XSIL vFinal DR 30/6/08 16:51 Page 11
COVER STORY
11
High throughput low CoO
industrial laser drilling tool
Recent advances in UV DPSS laser drilling of blind, micron sized Vias in
silicon (Si) are presented in this article. Alexey M.Rodin, Joseph
Callaghan and Niall Brennan from XSil highlight some of the attractive
features of such an approach
A
dvances in lithography CMOS sensors [4] and NAND flash depth, the beam size governs the Via
and packaging memory [5]. Advances in laser Via diameter while the overall drill rate is
consistent with Moore’s development and throughput will enable determined by the laser repetition rate
law are now placing even greater laser drilling for DRAM [6] in the short and the speed at which individual Vias
demands on existing packaging tools. term and likely for processors and logic, can be addressed.
Emerging from these demands is an in the longer term. Recent advances in the process
exacting set of requirements that are not Of the known laser drilling regimes of development of blind, micron sized Vias
easily satisfied by existing tool helical, trepanning and percussion, only drilled in Si by UV DPSS lasers exhibit a
capabilities and processes. In this article the latter provides a significant high throughput, clean top and an
it will be argued that Laser throughput advantages over DRIE. In a excellent sidewall quality along with a
Micromachining [1] offers a viable percussion drilling regime a consecutive negligible heat affected zone.
alternative to the incumbent processes sequence of laser pulses are focused to the
and that it will also meet the future same point in a workpiece to drill a Via Range of Via sizes in
demands of roadmaps for advanced of fixed depth and diameter. The number percussion laser process
packaging technology. The laser of pulses and the pulse energy dictate Via The range of Via diameters routinely
micromachining approach can be divided available in the percussion regime extends
into two main areas dicing/scribing [2] from 15 - 80µm in a standard Via drilling
and Via drilling [3-6]. This article is tool. Examples of the optimised laser
primarily concerned with Via drilling. process for Via diameters of 15µm,
Through Silicon Vias (TSV) are 30µm, 50µm and 80µm with
increasingly important in the corresponding depth range is shown in
semiconductor packaging industry to Fig.1. Intermediate diameter ranges are
provide compact interconnects in 3D accessible by utilising a variable beam
stacking applications [7]. Currently two expander while smaller diameters <10µm
technologies, Laser Drilling and Deep can be achieved through the use of shorter
Reactive Ion Etching (DRIE), are focal length scan lenses. This range of
employed to generate these Vias and sizes satisfies the majority of current
while each has certain benefits there is as requirements for industrial interconnect
yet no agreement on which provides the applications.
most effective solution.
During its early development laser Via CoO and maintenance of
processes suffered from throughput and Laser Drilling Tool
size limitations where typical drill rates The laser drilling process is insensitive to
were below 30 Vias/s and diameters Via position on the wafer and thus Via
exceeded 25mm. Laser technology was Fig.1 SEM image: range of Via depth uniformity of ±4% is attained over
then first directed towards applications diameters and depth machined on full 300mm wafers. The depth uniformity
with low density requirements such as laser drilling tool is largely determined by the shot to shot
July 2008 www.euroasiasemiconductor.com
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88