Browse Prior Art Database

Differential Linewidth Sensor

IP.com Disclosure Number: IPCOM000099510D
Original Publication Date: 1990-Jan-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 95K

Publishing Venue

IBM

Related People

Korth, HE: AUTHOR [+2]

Abstract

This article describes a device which generates a linewidth signal based on phase modulation by the line structure. All physical line structures produce phase modulation. Appropriate signal processing eliminates any other parameters (line height, reflectance, etc.) from the linewidth signal.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Differential Linewidth Sensor

       This article describes a device which generates a
linewidth signal based on phase modulation by the line structure.
All physical line structures produce phase modulation. Appropriate
signal processing eliminates any other parameters (line height,
reflectance, etc.) from the linewidth signal.

      A laser diode (Fig. 1) transmits linearly polarized light to
the object surface.  The light is collimated into a beam with a
Gaussian intensity profile.  After transmission through a polarizing
beam splitter, a quarterwave plate produces circularly polarized
light.  The objective lens focuses the light onto the object surface.
 A scanning mirror in the rear focal plane of the objective lens (or
a conjugate plane) allows controlling the beam position on the
surface.

      A good match between lens aperture and beam is obtained if the
beam amplitude at cut off is about 1/e of the value in the center.
This minimizes the spot size, whereas the spot shape does not deviate
too much from the Gaussian profile.

      The reflected light is recollimated by the objective lens.
Having passed the quarterwave plate, the beam is again linearly
polarized but rotated by 90o to the incident beam.  Therefore, the
beam is subsequently reflected by the polarizing beam splitter.

      Afterwards, the beam is separated into a "right" and a "left"
part which are fed to a pair of photodetectors.  An elegant way of
carrying out this separation uses a triple prism and a lens to
separate the right and the left beam and to transmit the center
portion of the beam that contains no phase information to an
autofocus sensor.  Triple prism and lens may be combined into a
single molded element including an aspherical surface allowi...