How to choose, use and maintain a PECVD boat ?

1. What is a PECVD boat?

1.1 Definition and core functions
PECVD boat (Plasma Enhanced Chemical Vapor Deposition) is a core tool used to carry wafers or substrates in the PECVD process. It needs to work stably in a high temperature (300-600°C), plasma-activated and corrosive gas (such as SiH₄, NH₃) environment. Its main functions include:

Precise positioning: ensure uniform wafer spacing and avoid coating interference.
Thermal field control: optimize temperature distribution and improve film uniformity.
Anti-pollution barrier: Isolates plasma from the equipment cavity to reduce the risk of metal contamination.

1.2 Typical structures and materials
Material selection:

Graphite boat (mainstream choice): high thermal conductivity, high temperature resistance, low cost, but requires coating to prevent gas corrosion.
Quartz boat: Ultra-high purity, chemically resistant, but highly brittle and expensive.
Ceramics (such as Al₂O₃): wear-resistant, suitable for high-frequency production, but poor thermal conductivity.

Key design features:

Slot spacing: Match wafer thickness (such as 0.3-1mm tolerance).
Air flow hole design: optimize reaction gas distribution and reduce edge effect.
Surface coating: Common SiC, TaC or DLC (diamond-like carbon) coating to extend service life.

2. Why must we pay attention to the performance of PECVD boats?

2.1 Four major factors that directly affect process yield

Pollution Control:
Impurities in the boat body (such as Fe and Na) volatilize at high temperatures, causing pinholes or leakage in the film.
Coating peeling will introduce particles and cause coating defects (for example, particles > 0.3μm can cause the battery efficiency to drop by 0.5%).

Thermal field uniformity:
Uneven heat conduction of the PECVD graphite boat will lead to differences in film thickness (for example, under the uniformity requirement of ±5%, the temperature difference needs to be less than 10°C).

Plasma compatibility:
Improper materials may cause abnormal discharge and damage the wafer or device electrodes.

Service life and cost:
Low-quality boat hulls need to be replaced frequently (e.g. once a month), and annual maintenance costs are expensive.

3. How to choose, use and maintain a PECVD boat?

3.1 Three-step selection method
Step 1: Clarify process parameters

Temperature range: Graphite + SiC coating can be selected below 450°C, and quartz or ceramic is required above 600°C.
Gas type: When containing corrosive gases such as Cl2and F-, high-density coating must be used.
Wafer size: 8-inch/12-inch boat structure strength is significantly different and requires targeted design.

Step 2: Evaluate performance metrics

Key Metrics :
Surface roughness (Ra) : ≤0.8μm (contact surface needs to be ≤0.4μm)
Coating bond strength : ≥15MPa（ASTM C633 standard)
High temperature deformation (600℃) : ≤0.1mm/m (24 hours test)

Step 3: Verify compatibility

Equipment matching: Confirm the interface size with mainstream models such as AMAT Centura, centrotherm PECVD, etc.
Trial production test: It is recommended to conduct a small batch test of 50-100 pieces to verify the uniformity of the coating (standard deviation of film thickness <3%).

3.2 Best Practices for Usage and Maintenance
Operation Specifications
Pre-cleaning process:Before the first use, the Xinzhou needs to be bombarded with Ar plasma for 30 minutes to remove impurities adsorbed on the surface.

After each batch of process, SC1 (NH₄OH:H₂O₂:H₂O=1:1:5) is used for cleaning to remove organic residues.

Loading taboos:

Overloading is prohibited (e.g. the maximum capacity is designed to be 50 pieces, but the actual load should be ≤ 45 pieces to reserve space for expansion).
The edge of the wafer must be ≥2mm away from the end of the boat tank to prevent plasma edge effects.

Tips for Extending Life

Coating repair: When the surface roughness Ra＞1.2μm, SiC coating can be re-deposited by CVD (the cost is 40% lower than replacement).

Regular testing:
Monthly: Check coating integrity using white light interferometry.
Quarterly: Analyze the crystallization degree of the boat through XRD (quartz wafer boat with crystal phase > 5% needs to be replaced).

4. What are the common problems?

Q1: Can the PECVD boat be used in the LPCVD process?

A: Not recommended! LPCVD has a higher temperature (usually 800-1100°C) and needs to withstand higher gas pressure. It requires the use of materials that are more resistant to temperature changes (such as isostatic graphite), and the slot design needs to consider thermal expansion compensation.
Q2: How to determine whether the boat body has failed?
A: Stop using immediately if the following symptoms occur:
Cracks or coating peeling are visible to the naked eye.
The standard deviation of wafer coating uniformity has been >5% for three consecutive batches.
The vacuum degree of the process chamber dropped by more than 10%.
Q3: Graphite boat vs. quartz boat, how to choose?

Conclusion : Graphite boats are preferred for mass production scenarios, while quartz boats are considered for scientific research/special processes.

Conclusion:

Although the PECVD boat is not the main equipment, it is the “silent guardian” of process stability. From selection to maintenance, every detail may become a key breakthrough point for yield improvement. I hope this guide will help you penetrate the technical fog and find the optimal solution for cost reduction and efficiency improvement!