Protective film detecting method for laser processing

Abstract

Disclosed herein is a protective film detecting method of detecting the formed condition of a protective film formed on the front side of a workpiece. The protective film detecting method includes a fluorescence intensity measuring step of forming a plurality of reference protective films having different thicknesses on the front sides of a plurality of reference workpieces, next applying excitation light absorbable by an absorbing agent contained in each reference protective film to each reference protective film, and next measuring the intensity of fluorescence emitted from the absorbing agent due to the absorption of the excitation light, and a threshold deciding step of deciding a threshold of the fluorescence intensity corresponding to a desired one of the different thicknesses of the reference protective films according to the fluorescence intensity measured above.

Description

BACKGROUND OF THE INVENTION[0001]Field of the Invention[0002]The present invention relates to a method of determining whether or not a protective film has a desired thickness, the protective film being formed on the front side of a workpiece such as a semiconductor wafer in dividing the workpiece by laser processing.[0003]Description of the Related Art[0004]As a method of dividing a workpiece such as a semiconductor wafer along streets (division lines), there is a method of laser-processing the workpiece along the streets to thereby divide the workpiece (see Japanese Patent Laid-open No. 1994-120334, for example). In the laser processing method described in Japanese Patent Laid-open No. 1994-120334, a laser beam is applied to the semiconductor wafer along the streets to generate thermal energy on the semiconductor wafer in an area corresponding to the streets, thereby continuously processing the semiconductor wafer in this area irradiated with the laser beam. There is a case that th...

AI Technical Summary

Benefits of technology

The present invention provides a simple and accurate method to detect the thickness of a protective film formed on a semiconductor wafer before laser processing. This method uses an absorbing agent in the protective film which emits fluorescence when excited by a specific wavelength of light. The intensity of the fluorescence is measured and compared to a predetermined value to determine the thickness of the protective film. This method ensures the protective film is sufficiently protected from debris and does not hinder laser processing. Additionally, this method can be carried out quickly, which improves productivity in laser processing.

Problems solved by technology

If the thickness of the protective film is less than the predetermined value, there is a possibility that the wafer cannot be sufficiently protected from the debris, whereas if the thickness of the protective film is greater than the predetermined value, there is a possibility that laser processing may be hindered by the protective film.

Further, if much time is required for the measurement of the thickness of the protective film, the productivity in laser processing is reduced.

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