Reflecting non-planar surfaces integrated with laser scan for Poseidon tool integration

An apparatus, comprising:

• a wafer holder configured to hold a wafer thereon;
• a first light reflection device located beside an edge of the wafer held on the wafer holder, the first light reflection device having a first light reflection surface tilted with respect to a wafer surface of the wafer;
• a coherent light source configured to generate incident light to perform a scan on the wafer surface of the wafer and the first light reflection surface of the first light reflection device, the wafer surface of the wafer and the first light reflection surface of the first light reflection device reflecting the incident light to generate reflection light;
• and
• a light detector configured to detect the reflection light,
• wherein the coherent light source, the first light reflection device and the light detector are arranged such that the incident light generated by the coherent light source directly passes by the edge of the wafer and the reflection light generated by the first light reflection surface of the first light reflection device is directly detected by the light detector.