Technical-Report

Introduction of Plasma Scribing Technologyon GaAs Wafers Using ICP Etching
Samco Inc.

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Introduction

GaAs-based devices find applications in photonics, including semiconductor
lasers, photodiodes, and LEDs. Emerging uses such as VCSELs for 3D facerecognition signal a market expansion. As the production of GaAs devices
intensifies, the need arises for smaller devices and increased chip yield within
wafers.
A viable solution for back-end processing of these wafers is plasma scribing
technology using ICP etching equipment. While diamond scribing and blade
dicing are common methods for wafer singulation, their wider scribing linewidths (ranging from 50 µm to 100 µm) limit chip production, resulting indevice defects and diminished yields. Plasma scribing, however, facilitates theprocessing of narrow scribe lines without substrate chipping.

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(a) Blade scribing

Plasma Scribing

Various methods are employed to segment wafers into chips, such as laser
scribing and breaking, blade and laser dicing, and a combination of thesemethods. As wafer thickness diminishes, a method known as DBG (DicingBefore Grinding) —where half dicing precedes backside grinding— has been
proposed to mitigate the risk of transporting thin wafers.
Plasma scribing circumvents mechanical contact like blade scribing, hence
avoiding chipping or cracking. Moreover, unlike mechanical dicing, where theblade continuously scribes the wafer and the scribing duration elongates withdecreasing chip size and longer lines, plasma scribing is all done at once
regardless of chip size. Notably, GaAs wafers, due to their material properties,
tend to chip, thus necessitating slower blade speeds compared to Si. Plasma
scribing, however, remains unaffected by chip size or shape as wafers areprocessed in batches, reducing processing time in some cases. Furthermore,
employing a dry process mask allows scribing line widths to narrow to 50 µm
or less. Nevertheless, deep scribing demands a specific aperture width.

(b) Plasma scribing
Plasma scribing processes all lines
simultaneously
Figure 1. Comparison of Blade Scribing (a)and Plasma Scribing (b)Since the 2010s, we have proposed plasma scribing as a deep scribing
technique for compound semiconductors like GaAs. This report showcases
the promising outcomes of plasma scribing on ø3-inch GaAs wafers using theICP etching system RIE-400iP and evaluates breaks post-scribing.
(a) Cross-section▪

Process Data

The process involving scribing a GaAs wafer using ICP etching aims to create
grooves several tens of micrometers deep using either a resist or SiO2 mask,
necessitating high-rate and high-selectivity etching. This study focused onplasma scribing ø3-inch GaAs wafers utilizing our ICP etching system, RIE400iP.
The SEM images in Figure 2 reveal the outcomes following plasma scribing.
Due to the initial oblique mask shape, the aperture width at the process's top
is wider than the mask pattern width, due to mask retraction. However, theshape is achieved without any problem for scribing applications. The etchingrate is 1.57 µm/min, and a uniform depth of 47.2 µm was achieved across theentire surface of the ø3-inch wafer.

Technical Report / 2023. JUN.

(b) Bird’s eye view
Figure 2. SEM images post-plasma scribing

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Plasma scribing structure

Figure 3. Cross-section analysis of the chip post-breakage

Following scribing, the chip's break quality was assessed. Figure 3 presents across-sectional image post-breakage. No lateral blurring of the break position
was evident, and the chips separated cleanly from the center of the scribe
groove, indicating consistent division across the entire wafer. Moreover, unlike
laser processing, no debris adhered to the wafer surface, maintaining anexcellent surface condition.

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ICP Etching Systems

This study utilized the RIE-400iP ICP etching system for plasma scribing,specifically tailored to process compound semiconductors used insemiconductor lasers. The RIE-400iP system is specialized for ø2, ø3, andø4-inch wafer processes, and excels in managing compound semiconductors
like InP, GaN, and GaAs. Featuring the cutting-edge ICP source HSTC™
(Hyper Symmetrical Tornado Coil), it ensures consistent generation of stable,
high-density plasma. Additionally, its optimized pumping structure guarantees
efficient performance and minimizes the redeposition of by-products. Theproduct range includes the load-lock RIE-400iP for R&D and the cassetteloading RIE-400iPC for mass production, both compactly designed for spaceefficient installation. As the exclusive provider of dedicated ICP etch systems
for compound semiconductors ø4 inches or smaller, our unique process
recipes, exceptional service, and support have earned high praise fromcustomers worldwide.

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Figure 4. Loadlock RIE system
RIE-400iP for R&D

Conclusion

This report showcases the results of plasma scribing on GaAs wafers andevaluates the post-scribing breakage. Plasma scribing holds significant
potential to reduce both process time and manpower compared toconventional blade scribing methods. We have proposed an ICP etchingsystem tailored for GaAs wafer scribing, specifically designed for compoundsemiconductors. Given the anticipated rise in miniaturization and production
volume within the compound semiconductor field, the adoption of plasma
scribing is highly likely. This report details the utilization of the RIE-400iP ICP
etching system for small-diameter wafers. In addition to the RIE-400 series,
the RIE-800iP series is designed for larger sizes such ø6-inch and ø8-inch
wafers. Our comprehensive equipment range spans from small-diameter toø8-inch wafers, catering to both R&D and mass production needs. Ourcommitment remains unwavering towards advancing process development as
leading manufacturers of plasma systems for compound semiconductors.

Figure 5. Cassette loading RIE system
RIE-400iPC for mass production

Samco Inc.
For more information please email: info@samco.co.jp

Technical Report / 2023. JUN.

URL: https://www.samco.co.jp/en/2