Currently, during the back-surface grinding of semi-conductor wafers, protective films are adhesively bonded to the wafer front surface, and the wafer which has been covered in this way is placed, by means of the applied film, onto a flat base, and then the wafer back surface is ground, typically using a diamond abrasive. The protective films which have been adhesively bonded to the semiconductor wafer front surface for back-surface grinding can currently only compensate for and planarize topography differences on wafer front surfaces of at most 150 μm. However, new types of mounting processes will in future require contact bumps with a height of up to 250 μm and a diameter of 300–500 μm on wafer front surfaces, instead of the gold or aluminum wire bonds which have hitherto been customary, in order to make contact with printed circuit boards, boards and the like. These high bumps can no longer be covered in a planarizing fashion by the grinding films which are currently employed. The conventional films are no longer able to compensate for these differences in topography, and consequently contact with the substrate surface is not complete, and in particular the film rear side, which rests on the base during grinding of the wafer back surface, is no longer planar, but rather has undulations. The grinding process then leads to local fluctuations in thickness (dimples) in the thinned wafers, which may cause the wafer to break.
The grinding films which are currently used are always composed of a support material (layer thickness 80–200 μm) and an adhesion film with a layer thickness of 10–30 μm. Films of this type are available, for example, from the companies Nitto, Adwill, Mitsui and are currently used for wafer processes. The adhesive film is polymerized in such a way that it has viscoelastic properties. As a result, it is possible to a certain extent to level out differences in topography, and the pulling of the protective film off the semiconductor wafer which is required after grinding takes place substantially without any residues of adhesive remaining on the substrate surface. However, a condition for this is for the contact bumps on the wafer front surfaces to be no more than 150 μm high. If the contact bumps are larger than this, the drawbacks which have been described above occur. Hitherto, there have been no leveling protective films which allow the back-surface grinding of wafers with larger contact bumps. A technical solution for the back-surface grinding of wafers with bumps which are 200 μm high is not currently known.
Furthermore, it is known to apply films to wafers which include a photopolymerizable substance in the adhesion layer, the adhesion layer being viscoelastic and being fully polymerized by the UV radiation. Films of this type are available, for example, from Nitto, Adwill, Mitsui and are currently in use for wafer processes. This process is likewise not suitable for the back-surface grinding of wafers which on their front surface have contact bumps or other structures with a height of more than 150 μm, since in this case too the abovementioned drawbacks occur.
EP 926 732 describes a process for producing semi-conductor devices in which a a [sic] pressure-sensitive adhesive tape is applied to a wafer, the tape is heated or pressed on, and then photochemical polymerization takes place after back-surface grinding of the wafer.
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