There is described a process for the preparation of 5-carboxy phthalide, which comprises adding terephthalic acid to fuming sulfuric acid containing at least 20% of SO3, then adding formaldehyde to the mixture, heating the mixture at a temperature of 120-145 C. The display device is formed by a light guiding body, and by two types of LED that emit light in different colors, for example, a green LED and a blue LED, and are packaged on a printed circuit board. The method starts by generating a sacrificial layer comprising a first material that can withstand temperatures typically encountered in subsequent conventional semiconductor processing steps. Further, in the front end side of the engagement pin passing through and protruding from the guide hole, the outer peripheral portion is spaced apart from the inner peripheral portion of the peripheral wall. The method is applicable to planar metal oxide semiconductor field effect transistors and fin field effect transistors. A photoactive adhesion promoter is described which helps reduce these and other undesired effects associated with the removal of photoresist in a semiconductor manufacturing process.