Appendix C: Wafer Process Engineering

Padullaparthi, Babu Dayal

doi:10.1002/9781119782223.app3

Cited by 1 publication

(1 citation statement)

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“…It is this strain that induces a convex bow to the epitaxial wafer, creating manufacturability issues such as in photolithography [8] and oxidation processes, as well as unintended wafer breakage. Silicon nitride (SiN x ) can be deposited on the backside of a wafer to reduce, or counteract wafer bow [9], but this increases the number of back-end processes and overall manufacturing time. Other compensative processes that may be used during fabrication also tend to increase fabrication complexity and cost to the customer.…”

Section: Introductionmentioning

confidence: 99%

Impact of thermal oxidation uniformity on 150 mm GaAs- and Ge-substrate VCSELs

Gillgrass

Allford

Peach

et al. 2023

J. Phys. D: Appl. Phys.

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Vertical cavity surface emitting laser (VCSEL) devices and arrays are increasingly important in meeting the demands of today’s wireless communication and sensing systems. Understanding the origin of non-uniform wet thermal oxidation across large-area VCSEL wafers is a crucial issue to ensure highly reliable, volume-manufactured oxide-confined VCSEL devices. As VCSEL wafer diameters approach 200 mm, germanium (Ge) is emerging as an alternative substrate solution. To this end, we investigate the uniformity of 940 nm-emitting VCSEL performance across 150 mm diameter GaAs- and Ge-substrates, comparing the oxidation method in each case. Nominally identical epitaxial structures are used to evaluate the strain induced wafer bow for each substrate type with Ge exhibiting a reduction of over 100 μm in the peak-to-valley distortion when compared with GaAs. This wafer bow is found to be the principal cause of centre-to-edge oxidation non-uniformity when utilising a conduction-heated chuck furnace, in comparison to a convection-heated tube furnace. Using on-wafer testing of threshold current, differential resistance, and emission wavelength, device performance is demonstrated for the first time across a 150 mm Ge wafer, and is shown to be comparable to performance on GaAs substrates, when the effects of oxidation uniformity are removed. These results provide evidence that there is a realistic path to manufacturing high yield VCSELs, over wafer diameters approaching those used in Si-photonics, via Ge substrates.

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Section: Introductionmentioning

confidence: 99%