Review—Recent Advancement in Charge- and Photo-Assisted Non-Contact Electrical Characterization of SiC, GaN, and AlGaN/GaN HEMT

Abstract

The charge-based corona-Kelvin non-contact metrology, originally developed for Si IC fabrication, has recently been extended to wide energy gap semiconductors. We discuss principles of this extension and key applications, namely: high precision dopant measurement on SiC and GaN; two-dimensional electron gas characterization in AlGaN/GaN HEMT structures; interface and dielectric characterization on epi-layers with SiO 2 and SiN; comprehensive interfacial instability characterization of oxidized SiC; and whole wafer mapping of defects with a charge-assisted surface voltage technique, QUAD. This powerful set of measurements is performed without fabrication of any test structures or electrical contact. Corresponding commercial tools are currently being introduced. Based on the historical example of silicon IC, we believe that this approach shall offer enhanced testing for research and for manufacturing process control with reduced cost and fast data feedback benefiting wide-bandgap device technology. . This paper is part of the JSS Focus Issue on GaN-Based Electronics for Power, RF, and Rad-Hard Applications.Development of semiconductor devices and control of the manufacturing process requires cost effective metrology with rapid feedback to pilot or manufacturing lines. In this respect, silicon IC's have been benefiting from inventions (by IBM, Fishkill, NY 1 and by SDI, Tampa, FL 2 ) that created a foundation for the unique charge-based non-contact electrical metrology. 3In this technique, an electrical biasing is produced by corona charging of a surface and the response is monitored by measuring the surface voltage with a vibrating probe, such as a Kelvin-probe. The technique is commonly referred to as the corona-Kelvin method. 4 Corresponding commercial tools designed for Si wafers reduced the need for fabrication of electrical test devices and electric contacts; lowering the manufacturing cost and shortening the data feedback time from weeks to less than one hour. 5 The metrology has been continuously improved in sensitivity, precision, repeatability, and spatial resolution; meeting the demands of new technology nodes. It has been used by all major silicon IC manufacturing companies and has also been adopted by smaller silicon device fablines looking for cost effective metrology solutions.Very recent developments in corona-Kelvin, discussed in this work, are intended for rapidly advancing wide-bandgap semiconductor technology that includes SiC, GaN, and AlGaN/GaN heterostructures.

Method for noncontact measurement of 2DEG mobility and carrier density in AlGaN/GaN on semi-insulating wafers

“…This is an analogy to identification of the pinch-off point in the capacitance voltage technique that uses the slope change of the integrated capacitance versus bias voltage to indicate a depleted 2DEG. 18,19) In previous work, [5][6][7] we have demonstrated for "normally on" heterostructures a practically one to one relation between the applied charge bias and the change of 2DEG density. The emptying or filling of the triangular well takes place in response to negative or positive charge bias, respectively.…”

“…[1][2][3] Later, it was extended to wide bandgap semiconductors, such as SiC, 4) GaN, and AlGaN/GaN. 5) A version of the technique known as corona noncontact C-V 5) was employed in previous research on the characterization of AlGaN/GaN heterostructures and 2DEG in the "normally on" HEMT configuration. [6][7][8] In the present work we report further developments in the noncontact corona charge-bias metrology realized with charge-assisted sheet resistance measurements.…”

“…1) In wide bandgap semiconductors the bare surfaces in depletion exhibit excellent corona charge retention that is a consequence of the lack of minority carriers that could neutralize ions. 5) Accordingly, the surface depletion condition at the initial state (before corona charging) is important for the stability of deposited charge. This condition was present for all wafers under study.…”

“…This is accomplished with short wavelength illumination that generates minority carriers. [5][6][7] For the charge-assisted mobility technique, the noncontact sheet resistance measurements were performed with an eddy current probe for R sh measurements in the range of 200-6000 Ω/sq. This was combined with wire corona charging for sequential -R Q sh data acquisition.…”

Review—Review of Research on AlGaN MOCVD Growth

“…In particular, ultraviolet and deep ultraviolet microelectronics and optoelectronic devices with AlGaN and AlGaN/GaN heterojunctions have broad application prospects. [2][3][4] For instance, they are used in deep ultraviolet light emitting diode (LED) and semiconductor laser (LD) in fields such as medical disinfection, data storage, biochemical detection and laser radar. 5 AlGaN barrier layer with a high Al composition can increase the density of two-dimensional electron gas (2DEG) generated at the interface of AlGaN/GaN, and realize high-power electronic devices.…”