| 摘要 |
PROBLEM TO BE SOLVED: To measure a height that is equal to or more than|λ/4|by detecting a reflection light intensity in addition to a phase and expanding the detection range of the phase. SOLUTION: 2-beam light 116 and 118 from an AOD 12 is applied to an object 124 to be measured, one portion of reflection light is reflected by a BS 13, and a light receiver 14 generates a reflection light beat signal 142. It is compared with a reference signal 144 by a phase comparator 15, and a phase difference corresponding to the surface shape of the object 124 to be measured being detected is recorded at a phase storage part 155 as phase dataϕ1 . On the other hand, reflection light through the BS 13 is divided by a light receiver 16 into two portions and an intensity is detected for each region. A differential intensity detector 17 detects a differential intensity Ia-Ib and an intensity ratio I/Ib from reflection light intensity signals 162 (an intensity Ia) and 164 (an intensity Ib) and a phase judging part 18 judges surface recessed and projections from the positive and negative signs of Ia-Ib and a count n whereϕ1 that cannot be judged by phase dataϕ1 exceeds an absolute value|π|from Ia/Ib. A phase correction part 19 corrects the phase dataϕ1 from the surface recess and projection information and the count n and measures a height that is equal to or more than|λ/4|.
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