NDLI: Characterization of a spray acid tool for selectively etching under bump metallurgy films used in flip chip applications

Content Provider	IEEE Xplore Digital Library
Author	Ramanathan, L.N. Mitchell, D.
Copyright Year	2003
Description	Author affiliation: Motorola Inc., Chandler, AZ, USA (Ramanathan, L.N.; Mitchell, D.)
Abstract	A methodology for optimizing and characterizing processes for selectively etching Cu underbump metallurgy in the presence of Pb-Sn solder in spray acid tools is discussed. Wafers with the following UBM and bump structure were used in this study: sputtered TiW/sputtered Cu/electroplated Cu stud/electroplated Pb-Sn solder. The development of a manufacturable etch process is illustrated by discussing the method used to establish the process for selectively etching the sputtered Cu film using a commercial, two-component, ammoniacal Cu etch chemistry. The average etch rate on monitors with blanket sputtered Cu films, placed in all slots of the tool clamshell, was used to establish a non-uniformity factor (/spl eta/), which is defined as the ratio of the etch rate in the slot displaying the fastest etch rate to the etch rate in the slot displaying the slowest etch rate. Under ideal conditions the non-uniformity factor should be unity. Over the parameter space investigated it was found that the non-uniformity factor was minimized with the following conditions: temperature of 27/spl deg/C, RPM of 20, pump pressure of 52 psi, etchant flow rate of 6 liters/min, and a 25% solution of the two-component etch chemistry, with the two-components in a 1:3 proportion. Flip chip packages containing electroplated Cu stud and solder bump structures require selective etching of the underlying underbump metallurgy layers that serve as a diffusion barrier and as an electrical bus layer for the electroplating process. In this paper the characterization of a spray acid tool for selectively etching the sputtered Cu bus layer from multiple wafers simultaneously is discussed. The use of the non-uniformity parameter, /spl eta/, defined earlier, to establish the preliminary process is presented. /spl eta/ was also used to understand the parameters that controlled the uniformity of the spray pattern. In particular the effect of pump pressure, flow rate, and etchant composition on /spl eta/ was used to establish the levels of these variables for the Cu etch process. The preliminary Cu etch process was confirmed with a full lot containing 25 blanket Cu wafers. A maximum overetch of 39% was obtained for the full lot.
Starting Page	313
Ending Page	317
File Size	397146
Page Count	5
File Format	PDF
ISBN	0780379330
ISSN	10898190
DOI	10.1109/IEMT.2003.1225919
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2003-07-16
Publisher Place	USA
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Spraying Flip chip Sputter etching Time of arrival estimation Chemistry Optimization methods Manufacturing processes Computer displays Temperature Packaging
Content Type	Text
Resource Type	Article
Subject	Industrial and Manufacturing Engineering Electrical and Electronic Engineering

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4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
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