Method to trap air at the silicon substrate for improving...

Semiconductor device manufacturing: process – Making passive device

Reexamination Certificate

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Details

C438S238000, C438S411000, C257S531000

Reexamination Certificate

active

06221727

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates to a method of forming an inductor in the fabrication of integrated circuits, and more particularly, to a method of forming a high quality inductor using air as a barrier in the manufacture of integrated circuits.
(2) Description of the Prior Art
The integration of radio frequency (RF) integrated circuits on silicon is one of the greatest challenges for the growing markets of wireless communications. The incorporation of RF inductors on silicon without sacrificing the quality factor (Q) due to substrate losses has been researched heavily in recent years. Some of the techniques include: (i) selectively etching out silicon under the inductor by micro-machining, (ii) employing multi-metal layer of aluminum interconnects or copper damascene interconnects, (iii) using a high resistivity silicon substrate, (iv) employing a biased well underneath a spiral inductor, (v) inserting various types of patterned ground shield between the spiral inductor and the silicon substrate, and (vi) increasing the thickness of the interlayer dielectric. This is not an exhaustive listing. The common objectives of all of these techniques are: 1) to enhance the Q value of the inductor and 2) to increase the self-resonance frequency so that the usable frequency range of the inductor is widened.
The self-resonance caused by the parasitic capacitance of the spiral inductor to the silicon substrate will limit the use of these inductors at high frequencies. The increasing series spreading resistance will degrade the Q factor. This impacts the usefulness of integrated spiral inductors implemented on silicon substrates. These problems can be overcome if the area under the inductor is made to appear locally insulating by selectively removing the underlying silicon resulting in inductors “hanging” in air. Air, which has the lowest dielectric constant, is the most ideal barrier. However, micro-machining, used to etch away the silicon under the inductor, is complex and is not compatible with any normal process flow. It is desired to utilize air as a barrier in a process that is implemented easily and is compatible with any process flow with minimal changes.
U.S. Pat. No. 5,539,241 to Abidi et al shows a method of etching out a pit under an inductor during CMOS processing. U.S. Pat. No. 5,844,299 to Merrill et al shows an inductor formed over a pit containing silicon oxide. U.S. Pat. No. 5,742,091 to Hebert et al teaches deep trenches filled with a low dielectric constant material. U.S. Pat. No. 5,773,870 to Su et al discloses backside etching of the substrate under an inductor. U.S. Pat. No. 5,770,509 to Yu et al teaches another inductor process.
SUMMARY OF THE INVENTION
A principal objective of the present invention is to provide an effective and very manufacturable method of forming a high quality inductor in the fabrication of integrated circuit devices.
Another objective of the invention is to provide a method of fabricating an inductor utilizing air as an underlying barrier in the manufacture of integrated circuits.
A further objective of the invention is to provide a method of fabricating an inductor having an air well within the silicon substrate thereunder.
In accordance with the objectives of this invention a new method of fabricating an inductor utilizing air as an underlying barrier in the manufacture of integrated circuits is achieved. A field oxide region is formed in and on a semiconductor substrate and then removed whereby a well is left in the semiconductor substrate. A polish stop layer is deposited over the substrate and within the well. The polish stop layer is covered and the well filled with a spin-on-glass layer. The spin-on-glass layer is polished back to the polish stop layer. The polish stop layer is removed. A first oxide layer is deposited overlying the spin-on-glass layer and the semiconductor substrate and is patterned using an inductor reticle whereby a plurality of openings are made through the first oxide layer to the spin-on-glass layer. All of the spin-on-glass layer within the well is removed through the plurality of openings. Thereafter, a second oxide layer is deposited overlying the first oxide layer and capping the plurality of openings thereby forming an air barrier within the well. A metal layer is deposited overlying the second oxide layer and patterned using the same inductor reticle to form the inductor in the fabrication of an integrated circuit device.


REFERENCES:
patent: 5539241 (1996-07-01), Abidi et al.
patent: 5742091 (1998-04-01), Hébert
patent: 5770509 (1998-06-01), Yu et al.
patent: 5773870 (1998-06-01), Su et al.
patent: 5844299 (1998-12-01), Merrill et al.
patent: 5856703 (1999-01-01), Manning
patent: 6081030 (2000-06-01), Jaouen et al.
patent: 6140197 (2000-10-01), Chu et al.

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