Browse Prior Art Database

Sub-Etch Ball Limiting Metallurgy Technology

IP.com Disclosure Number: IPCOM000045626D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Boyar, S: AUTHOR [+3]

Abstract

As shown in Fig. 1, one ball limiting metallurgy (BLM) process involves evaporating Cr-Cu-Au or others through a moly mask which is assembled mechanically to the wafer. It is then removed to another evaporator where Pb/Sn solder is evaporated. After this moly mask is removed, the wafer is heat treated in a hydrogen atmosphere to reflow the Pb/Sn to form a solder ball.

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Sub-Etch Ball Limiting Metallurgy Technology

As shown in Fig. 1, one ball limiting metallurgy (BLM) process involves evaporating Cr-Cu-Au or others through a moly mask which is assembled mechanically to the wafer. It is then removed to another evaporator where Pb/Sn solder is evaporated. After this moly mask is removed, the wafer is heat treated in a hydrogen atmosphere to reflow the Pb/Sn to form a solder ball.

This process limits the size of the BLM because of the wafer size. It may encounter a thermal mismatch between mask and wafer especially the larger wafers like 125 mm, causing a misaligned BLM to via holes. Since the same moly mask is used for BLM and Pb/Sn, the size of Pb/Sn is also limited.

A modified process aimed to solve the above mentioned problem is illustrated in Fig. 2.

The idea is to use sub-etch BLM instead of evaporating through a moly mask. BLM metals are blanket evaporated on a wafer which is then processed through a conventional photoresist process to form a pattern in which the area of the BLM is protected by photoresist.

A saturated KI solution at room temperature is used to etch Au and Cu metals, and concentrated HC1 solution is used to etch Cr. It can be repeated, if necessary, to ensure a clean etch of Cr-Cu-Au film, leaving no residues atop SiO(2) or other type of insulator. The phase-in layer of Cu and Cr can be etched sequentially in KI solution and HC1 solution.

After this sub-etch operation, photoresist is removed by liquid solven...