DD272737A1 - METHOD FOR PRODUCING A NARROW (100) ORIENTED RECTANGULAR MEMBRANE OF MONOCRYSTALLINE SILICON - Google Patents

Abstract

The invention relates to a method for producing a narrow (100) -oriented rectangular membrane of monocrystalline silicon for a piezoresistive pressure transducer. Taskgemaess the invention is designed to increase the rigidity of the clamping frame. This is accomplished by depositing on the (100) -oriented silicon substrate an etching mask containing a master mask opening with 110 mask edges and paired 100 mask edges in pairs, and which further includes minor mask openings having four 110 mask edges, the minor mask openings lie in the 110-direction of the intersection of two 100-mask edges of Hauptaetzmaskenoeffnung and lying in the radial direction to these intersections 110 edges has a length of at least 1 / 2fachten Aetztiefe. The substrate is subsequently exposed to an anisotropic etching agent in a wet-chemical etching process to form a primary etching pit with (100) -oriented bottom surface and (111) and (100) -oriented lateral boundary surfaces, and sub-etching groups each having at least one of the 110 mask edge (111) -Seitenflaeche be formed. Fig. 5

Description

For this 8 pages drawings

Field of application of the invention

The invention relates to the production of narrow rectangular membranes thinned by anisotropic wet chemical etching from a thick monocrystalline silicon substrate. The invention is applicable in micromechanics, microelectronics and sensor technology, in particular for pie * oresistive miniature pressure transducers for biomedical applications.

Charjk »eristik of the known technical solutions

The production of three-dimensional micromechanical structures in monocrystalline silicon substrates, in particular the production of right-handed membranes by means of anisotropic wet-chemical etching processes, is known and has found wide application in the art. I'KE Peterson: Silicon as a Mechanical Material. Proceedings of \\, e IEEE 70 [1982] 5, p.420-457). The main applications use (100j'oriented silicon wafers [DE 1.621.351].) An etch mask, ζ, for example, of silicon oxide or nitride, which has a rectangular opening, whose edges are oriented 110, is located on the dom silicon substrate. The wet-chemical etching process with sinamic anisotropic etchants, which is, for example, amine-containing (DE 1,963,665; EP 0,004,872; EP 0,009,677) or basic (DE 1,621,351; DE 1,806,225), produces silicon membranes , which are also (100) -oriented and have <110> -oriented misaligned edges. The laterally delimiting surfaces of the etch pit represent (111! -surfaces, those with the (100) -surfaces an angle of 54.7 ° For many applications, the part of the un-thinned silicon substrate around the thinned membrane serves as a chucking frame , where he the membr (protrudes and determined by its mechanical rigidity, the mechanical stability of the membrane and the influence of external disturbance forces or moments on the membrane. The size of the Einspannrahmens is 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. * 2 additional stabilization of these areas is usually not possible. Only measures are known which counteract a further loss of yield in these areas, in particular by undercutting of convex corners (DE 1,621,532; DD 241,976).

However, high mechanical stability is required above all in sensor technology in order to achieve a drift-poor and long-term stable transmission behavior of micromethanic sensors, eg. B. Biomedical pressure transducer (see, for example, M. Esashi et al., Fabrication of Catheter-Tip and Sidwall Miniature Prossure Sensors, IEEE Transactions on Electron Devices ED-29 [1982] 1, pp. 57-63) to secure. Even after installation and obstruction, external interference that acts on the thin membrane via the clamping frame must not exceed a permissible limit value. For example, due to insufficient stability of miniaturized chips with very small and narrow membranes, elaborate design measures for reducing external mechanical disturbances are necessary (for example DD 216.467).

Object of the invention

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

Essence of the invention

The object of the invention is to provide a method for producing (100) and <110> -oriented, narrow rectangular silicon membranes whose silicon clamping frame has increased rigidity. According to the invention, this object is achieved by

- In that on the (100) -oriented silicon substrate, an etching mask is applied, which has a Hauptätzmaskenöffnung with the following described shape and <110> and <100> -oriented mask edges and one or more side openings each having at least one <110> -oriented mask edge .

That the substrate is exposed to an anisotropic etchant in a wet-chemical etching process,

In that a main etching pit is formed by the anisotropic etchant in the region of the main etching mask opening, which has a (100) -oriented bottom surface and (100) -oriented side surfaces, and in the region of the secondary openings r ', self-etching pits each having at least one formed by the <110> mask edge (111!

That in the etching process, as a result of the large etching speed R i of the lateral (100) faces of the main etching pit, the (100) etch faces strike the side faces of the necene etching pits, so that the etch pits are connected to form a resulting etch pit, and

That the ÄUprozeß is aborted, after which the rectangular shape of the (100) -oriented bottom surface, which forms the membrane surface, has formed, but before the etch pit laterally delimiting (100) surfaces are completely removed. The shape of the etch mask results from local coverage of the shape of the etch mask opening for conventional rectangular (100) membrane with lateral (111! -Oriented areas of the etch pit, the dimensions of the etch mask opening being the size of the membrane to be fabricated, taking into account the etch depth The enlargement of the membrane, which is inclined by 54.7 ° (111), and the enlargement of the membrane by the ablation of the lateral (111) surfaces, corresponds to two equal-sized isosceles triangular areas of this rectangular area with <111> -oriented canton Areas in the corner are partitioned so as to form a main etch mask opening having <110> mask edges and two <100> mask edges meeting at right angles, thus intersecting the jewel's two <100> mask edges within the original rectangular area the covered pages d in the original rectangular shape, minor openings are made in the etching mask having four <110> edges, with a <110> edge on the line of conventional rectangular ropes and the center of the side of the original rectangular shape on the <110> Edge of the secondary opening is located and the right angles to <110> edges has a length of at least 1 / \ / 2 times the etch depth d _<100 >. The side openings of the mask are within the original rectangular shape. During the anisotropic wet chemical etch process, etch pits are formed in the silicon substrate which penetrate the <110> etch mask edges of the main and auxiliary etch mask openings through (11) faces and the <100> etch mask edges of the main etch mask opening by perpendicularly to the top and bottom faces. The ί 111! -Faces are thereby removed at an etching rate R _<) , ₁ >, which is negligibly small compared to the etching rate R <100> surfaces of the (100) surfaces. As a result of the ground and side surfaces with (100) orientation removed at the same etching rate R <, oo>, the (100) etch fronts reach the etch pits of the secondary etch mask openings and strike the slow etching (111) faces at their <110> mask edges , which are only eroded with Rm, thus forming the four (111) surfaces delimiting the membrane, and the (100) follicles are further removed by the etchant until the rectangular shape of the bottom surface of the remitent etching group has developed In this case, two laterally delimiting surfaces can enclose a lateral delimiting (100) surface in such a way that they intersect all three surfaces exactly at the corner of the bottom surface, or that the two (111) surfaces have a common edge and only the (111) surfaces in the vertex of the bottom surface intersect, and in the region of the corners Damii will greet the etch pit by two (111) and one lOOl-oriented surfaces Thus, there is less material compared to the boundary of only two (111) faces in the corner. etched out of the silicon substrate, so that the Einspannrahrnen is stiffened in this area.

For the preparation of the etching mask and for the anisotropic wet-chemical etching process, conventional semiconductor-technological and micromechanical layer deposition and structuring and etching processes are applicable.

-3- 272 737 Embodiment The invention will be described below with reference to exemplary embodiments. Showing:

FIGS. 1 to 5 show steps of the method according to the invention for producing scimal rectangular silicon membranes, which are shown in plan view,

FIGS. 6 to 8: FIGS. 1, 3 and 5 in a three-dimensional view, FIGS. 9 to 14: a rectangular membrane produced by the method according to the invention according to FIGS. 1 and 5 in plan view

and sectional views, an etching mask with characteristic dimensions used during the method according to the invention,

15 shows important geometric dimensions of the etching mask and the initial and final state of the listening position

16 and 17: square membranes with the method according to the invention.

1 shows a (100) -oriented monocrystalline silicon substrate 1, on which an etching mask 2 with conventional

Semiconductor technology and micromechanical process was generated. The etching mask 2 may for example consist of silicon oxide, nitride, of a metal or doped silicon. It has a Hauptätzmaskenöffnung 3 and a secondary opening 4. The shape of the etching mask results from the Ätmasmaskenform 5, dio conventionally for the production of (1 CO) -oriented membranes with <110> membrane edges and the etch pit laterally delimiting (111! -Flächen used becomes.

This Ätzmaskenform 5 results from the size of the membrane being produced plus the substrate broadening due to be realized etching depth d _{<1O o>} Oei 54.7 ° inclined (111 -oriented faces derÄtzgrube and considering the almost negligible kloinen etch rate of the (111 (! - From this originally rectangular shape 5, two isosceles triangular parts 6 and 7 are additionally masked in the region of the corners in such a way that <100> -oriented mask edges 9 are formed to the existing <110> oriented mask edges 8 of the main etch mask opening. Further, in the thus masked area 6 and 7, a sub-etching mask opening 4 is made to have four <110> mask edges, of which a <110> -oriented mask edge is in the middle of the narrow one Page 10 of the original rectangular shape 5 with the narrow side 10 even higher and that the <110> edges lying at right angles thereto have a length of at least 1/2 times the etching depth d < ₁ oo>, and that this opening 4 lies within the originally rectangular shape 5. Preferably, small square or rectangular minor openings 4 with four <110> -oriented mask edges are used. The arrangement of Figure 1 is shown spatially in Figure 6.

The substrate 1 processed in accordance with FIG. 1 is subsequently exposed to an anisotropic etchant in a wet-chemical etching process. Such etchants may be, for example, basic aqueous solutions of potassium or sodium hydroxide or amine-containing mixtures of hydrazine and water or ethylenediamine, catechol and water. All anisotropically acting etchants wear (100) -oriented silicon surfaces with a large etching speed R <ioo> and (111) -oriented surfaces with a small etching speed R <in> <ä R <ioo>. In all representations of FIGS. 2 to 5, 7 to 15 and 17

the etching rate R <, n> is neglected because of its very small size. For better clarity, the etching mask 2 has been omitted from FIGS. 2 to 5, 7, 8 and 17 in FIGS.

As a result of the action of the etchant, a main etching pit 11 in the region of the main etching mask opening 3 and a secondary etching pit 12 in the region of the auxiliary opening 4 are produced in the silicon substrate. The Hauptätzgrube in this case has a (100) bottom surface 13 and (111) side walls 15, which are inclined to the (100) plane 125.3 °, and (100) side walls 14, which is perpendicular both to.

(1 OO) surface as well as on each other, up. The auxiliary etching pits 12 have four (111! Side faces 15, so that an anisotropic etching stop occurs.

In the further course of the etching process with further removal of the side of the main etching pit bounding (100) surfaces 14, these (1001 surfaces 145 abut the auxiliary etching pit 12, so that a common etching pit 16 is formed (Figures 3 and 7).

Due to the (111 (-oriented surface of the secondary etching pit 12, which represents a slow axis surface, a continuation of the etching in the <011> direction is no longer possible.) The (111! -Face thus increases in the further etching process, just as the (111) Surfaces 13 of the main etching pit 11, while the perpendicular to the (100) -Bodsnfläche 14 standing (100) -side surfaces 14 decrease.

According to FIGS. 4 and 5, as a result of the further removal of the (100) side faces 14 of the etching pit 16, the rectangular shape of the bottom face 13 is formed. For this purpose, the laterally delimiting (111) surfaces 15 and 17 may punctiformly collide with the bottom surface 13 and the (100) side surface 14 (FIG. 4), or later in the etching process the (111) surfaces 15 and 17 form a common edge 18 so that the (100) side surface 14 is separated from the (100) bottom surface 13 (Figures 5 and 8).

Because the corner region 19 is bounded by lateral (100) -oriented surfaces 14, which is perpendicular to the bottom surface 13, and that therefore less material of the silicon substrate 1 has been etched out, the clamping frame 20 is substantially stiffer compared to the variants in which Corner area exclusively inclined surfaces, eg. B. (111 (surfaces) occur.

Fig. 9 shows Fig. 5 taking into account the etching mask 2, Fig. 10 to 14 show for better illustration different sectional views through Fig.9.

After the rectangular bottom surface 13 according to Figures 4 and 5 has emerged, the etching process is stopped.

Subsequently, the etching mask can be removed.

Figure 15 shows important geometric dimensions of the etching mask 2, in particular the triangular areas 6 and 7 in the corner of the membrane to be created, described by the bottom surface 13. The distances d _<m> correspond to the distance, with the (100) surfaces 13 and 14 were removed in the etching time by the etching rate R <ioo>.

Fig. 15 shows the case that the depth of the etching pit 16 is limited by no etching stop mechanisms. In the case of limiting the vertical etch depth by etch stop mechanisms, in Fig. 15b and c, the value for d < _{) O} o> is to be replaced by the etch depth. According to FIG. 15, the criterion is the stiffening of the corner area 19

a = \ / 2e

or with it

V2 <-j - ^ - <2 V2.

The following relationships d <ioo> apply to the etching mask recess 3

Δ / and

tan 54.7 °

^{2d <100>} = tan 54.7 °.

f-b

Furthermore, according to the invention csd _<100 .- / \ / 2.

FIG. 16 shows the possibility of applying the method according to the invention to the production of small square-shaped membranes as shown in FIG. The manufacturing steps correspond to those of FIGS. 1 to 5, only distinguished by the fact that a small square Hauptätzmaskenöffnung 3 with <1 OO-oriented edges is required and find four Nachätzmaskenöffnungen 4 according to the square membrane shape.

Claims (4)

A process for producing a narrow (100) -oriented rectangular monocrystalline silicon membrane with <110> -oriented membrane edges carried by a thick monocrystalline clamping frame having stiffeners around the corners of the membrane, characterized An etching mask is applied on the (100) -oriented silicon substrate, which comprises a main etching mask opening with <110> etching mask edges and pairwise mutually perpendicular <110> etching mask edges, and which also contains secondary etching mask openings having four (110) etching mask edges wherein the secondary etching mask openings are in the direction of the intersection of two <100> etching mask edges of the main etching mask openings and the <110> edges lying radially to this point of intersection have a length of at least 1/2 times the etching depth, That the substrate is exposed to an anisotropically acting etchant in a wet-chemical etching process, That a main etching pit is formed by the anisotropic etching agent in the region of the main etching mask opening, which has a (100) -oriented bottom surface and (111) and (100) -oriented side surfaces, and that in the region of the secondary opening auxiliary etching pits each having at least one of the <110> mask edges are formed on certain (111) side surfaces, - That in the etching process, the etching fronts of the (100) side surfaces of the main etching pit meet the side surfaces of the Nebenätzgruben, so that a common etching pit is formed and - That the etching process is stopped, after which the rectangular shape of the (100) -oriented bottom surface has formed, but before the etching pit laterally delimiting (100) surfaces are completely removed 2. The method according to claim 1, characterized in that the etch depth of the membrane pit is determined by an etch stop mechanism. 3. The method according to claim 1, characterized in that following the etching process, the Ätzmaskierung is removed. 4. The method according to claim 1, characterized in that the Hauptätzmaskenöffnung has a square shape with <100> edges and in square symmetry in each of the four <110> directions are the Nachätzmaskenöffnungen in the etching mask.