各种薄膜颗粒有效湿清洗方法的评价

Conventional manufacturing process of a metal– oxide–semiconductor (MOS) involves various steps such  as etching, deposition, CMP etc. During each process,  wafer can be easily contaminated by the nano-size  particles. These particles on wafer surface might affect the  yield reduction. Many literatures reported about wafer  cleaning process using physical and chemical method to  remove particle effectively. According to the  International Technology Roadmap for Semiconductors  (ITRS) 2011, critical particle diameter is decreasing to 1x  nm with shrinking dynamic random access memory  (DRAM) half pitch. Physical cleaning process such as  megasonic, jet spray, aerosol, etc., could not prevent  pattern damage below 30 nm sized because of its  uncontrollable physical force. Therefore, it is essential  to clean the surface using wet chemical cleaning process  for preventing pattern damage. There are two main factors  in wet chemical cleaning process. One is etching of  surface and the other is interaction force between particle  and substrate. SC1 cleaning mechanism is well known to  remove particles on Si substrate representatively. However, particles contaminated on surface not only  silicon surface but also many kinds of surface such as  poly-silicon, silicon nitride, silicon dioxide. Therefore, it  has to be demonstrated particle removal efficiency (PRE)  on various surfaces with chemicals based on its etching  mechanism and interaction force.

In this study, we investigated critical factor on particle  removal using various surface based on silicon substrates  with cleaning chemicals which is conventionally used in  semiconductor cleaning process. Poly-silicon (poly-Si),  thermal silicon-dioxide (Th-oxide) and high temperature  silicon-nitride (HT-SiN) were used as substrates for the  experiments. Dilute NH4OH (NH4OH:DIW = 1:1000),  SC1 (NH4OH:H2O2: DIW = 1:2:50, 60 ºC) and dilute HF  (HF:DIW = 1:1000) solutions were used for etching and  cleaning test. Etching rate of each substrate was measured  using ellipsometer. Zeta-potential was measured to  calculate interaction force of each substrate in cleaning  solutions. Si3N4 (<1 μm) particles were contaminated on  couponed wafer using dipping method for cleaning test.  Cleaning process was performed using spin type single  tool as following sequence: (1) cleaning 30 sec with  cleaning chemicals at 500 rpm (2) rinsing 30 sec with  DIW at 500 rpm (3) drying 30 sec with N2 blowing at  1500 rpm.

Fig. 1 shows the etching rate of Th-oxide, poly-Si and  HT-SiN in cleaning chemicals for 60 min. The etching  rate of all the substrates was lowest at dilute NH4OH  solution as compared with other solutions. Poly-Si  substrate was highly etched by SC1 solution. HF solution  has the highest etching rate on HT-SiN substrate. Fig. 2 shows the interaction force between each substrate and  Si3N4 particles based on zeta-potential results. pH of  NH4OH, SC1 and HF cleaning solutions were 10.8, 10.3  and 2.4 respectively. Repulsive force revealed on Thoxide and poly-Si at pH 10. On the other hand, HT-SiN  appeared attraction force at all the conditions. Based on  results of etching rate and interaction force, PRE was  evaluated as shown in Fig. 3. PRE of Th-oxide was higher  at dilute NH4OH solution and SC1 solution. PRE was  affected by etching of Th-oxide surface and strong  repulsive force between Th-oxide surface and particles in  alkaline solution. In spite of high etching rate in HF  solution, it could not remove particles effectively due to  particle recontamination by attraction force in acidic  condition. PRE of Poly-si was similar with Th-oxide in  alkaline solution. This means that Th-oxide was affected  by interaction force as critical factor for wet chemical  cleaning. PRE of HT-SiN surface increased with  increasing etching rate. Therefore, etching rate is the most critical factor than interaction force on HT-SiN surface.

Thus, each substrate has dominant factors in wet  chemical cleaning. It may be etching rate or interaction  force or both of them. If these factors are considered when  conducted cleaning of various substrates, the substrates  will be cleaned effectively.