HEMT degradation in hydrogen gas

International Electron Devices Meeting 1998. Technical Digest (Cat. No.98CH36217)

Chao

et al.

Self Cite

Hydrogen degradation is a serious reliability concern for III-V FETs. Exposure can occur when hydrogen out-gasses from packaging material and becomes trapped inside hermetically sealed packages. The detailed mechanism by which H2 degrades FETs is not understood and a device-level solution to this problem has not been reported.This work investigates the hydrogen degradation of InP High-Electron-Mobility Transistors (HEMTs) fabricated at MIT. We show that there are three independent degradation mechanisms: two that affect the intrinsic portion of the device and one that affects the extrinsic portion of the device.In the intrinsic region, H reacts with Ti in the Ti/Pt/Au gate metallization to form TiH,. Since TiH has a larger lattice than Ti, this causes compressive stress in the gate. This stress affects the transistor threshold voltage, VT, through the piezoelectric effect, which alters the equilibrium carrier concentration in the channel. This hypothesis is supported with both theoretical calculations and material characterization (Auger spectroscopy and stress measurements) of Ti/Pt bilayers. Along with the piezoelectric effect, there is an additional, negative AV which we hypothesize is due to H+1 penetration into the semiconductor. Both AVT mechanisms are found to be largely recoverable with further annealing in N 2 .In the recessed regions next to the gate, hydrogen modifies the surface stoichiometry of the exposed InAlAs by facilitating As desorption through the formation of AsH 3 . This causes a reduction in the sheet carrier concentration underneath, and an improvement in the breakdown voltage. Changes in the InAlAs surface stoichiometry have been confirmed through XPS. This mechanism is not found to be recoverable.The physical understanding obtained through this work should be instrumental in identifying a device-level solution to this problem. That I have emerged from this process wiser, more confident, and most importantly still smiling, is testimony to the support and encouragement that I have received from many people. It will be impossible to do justice to them all.To my advisor, Prof. Jesd's del Alamo, I owe a debt of gratitude that I can only repay by trying to maintain his same standards of excellence, dedication and integrity in my own career. It has been an honor and privilege to work under his direction.This work has benefitted greatly from interactions with Sanders Lockheed-Martin.

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“…3.2. This is consistent with previous reports InP HEMTs [10,16]. While the measured VT shifts are small, they are statistically significant when compared to the N 2 control.…”

Section: Pre/post Degradation Measurementssupporting

confidence: 82%

Section: Chapter 2 Fabrication Technologymentioning

confidence: 99%

Hydrogen degradation in InP HEMTs

International Electron Devices Meeting 1998. Technical Digest (Cat. No.98CH36217)

Chao

et al.

Self Cite

show abstract

“…is generally reported to decrease in InP HEMT's, although exposure times for published data are under 20 min [2]. To our knowledge, a device-level solution to this problem has not been reported for either InP or GaAs technologies.…”

Section: Introductionmentioning

confidence: 84%

Hydrogen-induced piezoelectric effects in InP HEMT's

IEEE Electron Device Lett.

Adams

et al. 1999

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“…Over time, hydrogen causes changes in device characteristics that can ultimately lead to parametric module failures. Compared with more extensive studies of H degradation of GaAs MESFETs and PHEMTs [3]- [6], only limited data on the H sensitivity of InP HEMTs is available [1], [2], [5]. To our knowledge, a device-level solution to this problem has not been reported for either InP or GaAs technologies.…”

Section: Introductionmentioning

confidence: 93%

“…This recovery anneal is designed to see if H degradation can be annealed out with further thermal processing in pure N . Recovery behavior has been frequently reported following H degradation [1], [4], [5].…”

Section: Methodsmentioning

confidence: 99%

Hydrogen-induced changes in the breakdown voltage of InP HEMTs

IEEE Trans. Device Mater. Relib.

Calveras

2005