United States Patent  cm Patent Number: 4,869,593
Biegen  Date of Patent: Sep. 26, 1989
 INTERFEROMETRIC SURFACE PROFILER
 Inventor: James F. Biegen, Middletown, Conn.
 Assignee: Zygo Corporation, Middlefield, Conn.
 Appl. No.: 185,075
 Filed: Apr. 22, 1988
 Int. CI.* G01B9/02
 U.S. CI 356/351; 356/359
 Field of Search 356/351, 359
 References Cited
U.S. PATENT DOCUMENTS
4,632,556 12/1986 Akatsu 356/359 X
4,639,139 1/1987 Wyant et al 356/359
4,732,483 3/1988 Biegen 356/351
Primary Examiner—Davis L. Willis
Assistant Examiner—Matthew W. Koren
Attorney, Agent, or Firm—Bryan, Cave, McPheeters &
In accordance with several embodiments of the instant invention, an interferometric profiler is provided which is capable of measuring accurately the topography of a test surface comprising a light source with high spatial and temporal coherence, a rotating diffuser disc, onto which light from said source impinges to form a second
extended light source having greatly reduced spatial coherence while retaining high temporal coherence; a first lens and beamsplitter assembly, most preferably a polarizing beamsplitter and quarter-wave phase retardation plate, to collect a direct, preferably without significant light loss, a light beam produced from the light from said extended second light source; a second lens for focusing said light beam onto test and reference surfaces; a two-beam interferometer which divides said light beam into test wavefronts and reference wavefronts and directs said test wavefronts and reference wavefronts onto said test and reference surfaces; and a piezoelectric transducer, for varying the relative distance between said test and reference surfaces; said two-beam interferometer, recombining said test wavefronts and reference wavefronts after they have interacted separately with said test and reference surfaces to produce an interference pattern; said second lens, imaging said test and reference surfaces onto the photosensitive elements of an imaging device.
In accordance with another embodiment of the instant invention, the interferometric profiler can have a light source which can be either spatially coherent or incoherent of either temporally coherent or incoherent electromagnetic radiation.
80 Claims, 5 Drawing Sheets