The variation pattern of the selectivity ratio between SiO₂ and Si₃N₄ in BOE buffer solution at different temperatures.

BOE buffer solution, with its controllable etching rate and excellent material selectivity, is often used in integrated circuit manufacturing. SiO ₂ Graphical representation and removal of layers. SiO ₂ With Yes ₃ N ₄ As a common interlayer and mask material, the etch selectivity of BOE directly affects device performance and process accuracy. Temperature is one of the key parameters influencing the kinetics and selectivity of BOE etching.

I. Mechanism of the Influence of Temperature on the Etching Rate of BOE

1. Enhanced HF activity

An increase in temperature will accelerate the thermal motion of HF molecules, enhancing their interaction with SiO. ₂ The rate of the surface chemical reaction. Experiments show that 40% HF at 21°C reacts with SiO₂. ₂ The etching rate is approximately 80 nm/min, but it can increase to over 2500 nm/min at 60℃.

2. NH ₄ The buffering effect of F

NH ₄ F reacts with HF by releasing F⁻ ions to form HF₂⁻ (HF + F⁻ → HF₂⁻). ₂ ⁻), inhibiting silicon substrate corrosion caused by excess HF. High temperatures promote NH ₄ The decomposition of F weakens its buffering capacity, leading to an increase in the concentration of free HF and accelerating... SiO ₂ Etching may also cause excessive corrosion of silicon.

II. Temperature’s Effect on Selectivity ( SiO ₂/ Yes ₃ N ₄ )’s impact

1. BOE against SiO ₂ and Yes ₃ N ₄ The selectivity of the choice primarily depends on the kinetic differences in their reactions with F⁻ ions:

• SiO ₂ Etching: SiO ₂ Reacts with HF to form soluble H. ₂ SiF ₆ ( SiO ₂ + 6HF → H ₂ SiF ₆ + 2H ₂ O), the reaction activation energy is relatively low (approximately 20–30 kJ/mol) and is highly sensitive to temperature.
• Yes ₃ N ₄ Etching: Yes ₃ N ₄ The Si–N bond, which has high bond energy, needs to be broken; the reaction activation energy is relatively high (approximately 50–60 kJ/mol), and the etching rate exhibits lower temperature sensitivity than... SiO ₂。

2. Temperature-Selectivity Relationship Analysis:

• Low temperature (20–30°C): BOE has strong buffering capacity. SiO ₂ The etching rate is relatively low (e.g., about 80 nm/min at 21°C). Yes ₃ N ₄ It is almost immune to corrosion, and the selectivity ratio can exceed 80:1.
• Medium temperature (40–60°C): NH ₄ F decomposition intensifies, and HF activity increases. SiO ₂ The etching rate has been significantly enhanced (e.g., reaching up to 1500 nm/min at 50°C). Yes ₃ N ₄ The etching rate remains low, with a selectivity ratio of approximately 50:1–75:1.
• High temperature (>70°C): NH ₄ F decomposes extensively, and an excess of HF increases the risk of silicon corrosion. SiO ₂ The etching rate rises sharply (e.g., it can exceed 3,500 nm/min at 80°C). Yes ₃ N ₄ The etching rate has also improved significantly, and the selectivity has further decreased to approximately 35:1.

III. Temperature Control Strategies in Actual Processes

• Low selectivity requirement: If rapid removal is needed. SiO ₂ And allow a small amount. Yes ₃ N ₄ For losses (such as passivation layer trimming), a medium-to-high temperature BOE solution (50–60°C) can be used.
• High selectivity ratio requirements: Precise pattern transfer (such as gate oxide etching) demands strict temperature control within the range of 20–30°C to maintain a high selectivity ratio (>100:1) and avoid damage to the silicon substrate or silicon nitride mask.

IV. Data Examples and Table Presentation

The following table shows BOE’s performance at different temperatures. SiO ₂ With Yes ₃ N ₄ Etching rate and selectivity experimental data:

V. Process Optimization Recommendations

• Buffer ratio adjustment: In high-temperature processes, the amount of NH can be appropriately increased. ₄ F ratio (e.g., using a BOE of 10:1) to enhance buffering capacity and slow down HF decomposition.
• Real-time monitoring: By continuously detecting the etching rate and pH value online, dynamically adjusting the temperature and BOE concentration, we ensure the stability of the selectivity ratio and etching uniformity.
• Temperature-gradient process: For etching multilayer structures, segmented temperature control can be employed—first etching the critical layer at a low temperature with a high selectivity ratio, and then raising the temperature to enhance the overall resist removal efficiency.

Summary

BOE buffer solution for SiO ₂ With Yes ₃ N ₄ The selectivity decreases as the temperature increases; the core mechanism behind this phenomenon lies in NH. ₄ The buffering capacity of F weakens while the activity of HF increases. In actual semiconductor manufacturing processes, the etching temperature of BOE should be precisely controlled based on material properties and precision requirements, and the composition of the buffering system should be adjusted when necessary, to achieve efficient and highly selective wet etching.

For more technical details, please consult our technical advisor: 13861996325!

▲ Technical Consultation ▲ Follow the Kexinwei WeChat Official Account