is formed through epitaxial growth on the surface of the porous Si substrate. A thickness of the single crystal Si layer 9 was set to 0.1 µm in one experimental example. The epitaxial growth is performed by any of such usual methods as a thermal CVD process, reduced-pressure CVD process, plasma CVD process, molecular beam epitaxial process, and sputtering process. On the other hand, as shown in Fig. 4, the selective oxide films 5, 7 being as thick as about 1 µm are formed on the surface of the single crystal Si substrate in those regions which are to locate just below the source and drain regions. The selective oxide films 5, 7 can be formed by patterning an Si 3 N 4 film on the surface of the single crystal. Si substrate in the region which are to locate just below the channel region with an oxide film interposed therebetween, and making it subjected to wet oxidation at 1000°C. Then, as shown in Figs. 5 and 6, the Si 3 N 4 film is removed and SOG (Spin On Glass) is coated on the surface, followed by flattening through reflow. After the flattening, SiO 2 is etched to form the flattened selective oxide films 5, 7. Subsequently, the surface is oxidized to form the oxide film 6 as thin as 20 µm (200 Å). Next, as shown in Fig. 7, the single crystal Si substrate 1 having the selective oxide films 5, 7 and the oxide film 6 and the porous Si substrate 10 having the non-porous single crystal Si layer 9 are brought into close contact after cleaning, and then fixedly bonded to each other by being heated under an atmosphere of oxygen, nitrogen, hydrogen, rare gas or the like. In the above, an oxide film may be formed on the single crystal Si layer 9. A certain interface level is possibly produced when fabricating a thin film device through the interface, but such an interface level can be reduced by forming the oxide film on the single crystal Si layer 9. Generally, the higher the temperature of the heat treatment, the stronger is bonding strength at the interface. This is attributable to that at the temperature not lower than about 200°C, both atoms of hydrogen and oxygen having been bonded to each other through the hydrogen bond are removed by dehydration in the form of H 2 O and the condensed silanol bond (Si-O-Si) is left to be formed. While the dehydrated H 2 O still remains near the interface in the form of voids or the like, the bonding strength does not yet reach the maximum level, and it is maximized when those voids are dispersed and vanished thoroughly. The bonding strength is saturated in that state and will no longer be intensified even by further increasing the temperature of the heat treatment. The temperature at which the bonding strength is saturated is about 1000°C. Therefore, the temperature of the heat treatment was set to about 1000°C in one experimental example. Then, as shown in Fig. 8, the porous Si substrate 10 is etched away by using an etchant below. An etchant which can selectively etch the porous Si substrate 10 alone without etching single crystal Si is given by a hydrofluoric acid-base etchant such as hydrofluoric acid and buffered hydrofluoric acid. By adding alcohol, such as methanol, ethanol, propanol and isopropanol, to the above etchant, voids of etching reaction product gases can be instantaneously removed from the etched surface without requiring agitation of the etched., so that porous Si can be uniformly and efficiently etched. Also, by adding an aqueous solution of hydrogen peroxide, the oxidation of Si can be accelerated so as to realize a greater reaction speed than the case where hydrogen peroxide is not added. Additionally, the reaction speed is controllable by varying the content of the aqueous solution of hydrogen peroxide. In one experimental example, the porous Si substrate 10 was subjected to selective etching using a mixture solution of 49% hydrofluoric acid, alcohol and a 30% aqueous solution of hydrogen peroxide (10 : 6 : 50) without agitating the etchant. The porous Si subtrate 10 was selectively etched and removed completely. The single crystal Si layer formed on the oxide film in that way had a uniform layer thickness. Thereafter, as shown in Fig. 9, the gate electrode 8 is formed through a gate insulating film. Then, impurity ions are implanted by using the gate electrode 8 as a mask and annealed to form the source and drain regions 2, 4. In the foregoing, the gate electrode 8 can be formed on the oxide film 6 with high accuracy by detecting the edges of the selective oxide films 5, 7 by an He-Ne laser from above and forming the gate electrode 8 with the detected edges being as reference. Alternatively, apart from the selective oxide films 5, 7, other selective oxide regions may be formed to serve as alignment marks. Thus, the N-type MOS transistor shown in Fig. 2 is manufactured. According to this example, a short channel effect can be suppressed by reducing the thickness of the single crystal Si layer and the thickness of the oxide film below the channel region. As a result, it is possible to manufacture a MOS transistor with a rule not larger than 1 µm. (Embodiment ) A description will now be given of an embodiment of the present invention with reference to Fig. 10. This embodiment is different from the above explanatory example in that the single crystal Si film is formed over the thick oxide films just below the source and drain regions and the thin oxide film just below the channel region with BPSG (Boron Phospharus Silicate Glass) 31 interposed therebetween. By adopting this structure, even when a difference in level is present between the LOCOS oxide films 5, 7 and the non-LOCOS oxide film 6, the interface between the single crystal Si layer 9 and those oxide films is surely flattened by virtue of the BPSG which has good reflow characteristics, with the result of good bonding characteristics. It should be noted that the intermediate layer may be formed of any other material than BPSG so long as it has superior reflow characteristics, and SOG or the like is also applicable. As fully described above, the semiconductor device of the present invention has superior performance and high reliability because it is more simply manufactured than conventional and is free from a fear of reduction in characteristics caused by connection wiring leads. In a liquid crystal display in which the present semiconductor device can be employed in a peripheral driver circuit, it is possible not only to cut down the production cost, but also to drive the'display at a higher power supply voltage than conventional and to increase the degree of freedom in voltage setting, making studies for higher image quality easily made from the viewpoint of circuit arrangement. For instance, a voltage margin necessary for obtaining display with finer gradations is enlarged and, therefore, an allowable maximum value of parasitic capacity in the pixel section is also increased. Also, the timings in driving of circuits and so forth required for the higher image quality can be combined in various manners. This means that the present semiconductor device has essential conditions for realizing a finer, high-quality display in future. Furthermore, the liquid crystal display in which the present semiconductor device may be employed in a peripheral driver circuit makes it possible, in addition to cut down of the production cost, to speed up the driver circuit and improve its driving characteristics by utilizing the peripheral driver circuit with superior characteristics.

Claims: A semiconductor device having an insulated gate transistor in which source and drain regions ( 2 , 4 ) are provided in a single crystal semiconductor layer ( 9 ) formed on an insulating layer ( 31 ) having reflow characteristics with a channel region interposed between said source and drain regions, wherein: a thick LOCOS oxide ( 5, 7 ) in a substrate ( 1 ) just below said source and drain regions is made thicker than a thin non LOCOS oxide ( 6 ) just below said channel region ( 3 ); a gate electrode ( 8 ) is formed above said channel region ( 3 ); wherein said insulating layer ( 31 ) has a smaller thickness just below said source and drain regions and a larger thickness just below said channel region; and the difference in level of said insulating layer ( 31 ), said thick LOCOS oxide ( 5,7 ) and said thin non LOCOS oxide ( 6 ) is so arranged that the interface between said insulating layer ( 31 ) and said single crystal semiconductor layer ( 9 ) is made substantially flat.

Inventors: INOUE SHUNSUKE, KOHCHI TETSUNOBU, MIYAWAKI MAMORU, INOUE, SHUNSUKE, KOHCHI, TETSUNOBU, MIYAWAKI, MAMORU
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: H01L21
IPC codes: H01L29, H01L27, H01L21