The present invention provides a surface-protection tape for semiconductor wafers having an even thickness accuracy, excellent surface smoothness, and excellent surface sliding properties such as freedom from blocking, etc., and a substrate film for the surface-protection tape. The substrate film for the surface-protection tape for semiconductor wafers has at least one layer containing a polyethylene-based resin and satisfies the following requirements: (1) the back and front surfaces of the substrate film have a surface roughness Ra measured based on JIS B0601 of not more than 0.8 µm, and at least one surface thereof has a surface roughness Ra of not less than 0.05 µm; and (2) the difference between the maximum and minimum thicknesses of the substrate film is not more than 4 µm. The present invention also provides a surface-protection tape for semiconductor wafers comprising the substrate film and an adhesive layer.
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