A typical routing application using a laser micro-machining system involves the delivery of laser energy to a substrate while the beam and/or the substrate itself is moving. In most cases, the energy delivery rate (the “power on the work surface”) and the rate at which the beam and/or the substrate moves (the “cutting speed”) are maintained at constant values to provide uniformity of the kerf or “trench” width and depth throughout the cut. The depth and the width of the resulting trench are governed by the beam spot size on the work surface, the energy of each laser pulse, the spatial separation between consecutive pulses (the “bite size”), and the laser-material interaction characteristics.
Generally, one or more of the spot size, pulse energy, and/or bite size are adjusted in order to cut trenches of different cross-sectional geometries on the same substrate. In typical laser micro-machining, changing one of these three system settings causes the system to process trenches with different cross-section geometries in different “passes.” For example, the system may process trenches of one type, change one or more of the three settings, then process trenches that correspond to the new settings. This process may be repeated for each type of trench. This simple approach is typically referred to as a “multi-pass” process.
The conventional multi-pass process for merging trenches of different widths discussed above has a number of problems. For example, processing trenches of different widths in different passes generally means that a beam-positioner will return to the same spot where it finished a trench in a previous pass to start routing a new trench having a different width. This places a significant demand on the repeatability of the beam positioner subsystem. It also typically reduces overall system throughput.
Another problem with using multi-pass processing to cut trenches of different geometries is that, even if the system repeatability/accuracy concerns were addressed, it is difficult to maintain constant depth throughout a transition region because of the differences between wall angles of trenches with different widths.
FIGS. 1, 2, and 3 illustrate the difficulty of maintaining a constant peak cumulative energy distribution within a transition region (e.g., when changing from one spot size to another spot size in multiple passes to achieve different trench widths). FIG. 1 includes two graphs (a two-dimensional graph and a three dimensional graph) representing a spatial distribution of cumulative pulse energy density resulting from an abrupt transition in spot size and cutting speed using a Gaussian spots. The cumulative pulse energy density shown in FIG. 1 corresponds, for example, to a two-pass implementation with substantially perfect repeatability. In this example, the first pass uses a 10 μm spot size and a 3 μm bite size. The second pass uses a 20 μm spot size and a 1.5 μm bite size. The two-dimensional graph in FIG. 1 conceptually illustrates the widening of the trench in a transition region 110. The three-dimensional graph in FIG. 1 illustrates a fluctuation 112 in the peak cumulative energy distribution within the transition region 110.
FIG. 2 also includes two graphs (a two-dimensional graph and a three dimensional graph) representing a spatial distribution of cumulative pulse energy density resulting from a two-pass implementation when a second (thicker) trench placement is misaligned by 3 μm due to a repeatability error. As before, both passes use Gaussian spots. The first pass uses a 10 μm spot size and a 3 μm bite size. The second pass uses a 20 μm spot size and a 1.5 μm bite size. The two-dimensional graph in FIG. 2 conceptually illustrates the widening of the trench in a transition region 210. The three-dimensional graph in FIG. 2 illustrates a fluctuation 212 in the peak cumulative energy distribution within the transition region 210.
FIG. 3 is a graph illustrating differences between the peak cumulative energy densities from the two abrupt transition scenarios illustrated in FIGS. 1 and 2. As shown, both the repeatable scenario and the scenario with the 3 μm repeatability error result in substantial fluctuations 112, 212 within their respective transition regions 110, 210. Both fluctuations 112, 212 in peak cumulative energy densities may result in undesirable changes in depth within the transition regions 110, 210.