Application Background
Wafer dicing is a critical step in semiconductor manufacturing, separating chips. Accurate detection of the height difference (segmentation) on the wafer surface before and after dicing directly impacts chip yield and subsequent packaging quality. Traditional contact-based measurements easily damage the wafer surface and are unsuitable for high-speed production lines. The ST-P series laser displacement sensors employ non-contact measurement using laser triangulation, effectively solving the challenge of detecting height differences during wafer dicing.
Detection Objects and Objectives
Detection Objects: The surface height difference (segmentation) before and after wafer dicing, including the wafer surface, dicing ridges, and chip edges. Detection Objectives: To monitor dicing depth consistency, avoiding over- or under-dicing; to assess wafer warpage and flatness; and to provide height compensation data for subsequent packaging.
On-site Pain Points
Wafer surfaces are highly reflective, transparent, or have thin films, making traditional sensors susceptible to interference.
Edge burrs or chipping after dicing lead to measurement instability.
High production line cycle times require high-speed sampling and real-time feedback.
Limited installation space necessitates miniaturized sensors that are easy to integrate.
Product Principle and Selection Guide
The ST-P series laser displacement sensor is based on the laser triangulation principle. It emits a laser beam to the surface being measured, and the reflected light is imaged onto the CMOS sensor via a lens. The displacement is calculated by the change in the position of the laser spot. Non-contact measurement avoids damage to the wafer. When selecting a model, the installation distance and accuracy requirements must be considered:
Model | Reference Distance | Measurement Range | Repeatability | Linearity Error
ST-P25: Reference distance 25mm, Measurement range ±1mm, Repeatability 0.05μm, Linearity error < ±0.6μm
ST-P30: Reference distance 30mm, Measurement range ±5mm, Repeatability 0.15μm, Linearity error < ±3μm
ST-P50: Reference distance 50mm, Measurement range ±10mm, Repeatability 0.25μm, Linearity error < ±4μm
ST-P80: Reference distance 80mm, Measurement range ±15mm, Repeatability 0.5μm, Linearity error < ±6μm
ST-P150: Reference distance 150mm, Measurement range ±40mm, Repeatability 1.2μm, Linearity error < ±16μm
For wafer dicing height difference detection, ST-P25 or ST-P30 are recommended, but the specific model should be confirmed based on the actual installation distance and accuracy requirements.
Recommended Solution
Install sensors before and after dicing, or use dual-sensor differential measurement. The sensor is fixed above the wafer stage, and the laser perpendicularly illuminates the measurement point. Data is uploaded to a host computer via Ethernet or RS485 for real-time height difference calculation. The sampling frequency is up to 160kHz, meeting the requirements of high-speed production lines.
Installation and Debugging Recommendations
Ensure the sensor is securely installed to avoid vibration interference.
Adjust the laser angle to ensure the spot is clearly focused on the wafer surface.
For highly reflective or transparent wafers, sample testing is required; adjust the exposure time or use a polarizer if necessary.
Set an appropriate measurement range to avoid exceeding the measurement limits.
Frequently Asked Questions
Q: Does wafer surface reflection affect measurement? A: Reflection may cause spot saturation or signal loss. Sample testing is recommended to adjust sensor parameters or add filters based on actual reflective characteristics.
Q: How to handle edge burrs after dicing? A: Increasing the measurement spot size or using multi-point averaging algorithms may help. The specific approach should be confirmed based on the model.
Q: How to interface with a PLC? A: The ST-P series supports analog, IO, and RS485 outputs, allowing direct connection to PLC analog modules or via communication modules.
Conclusion
The ST-P series laser displacement sensors, with their high precision, non-contact measurement, and high-speed sampling, are suitable for wafer dicing height difference detection. Selection should be validated through sample testing under actual working conditions to ensure measurement reliability. This article is for technical reference only and requires manual review before publication.