Chemical mechanical planarization (CMP) has been widely used in
the integrated circuit (IC) manufacturing industry to achieve both
local and global planarities. In CMP processes, diamond conditioner
disks are used to regenerate pad asperities and remove used slurry
and pad debris fromthe pad surface [1–3]. During pad conditioning, diamonds
embedded in the disk plow and cut the pad surface to impart
and maintain adequate pore structure and surface roughness. Physical
contact with pad asperities and slurry abrasives causes the diamonds
to wear thus leading to a drop in the cutting effectiveness of the disk.
More importantly, any possible diamond pull-out, fracture and associated
debris and fragments are known to cause catastrophic scratches on
the wafer surface.
In general, the useful life of a diamond conditioner disk is about
100 h [4]. Mechanisms that determine end-of-life for conditioner disks
include diamond micro-wear, partial fracture and complete pull-out.
Previously reported work on diamond fracture describes a highpressure
water jet employed to demonstrate the failure mechanism in
the diamond bonding and to quantify the effective strength of the
bond [5]. Subjecting individual diamonds to a “pick” test is another
method for measuring the force necessary for diamond pull-out which
involves the release of a particular diamond from its bond matrix [5].
Tan and Cheng [6] conducted a wear–corrosion test on three types of conditioners. All disks were first immersed in a slurry with pH value
of 7.7 for 50 h and then polished against Al2O3 rings. Results showed
that electroplated disks were prone to diamond loss while brazed
disks left the diamonds intact. It is important to note that all of the
above studies focused on diamonds in general and made no effort to
isolate and study whether any of these diamonds were “active” or
“inactive” as described below.
In a recent work, Borucki et al. [7,8] found that among the several
tens of thousands of diamonds present on the surface of a conventional
diamond conditioner, the percentage of “active diamonds” (i.e., those
diamonds that actually work and do the pad cutting) was typically
less than 1%. The remaining diamonds, which either did not touch the
pad surface or merely supported the load of the disk, were referred to
as “inactive diamonds”. The work also reported that all “active diamonds”
were not the same as only a small fraction of them, referred
to as “aggressive diamonds” didmore than 80% of the cutting of the pad.
Borucki's work underscored the importance of undertaking a new
study to investigate and quantify whether and how “aggressive diamonds”
maintain their integrity during pad conditioning and the extent
of pull-out, fracture and micro-wear that may happen during CMP processes.
However, as onemay expect, any such studieswould have to last
100 or more hours in order to see any appreciable micro-wear or fracture
on the diamonds,whichwould be quite costly in terms of consumables
and time, and also impractical. As such, instead of using a polishing
pad, this study employs a pad-sized thin aluminum plate as the surface
of contact with the diamond conditioner disk. Details of the aluminum
plate and the procedures and equipment involved in the accelerated
fracture tests are described in the next section.