GB2260282A

GB2260282A - Three-dimensional silicon structure

Info

Publication number: GB2260282A
Application number: GB9221282A
Authority: GB
Inventors: Udo Jauernig
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1991-10-12
Filing date: 1992-10-09
Publication date: 1993-04-14
Anticipated expiration: 2012-10-09
Also published as: DE4133885C2; DE4133885A1; JPH05293965A; GB2260282B; GB9221282D0

Abstract

A three-dimensional silicon structure is proposed which can be used as a silicon nozzle e.g. petrol injection nozzles with a feed channel. The three-dimensional silicon structure comprises a first silicon part 1 having an opening 6 and a second silicon part 2 having a channel 14. The two silicon parts are joined by a bonding process so that the channel 14 is located on the opening 6 (Figure 1). <IMAGE>

Description

2r- 2 5 3 -2 1 -2 Three-dimensional silicone structure

Prior art

The invention proceeds from a three-dimensional silicon structure in accordance with the generic class of the main claim. Three-dimensional silicon structures are already known (Csepregi L. in Heuberger A., Mikromechanik, Springer-Verlag, 1989, pages 230-234) which are produced by joining together silicon wafers placed one upon the other by means of bonding techniques. These structures remain, however, essentially restricted to planar components.

Advantages of the invention The three-dimensional silicon structure according to the invention having the characterising features of the main claim have [sic], on the other hand, the advantage that the third dimension is better developed and, consequently, applications other than those for planar components are also possible. The freedom thereby gained in structuring silicon can be- utilised for novel silicon components.

As a result of the measures cited in the subclaims, advantageous further developments and improvements of the three-dimensional silicon structure specified in the main claim are possible. The use of silicon parts which have been produced in turn by bonding two silicon wafer parts expands the structuring possibilities yet again. Such components are suitable, in particular, for producing high-precision channels. Said channels are prepared for the application case concerned in a particularly simple manner by cutting up the wafer parts and then polishing the cut face. Nozzles with feed channels are produced by joining the channels to a silicon part having openings. The basic elements f or fluidics, channels and nozzles are consequently produced in a particularly advantageous manner and with great structuring freedom as a result of the silicon structure according to the invention.

Drawings An exemplary embodiment of the invention is shown in the drawings and is described in greater detail in the description below. Figure 1 shows a first embodiment of the invention and Figure 2 shows the second silicon part during production.

Description of the exemplary embodiment

In Figure 1, a first silicon part is denoted by 1 and a second silicon part by 2. The first silicon part 1 has an opening 6. The second silicon part 2 is composed of two sub-parts 11, 12 and has a channel 14. The channel 14 extends through the entire second silicon part 2. The silicon part 1 and the silicon part 2 are joined one to the other, as indicated by the arrows. This joining takes place by a process of bonding the surface 4 of the first silicon component 1 to the end-f ace surface 5, here concealed, of the second silicon component 2. The two surf aces 4 r 5 have been prepared in a suitable manner f or the bonding process. Both surfaces 4,, 5 have to be sufficiently flat. The surface 4, which is the surface of a silicon wafer, is provided with a sufficiently good surface quality by the wafer manufacturer as a result of polishing and etching processes. A sufficiently flat surface 5 is produced by mechanical machining. The further preparation of the surfaces 4, 5 for the bottom [sic] process may comprise the sputtering-on of thin layers of sodium-containing glasses, the thermal oxidation of silicon dioxide layers or the hydrophilisation of the silicon surface. The actual bonding process then comprises the application of an electrical voltage to the two components and/or a heat treatment. The relevant bonding processes are described in the literature reference mentioned at the outset. The geometry of the openings 6 is not specified in a mandatory manner. Long slots extending in parallel having walls oriented perpendicular to the surface can be produced in 110 silicon by using anisotropic wet-chemical etching processes, while in 100 silicon, the side walls have an angle of approximately 55 with respect to the surface. Openings whose smallest cross section is inside the silicon part 1 can also be produced in 100 silicon by double-sided anisotropic etching of the silicon part 1. In the case of the wet-chemical anisotropic etching processes, however, the geometry of the openings 6 is governed by the crystal structure of the silicon. Any desired plan-view shapes of the opening 6 with virtually perpendicular walls can be produced by using anisotropic plasma etching processes, such as, for example, reactive ion etching. Any desired shapes of the opening 6 can also be produced by using isotropic etching processes, but in this case, the angle of the side walls with respect to the surface 4 depends on the shape of the opening 6.

In an equivalent manner, multiple arrays of the openings 6 or the channels 14 having openings 6 are conceivable. In this case, a plurality of openings 6 may either be assigned to a channel 14, or a plurality of channels 14 may be arranged side-by-side, each having one or more openings 6. In the latter case. a multiplicity of individual channels 14 having openings 6 may be manufactured in parallel by cutting up this structure.

The three-dimensional silicon structure shown here can be used as a silicon nozzle having a feed channel. These nozzles can be manufactured with great precision by using anisotropic etching processes. Owing to the chemical passivity and high temperature resistance of silicon, said nozzles can also be used in an aggressive environment, for example as petrol injection nozzles.

Figure 2 shows the production of the second silicon part 2 from two wafers 21, 22 situated one on top of the other. 13 denotes trenches introduced into the wafers 21, 22. The channels 14 are formed during bonding by capping a trench 13 with the other wafer or by placing two trenches 13 one on top of the other. Cutting up the wafers along the lines 15 produces the second silicon parts 2, the cuts 16 defining the number of channels 14 in the second silicon part 2. At least one of the surfaces produced by the cuts 15 perpendicular to the surface of the wafers 21, 22 is subsequently processed by suitable processes to form a flat surface 5 suitable for the bonding process.

The cross section of the channels 14 results from the geometry of the trenches 13. V-shaped trenches having an opening angle of approximately 70 can be produced in 100 silicon by anisotropic etching processes while trenches having vertical walls can be produced in 110 silicon. In 110 silicon, the depth of the trenches is produced with great precision by buried etching stop-off layers. Approximately semicircular cross sections of the trenches 13 are achieved by isotropic etching techniques. The channels 14 are cut up along the cuts 15 by using a diamond saw or a laser beam. The surface quality achieved by this process is as a rule unsuitable f or a bonding process. A sufficiently good surface quality is achieved only by a subsequent mechanical machining, f or example by lapping or polishing. The cutting up of the wafers 21, 22 along the cuts 16 has the object of providing the silicon parts 2 with a predetermined number of channels 14. The cuts 16 can be carried out by sawing, or, alternatively, by anisotropic wet-chemical etching processes. Thus, for example, in the case of silicon components having two channels 14. only every second cut 16 is carried out.

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Claims

1. Three-dimensional silicon structure comprising at least two silicon parts which are joined one to the other by bonding, characterised in that the silicon parts (1, 2) are produced from silicon wafers, in that a first silicon part (1) has a high-quality surface (4) formed from the surface of one silicon wafer, in that a second silicon part (2) has a surface (5) having high surface quality. which surface is perpendicular to the wafer surf ace of said silicon part (2), and in that the two parts (1, 2) are joined at the surfaces (4, 5) mentioned by the bonding process.

2. Three-dimensional silicon structure according to Claim 1. characterised in that the second silicon part (2) is produced by bonding two silicon wafers (21, 22).

3. Three-dimensional silicon structure according to Claim 2, characterised in that one of the silicon wafers (22) has a trench (13) which is capped during bonding by the other silicon wafer (21) in such a way that a channel (14) is produced.

4. Three-dimensional silicon structure according to Claim 2, characterised in that the two silicon waf ers (21, 22) each have at least one trench (13) which lie one on top of the other during bonding in mirror image f ashion in such a way that at least one channel 14 is produced.

5. Three-dimensional silicon structure according to Claim 3 or 4, characterised in that the at least one channel (14) is cut up by cuts (15) perpendicular to the surf aces of the two wafers (21, 22) bonded one to the other.

6. Three-dimensional silicon structure according to Claim 5, characterised in that the cut face produced by the cut is subsequently processed by polishing and/or lapping to produce a surf ace (5) having high surface quality.

7. Three-dimensional silicon structure according to one of the preceding claims, characterised in that the first silicon part (1) has at least one opening (6), in that the at least one opening (6) is smaller than the at least one channel (14), and in that the opening (6) and the channel (14) lie one on top of the other during bonding.

8. A three dimensional silicon structure substantially as herein described with reference to the accompanying drawing.