Patent GB-1469436-A (GB)
Title: Process for producing semiconductor devices
Inventor: NOMURA KOUSI
IPC: H01L21/3205
Filed: 1974-03-25
Abstract: 1469436 Semi-conductor devices MITSUBISHI DENKI KK 25 March 1974 [23 March 1973 31 March 1973 18 May 1973] 13179/74 Heading H1K In the manufacture of semi-conductor devices an oxide layer is formed on a semi-conductor substrate body by selectively masking regions of the substrate surface and irradiating the substrate with energetic particles to implant them into the unmasked regions of the substrate and, after removing the mask, heating the body in an oxidizing atmosphere, to grow an oxide insulation from the material of the substrate, whereby those regions which have been irradiated oxidize faster and to a greater depth within the body than the non-irradiated regions of the body. The technique may be employed in the manufacture of ultra-high frequency transistors for example, as shown in Fig. 5. A patterned mask, Fig. 5b, selectively protects surface regions of a silicon substrate 10 from irradiation by a beam of ions 42. The shielding coating or mask is then removed and the upper surface heated in oxygen or steam above 900‹ C. to form the relatively thick oxide film 46 over the irradiated regions 44 and the relatively thin oxide film 48 over the non- irradiated regions, Fig. 5c. The oxide films 46, 48 are then etched until the substrate regions under film 48 are exposed to form a window for the base diffusion region 56, Fig. 5g, Thereafter a further shielding coating is formed in the window, patterned to form windows for the emitter diffusion and the emitter and base electrodes, and the surface of the substrate is again irradiated with an ion beam 42 to form the preferentially oxidized regions 60. The shielding coating is removed and the substrate surface oxidized to form an oxide coating of the form shown in Fig. 5h. The width of the semiconductor regions underlying the thinner parts of the oxide coating, one of which defines the emitter stripe, is less than the width of the corresponding part of the shielding coating used in forming it, thus enhancing the range of high frequency characteristics obtainable. By selective masking and etching the emitter diffusion 68 and the emitter electrode 76 and base electrode 78 are formed, Fig. 5m. Both diffusion regions 56 and 68 are formed so that the edges of the respective P-N junctions are surrounded by the buried parts of the preferentially oxidized regions 46 and 62. The irradiating beam may comprise ions of In, Ga, Sb, Sn, As, B, electrons, neutrons, α-particles or argon or xenon. To obtain a very deep preferentially oxidized region protons or helium ions may be used first followed by heavier ions. The shielding coating may comprise one or more layers of silicon dioxide, silicon nitride, aluminium oxide, photoresist, Al, Mb or W or combinations thereof. The electrode materials may comprise Al, Tz, Mb, Au or platinum silicide. The technique may also be utilized in the manufacture of large scale integrated circuits, Fig. 7 (not shown). In this manufacturing process use is made of the fact that polycrystalline silicon is more rapidly oxidized than monocrystalline silicon and the technique of the present invention of selectively irradiating the substrate with a beam of energetic ions prior to oxidation is utilized to reduce the length of time the oxidation step takes, resulting in less unwanted oxidation in the active regions of the device.