NON-CONTACT  ON-LINE PROCESS MONITORING
IN  FABRICATION  OF  Wide Bangap Semiconductor Devices 

A patented semiconductor characterization method based on the inductive (RF) detection of optically generated charge carriers offers new non-contact metrologies for wide bandgap  semiconductor  devices.


GEKA ASSOCIATES is involved in the productization of the patented
non-contact, RF-based, electrical measurement tool referred to as
Defect Specific Lifetime Analyzer (DSLA)

For more information contact:  info@gekallc.com

Defect Specific Lifetime Analysis [DSLA©

Based on the proprietary analysis of the time dependent density of optically generated charge carriers, DSLA  simultaneously differentiates properties of the surface and bulk of semiconductor focusing, depending on the probe configuration, on the bulk or surface regions of devices.

DSLA identifies point and extended defects that directly affect performance
of wide bandgap  semiconductor devices
such as
photo-current CZT radiation detectors
for security, industrial and medical applications
&
galium-nitride (GaN) and silicon-carbide (SiC) devices
for automotive, industrial, and telecom applications

Since DSLA measurements do not involve the collection of charges at the electrodes but are solely based on the absorption of the RF radiation,  DSLA can be used for the characterization of monocrystalline, polycrystalline and amorphous materials.

E. Kamieniecki, J. App. Physics 112, 063715 (2012);   Patents:  US 7,898,280,B2; US 8,896,338,B2   

Defect Specific Lifetime Analyzer [DSLA©]

E. Kamieniecki, J. App. Physics 112, 063715 (2012);   Patents:  US 7,898,280,B2; US 8,896,338,B2 

This deficiency of existing metrologies, and specifically the Surface Charge Analyzer which requires the use of monitor wafers is addressed by non-contact Defect Specific Lifetime Analyzer (DSLA) which is based on the proprietary analysis of the time dependent density of optically generated charge carriers, DSLA simultaneously differentiates properties of the surface and bulk of semiconductors focusing on, depending on the probe configuration, on the surface or bulk regions. Unlike Surface Charge Analyzer and Surface Charge Profiler, DSLA operates at wide probe-semiconductor distance making it particularly useful for on-line process monitoring of product wafers in microelectronic and wide bandgap semiconductor device manufacturing. The probe-semiconductor gap can be tailored to process requirements and configuration of the probe can be adjusted enhancing monitoring of the process parameters critical for device performance e.g. by separating contacts or bulk characteristics of the devices.

Since DSLA measurements do not involve current flow and the collection of charges at the electrodes but are solely based on the absorption of the RF radiation,  DSLA can be used for the characterization of monocrystalline, polycrystalline, and amorphous materials.

The capabilities of the DSLA in monitoring of the wide bandgap semiconductor device fabrication are illustrated below for the photo-current radiation detectors. In this application DSLA not only identified point and extended defects that directly affect performance of the detectors but also showed that electrode formation is a critical factor affecting reproducibility of the fabrication process. In the defect enhanced mode of operation the DSLA signal increases with density of defects which may be particularly important in evaluation of compound semiconductor wafers (see Physics of Inductive Detection) .

DSLA© Application to PHOTOCURRENT  RADIATION  DETECTORS

SUBSTRATE  CHARACTERIZATION

The key factor affecting performance of semiconductor radiation detectors is quality of the starting material. Defect Specific Lifetime Analysis  (DSLA) allows for the rapid, non-contact evaluation of substrate (such as CdZnTe) parameters directly related to the detector performance.

The effect of the relative volume of the space-charge regions, Vsc/V, at extended defects in n-type, high resistivity CZT, and of the electron capture time constant, tc, on the energy resolution of detectors, FWHM.

While the energy resolution of detectors strongly depends on the density of extended defects (represented by Vsc/V), this resolution is only weakly dependent on the electron capture at point defects characterized by the electron capture time constant, tc (a component of "mu-tau product" commonly used in specifying semiconductors in fabrication of photo-current radiation detectors).

More details see: "Dominant role of extended defects in CdZnTe photocurrent radiation detectors".
DOI: 10.13140/RG.2.2.28287.15526 

ELECTRODE FORMATION

Tight control and optimization of the electrode formation process, which depends on the surface characteristics, is a critical factor limiting reproducibility and the fabrication yields of photocurrent radiation detectors. Hence, monitoring of the surface properties before and after electrode formation is an important factor required for yield improvement.

Dependence of the electrostatic surface potential barrier controlled recombination time constants at Cd and Te faces on the energy resolution of detectors fabricated with a high quality n-type high resistivity CZT.

The samples of the figure above were prepared from a single ingot and were subject to the same treatment. The electrodes were removed prior to the DSLA measurements.

The surface recombination time constant, te, is exponentially dependent on the height of the electrostatic surface potential barrier. Therefore, even small variations in the surface properties would substantially affect energy resolution of detectors.      

More details see: "Electrode subsurface depletion zones limiting reproducibility and performance of CZT radiation detectors".
DOI: 10.13140/RG.2.2.28902.65608/1