Laser assisted focused-ion-beam-induced deposition of copper

Abstract

As the minimum feature size becomes on the order of submicron dimensions, techniques to directly repair VLSI circuits and x-ray masks, techniques for so-called "microsurgery", are increasingly important. Focused ion beam (FIB) techniques have been commercially used to deposit conductors and insulators and remove materials in a localized area on substrates. Copper, which is a candidate future conductor material in VLSI circuits due to its low resistivity and high electromigration resistance, has been deposited from the organometallic complex, Cu(hfac)TMVS, using 25 keV gallium ions from liquid ion source. Earlier work has shown that substrate heating can lead to FIB-induced deposition of high conductivity Cu lines. In this work, use of a laser for localized heating for FIB-induced deposition has been investigated as an alternative to heating of the entire substrate. For laser-assisted FIB-induced deposition, a "high power" :semiconductor laser, of wavelength 977 nm and output power ranging continuously from 0 to 1.2 W, was used. The laser was focused onto a thermally oxidized Si substrate, and its spot area is estimated to be 5.90x10 -5 cm 2 , which gives the maximum intensity of 2.0x10 4 W/cm 2 . Cu(hfac)TMVS has no absorption in the gas phase at 977 nm. As a result, for films deposited using this laser, the dependencies of the growth rate and resistivity on the estimated substrate temperature are in good agreement with those of films deposited using conventional resistance heating. The growth rate ranges from 2.0 to 4.3 A/s, depending on the laser power. A small decline in the growth rate in the relatively low laser power regime was observed. At higher laser powers, the growth rate is significantly increased. The lowest resistivity lines, 3 gQ-cm (close to the resistivity of bulk copper, 1.7 gQ-cm), has been achieved when deposited at 1.1 W of laser power. At this laser power, the substrate temperature is estimated to be 120 °C. The smallest line width, 0.8 gm, has been achieved when deposited without using the laser. The deposited lines become slightly wider for higher laser powers, causing the aspect ratio to be smaller. When deposited at high temperature, the deposited film becomes coarse and granular. Laser-assisted, FIB-induced deposition has been demonstrated as a means of 'writing high conductivity submicron Cu lines.

Ion beams in silicon processing and characterization

“…In the case of copper and gold deposition the resistivity of the deposit can be reduced to near the value of pure metal by heating the substrate during deposition to about 100°C, 223,224 or by using local laser illumination. 225 An example of a rewired IC is shown in Fig. 64.…”

Enhanced material purity and resolution via synchronized laser assisted electron beam induced deposition of platinum

“…Previously substrate heating has been introduced for EBID and gallium focused ion beam induced deposition with the use of a well-controlled heated stage 28 as well as focused continuous wave (cw) laser irradiation. 42 Higher deposit purities have been reported for some precursor chemistries, but are oen accompanied by reduced growth rates due to reduced precursor residence times at elevated temperatures. Furthermore, bulk substrate heating can lead to thermal dri, and in some cases devices and/or structures on the substrate cannot undergo elevated temperature processing.…”

Fundamentals of Focused Ion Beam Nanostructural Processing: Below, At, and Above the Surface

“…110 Heating the target via a remote laser led to Cu lines with a resistivity of 3 mW cm (compared with 150-200 mW cm when no laser radiation is used). 87 Lower resistivity correlates to reduced incorporation of decomposition products. FIB-CVD studies have improved electrical and optical properties for deposited dielectrics, 109,112 where the addition of oxygen (or water) during deposition can significantly decrease the carbon content in SiO 2 .…”