Etching a substrate: processes – Etching of semiconductor material to produce an article...
Patent
1996-05-10
1997-12-02
Breneman, R. Bruce
Etching a substrate: processes
Etching of semiconductor material to produce an article...
216 41, 216 67, 1566431, 1566621, H01L 213065
Patent
active
056932340
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a method for producing at least one recess in a surface of a substrate, an apparatus for carrying out the said method, and a use of the substrate with the recess produced with the method.
Membranes are used in many technical fields. One important area of application is sensor technology, in which the deflection or vibration of a membrane is utilized to measure a physical quantity. Examples of this are noise sensors or pressure sensors, made in most cases of silicon. An important consideration in all applications is that the membrane can be destroyed by excessive impact or pressure effects in the event of overload. This is particularly the case when the membrane consists of a relatively brittle material such as silicon. To protect the membrane against overload, a shaped bed against which the membrane can rest in the event of overload is generally provided.
Several methods for producing such shaped beds, in which a recess is produced in a flat surface of a substrate, are known.
In a first method, a recess with a trapezoidal contour is produced in the (100) surface of a silicon substrate by anisotropic wet etching with potassium hydroxide (KOH). In the event of overload, the membrane rests against the center region of the flat bottom of the recess. The support function of the shaped bed can therefore be effective only in this small center region, so that the membrane can be destroyed by further stress.
A second possibility for manufacturing such shaped beds consists in producing a recess with a stepped contour in a silicon substrate by means of a plurality of lithography steps, carried out successively with photoresist masks of increasing diameter. The contour of the recess can be approximated to a smooth curve by increasing the number of lithography steps (WO 90/04701, in particular FIG. 3). Setback areas still remain, however, and are problematic because of their notch effect. In addition the method is complex because of the many process steps, and requires precise alignment of the etching masks for each lithography step.
A shaped bed can also be produced with gray-area lithography. With this third method a mask with a gray zone that becomes lighter toward the center of the desired recess is required for the substrate. Lithography then produces, under suitable exposure conditions, a resist contour with a thickness that decreases toward the center. When the substrate is then etched, the resist mask recedes and exposes more and more substrate surface. One disadvantage of this manufacturing method is that the resist mask can be made to recede up to, at best, a magnitude of 10 to 20 .mu.m. The method therefore cannot be used if the diameter of the shaped bed is to be substantially greater than its depth.
A fourth possibility for manufacturing the shaped bed is mechanical machining of the substrate by turning, milling, grinding, polishing, or blasting. With contour depths of a few .mu.m, the precision of this method is insufficient.
Etching methods referred to as "dry etching" are known for etching of substrate surfaces. The characteristic feature of such dry etching processes is the chemical reaction of radicals or ions of an etching gas with the substrate surface to form a volatile reaction product. The chemical reaction can be spontaneous, or induced by ions, electrons, or photons. The etching gas radicals are generally produced in a low-pressure plasma, typically between 10.sup.-1 and 10.sup.-3 Pa. In such cases reactive dry etching is therefore often also referred to as "plasma etching." The plasma can be produced by a high-frequency electromagnetic field that is either applied to electrodes or supplied directly as microwaves. Several types of plasma reactors are known for carrying out the dry etching process. All the types have a receptacle in which the substrate to be etched is arranged, and that is equipped with connectors for evacuation and for supplying the etching gas. In a first reactor type, called a tunnel reactor or barrel reactor, a perforated h
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Landolt, Bornstein: Numerical Data and Functional Relationship in Science & Technology Group 3--Crystal & Solid State Physics, vol. 17, Semiconductors, Subvolume c, Technology of Si, Ge and SiC, pp. 319-321, 326-328, 566-567.
Adjodha Michael E.
Breneman R. Bruce
Siemens Aktiengesellschaft
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