Ebic Investigation of Etch Induced Defects in Silicon Introduced by Rie and Ribe.
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EBIC INVESTIGATION OF ETCH INDUCED DEFECTS IN SILICON INTRODUCED BY RIE AND RIBE. H.-U. Habermeier M. Eckstein, C. Ruf, G. Ji.ger-Waldau and G. Zwicker Max-Planck-Institut fitr Festk6rperforschung, D- 7000 Stuttgart-80, FRG, * Fraunhoferinstitut fir Mikrostrukturtechnik, D 1000 Berlin 33, FRG ABSTRACT Silicon single crystal wafers are lithographically patterned and etched for via holes by means of RIBE, RIE and ECR based techniques. The damage introduced by etching is analyzed using charge collection microscopy. This technique probes sensitively the occurrence of electrically active defects due to their altered electron hole recombination properties compared to the bulk material. Furthermore, investigations of the temperature dependence of the EBIC contrast give informations about the physical mechanisms for the recombination. The experiments revealed a substantial increase [several % I of the EBIC contrast in the etched part of the pattern, i.e. electrically active damage is introduced by the etching technique, giving rise to enhanced recombination. Measurements of the diffusion length in etched and unetched areas of the specimen reveal identical values, i.e. the damage is confined close to the surface. Using the different etching methods quantitatively different defect levels are found. Measurements of the temperature dependence of the EBIC contrast aimed to reveal the physical nature of the defects show a drastic increase of the contrast with decreasing temperature. This increase can be described by two regimes in an Arrhenius plot with a linear characteristic of different slopes. INTRODUCTION Low energy ion-assisted dry etching processes such as ion-beam etching [ IBE ], reactive ion-beam etching [ RIBE Jor reactive ion etching [ RIE ] have become one of the key processing steps for silicon integrated circuit fabrication technologies. Inherent to all these processes is the energetic particle bombardment sufficient to cause lattice damage in silicon either by simple momentum transfer in the case of IBE or by momentum transfer coupled with chemical reactions in RIBE and RIE. The consequences of low energy ion bombardment on semiconductor surfaces result in material modifications often denoted as "etch damage". A list of this etch damage includes [ 1]: 1. Surface residues either etch process related [ e.g. formation of nonvolatile products like fluorocarbon films using CF 4 chemistry for silicon etching ] or chamber configuration specific [ e.g. quartz vs. teflon electrodes], 2. Impurity penetration [ diffusion, implantation], 3. Lattice damage due to atom displacement, 4. Surface roughness, 5. Gate oxide breakdown or introduction of traps, 6. Mobile ion contamination, 7. Dopant loss or loss of dopant activity. The assessment of the surface damage which is usually a combination of several of the effects mentioned above was previously studied either by the electrical characteristics of subsequently formed metal-silicon contacts especially Schottky contacts [[2 ]or by a variety of different analytical tools such as
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