Main application scenarios of SPM in wafer cleaning

1. Introduction

SPM (a mixture of H₂SO₄ and H₂O₂) is a critical step in the wafer‑cleaning process. Its strong oxidizing power and dehydrating ability make it the solution of choice for removing stubborn organic contaminants and stripping hardened photoresist.

2. Core Application Scenarios

2.1 Removal of Hardened Photoresist After Ion Implantation

Process requirement: After ion implantation—particularly at high doses exceeding 1×10¹⁵ ions/cm²—the top layer of the photoresist undergoes carbonization and hardening due to high-energy ion bombardment, rendering it resistant to removal by conventional organic solvents.

Mechanism of action: At temperatures above 130°C, SPM leverages the strong dehydrating power of hot sulfuric acid and the oxidizing properties of hydrogen peroxide to induce the cleavage and removal of the cured adhesive layer.

Typical process flow:

• First, immerse the sample in SPM for 3–10 minutes to remove the bulk of the hardened photoresist.
• Subsequently, perform an SC-1 rinse (NH₄OH/H₂O₂/H₂O) to remove residual particles and trace organic contaminants.
• Comparison with dry ashing: Dry ashing (plasma oxidation) may damage certain sensitive structures, such as low‑k dielectrics and metal gates; SPM wet stripping causes significantly less damage. In practical production, the two methods are often used in combination: first, SPM is employed to remove the primary photoresist, followed by a brief plasma ashing of any residual material, or vice versa.

2.2 Removal of Organic Contaminants

Pollutant types: oils and fats, waxes, residual organic solvents, hydrocarbons, and other organic contaminants.

Cleaning efficiency: The removal efficiency for hydrocarbon contamination on silicon wafer surfaces approaches 100%, and the residual total organic carbon (TOC) after treatment can be reduced to the ppb level.

Process positioning: As a pre‑treatment step in the RCA cleaning sequence, it establishes an organic‑contamination‑free surface for subsequent cleaning steps such as SC‑1 and SC‑2.

3. Other Process Characteristics and Technological Evolution

3.1 Full-Process Applicability

SPM is widely used in both the front-end-of-line (FEOL) and back-end-of-line (BEOL) processes of chip manufacturing, spanning the entire workflow—from substrate preparation and gate formation to metal interconnect layer cleaning.

3.2 Surface Modification Effects

After SPM cleaning, the silicon surface exhibits hydrophilicity (with a significant reduction in the water contact angle). This property facilitates uniform wetting and chemical reactions with subsequent cleaning solutions, such as SC‑1 and dilute HF, thereby preventing uneven cleaning or drying defects caused by localized hydrophobicity.

3.3 Continuity of Technology Nodes

From 28 nm down to 3 nm and beyond in advanced logic processes, despite the introduction of numerous novel stripping methods, SPM remains the indispensable wet‑process solution for removing hardened photoresist following high‑dose ion implantation.

4. Conclusion

SPM’s core value in semiconductor manufacturing is embodied in two key application scenarios: the efficient removal of ion‑implantation‑induced hardened photoresist and the thorough elimination of organic contaminants. Its superior oxidative dehydration capability, low‑damage profile for device structures, process‑wide compatibility, and ability to impart hydrophilic surface modifications ensure that SPM remains indispensable—from micron‑scale nodes to the most advanced 3nm processes. Looking ahead, as device architectures become increasingly sensitive, the combined use of SPM with other cleaning technologies will enable further optimization.

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