This Materials World Network collaborative program brings researchers (Alford and Mayer) from Arizona State University (ASU) and (D. Adams and N. Tile) from the University of the Western Cape South Africa (UWC, a historically disadvantaged university) to investigate the fundamental aspects of hydrogen transport and trapping in ion-induced delaminating of thin surface layers from silicon and other semiconductors (see Figs. 1 a-d).

Ion-cut fabrication is a desirable alternative in silicon-on-insulator (SOI) technology because:• end product is a single coherent layer of silicon (less

power needed for devices).• transferred layer has higher electron mobility (faster

switching times).

Major significance of this work:• hydrogen trapping can be activated by microwaves at

temperatures lower than that needed in conventional processing [Thompson et al. Appl. Phys. Lett. 87, 224103 (2005)]

• Results in lower temperature processing for use in flexible display technology.

• The transferred layer electrical properties are similar to those in high temperature processes (Table 1).

Material science issues, this study will determine:• How microwaves and trapped hydrogen interact with

material properties during ion-cut layer transfer• How ion implant damage aids microwave power

absorption during ion-cut layer transfer

Materials World Network: Hydrogen Transport and Trapping in Ion-Cut Phenomena

T.L. Alford and J.W. Mayer, Arizona State University DMR-0602716

Schematic of the ion-cut process for layer transfer: (a) Ion implant introduces H trapping sites within the donorwafer; (b) chemical surface preparation ensures enhanced bonding strength; (c) direct bonding of the donor and handle substrate; (d) microwave annealing to activate exfoliation. Resultant product is single crystal layer transfer on differing substrates

p-Si

a) H+ and B+ ion implant

Stiffener (Silicon wafer)

SiO2

b) Cleaning and activating surfaces

Surfaces

p-Si

c) Bonding

Stiffener (Silicon wafer)

SiO2

p-Si

Exfoliated layer

d) Μ wave anneal (exfoliation)

Stiffener (Silicon wafer)

SiO2

p-Si

TableCarrier mobility (CM) in microwave exfoliated Si layers prior to and after a thermal anneal. These values compare well to CM values from layers transferred using conventional anneals.

A unique aspect of this program is that the investigation is done by way of an international exchange of students and staff from both ASU and UWC. Students working in this ASU-UWC collaboration have gained significantly from the expertise and facilities at both institutions – ASU materials processing is a world leader in materials characterization; whereas, UWC’s access to new iThemba Labs - Ion implantation Facilities is crucial to the ion implantation component of this process.

During this period, Prof. Adams and Ngcali Tile visited Prof. Alford’s lab at ASU to initiate the research activities. Mr. Tile’s stay was extended for six additional weeks to optimize the time spent working together with ASU graduate student Douglas Thompson (Fig. 1) on the processing and characterization of microwave induced ion-cut samples.

Prof. Mayer of ASU traveled with Mr. Tile back to UWC to initiate research activities there. Douglas Thompson traveled to UWC to continue the collaboration during a two-month stay. The students demonstrated the first successful ion implant experiment at new iThemba facility. The students also designed and built a pyrometer inlet to UWC’s microwave furnace, and successfully demonstrated microwave induced exfoliation at UWC.

Fig. 1. Graduate student N. Tile (UWC) and D. Thompson (ASU) collecting Rutherford backscattering data for characterization of exfoliated layers of silicon, at ASU.

Fig. 2. D. Thompson (ASU) holding a designed pyrometer input which includes infrared sensor, purge line, and electronics housing (not shown), for a microwave furnace at UWC.

Materials World Network: Hydrogen Transport and Trapping in Ion-Cut Phenomena

T.L. Alford and J.W. Mayer, Arizona State University DMR-0602716