Advanced Alkali Cleaning Solution for Simplification of Semiconductor Cleaning Process
- PDF / 805,488 Bytes
- 12 Pages / 414.72 x 648 pts Page_size
- 70 Downloads / 202 Views
Table 1. Typical wet cleaning sequence based on RCA cleaning [1] and its problems Cleaning Solutions
Cleaning Targets
Side Effects (Contamination)
H 2 SO4/H 2 0
Organic [Resist, Metal]
Particle, Sulfate
HF/H20 (DHF)
Native Oxide, Metal
Noble Metal,
NH 4OH/H 20 2/H 20 (APM)
Particle, Organic
Metal
HCI/H 20 2/H20 (HPM)
Metal
Particle,
HF/H 20 (DHF)
Native Oxide
Noble Metal,
2
(SPM)
Particle
Chlorine Particle
PARTICLE REMOVAL EFFICIENCY OF APM CLEANING AND ITS CLEANING MECHANISM Cleaning by means of acid oxidizing agent such as HCl/H 20 2/H20 (called HPM or SC2) cleaning and H2SO4 /H2 O2 (called SPM) cleaning is generally considered effective in removing metallic impurity from substrate. This is because many metals get ionized and dissolved in acid solution featuring strong oxidizing action. When metal is dissolved in an equilibrium state in solution, its state can be expressed with redox potential-pH diagram. Figure 1 shows redox potential-pH diagram of Cu while Figure 2 shows pH and redox potential (measured value and calculated value) of various solutions [2]. Featuring low pH, Cu is dissolved into solution with high redox potential in a form of Cu2 รท (Figure 1). Both HPM solution and SPM solution feature extremely low pH and high redox potential, which
,iii Z
zXZ
z
6
uJ LU,
0
pH Figure 1. Potential-pH diagram diagram) of the Cu-water system.
2
4
6
5
10
12
14
pH F (Pourbaix
Figure 2. The pH level and redox potential(E) of various solutions (measured value and calculated value). E of SPM, HPM and APM are calculated. Others are measured.
36
means Cu is very easy to be dissolved in these solutions (Figure 2). Cleaning with HPM solution or SPM solution, therefore, can effectively dissolve and remove Cu from substrate surface. The same cleaning mechanism is applied to other metals. On the other hand, alkali solution turns metal into hydroxide. This is why alkali solution can hardly remove metal impurity. Alkali solution such as APM solution is very effective in removing particle and organic impurity while acid cleaning solution such as HPM solution can not remove particle. In an attempt to study removal efficiency of APM cleaning for various types of particulate contamination, cleaning test was performed by using substrate surface which was intentionally contaminated with the following particles : Fe 20 3, A120 3, Si0 2, Si 3N4, PSL (polystyrene latex widely used as standard particle), and PFA (perfluoroalkoxy resin)[3],[4]. The following procedure was employed to intentionally deposit these particles on substrate. Particles to be deposited are first dispersed in acid solution (HCI solution with pH of 3) at high concentration (104 to 10'0 particles/ml), and four-inch bare Si wafer is immersed into this solution. As particles easily adhere onto substrate in acid solution, appropriate number of particles get deposited on wafer surface during immersion of 10 to 30 minutes. Then wafer is treated with ultrapure water overflow rinsing, and it is dried with N 2 gas blow. This makes sam
Data Loading...
