Mechanism of megasonic damages for micropatterns

Reducing the amount of ionic residues coming from cleaning chemistry became necessary for photomask manufacturing process in order to eliminate the major cause of haze. The achievement of this target involves using sulphate-free steps from resist removal to final cleaning, maintaining good performances on particles or residues removal as well as minimization of pattern damages and preservation of the substrate properties. In this paper the cleaning strategies for high-end masks are discussed and a tight dependency on substrate and contamination type is highlighted as the major aspect that influences the good performances for ozone-based technique. The data collected from both tests and real production for sulfate-free cleaning show that the key point to achieve the full effectiveness is the careful definition of the sequence of treatments and rinses, allowing also the minimization of pattern damages.The cleaning capability of the full sulphate-free process is tested on various types of contaminants and the achieving of excellent removal performance is demonstrated for contaminations of sizes down to 100nm. When the sulfate-free cleaning is not fully effective, a pre-treatment is applied before the cleaning in order to reduce the interaction between contamination and substrate, thus enlarging the removal capability of the ozone-based cleaning. The ion chromatography confirms that the sulphate residues can be reduced below the threshold value for haze formation.

Section: Pattern Damagesmentioning

confidence: 99%

Full sulfate-free process: joint achievement of minimal residual ions and yield improvement

Perissinotti¹,

Sartelli²,

Cassago³

et al. 2007

“…3,4 Furthermore, it has been reported that cavity size has a wider distribution at fixed megasonic conditions, and SRAFs damages caused by large cavity sizes with large cavitation energy would occur at a certain probability. 3,5 Therefore, it is important to control the distribution of the cavitation energy and cavity size on photomask surface within an adequate range to achieve maximum cleaning efficiency without SRAFs damage. However, a correlation between cavity size distribution, cavitation energy distribution and SRAFs damage still remains much to be explored.…”

Section: Introductionmentioning

confidence: 99%

The effect of puddle megasonic cleaning for advanced photomask with subresolution assist features (SRAFs)

Chen¹,

Yang²,

Tseng³

2012

Sub-resolution assist features (SRAFs) damage-free cleaning by use of megasonic nozzle becomes main challenge in photomask industry. Using non-sulfate cleaning tool, the effect of key performance parameters of 1 MHz puddle megasonic nozzle such as megasonic power, and the gap between puddle nozzle and cleaned surface were investigated for opaque SRAFs sizes of 107 nm, 93 nm, 81nm, 71 nm, 63 nm, and 56 nm. Damage-free and high efficiency on particle removal cleaning for SRAFs size down to 71 nm for 38 nm technology node (MPU/ASIC ½ pitch, as outlined in ITRS 2010) has been demonstrated on advanced photomask with MoSi layer in this paper. Furthermore, conducting atomic force microscopy (CAFM) was employed to investigate the nanoscale surface electrical properties of chrome binary blanks cleaned by 1 MHz puddle megasonic nozzle. The results show that highly conducting regions on chromium oxide surfaces can be considered as "cavitation-rich and/or cavitation energy-strong" regions. And their sizes range from 15 to 100 nm, which are comparable to the sizes of SRAFs damage. Finally, in the future, CAFM may be a useful tool to inspect intrinsic defects on advanced photomasks at nanoscale, such as EUV blanks.

“…However, SRAF (sub resolution assist feature) damage has become major concern as pattern size gets smaller over haze issue nowadays. 1,2,3 Mask cleaner makers are developing smarter acoustic nozzles to get the two goals, no damage and high PRE. In ITRS roadmap 4 for optical mask requirement (Table 1), Opaque SRAF size for 32nm tech device (flash) is 81nm and the defect size is 36nm.…”

Section: Introductionmentioning

confidence: 99%

Advanced photomask cleaning for 32nm and beyond

Kim¹,

An²,

Lee³

et al. 2010

High PRE (Particle removal efficiency) and damage free cleaning became main cleaning challenges over haze prevention in photomask industry, nowadays. SRAF (Sub-resolution assist feature) size became small down below 0.1um as pattern size become small. Acoustic frequency and power is the main parameter to increase PRE in photomask cleaning. 1 MHz of acoustic frequency was good enough to remove particles and soft defects until recently. But it has shown pattern damages for SB (Scattering bar) size of below 0.1um unfortunately. In this paper, we optimized photomask cleaning process to achieve high PRE and low pattern damage. Its haze prevention capability and cycle cleaning durability was verified with in-house-built HATB and AIMS, respectively.