Adhesive bonding and miscellaneous chemical manufacture – Delaminating processes adapted for specified product – Delaminating in preparation for post processing recycling step
Patent
1991-11-12
1994-05-31
Dang, Thi
Adhesive bonding and miscellaneous chemical manufacture
Delaminating processes adapted for specified product
Delaminating in preparation for post processing recycling step
156647, 156651, 1566591, 1566611, 156662, H01L 2100
Patent
active
053166183
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention concerns an etching method for obtaining at least one cavity in a substrate and a substrate obtained by this method, such method in particular being adapted for micromachining of small plates in the micromechanical domain. The element to be etched is often a plate of semiconducting material such as a silicon wafer.
BACKGROUND OF THE INVENTION
It is sometimes necessary to provide cavities in such a wafer having a substantially flat bottom with different depths. Although it is obviously possible to obtain such cavities sequentially, it may be readily seen that such a solution is not advantageous since it requires as many masking operations and as many etching operations as there are cavities to be obtained .
U.S. Pat. No. JP-A-58/98927 describes an etching method enabling the simultaneous obtaining of cavities having different depths. This method comprises an anisotropic etching step followed by an isotropic etching step. During the first step, the cavities are formed with inclined sides, the etching stopping as soon as the sides come together. It is thus understood that the maximum depth of such a cavity is a function of the surface dimension of the latter. The second step (isotropic etching) has as effect to increase the depth of all the cavities to the same amount.
This method shows a certain number of disadvantages. First of all, it is not possible to form two cavities of the same surface area and of different depths, nor a deep cavity of small surface at the same time as a shallow cavity of large surface, since the etching speed is the same for all cavities and the maximum depth during the first step is directly proportional to the surface of the cavity.
Furthermore, this method does not enable obtaining a flat surface in all cavities, certain among them having to the contrary a V-shape bottom.
Next, this method does not enable one to control exactly the depth of all the cavities Effectively, as has been shown in FIG. 1 of the above mentioned document, if one wishes to form two cavities having different surface areas exhibiting between themselves a difference in depth less than the difference between their respective maximum depths, it is necessary to stop the etching of the cavity having the greatest surface before its maximum depth is attained. Thus, the moment when it is necessary to stop the etching may not be determined in a particularly precise manner since the etching speed can only be roughly estimated.
SUMMARY OF THE INVENTION
This invention has as its purpose to overcome the disadvantage of known etching methods. Such purpose is attained by the claimed method.
This method essentially consists in a first step of effecting an anisotropic etching through a mask partially covering the zones to be etched in order to form in each zone a set of V grooves, the depth of which depends on the width of such section. The depth of the etching in each zone is in this manner perfectly defined. In a preferred manner, the etching patterns assume the general form of rectangles. The latter are advantageously parallel to one another.
The second etching step, likewise anisotropic, increases uniformly the depth of each cavity The difference in depth between two cavities thus remains perfectly defined Such second etching step enables the obtaining in each cavity of a bottom which is substantially flat.
This may be profitably employed so as to control in a zone the thickness of a membrane or the depth of a cavity. It suffices in effect to etch during the first step such zone and another zone, referred to as the control zone, over depths such that during the second step the desired thickness for the membrane or the desired depth for the cavity are attained when the depth of the cavity in the control zone attains a precise and optically determinable value. This control depth may for instance be the thickness of the wafer or substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
The characteristics and advantages of the invention will be better brought forth in the description to follow giv
REFERENCES:
patent: 3844858 (1974-10-01), Bean
patent: 4761210 (1988-08-01), Ehrler et al.
patent: 4836888 (1989-06-01), Nojiri et al.
patent: 4899178 (1990-02-01), Tellier
patent: 4957592 (1990-09-01), O'Neill
patent: 5024953 (1991-06-01), Uematsu et al.
Article entitled "A Piezeoelectric Micropump Based on Micromachining of Silicon" by H. van Lintel, et al, Sensors and Actuators, vol. 15, pp. 153-167, 1988.
Article entitled "An IC Piezoresistive Pressure Sensor for Biomedical Instruments", by Samaun et al, IEEE Transactions on Biomedical Engineering, vol. BME-20, Nr. 3, pp. 101-107, Mar. 1973.
Article entitled "Novel V-groove structures on Silicon" by S. Siriam, vol. 24, No. 12, pp. 1784-1787, 15 Jun. 1985, New York, USA.
Dang Thi
Westonbridge International Limited
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