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WET CLEANING

18.10 WAFER PROCESSING

18.2.2 Back End-of-Line Cleaning
BEOL wafer cleans pose additional complexity issues because of the addition of interconnect metal.
Special chemistries have been developed for wet cleaning in order to minimize the negative effects
that the FEOL clean chemicals have on the metal layers.
Post-CMP (Cu). Post-copper chemical mechanical polish (CuCMP) clean is an important step to
remove the CMP slurry from the wafer prior to further processing the semiconductor device. The
most common method to remove the slurry from the wafer is with a brush cleaning system. Sonic
removal systems are gaining in acceptance and have shown to have a similar or better removal effi-
ciency than brush systems and work with very dilute chemistries. 20,21 The primary adhesion force in
post-CuCMP are electrostatic forces. HF-based chemistries are typically used in post-CuCMP but
have been found to create issues with corrosion in the copper and also promote the reattachment of
certain types of slurry particles. 22

Post-Etch Residue Removal. BEOL post-dry etch or ash residue removal is accomplished using a
wide range of chemicals depending on the type of resist used and how the bulk of it is etched away.
Some typical chemistries used for this are given in Table 18.3.
The current trends are moving toward dilute acid chemistries because of the cheaper cost for both
the initial chemical and subsequent waste processing. They also have a significant impact on envi-
ronmental and health issues. Researches are investigating the use of chemistries with ozone gas dif-
fused into water and some inorganic chemicals as a method of removing resist residues. 23 The
aforementioned chemistries are typically applied using a spray or chemical dispense system.

Backside and Bevel Cleans. BEOL backside and bevel cleans (see Fig. 18.3) are used to remove
particles and films that can either diffuse into the wafer substrate or cause handling equipment con-
tamination issues.

TABLE 18.3 Typical Polymer Removal Chemistries
Family of chemistry Manufacturer Name
Quaternary based Dupont-EKC EKC-525
EKC-505
Air Products ACT-K101
JT Baker REZI-28
Nonproprietary TMAH
ATMI ESC-775
Fluoride based Air Products CE-15
NE-12
NE-14
NE-88
NE-89
Dupont-EKC EKC-630
EKC-640
EKC-650
ATMI N.O.E.
ST-200 series
Mitsubishi Gas Chemicals ELM-C30 series
Amine based Dupont-EKC EKC-265
EKC-270
Air Products ACT-935
ACT-970
Inorganic Nonproprietary DHF
DSP (dilute sulfuric peroxide)

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