Semiconductor device and circuit

Abstract: A monolithic integrated circuit capable of operation in the microwave range which is fabricated using silicon technology wherein transmission line interconnects are fabricated along with active devices on the same substrate. The transmission line is provided using polycrystalline silicon since it can have much higher resistivity than single crystal silicon. Accordingly, a circuit is provided wherein active devices are provided in single crystal silicon and interconnects are formed overlying polycrystalline silicon to provide transmission line interconnects between devices and obtain the desired high frequency response. This is accomplished by providing a highly doped silicon substrate of predetermined conductivity type having a less highly doped silicon layer thereon of the same conductivity type with an oxide layer over the less highly doped layer, forming mesas for formation therein of active elements in the structure having valleys between the mesas extending into the substrate, filling the valleys with very high resistivity polysilicon, forming an electrically insulating layer over the polysilicon, forming active elements with contacts thereto in the mesas and forming interconnects between contacts of the active elements extending over the high resistivity polysilicon regions and the electrically insulating material thereover.

Description: This invention relates to integrated circuits and semiconductor devices capable of operation for example in the microwave range and, more specifically, to integrated circuits of the type defined in the precharacterizing portion of claim 1. An integrated circuit of that type is disclosed in EP-A-0 342 094. Integrated circuits capable of operation in the microwave range are finding increasing use, primarily in consumer and commercial applications, such as, for example, mobile communication. Prior art integrated circuits capable of operation in the microwave range have generally been fabricated using gallium arsenide substrates and possibly other group III-V semiconductor technologies. Gallium arsenide substrates have been generally preferred because of their intrinsic device performance, good isolation properties between devices at microwave frequencies due to the high resistivity of intrinsic GaAs substrates and the low loss transmission line interconnects formed as a result of the low dielectric loss of high resistivity GaAs substrates. Particular problems associated with group III-V substrates and particularly gallium arsenide substrates are their high starting cost, the low yields obtained compared with silicon technology. The result is that semiconductor devices such as integrated circuits fabricated in group III-V technologies and particularly gallium arsenide are high cost devices relative to silicon technologies. Furthermore, in order to provide a transmission line interconnect, it is necessary to provide a dielectric of very low loss which must also be relatively thick, for example 50 to 100 micrometers. In group III-V technology, the dielectric has generally been an "air bridge" wherein air is the dielectric or an intrinsic GaAs substrate which has very high resistivity relative to silicon. EP-A-0 534 271 shows a silicon substrate with polysilicon-filled trench isolation for surface field effect transistor devices together with a substrate bottom contact. That document falls within the terms of Art. 54(3) EPC. Its content is therefore merely relevant to the question of novelty. A semiconductor device of an integrated circuit having a groove isolation structure wherein the grooves are filled with polysilicon is known from EP-A-0 086 915. To reduce the stray capacity of conductor lines connecting elements of the integrated circuit, an electrostatic separating structure similar to the groove isolation structions is formed under the conductor lines. According to the present invention there is provided a semi-conductor circuit as defined in the claims 1-3. The invention provides inter alia for the monolithic integration of microwave silicon devices and low loss transmission lines. In accordance with the present invention in one aspect thereof, there is provided a monolithic integrated circuit capable of operation in the microwave range of about 2 to 4 gigahertz which is fabricated using silicon technology. The integrated circuit fabricated in this manner displays the properties required for use in the microwave range, yet is fabricated at much lower cost than can be obtained using gallium arsenide technology due to the lower cost of the initial starting material as well as the improved yield. BRIEF DESCRIPTION OF THE DRAWINGS FIGURES 1 to 11 are a process flow to obtain an integrated circuit in accordance with the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGURES 1 to 11, there is provided a process flow for fabrication of a monolithic integrated circuit in accordance with the present invention. As shown in FIGURE 1, there is provided a silicon n+ wafer 1 which has been arsenic doped to have a resistivity of 0.001 to 0.003 ohm-centimeters. A 4 micron n- layer of silicon 3 is epitaxially deposited over the wafer 1 and the surface of epitaxial layer 3 is oxidized to grow a 0.5 micron layer of silicon oxide 5 thereon. The oxide layer 5 is patterned to provide mesa location and the oxide is etched in the unpatterned areas. The silicon is then etched to a depth of 125 micrometers, extending the mesa with sloping sidewalls into the substrate 1. An oxide layer 7 is then grown over the surface of the exposed silicon 1 and 3 to a thickness of 0.5 microns as shown in FIGURE 2. The active devices will later be formed in the mesas. A 150 micrometer thick layer of high resistivity polysilicon layer 9 is then deposited over the surface of the structure of FIGURE 2 and the polysilicon is ground back along with the remaining portion of the oxide layer 5 to provide a substantially planar surface as shown in FIGURE 3. A pad oxide layer is grown over the surface of the structure of FIGURE 3, and an oxide layer is formed thereover, these layers being patterned and plasma etched to leave a 10,000 Å layer of oxide 11 over the polysilicon 9 and the exposed silicon region 3 at the moat region 13 as shown in FIGURE 4. Silicon dioxide of 1000Å thickness is regrown on the moat area. The moat region 13 is then patterned with resist to provide an n+ sinker and phosphorus is implanted into the sinker region 15 through the n-layer 3 to the n+ substrate 1 as shown in FIGURE 5. The moat region 13 is again patterned for p+ implants and boron is implanted to form p+ regions 17. This boron is driven into the layer 3 by thermal drive-in method. A second patterning step followed by a second boron implant provides intrinsic base p regions 19 between and in contact with the p+ regions 17. The device is then annealed in standard manner to provide the structure shown in FIGURE 6. An oxide layer 23 of about 2000Å is then deposited over the moat region and the emitter regions are patterned thereon to be formed within the base regions 19. The oxide layer 23 is etched at the emitter regions and a 0.3 to 0.5 micrometer polysilicon layer is deposited and arsenic is implanted thereinto. The polysilicon layer is patterned, etched and thermally treated to form n+ emitters 21 as shown in FIGURE 7. Contacts 25 are formed in standard manner to each of the emitter regions 21, base regions 17 and N+ sinkers 15 and interconnects 27 between devices are formed over the polysilicon 9 and oxide layer 11 thereover in standard manner as shown in FIGURE 8. A wafer of silicon 29 is then adhered to the active surface of the structure of FIGURE 8 by means of a removable adhesive, preferably a polyimide 31, and the wafer portion 1 is ground back either through or to the oxide layer 7 to the polysilicon region 9 as shown in FIGURE 9. A further epoxy adhesive 33 then secures a further highly thermally conductive substrate 35 (e.g. copper for an electrically conductive region or AlN for a dielectric region) to the ground back side of the structure of FIGURE 9 as shown in FIGURE 10. The substrate 29 and adhesive 31 are now removed by removing the temporary adhesive 31 by wet etching in a solvent to provide the structure as shown in FIGURE 11. As can be seen in FIGURE 11, there is provided a structure having interconnects 27 disposed over polysilicon 9 having resistivity in the 10 5 to 10 7 ohm-centimeter range. When the device is attached to a substrate which is a dielectric of very high quality (e.g. AlN substrate 35), there is a good microwave interconnect. Then a metal layer is provided as the back of the dielectric substrate 35 to provide a ground plane. When the substrate 35 is an electrical conductor, preferably copper, the substrate can be used as the ground plane for the transmission lines. Accordingly, the active device are formed in single crystal silicon and the interconnects are disposed over polycrystalline silicon with a metal or another dielectric under the structure. Though the invention has been described with respect to specific preferred embodiments thereof, many variations and modifications will immediately become apparent to those skilled in the art. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modification.

Claims: An integrated circuit comprising devices in a silicon body (1, 3) with regions (7, 9) including a high-resistivity polysilicon layer (9) formed over a silicon oxide layer (7) characterized in that the regions (7, 9) extend through the silicon body (1, 3) to an epoxy adhesive layer (33) which is attached to a thermally-conductive substrate (35) which is electrically conductive. An integrated circuit of claim 1 characterized in that the regions (7, 9) extend through the silicon body (1, 3) to an epoxy adhesive layer (33) which is attached to a thermally-conductive substrate (35) which is dielectric and has an attached metal ground plane. The circuit of claim 1 or claim 2 including transmission line interconnects (27) over the regions (7, 9).

Inventors: KWON OH-KYONG, MALHI SATWINDER, SHEN CHI-CHEONG, KWON, OH-KYONG, MALHI, SATWINDER, SHEN, CHI-CHEONG
Applicants: TEXAS INSTRUMENTS INC, TEXAS INSTRUMENTS INCORPORATED
Application year: 1993
Main classification: H01L21
IPC codes: H01L21, H01P11, H01L23