DRY ADHESIVE FOR TEMPORARY BONDING OF SEMICONDUCTOR DEVICES

Abstract

A dry adhesive microfiber array comprising a plurality of fibers with enlarged tips, where the dry adhesive is capable of adhering to a surface of a silicon wafer and/or carrier, in which the dry adhesive can be debonded without the use of chemicals or heat and does not leave a residue on the surface of the wafer, and, a liquid can be introduced to the interface between the dry adhesive and semiconductor device to adjust the force of adhesion.

Claims

1. A method of bonding a semiconductor device comprising: providing a dry adhesive including a microfiber array having a plurality of fibers; and adhering tips of the microfiber array to a surface of the semiconductor device, wherein the microfiber array is in a wet state.

2. The method of claim 1, wherein the wet state is due to a liquid, and the liquid has a characteristic that the liquid does not provide direct adhesion.

3. The method of claim 1, wherein the wet state is due to a liquid, and the liquid is not an adhesive.

4. The method of claim 1, wherein the dry adhesive is formed as a thin film or a tape, from whose surface the microfiber array extends.

5. The method of claim 1, further comprising: debonding the microfiber array from the semiconductor device through a mechanical movement.

6. The method of claim 5, wherein the mechanical movement comprises peeling the microfiber array from the semiconductor device, or the mechanical movement comprises a movement of the semiconductor device in a direction parallel to the surface of the dry adhesive.

7. The method of claim 5, further comprising: drying the microfiber array before the debonding the microfiber array from the semiconductor device.

8. The method of claim 7, wherein the drying utilizes cold or heated air.

9. The method of claim 1, wherein the bonding is performed at room temperature.

10. The method of claim 5, wherein the debonding is performed at room temperature.

11. The method of claim 1, further comprising: processing the semiconductor device while the semiconductor device is adhered to the microfiber array.

12. The method of claim 11, wherein the processing the semiconductor device includes processing a backside of the semiconductor device.

13. The method of claim 1, wherein the semiconductor device is a silicon wafer, chip, die, or semiconductor package.

14. The method of claim 1, wherein the method is applied to a wafer-level packaging process.

15. A method of manufacturing a semiconductor device, comprising processing the semiconductor device according to the method of claim 11.

16. A method of manufacturing a semiconductor device, comprising processing the backside of the semiconductor device according to the method of claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is an image showing the structure of the dry adhesive, according to one embodiment.

[0010] FIG. 2 is a graph showing adhesion forces for an adhesive in a dry and wet state.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0011] In one example embodiment, the dry adhesive microfiber array 100 comprises a plurality of fibers 101 attached to a backing layer, carrier, or substrate 102. In one embodiment, the fiber 101 attaches to the backing layer, carrier, or substrate 102 at a substantially perpendicular angle. Each fiber includes stem 103 and an enlarged tip 104 (i.e. the radius of the tip is greater than the radius of the stem). In one embodiment, the tip 104 is a mushroom-shaped tip 104 with a flat surface. The stem 103 and tip 104 are symmetrical about symmetry axis, such that radius a of the stem 103 (up to the point of connection 105 with the tip 104) is constant along the length of stem 103. However, in alternative embodiments, the radius of the stem 103 can vary along its length, including one embodiment where the radius of the stem 103 near the backing layer 102 is enlarged. The tip 104 is also symmetrical and is fixed in radial direction to enable increased contact with the surface of the semiconductor device, such as a silicon wafer, chip, die, semiconductor package, or other similar device. In one embodiment, the surface of the tip 104 and the cross-section of the stem 103 are circular. In other embodiments, however, an oval or elliptical shape and/or cross-section may be used. The shape of the sides on the underside of the mushroom tip 104 is linear but, alternatively, can be convex or concave with respect to the stem axial direction and tip surface.

[0012] In an alternative embodiment, the dry adhesive 100 may comprise a film or tape having fibers on opposing sides, similar to double-sided tape. In this configuration, the tape 100 can be placed on the carrier, with the semiconductor device then placed on top of the tape 100. During debonding, the manufacturer has the option to remove the carrier from the device or to remove the device from the carrier. For example, if a wafer will be transferred to a different carrier for a subsequent processing step, the wafer and tape 100 can be removed from the carrier and be placed on the surface of the different carrier. Because the dry adhesive fiber array 100 does not lose adhesion when removed, it will adhere to the different carrier. By leaving the dry adhesive 100 affixed to the wafer, the handling steps involving the device-side of the wafer is reduced.

[0013] During the bonding process, a plurality of fibers 101 of the dry adhesive 100 attaches, adheres, or otherwise bonds, as is known in the art, to the surface of the device. More specifically, the tip 104 of the fibers 101 contacts the surface of the device and provides an adhesive force. The bonding strength of the dry adhesive 100 can be tailored to a particular processing step. For example, if the device is undergoing a cleaning step where it will not be subjected to large forces or rough handling, a lower bonding strength can be used. The use of a lower bonding strength decreases the chances damaging the device when debonding. Bonding strength can be adjusted by varying the parameters of the fiber design, including fiber length, fiber radius, backing layer thickness, tip diameter, tip height, the angle between the surface of the tip and the side of the tip, fiber density, and material choice. In one example embodiment, the fiber 101 is constructed from polyurethane in a molding process known to those having skill in the art. In this example embodiment, the dry adhesive 100 may have fibers 101 with a 4 m stem radius, 8 m tip radius, and 20 m length.

[0014] As previously discussed, the fiber characteristics can be varied to adjust bonding strength. The presence of a liquid, such as water or isopropyl alcohol, can also affect the adhesion properties of the dry adhesive 100. Although a liquid is present, the adhesive 100 is still considered a dry adhesive since the liquid is not providing direct adhesion, like a glue. That is, the liquid is not an adhesive. Rather, the liquid affects the interface between the surface of the device and the tips 104 of the fibers 101. FIG. 2 shows the force of adhesion for a dry adhesive 100 in two statesdry (bottom line) and wetted with isopropyl alcohol (top line). The y-axis of FIG. 2 shows the normal force in Newtons and the x-axis shows individual measurements for the same dry adhesive 100. FIG. 2 depicts a series of twenty measurements, followed by an additional five measurements after three days. The additional five tests are used to show the resiliency of the fibers after being subjected to isopropyl alcohol. As shown in FIG. 2, the presence of isopropyl alcohol increases the force of adhesion in the normal direction compared to the dry adhesive 100.

[0015] The difference in adhesion between dry and wet states can be utilized in the debonding phase to minimizing the force needed to remove the device from the carrier. For example, a semiconductor device can be bonded to a dry adhesive 100 and wetted with isopropyl alcohol before processing begins. The presence of isopropyl alcohol will increase the adhesion. After processing, the adhesive 100 can be dried using a flow of cold or heated air. Once dried, the force of adhesion will be reduced, allowing easy removal of the semiconductor device from the carrier.

[0016] The dry adhesive 100 provides unique advantages over existing mechanisms for bonding and debonding. For example, the dry adhesive 100 of the present invention can be bonded and debonded at room temperature, preventing any unnecessary heat exposure and potential defects from varying coefficients of thermal expansion. Further, since all debonding processes are different (i.e. there is no standard debonding process), the ability to tailor bonding strength means the adhesion only needs to be strong enough to maintain attachment throughout a process, while ensuring the mechanical removal step does not damage the device side of the wafer. Consequently, compared to existing bonding mechanisms, the dry adhesive fiber array 100 can increase process throughput, simplify processing, provide a low temperature bonding process, and enable a high yield.

[0017] The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilized for realizing the invention in diverse forms thereof. In particular, one or more features in any of the embodiments described herein may be combined with one or more features from any other embodiments described herein.

[0018] Protection may also be sought for any features disclosed in any one or more published documents referred to and/or incorporated by reference in combination with the present disclosure.