Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Patent
1996-11-25
1998-11-03
Mintel, William
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
257460, 257507, 257629, 257707, 438455, 438974, 228116, 228903, 156281, H01L 2900
Patent
active
058313095
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a semiconductor element in the form of a sandwich for an electronic or opto-electronic semiconductor component, wherein the sandwich consists of a transparent flat quartz glass substrate and a wafer of a semiconductor material, and wherein the surfaces of the quartz glass substrate and the wafer, joined directly together face-to-face, were polished before they were joined together.
Semiconductor elements of this kind are disclosed in EP-0 504 714 A2 and U.S. Pat. No. 4,883,215, it being stated in the latter patent that the joined surfaces are mirror-polished before bonding, while in the cited European patent application the term "polished" is used. The wafers are placed together with the polished surfaces face-to-face, and joined together by pressing. Afterward the thickness of the wafer of semiconductor material can be reduced in steps by chemical or mechanical treatment. As can be learned from EP-0 504 714 A2, the bond between the wafers is created by treatment at various temperature steps from a temporary bond (110.degree. C. to 350.degree. C.) to a full bond (250.degree. C. to 500.degree. C.), the thickness of the wafer of semiconductor material being reduced after each intermediate temperature step.
The known bonded semiconductor elements, however, cannot satisfy the requirements of semiconductor technology, for as it is known from EP-0 504 714 A2, an extreme reduction of the forces in adhesion between the wafers occurs if the laminate is exposed, for example, to a temperature of only 700.degree. C. for two hours. Therefore an at least partial separation of the wafers from one another as well as a destructive distortion of the sandwich cannot be avoided.
SUMMARY OF THE INVENTION
The invention is addressed to the problem of preparing semiconductor elements in sandwich from which can withstand temperatures as high as 900.degree. C., such as those employed in the manufacture of semiconductor circuits, for an economically realistic time period, without fear that a substantial reduction of the forces of adhesion a separation of the wafers from one another, or any undesirable distortion of the laminated body will occur.
According to the invention semiconductor element the quartz glass of the substrate is a synthetic quartz glass which has a viscosity of 10.sup.14.0 poise at 950.degree. C., and which does not fall below a level of 10.sup.12 poise at a temperature of 1050.degree. C. The total content of alkali elements in the quartz glass is no more than 1 ppm, and the quartz glass contains a total of no more than 1 ppm of metallic impurities of the elements nickel, copper, chromium and/or transition metals. At least one of the polished surfaces has a roughness depth R.sub.q of no more than 2 nm. The roughness depth R.sub.q is understood to mean the square of the average measured profile depth within a unit measured length. Preferably the roughness depth R.sub.q of the polished surfaces is less than 1 nm. It has proven particlarly advantageous to use for the laminate a quartz glass substrate whose polished surface has a roughness depth R.sub.q of no more than 0.5 nm.
In the semiconduct elements according to the invention, even after a heat treatment of two hours at 950.degree. C., no substantial deformation, especially sagging or distortion, could be observed. This is probably can be attributed to the fact that the selected quartz glass for the mechanically stabilizing part of the laminate, on account of its high viscosity, withstands high temperature stresses, such as those involved, for example, in the preparation of an insulating oxide in a silicon layer, without substantial mechanical deformation. Neither could any loosening of the quartz glass substrate from the wafer of semiconducting material be observed. The excellent strength of adhesion of the laminate is assured by the fact that the polished surfaces of the quartz glass substrate and of the semiconducting material which are to be joined face-to-face are polished such that at least one of them
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Englisch Wolfgang
Uebbing Reinhold
Heraeus Quarzglas GmbH
Mintel William
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