Excimer Laser Beam Interaction with Sintered Y 2 O 3 - Doped Aluminium Nitride Ceramic: Fundamentals and Appplication
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equipped with energy-dispersive X-ray analysis are used for
characterizing both the initial and processed materials. The results reveal that yttriumcontaining phases which are present at the AIN grain boundaries play an essential role in coupling the (X=248nm) excimer laser beam with sintered material. Moreover, the laserinduced decomposition of these pre-existing complex phases and the subsequent spinel-like formation upon autocatalytic copper (or nickel) deposition are associated with (and explain) the excellent adhesion of the so-formed metal layer onto the ceramic substrate. INTRODUCTION. Sintered aluminium nitride (AIN) is characterized by its high thermal conductivity, high electrical resistivity and nontoxic nature and is, therefore, a good candidate for applications in power electronic packaging. Usually, AIN sintering is performed in the presence of additives. Among these, Y20 3 is most often used for accelerating the densification of hot-pressed AIN substrates and for improving their mechanical strength [ 1]. Excimer lasers have recently proved to be efficient in ceramic processing for industry. In particular, studies have been performed on the effect of excimer laser irradiation of sintered AIN, resulting into the actual decomposition of AIN [2-7]. In parallel, little is known about the role of the densification and sintering aids (in particular Y20 3) in the optical coupling of the investigated sintered AIN ceramics with the incoming laser irradiation. This has motivated the present work using several complementary techniques (Raman spectroscopy, low-angle X-ray diffraction and EDAX) which were called to elucidate the eventual contribution of such aids to the reported AIN decomposition. 525
Mat. Res. Soc. Symp. Proc. Vol. 397 01996 Materials Research Society
EXPERIMENTAL. Materials which were investigated in this work consisted of commercial 0.6 mm thick AIN substrates (from Tokuyama Soda) with an average grain size of 0.6 Rm, containing 1 mol% (- 5% in mass) of Y20 3 as a sintering aid. Irradiation was performed with a KrF (k = 248 nm) excimer laser at fluences ranging from 2.5 to 4 J/cm 2. Raman spectra of virgin and processed materials were recorded with a micro-Raman system (Mole S-3000, from JobinYvon) equipped with a 1420 HQ photodiode array detector controlled by an OMA III system (EGG-PARC). The excitation radiation was the 514.5 nm line of an Innova 90-4 (Coherent) Ar÷ laser. The morphology of the samples was analyze with a scanning electron microscope (Philips SEM XL 30) at voltages between 5 kV and 25 kV. An EDS X-ray analysis has been performed with an EDAX DX4i system attached to the XL 30 SEM, utilized in the qualitative and semi-quantitative modes. Low-angle X-ray diffraction spectra (k (Cu Kj) = 1.5418 A, 45 KV, circular detector INEL) were measured on initial and laser-processed substrates over restricted spectral domains as a function of the angle of incidence, at and below 1' of incidence[16]. RESULTS. 1. Micro-Raman analysis. All Raman spectroscopy results on AIN published before
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