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4

LIGA and

Micromolding

4.1 Introduction ......................................................................4-1
4.2 LIGA — Background ........................................................4-3
History • Synchrotron Orbital Radiation (SOR)
• Access to the Technology
4.3 LIGA and LIGA-Like Process Steps ..................................4-9
X-Ray Masks • Choice of Primary Substrate
• Resist Requirements • Methods of Resist Application
• Exposure • Development • Comparison of Master
Guangyao Jia and Micromold Fabrication Methods • Metal Deposition
Marc J. Madou • Molding • Demolding • Alternative Materials in LIGA
University of California, Irvine 4.4 Examples ..........................................................................4-69

4.1 Introduction

LIGA is the German acronym for X-ray lithography (X-ray lithographie), electrodeposition (galvanofor-
mung), and molding (abformtechnik). The process involves a thick layer of X-ray resist (from microns to
centimeters), high-energy X-ray radiation exposure, and development to arrive at a three-dimensional
resist structure. Subsequent metal deposition fills the resist mold with a metal, and after resist removal,
a freestanding metal structure results [IMM, 1995]. The metal shape may be a final product or serve as
a mold insert for precision plastic molding. Molded plastic parts may in turn be final products or
lost molds (see Figure 4.1). The plastic mold retains the same shape, size, and form as the original resist
structure but is produced quickly and inexpensively as part of an infinite loop. The plastic lost mold
may generate metal parts in a second electroforming process or generate ceramic parts in a slip casting
process.
The bandwidth of possible sizes in all three dimensions renders LIGA useful for manufacture of
microstructures (micron and submicron dimensions) and packages for these microstructures (milli-
meter and centimeter dimensions), and even for the connectors from those packages to the “macro
world” (electrical, e.g., through-vias; or physical, e.g., gas in- and outlets).
Once LIGA was established in the research community, interest in other micro- and nano-replication
methods became more pronounced. Given the cost of the LIGA equipment, various LIGA-like processes
took center stage. These pseudo-LIGA methods involve the replication of masters created by alternate
means such as deep reactive ion etching (DRIE) and novel ultraviolet thick photoresists. This more
generalized lithography and replication procedure is illustrated in Figure 4.2.

4-1

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