Method Of Manufacturing A Plurality Of Through-Holes In A Layer Of Material

Abstract

A method of manufacturing a plurality of through-holes (132) in a layer of material by subjecting the layer to directional dry etching to provide through-holes (132) in the layer of material; For batch-wise production, the method comprises after a step of providing a layer of first material (220) on base material and before the step of directional dry etching, providing a plurality of holes at the central locations of pits (210), etching base material at the central locations of the pits (210) so as to form a cavity (280) with an aperture (281), depositing a second layer of material (240) on the base material in the cavity (280), and subjecting the second layer of material (240) in the cavity (280) to said step of directional dry etching using the aperture (281) as the opening (141) of a shadow mask.

Claims

1. A method of manufacturing a plurality of through-holes (132) in a layer of material, wherein an intermediate product is subjected to a plurality of method steps, the intermediate product defining a first side and a second side, and comprises a base substrate, said base substrate comprising a base material, wherein at the first side the surface of the base substrate defines a main plane; wherein the plurality of method steps comprises the steps of providing the base substrate of the intermediate product at the first side with a plurality of pits in said base material, and providing the base substrate with the layer of first material at the first side of the intermediate product, the first material being different from the base material so as to result in the intermediate product having pits comprising a layer of said first material, providing a plurality of holes in the layer of first material at the central locations of the pits, etching the base material at the central locations of the pits of the intermediate product so as to form a cavity separated from the first side by an aperture defining a waist, depositing a second layer of material on the base material in the cavity, the second material being different from the base material, and subjecting the first side of the base substrate provided with the second layer of material as the layer to said step of directional dry etching using the aperture as the opening of a shadow mask to provide through-holes in the layer of second material.

2. The method according to claim 1, wherein removing base material of the base substrate exposing the through-holes in the second layer of material.

3. The method according to claim 1, wherein the step of directional dry etching using the aperture as the opening of a shadow mask, is performed with said direction being at an angle α to the normal to the base main plane of at least 5°.

4. The method according to claim 1, wherein the method comprises at least one further method step for manufacturing a plurality of MEMS devices, a MEMS device comprising a through-hole in the material of a wall of the cavity, said through-hole formed by the step of directional dry etching using the aperture as the opening of a shadow mask.

5. The method according to claim 4, wherein the method comprises further steps for manufacturing a plurality of probes wherein each probe of the plurality of probes comprises a probe base section having a probe base main plane, and comprising a first opening of a conduit; and a cantilever protruding from said probe base section parallel with the probe base main plane, said cantilever having a proximal end connected to the probe base section, and a distal cantilever end; said cantilever comprising a tip having a distal tip end, said tip comprising a second opening of said conduit at a location away from the distal tip end; wherein the second opening is formed by at least one step comprising the step of directional dry etching using the aperture as the opening of a shadow mask.

6. The method according to claim 4, wherein the probe comprises a hollow cantilever.

7. The method according to claim 1, wherein the base material is a crystalline base material, and before the base substrate is provided with the first layer of first material, the method comprises the step of etching the base substrate at the first side to form a plurality of pits in said crystalline base material, the pits comprising a face that is at an angle to the main plane.

8. The method according to claim 1, wherein the step of directional dry etching is performed using reactive ion etching.

Description

[0066] The present invention will now be illustrated with reference to the drawing where

[0067] FIG. 1 shows a probe as can be manufactured using the method according to the invention, in top view (top) and cross-sectional view (bottom), both views being vertically aligned;

[0068] FIG. 2A to FIG. 2K illustrate a method of manufacturing the probe according to FIG. 1 in top view (top) and cross-sectional view (bottom), both views being vertically aligned; and

[0069] FIG. 3 shows a Scanning Electron Microscope image of a tip of a probe manufactured according to the invention.

[0070] FIG. 1 shows a probe 100 as can be manufactured using the method according to the invention, in top view (top) and cross-sectional view (bottom), both views being vertically aligned.

[0071] The probe 100 comprises a probe base section 110 and a cantilever 120 extending from the probe base section 110. The cantilever 120 has a proximal end 121 connected to the probe base section 110 and a distal cantilever end 122.

[0072] The distal cantilever end 122 comprises a pyramidal tip 130 comprising at its distal end a polygonal (here octogonal) tip section 131. In a face of the octogonal tip section 131, i.e. away from the distal end of the pyramidal tip 130, there is a through-hole 132 manufactured in accordance with the present invention.

[0073] The probe 100 comprises an elongated conduit 140 extending from a reservoir 150 at the probe base section 110 through the cantilever 120 to the through-hole 132.

[0074] The conduit 140 comprises a first opening 141 and the second opening is defined by the through-hole 132.

[0075] The method according to the invention will now be illustrated using FIG. 2A to FIG. 2K, which show in top view and cross-sectional view a method of manufacturing the probe 100 of FIG. 1. The method according to the present invention allows for a multitude of through-holes 132 and hence probes 100 to be manufactured at once, but the figures will show one probe 100 in the making only.

[0076] A silicon wafer 200 having a thickness of 380 um is shown (FIG. 2A) in top view. The silicon wafer 200 is of (1,0,0) silicon.

[0077] Using a mask, pyramidal pits 210 (only one shown, singulars are used in the remainder of the figure description) is etched by wet anisotropic etching of the silicon using 25% KOH (FIG. 2B). The pyramidal pit 210 is 10 um by 10 um.

[0078] A thin first layer of first material 220 (300 nm), here silicon nitride, is deposited (FIG. 2C) on the silicon wafer 200 comprising a pyramidal pit 210 (FIG. 2C). The silicon nitride will be part of a wall defining the conduit 140 and part of the pyramidal tip 130.

[0079] The first layer of first material 220 was provided with a small hole 221 centrally located at the bottom of the pyramidal pit 210 using corner lithography (FIG. 2D).

[0080] Other techniques can be used instead, for example deposition of silicon oxide by Low Pressure or Plasma Enhanced Chemical Vapor Deposition (LPCVD or PECVD) followed by optical lithography and silicon nitride etching.

[0081] By wet anisotropic etching of silicon through the small opening at the pyramidal apex of the pit 210 an octahedral cavity 280 is realised (FIG. 2E). The size of the octahedral cavity 280 can be controlled by choosing an appropriate etching time.

[0082] Silicon nitride is deposited, now forming a second layer 240 of material (35 nm) inside the octahedral cavity (FIG. 2F). A constricted aperture 281 (waist) is formed, connecting the lumen of the octahedral cavity 280 with the first side.

[0083] The wafer 200 provided with the second layer 240 of silicon nitride is directionally etched (RIE) at an angle α of 35° (FIG. 2G), using constricted aperture 281 as a mask opening for etching the layer of silicon nitride inside the octrahedral cavity 280.

[0084] This results in an off-center through-hole 132 in the layer 240 of material (FIG. 2H). Because a plurality of probes is manufactured using the present method, a plurality of through-holes 132 is formed at the same time, and not formed consecutively. The position and size of the through-hole 132 can to some extent be tuned by adjusting the etching angle α.

[0085] The remainder of the probe 100 is manufactured according to well-known practices, by providing the intermediate product resulting from the previous step with a patterned layer of sacrificial material 250, here polycrystalline silicon with a thickness of 1 um (FIG. 21).

[0086] A further layer 260 of silicon nitride having a thickness of 300 nm is deposited, covering the silicon nitride layer of first material 220 and the layer of sacrificial material 240.

[0087] It is subsequently etched by Reactive Ion Etching to create an etching window 261 so as to expose part of the sacrificial layer of material 240 at a location that will later on be at the probe base section 110 (FIG. 2J).

[0088] The further layer of material 260 is bonded to a glass cover 270 by anodic bonding (FIG. 2K). The glass cover 270 has a cover hole 271 (a through-hole) that will allow access of etchant to the polycrystalline sacrificial material at the location of the cover hole 271 and, once the silicon of the wafer has been etched away, at the through-hole 132.

[0089] Etching with hot Tetramethylammonium hydroxide (TMAH) solution results in the probe 100, shown in FIG. 1.

[0090] FIG. 3A shows a Scanning Electron Microscope image of a pyramidal tip 130 of a probe 100 manufactured according to the invention. Part of the base of the pyramidal tip 130 and the octagonal tip section 131 with a through-hole 132 are visible.