This paper discusses approaches for the isolation of deep high aspect ratio through silicon vias (TSV) with respect to a Via Last approach for micro-electro-mechanical systems (MEMS). Selected TSV samples have depths in the range of 170…270 µm and a diameter of 50 µm. The investigations comprise the deposition of different layer stacks by means of subatmospheric and plasma enhanced chemical vapour deposition (PECVD) of tetraethyl orthosilicate; Si(OC2H5)4 (TEOS). Moreover, an etch-back approach and the selective deposition on SiN were also included in the investigations. With respect to the Via Last approach, the contact opening at the TSV bottom by means of a specific spacer-etching method have been addressed within this paper. Step coverage values of up to 74 % were achieved for the best of those approaches. As an alternative to the SiO2-isolation liners a polymer coating based on the CVD of Parylene F was investigated, which yields even higher step coverage in the range of 80 % at the lower TSV sidewall for a surface film thickness of about 1000 nm. Leakage current measurements were performed and values below 0.1 nA/cm2 at 10 kV/cm were determined for the ParyleneF films which represents a promising result for the aspired application to Via Last MEMS-TSV

The high precision accelerometer consists of 5 silicon wafers and packages by silicon fusion bonding. The sensor has a capacitance measuring principle and works in an open loop or closed loop operation mode. The etching process for the realization of thin beams and the seismic mass, the silicon fusion bonding and the metallization process are described.

The requirements of future integrated circuits will result in shrinking dimensions and consequently new materials like copper or low k materials. TIN films are an interesting candidate as diffusion barriers because of their well known compatibility to semiconductor technology. Moreover TiN films were already shown to be stable barriers against copper diffusion [ 1,2].Based on a series of tests including the stochiometry variation (0,59 N/Ti 1) of films deposited by reactive magnetron sputtering on Si and SiOz and annealing in different atmospheres the interaction between film properties and barrier stability is studled. The applicability of optical, mechanical and analytical thickness measurement methods for thin TIN films is investigated. Advantages and drawbacks of the used measurement techniques given by method related boundary conditions are shortly discussed.It is found that texture and roughness of the deposited films is independent of the N/Ti ratio. Moreover the underlaying substrates (Si, Si02) did not affect the texture of the films. The effect of annealing in different atmospheres (N2, H2) on resistivity, stress and film composition is studied for films of different stochiometry.Finally the barrier stability after annealing in N2, H2 or in vacuum is investigated by analytical and electrical investigations on n' p diodes. The barrier stability clearly depends on the annealing atmosphere. It is observed, that the barrier fails already after annealing at 45OOC in N2 independent of the film stochiometry. This is accompained by a strong peeling of the Cu film. By contrast the failure occurs at higher temperatures, if the samples are annealed in H2 or vacuum.

Copper CVD has been investigated for a few years as a key process for copper metalization technology among others because of its capability for high step coverage and low process temperatures. Beside low resistivity a high film growth rate, along with strong adhesion of the Cu film to the underlayer are essential for practical use in fabrication line. This paper presents the effect of carrier gas and precursor composition on the characteristics of copper MOCVD using the Cu(hfac)TMVS precursor.Thin copper films were deposited by the MOCVD method in a coldwall LPCVD system using Cu(hfac)TMVS as precursor and argon or hydrogen as carrier gas. The experimental setup and procedure are described in detail elsewhere [I]. The films were deposited on different underlayers at 4" silicon wafers at wafer temperatures between 170°C and 250°C and a chamber pressure of 500 mTorr. Film properties were determined by four-point probe, surface profilometer, transmission and scanning electron microscope (TEM, SEM).The theoretical calculated deposition rate (limited only by the conversion efficiency of 50% for this process) of 240 n d m i n for the used conditions surpasses the experimental results (130 n d m i n ) clearly. One reason is the limitation of the experimental deposition rate by some more parameters like the reactor geometry and additional precursor consumption at the heater. A deposition rate improvement is possible by opening additional reaction pathways using additives like water [2] or the use of hydrogen as carrier gas [2, 31.Former investigations [ 11 showed a strong effect of a hydrogen pretreatment on the nucleation characteristics. In addition to these considerations the effect of hydrogen as carrier gas on the deposition characteristics was investigated. Without any other additives to the precursor only the known effect of the hydrogen on the nucleation behaviour was confirmed fig. 1).Under the deposition conditions mentioned above no sign of an additional reaction pathway was found, the deposition rate was the same for both Ar and H2 up to 220°C.Compared to the Cu deposition using inert carrier gas a significant influence on the Cu film properties was found depending on the substrate material. Using W as substrate material, in the nucleation phase different wetting angles were found. In the presence of H2 the wetting angle was > 90" causing not completely coherent nucleation layer. Also a higher film roughness was found caused by the isolated grains at the surface cfig. 2). As a result the film resistivity raises considerably to values > 3 p cm.These influences will be discussed for other substrate materials. MAM'97 -Materials for Avanced Metallization 25