ABSTRACT
I. Roles of Wet Cleaning Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
II. Improvement of RCA Cleaning Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
A. Current Status of Wet Cleaning Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
B. Improvement of RCA Cleaning Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
1. Surface Microroughness Caused by Wet Process . . . . . . . . . . . . . . . . . . . 65
2. Removal Efficiency of Particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
3. Effect of Surface Microroughness on Electrical
Characteristics of Thin Oxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
III. Effect of Megasonic Irradiation in UPW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
A. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
B. MS-Induced Chemical Reactions in UPW . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
C. MS-Induced Radical Formation in UPW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
IV. Specific Gas Dissolved Functional Water
and its Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
A. Definition of Functional Water for Wet Cleaning Process . . . . . . . . . . . . . . . . 74
B. Idea of H2-UPW Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
1. Effects of Dissolved Gas in MS Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . 75
2. Particle Removal by Means of Electrolytic Cathode Water . . . . . . . . . . . 75
3. Idea of Gas-Dissolving-Type H2-UPW . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
C. Adoption of Module with Built-in Gas Permeating Membrane . . . . . . . . . . . . 76
D. Control of Dissolved Gases (Application of Henry’s Law) . . . . . . . . . . . . . . . 76
E. Deaeration Using Water Vapor Sweep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
V. O2-Free Wafer-Cleaning Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
A. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
B. Microroughness of Silicon Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
C. Hydrogen Termination of Silicon Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
VI. Total Room-Temperature Cleaning Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
A. Total Room-Temperature 4-Step Cleaning Process . . . . . . . . . . . . . . . . . . . . . 86
1. O3-UPW for Wet Cleaning Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
a. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
b. Cleaning Efficiency of O3-UPW . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
i. Removal of Organic Impurities . . . . . . . . . . . . . . . . . . . . . . . . 87
ii. Removal of Metallic Contaminants . . . . . . . . . . . . . . . . . . . . . 88
2. H2-UPW for Wet Cleaning Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
a. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
b. Relation between Dissolved Hydrogen Concentration and
Particle Removal Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
c. Removal of Alumina Particle and Silica Particle . . . . . . . . . . . . . . . 91
d. Comparison between APM Cleaning and H2-UPW Cleaning . . . . . 91
e. Effects of H2-UPW Cleaning on Wafer
Surface Microroughness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
f. Cleaning by UPW with Other Gases than
Hydrogen Gas Dissolved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
g. Particle Removal Mechanism of H2-UPW Cleaning . . . . . . . . . . . 95
i. Effects of NH3 Spike . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
ii. Effects of MS Irradiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
iii. Effects of Dissolved Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . 97
iv. Model of Correlation between Dissolved Hydrogen
and MS Irradiation (Surplus Radical Model) . . . . . . . . . . . . . 97
v. Verification of Surplus Radical Model . . . . . . . . . . . . . . . . . . 99
h. Applications of H2-UPW Other than Particle Removal . . . . . . . . . . 100
i. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
3. Total Room-Temperature 4-Step Cleaning Process . . . . . . . . . . . . . . . . . 101
4. Purity of Gas-Dissolved Functional Water . . . . . . . . . . . . . . . . . . . . . . . 101
B. Total Room-Temperature 5-Step Cleaning Process . . . . . . . . . . . . . . . . . . . . 102
1. Design of 5-Step Cleaning Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
2. Cleaning by HFþO3-UPW (FOM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 3. Prevention of Decomposition of Surfactant . . . . . . . . . . . . . . . . . . . . . . . 106
C. Strategy in Cleaning Process in BEOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
VII. Surfactant and Chelating Agent Technologies for
Innovating Semiconductor Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
A. Challenges in Cleaning Technology to Address
Higher-Density ULSI Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
B. Solutions to the Challenges from the Viewpoint of
Cleaning Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
C. Preventing Metal Cross Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
D. Accelerating Fine Particle Removal without Device Pattern Damage . . . . . . 112
E. Single-Wafer Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
F. Cleaning of New Material Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
1. Challenges of New Material Surface Cleaning . . . . . . . . . . . . . . . . . . . . . 115
2. Preventing both Material Corrosion and Contaminant Redeposition . . . . 116
3. Use of Surfactant as Corrosion Inhibiter . . . . . . . . . . . . . . . . . . . . . . . . . . 117
4. Improvement of Wettability of Hydrophobic Surface . . . . . . . . . . . . . . . . 118
G. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
VIII. FTIR-ATR Calibration Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
A. FTIR-ATR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
B. Preparation of Reference Block with Organic Film Adsorbed to
Obtain Calibration Curve for Quantification of Organic Compound
Adsorption onto Si Surface: Langmuir-Blodgett Technique . . . . . . . . . . . . . . 119
C. Preparation of Calibration Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
D. Adsorption of Organic Compound to Si Surface in Cleanroom Ambience . . . 123
E. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
IX. Balanced Push Pull Nozzle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
A. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
B. Ultrasonic Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
1. Necessity of Ultrasonic Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
2. Fine Particle Elimination Mechanism of Ultrasonic Cleaning . . . . . . . . . 127
a. Elimination Principle of Adhesive Particles from Substrates . . . . . . 127
b. Possibility of Occurrence of Megasonic and Cavitation . . . . . . . . . 127
c. Noise Generation Research at the Time of
Megasonic Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
d. Estimation of Elimination Mechanism of Adhesive
Particles from Substrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
C. BPP Nozzle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
1. Concept of BPP Nozzle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
2. Ultrasonic Oscillator Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
a. Oscillator Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
b. Oscillator Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
c. Enclosure Materials and Surface Processing . . . . . . . . . . . . . . . . . . . 135
d. Board Thickness of Enclosures (Ultrasonic Radiant Boards) . . . . . 136
e. Oscillator and Enclosure (Radiant Board) Bonding . . . . . . . . . . . . . 136
f. Enclosure (Radiant Board) Structure . . . . . . . . . . . . . . . . . . . . . . . . . 136
3. Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
4. Cleaning Fluid Supply/Discharge Section (Rectification Mechanism) . . 137 a. Optimization of the Cleaning Fluid Supply/Discharge Section . . . . 139 b. Fluid Flow Calculation Method for the Current Plate
of the Drilling Tubule Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
i. Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
ii. Calculation Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
c. Fluid Flow Calculation Method for the Current Plate
Made by Porous Ceramics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
i. Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
ii. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
iii. Calculation Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
d. Validation of Calculation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
e. Structure of the Cleaning Fluid Supply/Discharge Section of the BPP Nozzle for Cleaning of 720 mm Substrate . . . . . . . . . . . 142
5. Optimum BPP Nozzles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
D. Cleaning Capacity of BPP Nozzles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
1. Cleaning Power Evaluation using 6-in. Glass
Substrates and Silicon Wafers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
2. Cleaning Evaluation using the 550 mm 650 mm Glass Substrate . . . . 145 3. Cause of Performance Differences with Traditional
Ultrasonic Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
a. Comparison of Acoustic Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
b. Comparison of Ultrasonic Applied Areas . . . . . . . . . . . . . . . . . . . . 147
4. Ideal Situation of Ultrasonic Cleaning Equipment . . . . . . . . . . . . . . . . . . 148
E. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
In order to improve the quality and yield in semiconductor manufacturing process, it is essential to
realize “ultraclean Si wafer surface” on which ultra-fine patterns are fabricated. The ultraclean Si
wafer surface is defined as a surface which satisfies the following eight requirements [1]:
1. Free from particles
2. Free from metallic impurities
3. Free from organic impurities
4. Free from unintended native oxide
5. Maintain atomic-order “microroughness”
6. With top surface completely terminated with hydrogen
7. Free from moisture adsorption
8. Free from charge-up
Si wafer goes through wet cleaning process before and after each cycle composed of film depo-
sition, photolithography, and etching steps. The number of cleaning steps is about twice as many as
the number of masks used in semiconductor manufacturing process. In addition, chemical mechan-
ical polishing (CMP) process which has been rapidly adopted to planarize wafer surface requires
cleaning step right after its completion. Needs for cleaning step keep increasing.
