Etching a substrate: processes – Forming groove or hole in a substrate which is subsequently...
Patent
1996-06-10
1997-11-25
Breneman, R. Bruce
Etching a substrate: processes
Forming groove or hole in a substrate which is subsequently...
216 51, 216 80, 1566441, H01L 21306, G01L 900
Patent
active
056908415
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of producing cavity structures, suitable for use as capillary fluid flow systems, pressure sensors etc., by means of micromechanical manufacturing methods.
One type of micromechanical manufacturing techniques is based upon microelectronic methods known from the semiconductor technology.
It is previously known to manufacture miniaturized analytical systems by means of microelectronic methods. For example, CH-A-679952 discloses the manufacture of an analytical chip, particularly for FIA (Flow Injection Analysis), by making channels in one or both of two plates of glass or silicon by photolithographic means, and then attaching the plates to each other such that a capillary system is defined between the two plates. The thickness of the plates reduces the possibilities of using microelectronic methods for integrating further functions in the system.
U.S. Pat. No. 4,996,082 discloses a method of producing a cavity in a semiconductor substrate, particularly for use as a pressure sensor. In brief, the process consists in depositing onto a semiconductor substrate, typically of crystalline silicon, an oxide layer to a depth equivalent to the height of the desired cavity, depositing a layer of polycrystalline silicon on top of the oxide layer, and then from uncoated side portions of the oxide layer etching out a cavity under the layer of polycrystalline silicon. The etch channel openings can then be sealed by subjecting the substrate to an oxidizing ambient which results in growth of silicon dioxide in the channels sufficient to seal off the channels. Due to the need of etching from a side edge in under the substrate surface, the process is time-consuming and complicated.
FIG. 1 presents the deposition of a masking layer 2 on a substrate 1.
FIG. 2 shows that after application of photoresist and patterning in a conventional manner, a hole 3 is made in the masking layer.
FIG. 3 shows that a selective etch of substrate 1 is carried out through the hole 3.
FIG. 4 shows the expansion of the masking layer by the oxidation of the polysilicon to quartz.
FIG. 5 shows the sealing of the etched cavity or flow channel by depositing a layer 5 of silicon dioxide (quartz).
The present invention provides a simplified and improved method of producing cavities of various types under the surface of an etchable substrate.
More particularly, the invention provides a method of producing sealed cavity structures in the surface layer of a selectively etchable substrate by: the substrate, to the substrate surface, substrate in under the masking layer so as to form one or more cavities which extend under the masking layer, and
The substrate material is preferably glass, quartz or silicon, while the masking layer preferably is polycrystalline silicon (polysilicon) or silicon nitride.
In one embodiment, the masking layer is polysilicon, and the sealing of the opening or openings in the masking layer is effected by oxidation of polysilicon to silicon dioxide, causing expansion of the polysilicon layer. Preferably, the substrate is of quartz, so that the whole finished product after the oxidation is totally of quartz.
In another embodiment, the sealing is effected by deposition of a material layer on the substrate surface and the hole walls. The deposited material may be a metal, a semiconductor or an insulator. The deposition may, for example, take place by sputtering, vaporization or a CVD (Chemical Vapor Deposition) method. If the substrate is of glass or quartz and the deposited material is silicon dioxide (quartz), a product that completely consists of quartz may be obtained.
In a further embodiment, the sealing of the opening or openings is effected by a combination of oxidation of a masking layer of polysilicon and deposition of an additional material layer.
The shape of the holes in the masking layer may vary depending on the desired cavity shape. As examples may be mentioned square and rectangular holes. A continuous cavity can be made in the substrate via etching of a plurality of holes in the m
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Adjodha Michael E.
Breneman R. Bruce
Pharmacia Biotech AB
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