Patent Application
20140262052
The present invention concerns the domain of semiconductor wafers manufacturing, in particular the process of detaping protective foils taped onto the front side of semiconductor wafers before the back-grinding thinning process.
In order to prepare semiconductor wafers for the back-grinding thinning process, a self-adhesive foil is taped onto the front-side wafer surface. This allows fixing the wafer (front-side) in the back-grinding tool by a vacuum holder without damaging the sensitive structures.
After the back-grinding, the protective foil must be detaped. In some cases, this is done manually by fixing the polished wafer (backside) onto a vacuum chuck and manually stripping down the front-side foil. However, in most cases, automated detaping tools are used, where the protective foil is removed by first sticking a strong adhesive tape onto the protective foil and thereafter removing the adhesive tape together with the protective foil.
In both processes, the main problem is a high generation of electrostatic charging, which is very difficult to be controlled. Indeed, electronic wafers with integrated circuits are electrostatic surface discharge sensitive devices (ESDS). State-of-the-art equipments use self-regulating air ionizer bars, following in short distance the detaping line (or delaminating line) of the protective foil. However, these approaches are expensive, need ionizer maintenance and sometimes even reduce detaping speed in order to avoid excessive charging by high-speed detaping. Electrostatic surface discharges (ESD), which may appear from the charged foil, include high risks for device functionality and reliability. Attempts to replace standard protective foils by an antistatic foil failed due to the lack of mechanical stability (tear-resistance, etc) of antistatic materials
The aim of the present invention is to overcome the drawbacks of the detaping processes of the prior art mentioned here-before.
Thus, a first implementation of the present invention concerns a detaping process for a protective foil taped onto a front-side of a semiconductor wafer, this detaping process comprising the successive steps of:
A) introducing the semiconductor wafer and the protective foil taped onto the front-side of the semiconductor wafer into an electrically dissipative liquid or into an electrically dissipative solid-state medium having a flowing behavior substantially similar to the one of a liquid;
B) removing the protective foil when the wafer is into said electrically dissipative liquid or into said electrically dissipative solid-state medium.
Thanks the electrically dissipative liquid or electrically dissipative solid-state medium which flows between the front-side of the semiconductor wafer and the protective foil when this protective foil is removed and thus fills the region adjacent the detaping or delaminating line, charges which are generated by the detaping at the surface of the semiconductor wafer and at the surface of the protective foil will immediately be neutralised in a soft and non-damaging manner. A fast and riskless detaping can thus be performed.
Substantially the same result can be obtained by the second implementation of the present invention which concerns a detaping process for a protective foil taped onto a front-side of a semiconductor wafer, this detaping process comprising, during the removing of the protective foil, a spray of an electrically dissipative liquid in the region adjacent to the detaping or delaminating line between the semiconductor wafer and the protective foil or an injection of an electrically dissipative liquid along this detaping or delaminating line.
The second implementation has the advantage over the first one not to necessitate the introduction of the wafer with its support in a basin filled with a conductive liquid.
The present invention will be described subsequently in more detail with reference to the attached drawing, given by way of examples, but in no way limited thereto, in which:
In a variant of a first implementation of the invention shown on
More generally, the detaping process according to a preferred variant of the first implementation of the invention comprises the successive steps of:
A) introducing the semiconductor wafer 2 and the protective foil 4 taped onto the front-side of the semiconductor wafer into an electrically dissipative liquid (
B) removing the protective foil 4 when the wafer 2 is into the electrically dissipative liquid (
It is to be noted that maintenance of the liquid bath needs less attention than that of a self-controlled ioniser bar.
In the variant shown on
In another variant of the first implementation of the invention, the semiconductor wafer is introduced, in step A), into an electrically dissipative solid-state medium having a flowing behavior substantially similar to the one of a liquid, and the removing of the protective foil 4 in step B) occurs into this electrically dissipative solid-state medium. Preferably, the electrically dissipative solid-state medium is formed by small balls of conductive material, in particular aluminium balls. For example, the diameter of the small balls is inferior to two millimeters (2 mm).
A variant of a second implementation of the invention is schematically shown on
