I. Abnormal Development Results

1. Underdevelopment

Phenomenon: Excessive photoresist residue, larger line width, and sidewall angle exceeding 90°.

Causes: Too short development time, insufficient developer concentration, too low temperature, or inadequate stirring.

Solutions:

• Adjust development time (extend by 5–10 seconds) or developer concentration (e.g., increase TMAH from 2.38% to 3%).

• Optimize spray pressure (≥2 bar) or introduce ultrasonic-assisted stirring.

2. Overdevelopment

Phenomenon: Edge collapse of patterns, smaller line width, and missing bottom resist residue.

Causes: Too long development time, excessively high temperature (>30°C), or fluctuations in developer pH.

Solutions:

• Shorten development time (reduce by 5–10 seconds) and control temperature within 18–25°C.

• Add buffers (e.g., phosphates) to stabilize pH and use an online pH monitor.

3. Incomplete Development

Phenomenon: Residual photoresist in localized areas, leading to short circuits or open circuits during subsequent etching.

Causes: Reduced developer activity (e.g., TMAH decomposition), excessive foam, or nozzle blockage.

Solutions:

• Replace developer regularly (once every 4 hours) and install a defoamer injection system.

• Clean nozzles daily and use a 0.1 μm filter to prevent blockage.

II. Developer-Related Problems

1. Developer Contamination

Phenomenon: Particle contamination or streaks on the wafer surface.

Causes: Contamination of the developer circulation system (e.g., metal ion precipitation) or environmental dust falling into the solution tank.

Solutions:

• Filter developer with an ultrafiltration membrane (0.01 μm) and test metal ion concentration weekly (e.g., Na⁺ < 1 ppm).

• Install a positive-pressure clean enclosure and upgrade the environmental cleanliness to Class 100.

2. Developer Degradation

Phenomenon: Reduced development rate and poor line width uniformity across wafers in the same batch.

Causes: Aging of developer (e.g., TMAH hydrolysis) or accumulation of by-products (e.g., silicate precipitation).

Solutions:

• Monitor developer conductivity in real time (standard TMAH value: 8.0–8.5 mS/cm) and automatically replace it when thresholds are exceeded.

• Use a dual-tank system: main tank for development and auxiliary tank for replenishing fresh solution.

III. Equipment and Process Parameter Problems

1. Uneven Spray

Phenomenon: Localized over-development or under-development on the wafer, resulting in non-uniform line width.

Causes: Nozzle wear, pressure fluctuations, or mismatched wafer rotation speed.

Solutions:

Use fan-shaped nozzles (spray angle ±2°) and control pressure with a precision of ±0.1 bar.

Implement closed-loop control for rotation speed (e.g., gradient adjustment from 2000 to 4000 rpm).

2. Temperature Fluctuations

Phenomenon: Significant variations in development degree across different regions of the same wafer.

Causes: Low efficiency of the developer circulation cooling system or fluctuations in ambient temperature/humidity.

Solutions:

Use a plate heat exchanger (temperature control precision ±0.5°C) and maintain ambient humidity at 40–60%.

Increase heat exchange area (e.g., with a finned condenser).

3. Residue Contamination

Phenomenon: Residual resist film or chemical deposits on the wafer surface post-development.

Causes: Insufficient purity of rinse water (TOC > 50 ppb) or incomplete spin drying.

Solutions:

Use ultrapure water (UPW, TOC < 5 ppb) and add a nitrogen purge step.

Optimize spin-drying parameters (centrifugal force ≥ 3000 rpm, time ≥ 30 seconds).