The present invention relates to a power amplifier; and, more particularly, to a Doherty power amplifier. This material includes an elastomer terpolymer having the following composition: a) 50-90 moles percent of ethylene; b) 10-50 moles percent of an -olefin; c) 0. The stopper film is made of an SiCN film having a low optical reflectance, thereby causing it to serve as an antireflective film when the photoresist film is exposed. The k-th amplifier stage includes a transistor with an amplification function. The present invention provides a method of producing an aminophenol compound represented by the formula : is substituted on the 2- or 4-position to the amino group on the phenyl ring), which comprises allowing a cyclohexanedione compound represented by the formula to react with an amine compound represented by the formula, under a neutral or basic condition. Patterns of events that led to the failure can be identified and documented for use in further problem analysis and for taking preventative andor corrective measures.