Background – Why Q-time matters
In semiconductor manufacturing, even a short delay between processing steps can degrade the wafer surface. This “queue time” (Q‑time) is especially critical when surfaces are highly reactive: oxygen, moisture, and carbon‑based contaminants begin interacting with freshly prepared silicon almost immediately after exposure to air.
Traditionally, the industry has addressed this vulnerability by relying on in‑situ process chaining, where wafers move directly between vacuum‑cluster tools without atmospheric exposure. This safeguards surface quality but prevents flexible process integration, slows technology evaluation, and limits the ability to validate new materials or treatments, such as SisuSemi’s atomic‑level surface restoration technology.
In a typical cleanroom atmospheric environment, Q‑times for sensitive surfaces can be as short as minutes to low tens of minutes, driven by:
- Rapid oxidation, shifting the silicon from Si³⁺ to Si⁴⁺ states.
- Airborne carbon absorption, even in cleanroom conditions.
To unlock broader adoption, SisuSemi needed to demonstrate that its treatment could extend Q‑time durability and enable ex‑situ workflows without performance loss.
SisuSemi solution: Stable and atomic-level clean Surface
SisuSemi’s elevated‑temperature, ultra‑high‑vacuum treatment removes contamination, restores the silicon crystal structure, and applies a stable, crystalline passivation layer. The goal of this study was to verify whether this surface stability could be maintained during atmospheric exposure – i.e., whether Q‑time could be extended from minutes to practically meaningful operational windows.
A durability test after controlled air exposure was conducted to measure change in:
- Oxidation progression, quantified by the Si⁴⁺/Si³⁺ ratio.
- Carbon contamination accumulation
As it is well known, the long-term storage in inert gas, e.g. nitrogen, works well. Here the focus has been in air exposure.
As an outcome from this study, we were able to conclude that:
- Carbon contamination was reduced by 70% compared to an untreated sample exposed to air for 48 hours.
- The critical Si⁴⁺ to Si³⁺ ratio remained stable after one hour of air exposure, validating the longevity of the treatment in an atmospheric environment.
These results drive major impact as discussed in the next chapter.
Impact from the results
SisuSemi’s validated over one‑hour atmospheric durability represents a major shift in handling sensitive wafer surfaces. By extending Q‑time from minutes to hours, fabs gain clear manufacturing, integration, and financial advantages.
1. Higher Yield and More Stable Performance
Longer surface stability results in fewer interface defects, lower process variation, reduced rework, and more consistent electrical performance, especially in defect‑sensitive flows such as dry etch → ALD, lithography → deposition, and post‑dicing steps.
2. Enables Practical Ex‑Situ Processing
With Q‑time measured in hours, fabs can test and adopt SisuSemi’s treatment in real production without tool rearrangements or strict in‑situ constraints. This opens the door to ex‑situ assembly flows, easier evaluation of new technologies, and reduced dependence on complex vacuum‑cluster systems.
3. Operational & Financial Upside
Extended Q‑time increases equipment flexibility, lowers CapEx pressure (fewer in‑situ modules needed), reduces cycle‑time sensitivity, improves scheduling robustness, and enhances assembly efficiency. These benefits translate directly into higher throughput, improved Overall-Equipment-Efficiency (OEE), and stronger ROI.
Summary
SisuSemi’s atomic‑level treatment stabilizes wafer surfaces for at least one hour in air – a capability previously limited to in‑situ vacuum transfers. This breakthrough turns Q‑time from a strict bottleneck into a manageable process parameter, delivering higher yield, greater flexibility, and measurable business impact.
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