Novellus Systems (NASDAQ:
NVLS) announced today that it has developed a multiple wavelength UV Thermal
Processing (UVTP) treatment on the company's SOLA® platform that results
in a 25 percent improvement in film hardness compared to a single wavelength
treatment of the same k-value dielectric.
At 32nm and beyond, ultra-low dielectric constant (ULK) materials must be introduced
into the semiconductor manufacturing process flow in order to improve device
performance. ULK materials, however, present challenges associated with adhesion
and the mechanical properties of the film. Adhesion issues are typically addressed
through interface engineering, while mechanical properties are improved using
a UVTP treatment. UVTP processing results in a lower bulk dielectric constant
(k), cross-links the chemical "backbone" (which increases mechanical
strength), and removes porogen (pore generation material) from non-dense ULK
films. Increasing the mechanical strength of the film ensures that it will withstand
downstream manufacturing processes such as chemical-mechanical planarization
(CMP) and final packaging.
It is well known that porous ULK materials require different process steps
for porogen removal and cross-linking. The unique SOLA UV treatment utilizes
Novellus' multi-station sequential processing (MSSP) architecture to independently
optimize the porogen removal and cross-linking steps, while maintaining high
system throughput. Wavelength, temperature, treatment time, and UV intensity
can be independently controlled at each of the four processing stations.
Cohesive and adhesive failures during CMP and final packaging steps can be
exacerbated by increasing the number of ULK layers in the interconnect stack.
A margin of safety in the packaging process can be ensured by tailoring the
assembly process and design rules; however, optimizing the bulk film properties
(i.e. hardness, modulus and residual stress) is also required. Figure 2 shows
the difference between soft and hard ULK films used in a simulated interconnect
stack. Eight layers of an IMD/barrier stack were deposited on a bare wafer to
simulate a ULK interconnect structure. For a given post-treatment film stress,
the softer film shows peeling and delamination at the wafer edge, while the
harder film shows none.
"Controlling the UV exposure parameters is critical to obtaining the maximum
mechanical performance of a given dielectric constant film," said Boaz
Kenane, director of technology for UVTP at Novellus. "SOLA UVTP with MSSP
enables the independent optimization of key UV treatment steps to enhance film
performance while maintaining a high level of manufacturability."