Surface profiling method and apparatus

A surface profiling apparatus for providing surface profile information for a sample surface, the surface profiling apparatus comprising:

• a support operable to support a sample having a sample surface;
• an optical system operable to direct light from a broadband light source to an interference zone along first and second light paths, the first light path including the sample surface and the second light path including a reference surface, wherein the optical system is operable to shape the beam of light travelling along the first light path to form a sample light beam which is incident on the sample surface, wherein the sample light beam has wavefronts which vary along the direction of propagation;
• an actuator operable to cause relative movement between the sample surface and the sample light beam;
• and
• a compensator operable to compensate for a difference between the path lengths of the first and second light paths caused by a relative movement between the sample surface and the sample light beam so that light from portions of the sample surface which substantially coincide with a wavefront of the sample light beam and light from corresponding portions of the reference surface produce an interference pattern in the interference zone.

A method of providing surface profile information for a sample surface, the method comprising the steps of:

• directing light from a broadband light source to an interference zone along first and second light paths, the first light path including the sample surface and the second light path including a reference surface, wherein the beam of light directed along the second light path is shaped to form a non-uniform reference light beam which is incident on the non-planar reference surface, with a wavefront of the reference non-uniform light beam substantially matching the non-planar reference surface, and wherein the beam of light travelling along the first light path is shaped to form a non-uniform sample light beam which is incident on the sample surface, wherein the non-uniform sample light beam substantially matches the non-uniform reference light beam;
• causing relative movement between the sample surface and the sample non-uniform light beam;
• and
• compensating for a difference between the path lengths of the first and second light paths caused by relative movement between the sample surface and the sample light beam so that light from portions of the sample surface which substantially coincide with a wavefront of the sample light beam and light from corresponding portions of the reference surface produce an interference pattern in the interference zone.