Patents by Inventor Natsuo Ajika

Natsuo Ajika has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Patent number: 5523596
    Abstract: A capacitor includes a polycrystalline silicon layer 1 as a lower electrode layer, a dielectric layer 112, and a polycrystalline silicon layer 113 as an upper electrode layer. The dielectric layer 112 is formed by an oxynitride film 2, a silicon nitride film 3 and a top oxide film 4. A film thickness t.sub.3 of the top oxide film 4 is controlled to be less than 20 .ANG.. Capacitance of the capacitor can be increased while improving the duration of life of the dielectric layer, resulting in a highly reliable capacitor.
    Type: Grant
    Filed: March 14, 1995
    Date of Patent: June 4, 1996
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Makoto Ohi, Hideaki Arima, Natsuo Ajika
  • Patent number: 5504376
    Abstract: In a method of manufacturing a stacked-type semiconductor device, firstly, a first semiconductor substrate having a first device formed thereon is covered with an interlayer insulating layer and a planarized polycrystalline silicon layer is formed on the interlayer insulating layer. The first semiconductor substrate and a second semiconductor substrate are joined together by putting the surface of the polycrystalline silicon layer in close contact with the surface of a refractory metal layer formed on the second semiconductor substrate, applying thermal treatment at 700.degree. C. or below and changing the refractory metal layer to silicide.
    Type: Grant
    Filed: April 4, 1994
    Date of Patent: April 2, 1996
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Kazuyuki Sugahara, Natsuo Ajika, Toshiaki Ogawa, Toshiaki Iwamatsu, Takashi Ipposhi
  • Patent number: 5489791
    Abstract: Disclosed is a semiconductor memory device in which defects in crystal in a junction region between a capacitor and a source/drain region, and a short channel effect of a transistor can be effectively reduced. The semiconductor memory device includes, on the side of a gate electrode at which the capacitor is connected, a sidewall formed to have a width larger than that of a sidewall on the side of a bit line, and a source/drain region to which the capacitor is connected and which is formed to have a diffusion depth larger than that of the opposite source/drain region. Therefore, the source/drain region effectively prevents defects in crystal from being produced in the junction region between the capacitor and the source/drain region connected to the capacitor and the sidewall effectively reduces the short channel effect.
    Type: Grant
    Filed: August 3, 1993
    Date of Patent: February 6, 1996
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Hideaki Arima, Makoto Ohi, Natsuo Ajika, Atsushi Hachisuka, Tomonori Okudaira
  • Patent number: 5446301
    Abstract: A semiconductor device capable of effectively preventing a dielectric breakdown of a gate oxide film without adversely affecting the characteristics of a transistor and a process of manufacturing the same are disclosed. The semiconductor device comprises a SOI film 2 whose upper angular parts are rounded off by sputter etching and a gate oxide film 3 formed on SOI film 2 with an almost uniform thickness. Therefore, electric field concentration in the upper angular parts of SOI film 2 is reduced. Furthermore, the control characteristics of the transistor are enhanced by the uniform gate oxide film 3. As a result, a dielectric breakdown of the gate oxide film is effectively prevented without adversely affecting the characteristics of the transistor. Sputter etching enabling processing at a low temperature is used, so that the upper angular parts of SOI film 2 are rounded off without adversely affecting a semiconductor element formed in the lower layer.
    Type: Grant
    Filed: July 13, 1994
    Date of Patent: August 29, 1995
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Koji Eguchi, Natsuo Ajika, Kazuyuki Sugahara
  • Patent number: 5444282
    Abstract: A semiconductor device of a field effect transistor having an SOI structure is formed as below. Using a gate electrode 20 as a mask, n type impurities are implanted into an SOI layer of p type to form additional source/drain regions of intermediate concentration. Then, a relatively thin sidewall spacer is formed at the sidewall of the gate electrode. Using the sidewall spacer as a mask, a titanium silicide layer is formed in self-alignment on the surface of the SOI layer. Next, a relatively thick sidewall spacer is formed. Using this sidewall spacer as a mask, n type impurities are implanted to form a source/drain region of high concentration. According to this manufacturing step, over-etching of the source/drain region are prevented in performing anisotropic etching at the time of sidewall spacer formation.
    Type: Grant
    Filed: June 30, 1994
    Date of Patent: August 22, 1995
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Yasuo Yamaguchi, Natsuo Ajika, Tsuyoshi Yamano
  • Patent number: 5434439
    Abstract: The DRAM according to the present invention comprises so-called cylindrical stacked type capacitors. Each of the cylindrical stacked type capacitors comprises a base portion extending flat on an insulation layer and a surface of a substrate, and a cylindrical portion extending vertically and upwardly from the base portion. Then, the cylindrical portion vertically and upwardly protrudes from an outermost peripheral position of the base portion. As a result, an area where electrodes of the capacitor and capacitance of the capacitor can be increased. Furthermore, with a bit line located below an electrode layer of the capacitor, adjacent capacitors above the bit line can be isolated. Accordingly, it is possible to prevent the bit line contact from defining an isolation distance between the capacitors.
    Type: Grant
    Filed: December 9, 1993
    Date of Patent: July 18, 1995
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Natsuo Ajika, Hideaki Arima, Atsushi Hachisuka
  • Patent number: 5428235
    Abstract: A memory cell of a DRAM comprises one MOS transistor and one capacitor. The MOS transistor includes a pair of source/drain regions and a gate electrode formed on the channel region. A bit line is formed so as to be connected to the source/drain region. A conductive layer is formed so as to be connected to the source/drain region. The gate electrode includes a first part formed on the channel region with an oxide film interposedand second and third parts extending from the first part, respectively, and formed on the bit line and the conductive layer with an interlayer oxide film interposed. The capacitor includes a lower electrode formed so as to be connected to the conductive layer and an upper electrode formed so as to be opposed to the surface of the lower electrode with a dielectric film interposed. The upper electrode is placed above the bit line. A word line is placed above the upper electrode and connected to the gate electrode.
    Type: Grant
    Filed: September 6, 1994
    Date of Patent: June 27, 1995
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Masahiro Shimizu, Takehisa Yamaguchi, Natsuo Ajika
  • Patent number: 5400278
    Abstract: In a semiconductor memory device according to the present invention, a conductive layer is formed on a field oxide film in a boundary region on the main surface of a semiconductor substrate. A floating gate electrode, an interlayer insulating film, and a control gate electrode are formed on the semiconductor substrate in a memory cell array region with a gate insulating film interposed therebetween. A gate electrode is formed in a peripheral circuit region with the gate insulating film interposed therebetween. An interlayer insulating film is formed on the conductive layer, the gate electrode, and the control gate electrode. A contact hole is formed at a predetermined position of the interlayer insulating film. An interconnection layer is selectively formed on the interlayer insulating film including the inner surface of the contact hole. According to the present invention, it is possible to prevent formation of a concave portion on the surface of the field oxide film in the boundary region.
    Type: Grant
    Filed: September 1, 1993
    Date of Patent: March 21, 1995
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Yuichi Kunori, Natsuo Ajika, Hiroshi Onoda, Makoto Ohi, Atsushi Fukumoto
  • Patent number: 5381365
    Abstract: The DRAM according to the present invention comprises so-called cylindrical stacked type capacitors. Each of the cylindrical stacked type capacitors comprises a base portion extending flat on an insulation layer and a surface of a substrate, and a cylindrical portion extending vertically and upwardly from the base portion. Then, the cylindrical portion vertically and upwardly protrudes from an outermost peripheral position of the base portion. As a result, an area where electrodes of the capacitor and capacitance of the capacitor can be increased. Furthermore, with a bit line located below an electrode layer of the capacitor, adjacent capacitors above the bit line can be isolated. Accordingly, it is possible to prevent the bit line contact from defining an isolation distance between the capacitors.
    Type: Grant
    Filed: June 30, 1993
    Date of Patent: January 10, 1995
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Natsuo Ajika, Hideaki Arima, Atsushi Hachisuka
  • Patent number: 5381029
    Abstract: A semiconductor device capable of effectively preventing a dielectric breakdown of a gate oxide film without adversely affecting the characteristics of a transistor and a process of manufacturing the same are disclosed. The semiconductor device comprises a SOI film 2 whose upper angular parts are rounded off by sputter etching and a gate oxide film 3 formed on SOI film 2 with an almost uniform thickness. Therefore, electric field concentration in the upper angular parts of SOI film 2 is reduced. Furthermore, the control characteristics of the transistor are enhanced by the uniform gate oxide film 3. As a result, a dielectric breakdown of the gate oxide film is effectively prevented without adversely affecting the characteristics of the transistor. Sputter etching enabling processing at a low temperature is used, so that the upper angular parts of SOI film 2 are rounded off without adversely affecting a semiconductor element formed in the lower layer.
    Type: Grant
    Filed: February 21, 1992
    Date of Patent: January 10, 1995
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Koji Eguchi, Natsuo Ajika, Kazuyuki Sugahara
  • Patent number: 5378643
    Abstract: An A-1 transistor type flash EEPROM is disclosed. The memory cell in the EEPROM comprises: a first control gate which is formed, through a first insulating film, on a first channel region formed between a source region and a drain region. A floating gate is formed on the second channel region through a second insulating film and on the first control gate through the first interlayer insulating film. A second control gate is formed on a surface of the floating gate through a second interlayer insulating film. One end of the second control gate and one end of the first control gate are electrically connected to each other through a third control gate, thereby enhancing capacitance between the control gates and the floating gate.
    Type: Grant
    Filed: December 31, 1992
    Date of Patent: January 3, 1995
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Natsuo Ajika, Hideaki Arima
  • Patent number: 5364811
    Abstract: A dynamic random access memory (DRAM) is disclosed that can effectively prevent the formation of steps in the boundary region of a memory cell array 101 and a peripheral circuit 102, even in high integrated devices. This DRAM includes a double peripheral wall 20 of peripheral walls 20a and 20b at the boundary region of the memory cell array 101 and the peripheral circuit 102 of a P type silicon substrate 1, extending vertically upwards from the P type silicon substrate 1. The upper surfaces of the devices formed on the memory cell array and the peripheral circuit 102 in forming devices on the memory cell array 101 and the peripheral circuit 102 are substantially planarized, by virture of the double peripheral wall 20, to effectively prevent steps from being generated in the boundary region of the memory cell array 101 and the peripheral circuit 102, even in high integrated devices.
    Type: Grant
    Filed: February 16, 1993
    Date of Patent: November 15, 1994
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Natsuo Ajika, Hideaki Arima, Kaoru Motonami, Atsushi Hachisuka, Tomonori Okudaira
  • Patent number: 5355022
    Abstract: In a method of manufacturing a stacked-type semiconductor device, firstly, a first semiconductor substrate having a first device formed thereon is covered with an interlayer insulating layer and a planarized polycrystalline silicon layer is formed on the interlayer insulating layer. The first semiconductor substrate and a second semiconductor substrate are joined together by putting the surface of the polycrystalline silicon layer in close contact with the surface of a refractory metal layer formed on the second semiconductor substrate, applying thermal treatment at 700.degree. C. or below and changing the refractory metal layer to silicide.
    Type: Grant
    Filed: August 28, 1992
    Date of Patent: October 11, 1994
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Kazuyuki Sugahara, Natsuo Ajika, Toshiaki Ogawa, Toshiaki Iwamatsu, Takashi Ipposhi
  • Patent number: 5355012
    Abstract: A semiconductor device is an SOI type field effect transistor in which an active region is isolated and insulated by a transistor for isolation. A contact hole for isolation is formed in a gate dielectric thin film for isolation between a gate electrode of the transistor for isolation and a channel region below the gate electrode. In the semiconductor device thus structured, surplus carriers produced in a channel region below a transfer gate electrode are drawn through channel region and isolation contact hole into isolation gate electrode, thereby preventing such a disadvantageous phenomenon as a kink effect or the like due to a floating-substrate effect.
    Type: Grant
    Filed: April 28, 1993
    Date of Patent: October 11, 1994
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Yasuo Yamaguchi, Natsuo Ajika, Tsuyoshi Yamano
  • Patent number: 5347151
    Abstract: Access transistors of memory cells in a DRAM are formed in a solid phrase epitaxial single crystalline layer on the surface of a silicon substrate. A bit line extending over the surface of an element isolation and insulation film is formed by patterning a polycrystalline silicon layer extending to the single crystalline silicon layer as a layer. A stacked capacitor is connected to one source/drain of the access transistor through a conductive layer extending to the single crystalline silicon layer and over a field oxide film. Part of the stacked capacitor extends over the bit line. The connection region of the bit line, the capacitor and the source/drain is formed above the element isolation and insulation film, so that the source/drain region of the access transistor can be reduced.
    Type: Grant
    Filed: November 26, 1991
    Date of Patent: September 13, 1994
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Masahiro Shimizu, Takehisa Yamaguchi, Natsuo Ajika
  • Patent number: 5341028
    Abstract: A semiconductor device of a field effect transistor having an SOI structure is formed as below. Using a gate electrode 20 as a mask, n type impurities are implanted into an SOI layer of p type to form additional source/drain regions of intermediate concentration. Then, a relatively thin sidewall spacer is formed at the sidewall of the gate electrode. Using the sidewall spacer as a mask, a titanium silicide layer is formed in self-alignment on the surface of the SOI layer. Next, a relatively thick sidewall spacer is formed. Using this sidewall spacer as a mask, n type impurities are implanted to form a source/drain region of high concentration. According to this manufacturing step, over-etching of the source/drain region are prevented in performing anisotropic etching at the time of sidewall spacer formation.
    Type: Grant
    Filed: October 3, 1991
    Date of Patent: August 23, 1994
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Yasuo Yamaguchi, Natsuo Ajika, Tsuyoshi Yamano
  • Patent number: 5338957
    Abstract: The width of a charge storage electrode and a control electrode in the column direction is set to be wider above an element isolation region than that above a channel region. Therefore, the capacitance between the control electrode and the charge storage electrode can be increased to improve the coupling ratio in a nonvolatile semiconductor memory device. Also, a first interconnection layer is equal in height above the control electrode and above the channel region, so that patterning of the first interconnection layer can be carried out easily and precisely.
    Type: Grant
    Filed: August 23, 1993
    Date of Patent: August 16, 1994
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Atsushi Fukumoto, Makoto Ohi, Hiroshi Onoda, Natsuo Ajika, Yuichi Kunori
  • Patent number: 5338699
    Abstract: A method of making a semiconductor device including a plurality of gate electrodes (6a, 6b, 6c, 6d) arranged on the surface of a semiconductor substrate (1) with insulating layers (5, 8) covering the top and the side walls of the gate electrodes. The spaces between the opposing side walls of adjacent gate electrodes on the surface of the element isolation region (2) are smaller than twice the thickness of the thinnest insulating layer (8) among the insulating layers of the side walls of the gate electrodes on the surface of the active regions. The space (14) between the gate electrodes on the element isolation region is filled with the insulating isolation layer (8) so that unevenness in the underlying portion on the element isolation region on which the conductive interconnection layer (10) to be formed is reduced, preventing thinning of the conductive interconnection layer and disconnection due to excessive etching of a resist film in patterning the conductive interconnection layer.
    Type: Grant
    Filed: January 29, 1993
    Date of Patent: August 16, 1994
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Makoto Ohi, Hideaki Arima, Natsuo Ajika, Atsushi Hachisuka, Yasushi Matsui
  • Patent number: 5275629
    Abstract: A semiconductor device manufacturing apparatus has a first space and a second space in a process chamber in which a semiconductor wafer is accommodated, the first and second spaces being separated by the semiconductor wafer. A process gas port opens into the first space adjacent to the obverse surface of the semiconductor wafer, and an infrared light transmission window is formed in a wall of the chamber at the second space facing the reverse surface of the semiconductor wafer. No layers are deposited on the reverse surface of the semiconductor wafer and the infrared light transmission window so that the emissivity at the reverse surface of the semiconductor wafer is not changed during layer deposition. The temperature during processing can therefore be monitored accurately with a pyrometer, and a reduction in the transmissivity of the window is prevented.
    Type: Grant
    Filed: September 19, 1991
    Date of Patent: January 4, 1994
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Natsuo Ajika, Masahiro Shimizu, Takehisa Yamaguchi
  • Patent number: 5276344
    Abstract: Disclosed is a semiconductor memory device in which defects in crystal in a junction region between a capacitor and a source/drain region, and a short channel effect of a transistor can be effectively reduced. The semiconductor memory device includes, on the side of a gate electrode at which the capacitor is connected, a sidewall formed to have a width larger than that of a sidewall on the side of a bit line, and a source/drain region to which the capacitor is connected and which is formed to have a diffusion depth larger than that of the opposite source/drain region. Therefore, the source/drain region effectively prevents defects in crystal from being produced in the junction region between the capacitor and the source/drain region connected to the capacitor and the sidewall effectively reduces the short channel effect.
    Type: Grant
    Filed: February 2, 1993
    Date of Patent: January 4, 1994
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Hideaki Arima, Makoto Ohi, Natsuo Ajika, Atsushi Hachisuka, Tomonori Okudaira