Specific Process Knowledge/Back-end processing/Laser Micromachining Tool/Silicon cutting and milling

Unless anything else is stated, everything on this page, text and pictures are made by DTU Nanolab.

All links to Kemibrug (SDS) and Labmanager Including APV and QC requires login.

Feedback to this page: click here

Surface morphology after milling

SEM view (tilted at 45deg) of a laser milling at a speed of 400mm/s and 10% of the power max of the laser for a wavelenght of 532nm. (a) After 10 iterations some spikes can be observed on the bottom of the groove.(b) Same groove after 20 iterations. The spikes are still present but tend to decrease on the borders of the groove which are now smoother. (c) Same groove after 40 iterations. The spikes on the bottom of the groove now disappeared to leave place at a narrower and deeper groove.

This test was performed on a Si wafer n-type single polish and the milling has been done by the laser Time-Bandwidth with a normal incident at the wavelength of 532nm and a focal distance of 255mm. The frequency of 200 kHz has been used and no adjustement of the focus has been made during the milling. The patern engraved was a serial of single lines separated from each other by 50µm (no influence between each line), and were milled at different speeds and at different number of iteration (irradiations). The wafer got a ultrasonic cleaning and a isopropanol cleaning before enter into the SEM.

The morphology from the laser mark is closely linked to the number of irradiations the substrate got. As the laser heats the substrat, spikes are forming as show in the figure (a) beside. The microstrucutre evolves with the number of iteration like the depth

Generated dirt after cutting

SEM view of a laser cutting with a wavelenth of 532nm on a Si wafer with 147nm of nitride on the top of it. (a) After laser cutting. A large amount of particles are visible (b) Same sample after 5min ultrasonic bath.

The among of dirt generated after a laser cut on Si is significant. An ultrasonic bath may reduce much particles produced.

Redeposition of material

SEM view of a laser trenche at a speed of 500mm/s for 100% of the power of the laser and 100 iterations without refocusing the beam, for a wavelenght of 532nm. A larger redeposition can be observed on the left side of the groove, which faces the exhaust air flow.

When machining silicon, a redeposition of material (mainly SiO2 according to the XPS survey - see table below) can be observed on both edges of the groove. However, a larger amount is redeposited on the groove's edge locates on the opposite side of the laser's exhaust stream air. The redeposite material has a significant influence on the width of the groove.

Elemental analysis of Silicon after machining using X-ray photoelectron spectroscopy

O Si C N At. % 55,7 26,17 16,86 1,28