Systems and Methods For Voltage Contrast Imaging Using Photoreflectance Microscopy
OwnerWilliam W. Chism, IIinventor
Life of this patent
Estimating the term…
Abstract
An optical technique for voltage contrast imaging of the active electronic properties of semiconductors, including semiconductor surfaces, periodic structures, and electrically active defects, is disclosed. A pump laser beam is used to produce a modulated photovoltage in a semiconductor sample and a second probe laser beam is used to detect synchronous changes in the reflectance of the sample, resulting in a non-contact voltage contrast imaging capability. Exemplary optical configurations enabling high-throughput voltage contrast inspection of electrically active defects are discussed.
Claims7
An apparatus for acquiring photoreflectance image data, comprising:
- (a) a first laser source operable to provide an intensity modulated pump laser beam suitable for inducing time periodic changes in the reflectance of a sample;
- (b) a second laser source operable to provide a continuous wave probe laser beam suitable for detecting pump induced changes in the reflectivity of the sample;
- (c) an optical system operable to focus the pump laser beam and the probe laser beam onto a surface of the sample, and to collect and project probe light reflected from the sample to an image plane;
- (d) a lock-in camera fixtured at the image plane operable to generate an electrical signal proportional to the reflected probe light intensity at each camera pixel, wherein each pixel comprises a demodulation circuit operable to output a demodulated signal corresponding to time periodic changes in the reflected probe light intensity;
- and
- (e) a computer operable to receive and record a plurality of demodulated output signals, said plurality comprising photoreflectance image data.
A method of acquiring photoreflectance image data, the method comprising the steps of:
- (a) directing an intensity modulated pump laser beam onto a surface of a sample to produce a time periodic modulation of the reflectance of the sample;
- (b) focusing a second probe laser beam onto at least a portion of the area obtaining the time periodic modulation of the reflectance, wherein the probe laser beam comprises at least one wavelength suitable for detecting the induced changes in the reflectivity of the sample;
- (c) collecting probe light reflected from the sample and projecting it onto a lock-in camera fixtured at an image plane to generate a plurality of demodulated signals, said plurality of demodulated signals comprising photoreflectance image data;
- and
- (d) recording the photoreflectance image data.
A method for quantifying the level of electrically active defects in a semiconductor sample, comprising:
- establishing an optical model correlating spatially resolved photoreflectance data at a back focal plane of a photoreflectance microscope with the level of electrically active defects in the sample;
- acquiring spatially resolved photoreflectance data at a back focal plane of the photoreflectance microscope from the sample;
- and
- using the acquired spatially resolved photoreflectance data to quantify the level of electrically active defects in the sample.
Dependencies are inferred from the claim text.