Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
  • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
  • G02B6/13—Integrated optical circuits characterised by the manufacturing method
  • G02B6/134—Integrated optical circuits characterised by the manufacturing method by substitution by dopant atoms
  • G02B6/1342—Integrated optical circuits characterised by the manufacturing method by substitution by dopant atoms using diffusion
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S148/00—Metal treatment
  • Y10S148/03—Diffusion
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S148/00—Metal treatment
  • Y10S148/035—Diffusion through a layer

Definitions

• the invention relates to a method for producing a low-loss optical waveguide in an epitaxial silicon layer of a silicon component with integrated electronic components in a silicon substrate
• An advantage of an optical waveguide produced in this way is that interactions between an electric field and an optical field through charge carrier injections.
• the waveguide is advantageously very low-loss because its insulation is less than 1 dB / cm.
• the manufacture of such an optical waveguide presents difficulties insofar as the previously rare SOI material has to be used for its manufacture.
• the invention is based on the object of applying a method for producing a low-loss optical waveguide in an epitaxial silicon layer of a silicon component. admit, with which an optical waveguide with low attenuation can be produced in an integrated manner in a comparatively inexpensive manner.
• an epitaxial silicon layer with weak doping is applied to the silicim substrate in a method of the type mentioned above and a substance with an element from group IV of the periodic table with a higher real part of the refractive index than that of silicon diffused into the epitaxial silicon layer.
• An advantage of the method according to the invention is that, owing to the use of widespread substances, it can be carried out with little effort and allows the production of an optical waveguide which, apart from a low attenuation, has the property that an interaction between an electrical and an optical field results from Charge carrier injection can be achieved. Additional losses due to free charge carriers are avoided by using the substance with an element from group IV of the periodic table.
• the weak doping of the epitaxial silicon layer ⁇ 10 / c leads to sufficiently small attenuations in the optical waveguide.
• germanium can be used as the substance of group IV of the periodic table. It should be noted, however, that because of the low diffusion constant of germanium in silicon, a high process temperature of approximately 1,200 * C is required, which is above the melting temperature of germanium ⁇ the melting temperature of germanium is 937 * C. As a result, u. U. Inhomogeneities result from drops of germanium-silicon alloy which can lead to absorption of the optical wave in the waveguide.
• a Ge x si ⁇ _ x) alloy is used as the substance is used . Care should be taken to ensure that this alloy has a higher melting temperature than germanium. An optical waveguide made with this substance can then be formed very homogeneously.
• the substance is applied in strips to the epitaxial silicon layer in accordance with the desired shape of the waveguide. This can be done, for example, after coating with photoresist by vapor deposition of a Ge ⁇ Si, _ ⁇ alloy.
• the epitaxial silicon layer is provided with an SiO 2 coating on its surface carrying the substance before it diffuses in .
• the silicon component is exposed to the diffusion temperature under protective gas for several hours and then the SiO 2 coating is etched away.
• FIG. 1 a germanium-silicon state diagram is shown in FIG. 1 and the individual steps of the method according to the invention are shown in FIGS. 2 to 7.
• an epitaxial silicon layer 2 is applied to a silicon substrate 1, which is weakly doped to achieve sufficiently low attenuations, that is to say, for example, has a doping of ⁇ 10 / cm.
• a photoresist layer 4 is applied to the surface 3 of the epitaxial silicon layer 2 facing away from the silicon substrate 1 in a structure which corresponds to the shape of the optical waveguide to be created.
• the photoresist coating consists advantageously of a reversible photoresist with which the inwardly drawn edges shown in FIG. 2 can be achieved in a known manner. The negative steepness of these edges enables the structuring of larger layer thicknesses, as are required when carrying out the method according to the invention for the application of the substance as a diffusion source.
• the silicon component 5 treated so far is then introduced into a high vacuum system and surface-cleaned there by glowing. This is followed by vapor deposition with a Ge Si /.% Alloy in the high-vacuum system at a pressure of less than 10 " bar, as a result of which a layer 6 of such an alloy is formed both on the photoresist layer 4 and on the area 7 left by it is formed on the epitaxial silicon layer 2, as shown in FIG. 3.
• the Ge Sir, • .- alloy can be made in different ways.
• One method is that a
• Electron beam is keyed between a germanium-filled and a silicon-filled crucible, wherein the alloy ratio x can be adjusted by the duty cycle.
• Beam shift keying is typically carried out at a frequency of one Hz.
• the alloy by alternating layers of germanium and silicon.
• the component is removed from the high-vacuum system and then exposed to an organic solvent for lifting off the photoresist layer 4, the lifting off being able to be assisted by ultrasound, if necessary. All that then remains on the side 3 of the epitaxial silicon layer 2 is a strip 8 of the Ge Si *, - »- alloy as a diffusion source.
• the silicon component 5 treated so far is shown in FIG.
• the silicon component 5 is coated with an SiO 2 layer 9, for which a thickness of approximately 600 nm, on the surface 3 of the epitaxial silicon layer 2 carrying the substance or the diffusion source, with the aid of a high-frequency sputter system will (see Figure 5).
• heating of the silicon component 5 to about 200 * C may be used to increase the packing density of the Si0 2 layer take place during the sputtering.
• the silicon component 5 is diffused at a temperature of 1200 * C for a period of several, for example 50 hours under flowing argon with a flow rate of about 0.5 1 / min, so that the silicon component 5 then has a state has, as shown in Figure 6.
• the substance 8 has diffused into the epitaxial silicon layer 2.
• the Si0 2 layer 9 is etched away with hydrofluoric acid as the last method step, and a germanium-doped channel 10 with an increased refractive index is created in the silicon component 5 as a low-loss optical waveguide, as shown in FIG. 7.
• a pure Si, *, •, - alloy as the diffusion source, but a Ge Si, *, •, alloy whose melting temperature is above the necessary diffusion temperature of 1200 ° C.
• the germanium content x of the alloy must be chosen to be x 432 ⁇ .
• a pure melt can also be used as the diffusion source.
• spot sizes with a vertical dimension of 7 ⁇ m and a horizontal dimension of 11 ⁇ m can be achieved in this way.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Integrated Circuits (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 1989
  • 1989-06-30 DE DE3922009A patent/DE3922009C2/de not_active Expired - Fee Related
• 1990
  • 1990-06-29 EP EP90909623A patent/EP0479837A1/de not_active Withdrawn
  • 1990-06-29 JP JP2509142A patent/JPH04506577A/ja active Pending
  • 1990-06-29 WO PCT/DE1990/000497 patent/WO1991000534A1/de not_active Application Discontinuation
  • 1990-06-29 US US07/781,249 patent/US5252514A/en not_active Expired - Fee Related

Non-Patent Citations (1)

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