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: 5240872
    Abstract: A semiconductor device includes a MOS type field effect transistor whose gate electrode (4) has its surface covered with a first insulating film (5) and left and right sides provided with a pair of second insulating films (10). A first conductive layer (12, 13) is formed on the surface of the source/drain region (8, 11) and the surface of one of a pair of second insulating films (10) which are positioned on one side of the gate electrode (4). A third insulating film (24b) is formed at least on the surface of the second insulating film (10) on which the first conductive layer (12, 13) is not formed. A second conductive layer (18) is provided on the surface of the third insulating film (24b) and on the source/drain region (8, 11) on which the third insulating film (24b) is formed. This structure enables provision of a semiconductor device in which a contact hole can be formed in self-alignment, independent from the influence of errors in the step of patterning a resist mask.
    Type: Grant
    Filed: August 6, 1992
    Date of Patent: August 31, 1993
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Kaoru Motonami, Natsuo Ajika, Atsushi Hachisuka, Yoshinori Okumura, Yasushi Matsui
  • Patent number: 5233212
    Abstract: A semiconductor device includes 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) re 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 resin film in patterning the conductive interconnection layer.
    Type: Grant
    Filed: April 25, 1991
    Date of Patent: August 3, 1993
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Makoto Ohi, Hideaki Arima, Natsuo Ajika, Atsushi Hachisuka, Yasushi Matsui
  • Patent number: 5218219
    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: April 4, 1991
    Date of Patent: June 8, 1993
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Natsuo Ajika, Hideaki Arima, Kaoru Motonami, Atsushi Hachisuka, Tomonori Okudaira
  • Patent number: 5194925
    Abstract: A one transistor memory cell for a flash EEPROM includes: a first control gate which is disposed on a first channel region between a source region and a drain region and separated therefrom by a first insulating film; a floating gate disposed on a second channel region and is separated therefrom by a second insulating film, the floating gate disposed on the first control gate and separated therefrom by a first interlayer insulating film; and a second control gate disposed on a surface of said floating gate and separated therefrom by a second interlayer insulating film; and wherein 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 capacity between the control gates and the floating gate.
    Type: Grant
    Filed: February 21, 1991
    Date of Patent: March 16, 1993
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Natsuo Ajika, Hideaki Arima
  • Patent number: 5173752
    Abstract: A semiconductor device incloudes a MOS type field effect transistor whose gate electrode (4) has its surface covered with a first insulating film (5) and left and right sides provided with a pair of second insulating films (10). A first conductive layer (12, 13) is formed on the surface of the source/drain region (8, 11) and the surface of one of a pair of second insulating films (10) which are positioned on one side of the gate electrode (4). A third insulating film (24b) is formed at least on the surface of the second insulating film (10) on which the first conductive layer (12, 13) is not formed. A second conductive layer (18) is provided on the surface of the third insulating film (24b) and on the source/drain region (8, 11) on which the third insulating film (24b) is formed. This structure enables provision of a semiconductor device in which a contact hole can be formed in self-alignment, independent from the influence of errors in the step of patterning a resist mask.
    Type: Grant
    Filed: April 26, 1991
    Date of Patent: December 22, 1992
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Kaoru Motonami, Natsuo Ajika, Atsushi Hachisuka, Yoshinori Okumura, Yasushi Matsui
  • Patent number: 5162262
    Abstract: An interconnection layer of a semiconductor device according to the present invention has in a contact portion with a conductor layer a multi-layered structure formed from the bottom, of a refractory metal silicide layer, a first refractory metal nitride layer, and a secondary refractory metal nitride layer. Titanium or tungsten is used as a refractory metal. The second refractory metal nitride is formed by thermally nitriding the refractory metal layer. The second refractory metal nitride layer formed by the thermal process has a close packed crystal structure and has an excellent barrier characteristic.
    Type: Grant
    Filed: July 8, 1991
    Date of Patent: November 10, 1992
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Natsuo Ajika, Hideaki Arima
  • Patent number: 5141891
    Abstract: An MIS-type semiconductor device comprises PSD structure and LDD structure. The LDD structure comprises high concentration impurity regions formed by thermally diffusing impurities which have been contained in source/drain electrode conductive layers made of polysilicon onto a semiconductor substrate, and low concentration impurity regions formed through ion implantation using resist patterned on channel regions and the source/drain electrode conductive layers as mask. A gate electrode is formed, after formation of the low concentration impurity regions, to cover them and have its edges overlap the source/drain electrode conductive layers. The LDD structure suppresses the short channel effects which might be caused in the MIS-type semiconductor device and thus enables channels length to be miniaturized while the PSD structure enables also miniaturization of source/drain structure.
    Type: Grant
    Filed: October 17, 1991
    Date of Patent: August 25, 1992
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Hideaki Arima, Natsuo Ajika
  • Patent number: 5100818
    Abstract: First, second, third and fourth impurity regions are formed on a major surface of a semiconductor substrate with prescribed spaces, to define first, second and third channel regions in portions held between the same. A select gate is formed on the first channel region through an insulating film, to define a transistor with the first and second impurity regions. A part of a control gate is formed on the third channel region through an insulating film, to define a transistor with the third and fourth impurity regions. A floating gate is formed on the second channel region and parts of the select gate and the control gate through an insulating film, to define a transistor with the second and third impurity regions. Both end portions of the floating gate are inwardly separated from upper positions of respective outer ends of parts of the select gate and the control gate, in order to improve an effect of shielding the floating gate against a fourth impurity region.
    Type: Grant
    Filed: January 4, 1991
    Date of Patent: March 31, 1992
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Hideaki Arima, Natsuo Ajika
  • Patent number: 5093277
    Abstract: Here is disclosed an improved polysilicon pad LOCOS method. An underlying oxide film is formed on a main surface of a semiconductor substrate. Over the underlying oxide film, polysilicon to be a field oxide film is then deposited. Subsequently, a nitride film is formed on the polysilicon. Thereafter, the nitride film is patterned to leave patterns of a predetermined configuration in an area to be a device region. Using the patterned nitride film as a mask, the polysilicon other than a portion beneath the mask is thermally oxidized to form a field oxide film on the main surface of the semiconductor substrate. The nitride film having served as a mask is then removed to expose the unoxidized polysilicon remaining under the mask. Subsequently, the unoxidized polysilicon is etched away under predetermined conditions which do not allow any etching of the underlying oxide film.
    Type: Grant
    Filed: March 2, 1990
    Date of Patent: March 3, 1992
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Hideaki Arima, Natsuo Ajika
  • Patent number: 5051948
    Abstract: In a content addressable memory (CAM) cell according to the present invention, a pair of non-volatile memory transistors hold data, whereby stored data will not disappear even if power is cut. Conducting terminals of these non-volatile transistors are connected to a bit line pair, so that the stored data can be directly read out from the bit line pair. Further, the invention CAM system converts the value of a current flowing in a match line into a voltage value to perform content reference, and hence the same can be employed as an associative memory system.
    Type: Grant
    Filed: October 20, 1989
    Date of Patent: September 24, 1991
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Kiyoto Watabe, Hirofumi Shinohara, Takahisa Eimori, Hideaki Arima, Natsuo Ajika, Yuichi Nakashima, Shinichi Satoh
  • Patent number: 5049975
    Abstract: An interconnection layer of a semiconductor device according to the present invention has in a contact portion with a conductor layer a multi-layered structure formed from the bottom, of a refractory metal silicide layer, a first refractory metal nitride layer, and a second refractory metal nitride layer. Titanium or tungsten is used as a refractory metal. The second refractory metal nitride is formed by thermally nitriding the refractory metal layer. The second refractory metal nitride layer formed by the thermal process has a close packed crystal structure and has an excellent barrier characteristic.
    Type: Grant
    Filed: March 12, 1990
    Date of Patent: September 17, 1991
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Natsuo Ajika, Hideaki Arima
  • Patent number: 4988635
    Abstract: A memory cell of 1 bit is constituted by 1 selecting transistor and 1 memory transistor in an EEPROM. One of the source-drain regions is commonly used by the selecting transistor and the memory transistor. The commonly used source-drain region is manufactured through the following steps. First, a gate electrode of the transistor is formed. An oxide film is deposited on the entire surface. A resist is applied thereon and is etched back to expose a surface of the oxide film on the gate electrode. Thereafter, the oxide films deposited on the side surfaces of the gate electrode are removed to form opening portions. Impurities are implanted to the silicon substrate utilizing the opening portions.
    Type: Grant
    Filed: May 24, 1989
    Date of Patent: January 29, 1991
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Natsuo Ajika, Hideaki Arima
  • Patent number: 4989054
    Abstract: First, second, third and fourth impurity regions are formed on a major surface of a semiconductor substrate with prescribed spaces, to define first, second and third channel regions in portions held between the same. A select gate is formed on the first channel region through an insulating film, to define a transistor with the first and second impurity regions. A part of a control gate is formed on the third channel region through an insulating film, to define a transistor with the third and fourth impurity regions. A floating gate is formed on the second channel region and parts of the select gate and the control gate through an insulating film, to define a transistor with the second and third impurity regions. Both end portions of the floating gate are inwardly separated from upper positions of respective outer ends of parts of the select gate and the control gate, in order to improve an effect of shielding the floating gate against a fourth impurity region.
    Type: Grant
    Filed: April 17, 1989
    Date of Patent: January 29, 1991
    Assignee: Mitsubishi Denki Kabushiki Kaisha
    Inventors: Hideaki Arima, Natsuo Ajika