DD272704A1 - SQUARE OR RECTANGULAR SOUND (100) ORIENTED MEMBRANE OF MONOCRYSTALLINE SILICON AND METHOD OF MANUFACTURING THEREOF - Google Patents

Abstract

The invention relates to a square or rechteckfoermige silicon membrane for a piezoresistive pressure transducer and a manufacturing method for the membrane. Taskgemaess the invention is designed to increase the rigidity of the clamping frame. This is achieved in that the lateral boundary surfaces of the clamping frame represent both (111) and (100) surfaces, wherein the (100) surfaces perpendicular to the membrane plane are arranged in one or more membrane corners between two (111) boundary surfaces are. The method is characterized in that on the (100) silicon substrate an etching mask is applied, which has an opening corresponding to the number n of stiffened clamping frame corners of (4n) -square shape with 100 and 110-oriented edges. Subsequently, the substrate is exposed to an anisotropic etching agent in a wet-chemical etching process, forming an etching pit which defines a (100) -oriented bottom surface (membrane) and 111 surfaces laterally delimiting the 110 mask edges and bounding the 100 mask edges Has (100) surfaces. The etching process is aborted, after which the square or rectangular shape of the floor surface has developed and before the (Aetzgrube) laterally delimiting (100) surfaces are completely removed. Fig. 3

Description

For this purpose 3 pages drawings Field of application of the invention

The invention relates to a square or rectangular silicon membrane and a method for producing such a membrane, which is thinned by anisotropic wet chemical etching from a thick monocrystalline silicon substrate. The invention is particularly applicable in micromechanics, microelectronics and sensor technology.

Characteristic of the known technical solutions

The production of three-dimensional micromechanical structures in niocrystalline silicon substrates, in particular the production of square or rectangular membranes by means of anisotropic wet chemical etching processes, is known and has found wide application in the art (KE Petersen: Silicon as a Mechanical Material, Proceedings of the IEE 70 [1982] 5 , P.420-457). The main applications use (10000) oriented silicon wafers (DE 1.621.351). An etching mask, ζ, is located on the silicon substrate. For example, of silicon oxide or nitride, which has a rectangular or square-shaped opening whose edges are <100> -oriented. By the wet-chemical etching process with an anisotropic etchant, the z. For example, if it contains amines (DE 1,953,665, EP 0,004,872, EP 0,009,677) or basic (DE 1,621,351; DE 1,806,225), silicon membranes are also prepared which are also (100) -oriented and <100> have aligned mask edges. The laterally delimiting surfaces of the etch pit represent (111 (faces which enclose an angle of 54.7 ° with the (100) face (Al Stoller: The Etching of Deep Vertical Walled Patterns in Silicon, RCA Review 31 (1970), For many applications, the part of the un-thinned silicon substrate serves as a clamping frame around the thinned membrane, carrying the membrane and determining, by its mechanical rigidity, the mechanical stability of the membrane and the influence of external disturbing forces or moments on the membrane The size of the clamping frame is thereby

limited by several factors, such. As the realization of a certain number of chips on a disc or the requirement of a certain degree of miniaturization of the structures, as occurs for example in biomedicine. The rigidity of the clamping frame or the rigidity of the webs, which hold the membrane directly, is decisively influenced by the stability of the clamping frame in the region of the corner points of the membrane. An additional stabilization of these areas orfoli * usually not. Only measures are known which counteract a further decrease in stability in these Beieichen, in particular by undercutting of convex corners (DE 1,621,532; DD 241,976).

Aim of the invention

The object (he invention is to reduce the influence of external disturbing forces or moments on the clamping frame on the membrane.

Explanation of the essence of the invention

The object of the invention is to provide a (100) -oriented quadrangular silicon membrane and a manufacturing method for the same, which is carried on a clamping frame with increased mechanical rigidity.

According to the invention, this object is achieved in that the lateral boundary surfaces of the clamping frame in addition to (111! -Faces also (100) surfaces which are in each case one or more corners of the membrane between two (11D boundary surfaces substantially perpendicular to the membrane plane. The method for producing such a membrane is characterized in that on the (100) -oriented silicon substrate an etching mask is applied, which has an opening with a five- to octagonal shape such that of a square or rectangle with edges in crystallographic <100 > Direction is at least a corner triangular masked, that the long edge that limits the Ätzmaskenöffnung has a krictallografische <100> orientation, that the substrate is exposed in a wet chemical etching process an anisotropic etchant, and that the etching process is stopped, after getting a square or rectangular Floor surfaces in the etching pit has emerged. The anisotropic wet-chemical etching process forms in the (100) -oriented silicon substrate

A bottom surface also having (100) orientation,

- four \ 111! -Oriented side surfaces intersecting the (100) face at the mask edges in the <100> direction, and

Corresponding to the one to four triangularly masked parts, one to four (ICO) -oriented side surfaces intersecting the (100) surface at the <100> -oriented mask edges and bordering two (111) -oriented side surfaces,

out. At the beginning of the etching process, the (100) -oriented side surfaces and the (100) -oriented bottom surface adjoin one another. In principle, anistropic wet-chemical etchant (100) surfaces are removed much faster than (111) surfaces. As a result, after a certain etching time, the etching pit laterally and at the bottom bounding (100) surfaces are removed so far that the laterally delimiting (100) surfaces abut the ground bounding (100) surface or only in each case in one point. The bottom surface is thus determined in its dimensions completely by the four (111) -oriented side surfaces and thus forms a square or a rectangle with <100> -oriented edges.

The etching pit is delimited by two (111) and one (100) -oriented surfaces in the area of the corners of miot <100! »-Oriented mask edges. As a result, less material of the silicon substrate is etched out from the boundary by only two (111) surfaces in the corner region, so that the clamping frame is stiffened in this area.

For the production of the etching mask and for the anisotropic wet-chemical etching process, it is possible to use customary semiconductor-based and micromechanical layer deposition and structuring and etching processes.

embodiment

The invention will be explained in more detail below by exemplary embodiments. Show

FIGS. 1 to 5: Steps of the method according to the invention for a clamping corner of a 1000-oriented square-wave

or Rectangular membrane Figure 6 and 7: the top view of a pressure membrane according to the invention prepared in the initial and final state

the production and Figure 8 and 9: the plan view and the sectional view of a membrane corner according to the invention with thickened Eirispannradmen.

FIG. 7 shows a plan view of a square (100) -oriented silicon membrane, which is held by a clamping frame 8. The upper opening of the Einspannrahmens has the shape of an octagon, ie the clamping frame is in all viet ι / it. ., industry sectors is enhanced by the creation of (100) delimiting surfaces on the membrane, thus providing increased mechanical stability. As can be seen from Fig.5, the ^! enclosed in the corners (100) boundary surface of each two (111) boundary surfaces 6 and does not touch the membrane 9 or only at one point.

In Fig. 1, the corner region of a square or rectangular membrane to be created is shown. For this purpose, an etching mask 2 is produced on a silicon substrate 1 with (100) orientation by conventional semiconductor technology or micromechanical methods, which has an octagonal opening 3 such that from a square or rectangle with edges in the crystallographic (110) direction 4 corners are masked triangular with the long edge of the isosceles triangles bounding the etch mask opening and oriented in the crystallographic (100) direction. The opening 3 of the etching mask 2 has

therefore only edges in the (110) and (100) directions, with exactly four (110) edges (in the detail corresponding to FIG. 1 the edges in the (011) and (0it) directions) and 4 (100) - Edges (in the cut corresponding to FIG. 1, the edge in (01O) direction) are generated. The etching mask 2 may consist of silicon oxide, nitride, a metal or doped silicon, for example. In the next step, the silicon substrate 1 on the side of the etching mask 2 is exposed to an anisotropically acting wet chemical etchant. Such etchants may be, for example, basic aqueous solutions of potassium or sodium hydroxide or aminhaliige mixtures of hydrazine and water or ethylenediamine, pyrocatechol and water. In the etching process, an etching pit 4 forms in the silicon substrate 1, the bottom surface 5 of which, like the silicon substrate 1, has a (100 "orientation (FIG. 2).

The etch pit is bounded laterally by (111) -oriented side surfaces 6 and (10) OOJ-oriented side surfaces 7. The (11D-oriented side surfaces 6 appear at the (110) -oriented masking edges and make an angle with the bottom surface 5 125.3 ° C. They are removed at an etch rate R 1n which, for wet-chemical anisotropically acting etchants, is in principle smaller than the etching rate R 100 of the bottom surface. oriented mask edges and are perpendicular to the bottom surface 5. They are removed at the same etching rate R ^ ₀₀ ) as the bottom surface 5.

Because of the greater etch rate R (too) of the (100) -oriented side surfaces 7 with respect to the etch rate R <in> of the (111! -Oriented side surfaces 8 and the greater resistance of slow-etching surfaces to concave corners of three-dimensional etches, at the time shown in FIG. 3, the side surface 7 is removed so far that the (111) and (100) -oriented side surfaces 6 and 7 abut each other at a point with the bottom surface 5. The bottom surface 5 of the etching pit 4 has the square or rectangular shape corresponding to the etching mask opening 3 of the etching mask 2 The etching process may be stopped or continued at this point in time, with the termination taking place before the (100) -oriented side surface 7 has been completely removed (Figure 4) The side surfaces 7 are here distinguished from the (111! Side surfaces included, which determine the square or rectangular shape of the bottom surface 5. Compared to the case that the et Zgrube 4 laterally limited only by (111! -faces, occurs in the field of Ätzgrubenecken by the vertical surface to the bottom surface 5 side surfaces 7 thickening of the Einspannrahmens 8 of the membrane 9.

Fig. 5 shows the arrangement according to Fig. 4 after the possible, but unnecessary removal of the etching mask 2. Fig. 6 shows a silicon substrate 4 for the manufacture of a square membrane according to the invention, for. B. for a pressure sensor. On the substrate 1 in the manner described above, an etching mask 2 is applied with an octagonal etching mask opening 3, the Ätzmaskenkanten (110) - and (100) -oriented. To prevent the corner undercut at convex corners of three-dimensional etches additional compensation etching mask parts 10 are realized. Fig. 7 shows the substrate 1 of Fig. 6 after completion of the etching process and removal of the etching mask 2. Within the substrate 1, the membrane 9 is thinned square. The etching pit in the substrate 1 is bounded laterally by (111) -oriented side surfaces 6 and (10C) -oriented side surfaces 7. The thickening of the clamping frame 8 is given by the corner regions 11 in which the etching pit is perpendicular to the bottom surface of the membrane 9 Side walls 7 and not by suitable side surfaces, such as (111! -Laces is limited.

FIGS. 8 and 9 show the geometric relationships between the dimension of the etching opening 3, in particular of the triangular areas 11 in the region of the corners of the membrane 0 in comparison to the etching depth dpoo) in the case where no etching stop mechanism in the vertical direction in the silicon substrate 1 Changing the etching rate R <ioo> causes. As a result, the stiffening of the corner region is achieved when, for the dimension b, the relationship

d (ioo) <b S 2d (ioo)

applies

 Because of

a = V2b for isosceles triangles, the isosceles sides must have a dimension a of

respectively.

By the use of etch stop mechanisms in the vertical etching direction, ratios a> 2 \ J2 d < ₁₀ > are also possible.

Claims (5)

A square or rectangular (100) -oriented tnonocrystalline silicon membrane with <100> -oriented membrane edges carried by a thick monocrystalline silicon clamping frame surrounding the membrane, characterized in that the lateral boundary surfaces of the clamping frame are both (111) and (100) surfaces, wherein the (100) surfaces perpendicular to the membrane plane are arranged in one or more membrane tuyeres in each case between two (111) boundary surfaces. 2. A process for the production of square or rectangular, (100) -oriented or rectangular membranes of monocrystalline silicon with <100> -oriented membrane edge according to claim 1, which is supported by a thick gripping frame of monocrystalline silicon, the η = 1 ... 4 stiffeners in the region of the membrane corners, characterized - That on a (100) -oriented silicon substrate, an etching mask is applied, which has an opening corresponding to the number η of stiffened Einspannrahmenecken with (4 + n) -eckiger form such that of a square or rectangle with <100> -oriented edges precisely η corners are triangularly covered by the etching mask, that these etching mask edges have a <100> orientation, - that the noun at ^r in a wet chemical etching process is exposed to an anisotropically acting etching agent, In that an etching pit is formed in the etching process by the anisotropic etchant, which has a (100) -oriented bottom surface, which is the membrane surface, as well as at the <100> mask edges laterally delimiting (111) surfaces and at the <100> mask edges having laterally delimiting (100) surfaces, which are side surfaces of the clamping frame, and - That the etching process is stopped after the square or rectangular shape of the (100) -oriented bottom surface has formed, but before the etching pit laterally delimiting (100) surfaces are completely removed. 3. The method according to claim 2, characterized in that the removal rate of the etchant in the depth of the diaphragm pit undergoes no change and the isosceles sides of the triangular Ätzmaskenbereiche in the square or rectangular Ätzmaskenöffnungen dimensions between the \ / 2-fold and because 2 · / 2 times the required etch depth. 4. The method according to claim 2, characterized in that following the etching process, the Ätzmaskierung is removed. 5. The method according to claim 2, characterized in that the etching depth of the membrane pit is determined by an etch stop mechanism.