IE20010596A1 - Cleaning of laser machined substrates - Google Patents

Abstract

A method for laser cleaning a laser machined substrate by modifying the properties of the machining laser so that in situ laser cleaning of the substrate can be performed at any time in the laser machining process is described. For cleaning, there is a larger spot size than for machining. <Figure 1>

Description

Cleaning of laser machined substrates” The invention relates to cleaning of machined substrates.

Statements of Invention υ According to the invention, there is provided a method of cleaning a substrate during 10 or after laser machining by using a laser with a larger spot size than that used for machining.

In one embodiment, the spot size is increased by one or more lenses at a point before the beam enters a scanning XY galvanometer.

In another embodiment, the focus is shifted to a point below the surface of the wafer.

In one embodiment, the beam waist in increased at the surface through a reduction of the spot size prior to entry into the galvanometer.

In another embodiment, the cleaning laser is the same laser as the machining laser.

In one embodiment, the cleaning laser is a different laser to the machining laser, and the lasers are collinear.

In another embodiment, wherein the laser is a q switched solid state laser with greater than 1 kHz repetition frequency and a pulsewidth less than 100ns.

According to another aspect, the invention provides a cleaning system comprising 30 means for performing a method as described above. -21Ε01β59· Detailed Description of the Invention The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which: Fig. 1 is a perspective view of a beam delivery system of the invention; and Fig. 2 is a view of a beam expander.

Laser machining and processing stations generate particulate and gaseous debris as a result of the machining process. In particular, the process of laser photo-ablation through the use of high peak power Q switched laser systems as used in high throughput manufacturing systems, results in the generation of large amounts of submicron and micron sized particles as well as various gasses and chemical emissions.

This debris is hazardous to environment and to human health and accordingly must be removed as effectively as possible form the machining region and substrate material for disposal. To a large extent most of this debris can be removed through an efficient fume extraction system, however, surface adhesion to the substrate material can render this form of extraction ineffective.

A further requirement of a laser machining platform is that the product produced is clean room compatible and that excess debris fixed to the product as a result of the laser machining process is removed.

The invention provides a laser based system (shown in Figs. 1 and 2) for cleaning the substrate or product material at any point in the machining cycle. The technique requires the use of a dual lens beam expander with variable lens separation before the 1E0 1 85 98 -3input to a scanning galvanometer. The separation of the lenses in the beam expander is controlled through a computer and processor. In laser machining mode, the beam expander is configured so that the laser spot size at focus is as required for the machining process: i.e. above the machining threshold. By changing the separation to create a diverging or converging beam the beam diameter at the substrate may be varied. When the beam diameter is below the ablation threshold for the material being processed, the beam is effective at removing debris and particulate matter from the region where micromachining was performed.

The machining laser source may be a second or third harmonic solid state YAG laser and the substrate material is a semiconductor. For high speed machining using a Q switched green (532nm) laser or 355nm UV laser with 4W output power a spot size of 25 to 60 microns is generally acceptable for machining.

Increasing the spot size to 200 microns and scanning at up to lOOmm/s removes debris from the edges of the laser machined region over most of this beam diameter.

The process of cleaning follows laser machining of semiconductor wafers. The function of the machining is to singulate semiconductor integrated circuits and to define blind and through apertures or vias in the wafer. Cleaning surface and inside edge debris during such a process provides significant cost reduction.

In another embodiment, the “cleaning” beam is used to remove debris from a partially machined slot section in a semiconductor wafer. As debris and the removal of debris is critical to the quality and speed of the machining process, the in situ aspect of this cleaning capability can be used to assist the machining process itself.

The invention is not limited to the embodiments described but may be varied in construction and detail. ΙΕΒ 105 9 β

Claims (7)

Claims

1. A method of cleaning a substrate during or after laser machining by using a laser with a larger spot size than that used for machining.

2. A method as claimed in claim 1, wherein the cleaning laser spot size is increased by one or more lenses at a point before the beam enters a scanning XY galvanometer. 10

3. A method as claimed in claim 1 or 2, wherein the cleaning laser focus is shifted to a point below the surface of the wafer.

4. A method as claimed in claims 2 or 3, wherein the cleaning laser beam waist is increased at the surface by a reduction of the spot size prior to entry into the 15 galvanometer.

5. A method as claimed in any preceding claim, wherein the cleaning laser is a Q switched solid state laser with greater than 1 kHz repetition frequency and a pulsewidth less than 100ns.

6. A method substantially as described with reference to the drawings.

7. A cleaning system comprising means for cleaning a substrate in a method as claimed in any preceding claim.