Scatter melt detection to determine phase transition of semiconductor during laser annealing
High bandwidth time-and-space resolved scatter phase transition microscopy systems configured to detect melt onset in a wafer being processed by laser annealing systems with ultra-short dwell times and spot size.
1 . A method of determining the occurrence of a solid to liquid material phase transition of a semiconductor material during a laser annealing process, the method comprising:
forming an annealing image on a surface of the semiconductor material with an annealing laser beam from an annealing laser;
forming a scatter image of a region of the semiconductor surface that includes the annealing image; and
identifying a solid to liquid material phase transition of the semiconductor material according to an intensity of light collected in the scatter image.
2 . The method of claim 1 , wherein the identifying includes the detection of an intensity in the scatter image that meets or exceeds a threshold value, the threshold value corresponding to the onset of the solid to liquid phase transition of the semiconductor material.
3 . The method of claim 2 , wherein the identifying includes the detection of a intensity in the scatter image in an area of the scatter image that is within the annealing image and smaller than an area of the annealing image.
4 . The method of claim 1 , wherein the identifying includes identifying a discontinuity in the intensity of light collected in the scatter image as compared to a below-melt reference image.
5 . The method of claim 1 , wherein the identifying includes identifying a non-linear scaling relationship between the intensity of light and a process parameter.
6 . The method of claim 5 , wherein the process parameter is a power level of the annealing laser or a local power-density of the annealing laser.
7 . The method of claim 1 , wherein the laser annealing process includes performing sequential sweeps of the annealing image across the semiconductor surface, wherein each sweep forms an annealing illumination line, wherein forming a scatter image includes forming an image of at least one annealing illumination line.
8 . The method of claim 7 , wherein the step of identifying includes analyzing an intensity of light along the annealing illumination line to determine the extent of a material phase transition of the semiconductor material along the annealing illumination line.
9 . The method of claim 7 , wherein the step of identifying includes analyzing an intensity of light along the annealing illumination line to determine a proportion of the annealing illumination line where an onset of the solid to liquid phase transition has occurred.
10 . The method of claim 7 , wherein the step of identifying includes analyzing an intensity of light at a first location along the annealing illumination line in a plurality of the sequential sweeps of the annealing image to determine at least one of a melt threshold power level or a statistical power fluctuation of the annealing laser.
11 . The method of claim 1 , wherein the laser annealing process includes performing sequential sweeps across the semiconductor surface at a sweep frequency, fsweep, the method further comprising irradiating the semiconductor surface with a probe light source with pulses of radiation at a pulse frequency, fProbe, wherein fProbe<fsweep.
12 . The method of claim 1 , wherein the identifying includes application of one or more of fitting algorithms, edge detection algorithms, eigenbasis decompositions, feed-forward classifiers, or the detection of any intensity in a captured image frame that exceeds a threshold value.
13 . The method of claim 1 , wherein the identifying includes:
creating a melt-detection image that references the scatter image to a corresponding below-melt reference image.
14 . The method of claim 13 , further comprising comparing values of the melt-detection image to a threshold value to determine whether melting occurred in one or more regions of the melt-detection image.
15 . The method of claim 13 , further comprising applying a one-dimensional profile analysis of the melt-detection image to identify narrow peaks in a stage scan direction that have a width that is less than a width of the annealing laser beam.
16 . The method of claim 13 , wherein the below-melt reference image was obtained by performing steps comprising:
annealing a wafer below melt;
capturing image frames with a scatter melt detector;
recording an annealing laser power level;
creating a below-melt reference image from the captured image frames;
processing the below-melt reference image to generate a plurality of below-melt one-dimensional stage scan direction intensity profiles;
identifying a region of interest (ROIref) of the below-melt reference image; and
creating an average one-dimensional stage scan direction intensity profile.
17 . The method of claim 1 , wherein the identifying includes:
calculating a statistical variation of pixel values within a region of interest, ROIref, of a captured image frame, wherein ROIref is a region of the image where the annealing image was formed on the surface of the semiconductor material; and
comparing the calculated statistical variation to identify the onset of melt.
18 . A scatter melt detection system, comprising:
a stage configured to support a semiconductor wafer;
an annealing laser configured to anneal the semiconductor wafer; and
a scatter melt detector that includes:
an image capture device that includes a focal plane array (FPA); and
a scatter optical arrangement configured to block or avoid a specular reflection of a beam formed by the annealing laser and form a scatter image of a surface of the semiconductor wafer on the FPA.
19 . The system of claim 18 , further comprising a processor and a machine readable storage media containing program instructions for execution by the processor for performing the steps including:
forming an annealing image on a surface of the semiconductor wafer with an annealing laser beam from an annealing laser;
forming a scatter image of a region of the semiconductor wafer surface that includes the annealing image; and
identifying a solid to liquid material phase transition of the semiconductor wafer according to an intensity of light collected in the scatter image.
20 . A laser annealing system, comprising:
an annealing laser;
a storage device containing at least one annealing laser melt threshold calibration setpoint that specifies an operating parameter of the annealing laser to raise a temperature of a local region of a semiconductor material to a melt threshold under a set of predetermined annealing process conditions, wherein the calibration setpoint was derived from scatter images of the semiconductor material taken during a laser annealing process of the semiconductor material; and
a controller configured to control the annealing laser according to the annealing laser melt threshold calibration setpoint.
21 . The system of claim 20 , wherein the calibration setpoint was determined by a process that that includes:
forming an annealing image on a surface of the semiconductor material with an annealing laser beam from an annealing laser;
forming a scatter image of a region of the semiconductor surface that includes the annealing image; and
identifying a solid to liquid material phase transition of the semiconductor material according to an intensity of light collected in the scatter image.