WAFER ASSEMBLY FOR MEMS FABRICATION

Abstract

A wafer assembly for use in a MEMS fabrication process. The wafer package includes: a MEMS wafer having a first side and an opposite second side; a silicone-free peel tape releasably attached to the first side of the wafer; a wafer bonding tape attached to the peel tape; and a carrier substrate releasably attached to the first wafer bonding tape.

Claims

1. A wafer assembly for use in a MEMS fabrication process, the wafer package comprising: a MEMS wafer having a first side and an opposite second side; a silicone-free peel tape releasably attached to the first side of the wafer; a first wafer bonding tape attached to the peel tape; and a first carrier substrate releasably attached to the first wafer bonding tape.

2. The wafer assembly of claim 1, wherein the first wafer bonding tape contains silicon.

3. The wafer assembly of claim 1, wherein the MEMS wafer comprises MEMS inkjet devices.

4. The wafer assembly of claim 1 wherein the first side of the MEMS wafer has a plurality of inkjet nozzles.

5. The wafer assembly of claim 1, further comprising: a second wafer bonding tape attached to the second side of the wafer; and a second carrier substrate releasably attached to the second wafer bonding tape.

6. The wafer assembly of claim 5, wherein the second wafer bonding tape is different than the first wafer bonding tape.

7. The wafer assembly of claim 5, wherein the first and second wafer bonding tapes are selected from the group consisting of: UV-release tape and thermal-release tape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0035] FIG. 1 is a schematic side view of a MEMS wafer;

[0036] FIG. 2 shows the MEMS wafer with a frontside attached to a first carrier substrate;

[0037] FIG. 3 shows the MEMS wafer after backside MEMS processing;

[0038] FIG. 4 shows the MEMS wafer with a backside attached to a second carrier substrate;

[0039] FIG. 5 shows the MEMS wafer after release of the first carrier substrate from the frontside; and

[0040] FIG. 6 shows the MEMS wafer after peeling away a peel tape from the frontside.

DETAILED DESCRIPTION OF THE INVENTION

[0041] FIGS. 1 to 6 show schematically an exemplary process for handling MEMS wafers according to the first aspect. In FIG. 1, there is a shown a MEMS wafer 1 comprising a bulk silicon substrate 3 and a frontside MEMS layer 5. The MEMS layer 5 may comprise, for example, a plurality of MEMS inkjet devices disposed on integrated circuitry with nozzles (not shown) defined in a frontside surface 6 of the MEMS wafer 1. Examples of MEMS layers comprising inkjet devices, as well as corresponding fabrication processes, are described in U.S. Pat. Nos. 9,044,945; 8,608,286; 7,246,886; and 6,755,509, the contents of each of which are incorporated herein by reference.

[0042] FIG. 2 shows a wafer assembly 10 after attachment of a first carrier substrate 7, such as a glass handle wafer, to the frontside surface 6 of the MEMS wafer 1. The first carrier substrate 7 is attached to the frontside surface 6 via a UV-release tape 11 and a separate peel tape 13. The peel tape 13 contacts the frontside surface 6 while the UV-release tape 11 is sandwiched between the peel tape and the first carrier substrate 7.

[0043] The wafer assembly 10 may be assembled in any order. For example, the peel tape 13 may be bonded to the frontside surface 6 of the MEMS wafer 1, the UV-release tape 11 bonded to the peel tape and then the first carrier substrate 7 bonded to the UV-release tape. Alternatively, the UV-release tape 11 may be bonded to the first carrier substrate 7, the peel tape 13 bonded to the UV-release tape and then the peel tape 13 bonded to the frontside surface 6 of the MEMS wafer. Alternatively, the peel tape 13 may be bonded to the frontside surface 6 of the MEMS wafer 1, the UV-release tape 11 bonded to the first carrier substrate, and then the UV-release tape bonded to the peel tape so as to join the MEMS wafer and the first carrier substrate.

[0044] UV-release tapes are well known to those skilled in the art and are commercially available from vendors, such as Kingzom Electronic Technology Co Ltd, Nitto Denko Corporation and Furakawa Electric Group. Typically, UV-release tapes comprise at least one layer of UV-curable adhesive disposed on a base film, whereby the UV-curable adhesive loses its adhesion properties on exposure to UV light. In the embodiment shown, the UV-curable tape 11 comprises two layers of UV-curable adhesive disposed on opposite sides of a base film, whereby an upper layer of adhesive is selectively curable via exposure to UV light through the first carrier substrate 7. Typically, UV-release tapes contain silicon in the form of silicone polymers.

[0045] Peel tapes are, likewise, known to those skilled in the art. The peel tape 13 according to the present invention is selected so as to be absent any silicon. One example of a suitable peel tape for use in the present invention is Adhesive Plastic Film 1009R, available from Ultron Systems, Inc.

[0046] Turning to FIG. 3, after attachment of the first carrier substrate 7, a backside 15 of the MEMS wafer 1 is subjected to MEMS processing steps. The first carrier substrate 7 is used as a handle for holding the MEMS wafer 1 during backside MEMS processing. By way of example, the backside surface 15 of the silicon substrate 3 may be subjected to wafer thinning (e.g. grinding and/or plasma thinning), lithographic etching (e.g. etching of backside ink supply channels) and oxidative ashing. At this stage, backside etching of dicing streets (not shown) may be useful for singulating (or “dicing”) the MEMS wafer 1 into individual dies (or “chips”) attached to the first carrier substrate 7. In FIG. 3, a backside ink supply channel 17 is shown schematically corresponding to the ink supply channels described in, for example, U.S. Pat. No. 7,441,865, the contents of which are incorporated herein by reference.

[0047] Following backside processing of the MEMS wafer 1, and referring now to FIG. 4, a second carrier substrate 20 (e.g. glass handle wafer) is attached to the backside 15 of the silicon substrate 3 using a thermal-release tape 22. The use of different wafer bonding tapes on the frontside surface 6 and the backside surface 15 of the MEMS wafer 1 facilitates selective removal of the first carrier substrate 7 from the frontside whilst the second carrier substrate 20 remains attached to the backside. Thermal-release tapes will be well known to the person skilled in the art, such as Revalpha™ tape, commercially available from Nitto Denko Corporation.

[0048] With the MEMS wafer 1 attached to the second carrier substrate 20 via the thermal-release tape 22, the frontside 6 of the wafer is exposed to UV radiation, which cures an upper layer of adhesive in the UV-release tape 11 and releases the first carrier substrate 7. FIG. 5 shows the wafer assembly after release of the first carrier substrate 7. The MEMS wafer 1 is held by the second carrier substrate 20 attached to the backside while the peel tape 13 and cured UV-release tape 11 cover the MEMS layer 5 on the frontside. The peel tape 13 acts as a protective barrier for the underlying MEMS layer 5, thereby minimizing any contamination from silicone resins contained in the UV-release tape 11.

[0049] Referring to FIG. 6, the peel tape 13 is finally peeled away from the MEMS layer 5, with simultaneous removal of the UV-release tape 11 attached to the peel tape, to reveal the frontside surface 6. After removal of the peel tape 13 and UV-release tape 11, oxidative ashing (e.g. oxygen plasma ashing) may be used to clean any organic residues from the frontside surface 6, as well as remove any sacrificial resist inside MEMS structures (e.g. inkjet nozzle chambers). Since the peel tape 13 is absent any silicon, this ashing step provides a clean frontside surface 6 and MEMS devices free of any silica particles. Individual dies may be picked from the second carrier substrate 20 using a thermal-release process, as described in, for example, WO2008/141359.

[0050] From the foregoing, it will be appreciated that the wafer handling process described herein advantageously provides MEMS devices having minimal inorganic contaminants, such as silica particles. Accordingly, the process is highly suitable for handling MEMS wafers during fabrication of MEMS printheads chips having inkjet MEMS devices that are sensitive to such contaminants.

[0051] It will, of course, be appreciated that the present invention has been described by way of example only and that modifications of detail may be made within the scope of the invention, which is defined in the accompanying claims.