晶圆级激光光刻

Mechanisms for laser-driven pyrolytic deposition of micron-scale metal  structures on crystalline silicon have been studied. Models have been  developed to predict temporal and spatial properties of laser-induced  pyrolytic deposition processes. An argon ion laser-based apparatus  has been used to deposit metal by pyrolytic decomposition of metal  alkyl and carbonyl compounds, in order to evaluate the models. These  results of these studies are discussed, along with their implications  for the high-speed creation of micron-scale metal structures in ULSI  systems.  

In order that state-of-the-art computers can reproduce with less human interference  and thus with lower error rates and latencies, it is necessary for them to be able to  micropattem semiconductor substrata directly and at high speed. Contemporary supercomputer systems composed of 10s  transistors, each constituted of as many as 10* 'tiles'  of various materials stacked in particular arrangements, contain as many as io1 0  'tiles'  in their ultra-large scale integrated (ULSI) patterns. In order that latencies involved in  computer-directed generation of new computer-scale micropatterns be not much greater  than a day, creation of a single 'tile' must be accomplished in an interval of the order of  13~5  seconds.

Monolithically implemented computers of the present era consist of sheets of metal  traces of micron-scale width and thickness, separated almost (but not quite) everywhere  from each other by nearly hole-free dielectric sheets, and occasionally touching the terminals of transistor devices which are embedded for convenience in a semiconductor substrate common to all such devices. The large majority of the structure (indexed by  the fraction of total 'tiles' in the pattern) of computers implemented in the ever more  popular metal-oxide semiconductor (MOS) family of technologies is expressed in metal (or  in surrogate metal, highly doped polysilicon). It is thus quite crucial to greatly extend  the hitherto highly limited ability to create suitable metal microstructures directly with  laser processing techniques, as this approach is qualitatively superior to all other current  prospects for high-speed, computer-controlled micropatteru generation directly on semiconductor substrates.  

We report here an order of magnitude enhancement in the rate of metal micropatternin£ in the ULSI context, relative to the highest rates previously reported. Taken together  with results from other workers on rapid semiconductor substrate doping and dielectric  layer creation, this advance makes feasible in principle the generation of monolithic, ULSI  supercomputers on day time scales.  

Fig1

Desired metal patterns (frequently lines) were created by moving the reaction cell with  an x-y table stepper drive (1 pm steps; 1500 pmjtec maximum speed), and by amplitude  modulating the argon-ion laser beam by an optics chain which often included a halfwave plate followed by an electro-optics switch that was sandwiched between two GlanThompson prisms. During the course of each run, the laser patterns on the substrate and  the deposited metal features were viewed through a microscope via a vidicon outputting  to a color monitor. Laser beam profiles on the substrate were measured using a pinholephotodiode arrangement mounted on a calibrated x-y drive located after the microscope.  The samples were analyzed using optical and scanning electron microscopy (the latter with  X-ray fluorescence capability) and stylus profilometry.  

Variations in height within a given metal line and between different lines drawn under  similar conditions are attributed to the nature of nucleation on the surface. At lower power  levels, the method of surface preparation (various methods of cleaning polished Si surfaces  covered by its native oxide, including cleaning and stripping away the Si02 ) greatly affected  the production of nucleation sites. Prenucleation due to boiling of metal from nearby  nickel lines was observed to greatly lower the nucleation threshold for subsequent low laser  power pyrolytic metal deposition runs. Nucleation effects are expected to be of much less  importance in planned work involving substrate temperatures raised to far above threshold  temperatures for sub-microsecond periods.