Effect of Cl in Gate Oxidation
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Olin, 350 Knotter Drive, Cheshire, CT, USA ' ASM Europe, Rembrandtlaan 7-9, 3723 BG Bilthoven, The Netherlands 4 currently at the University of Arizona, Tucson, AZ, USA 2
ABSTRACT The present study reviews the use of C1 in gate oxidation furnaces for growth of high quality gate oxides with a thickness in the range of 2 to 15 1nm. The following, commercially available, "state of the art" Cl-precursors have been tested: 1,1,1- trichloroethane (TCA), trans-1,2-dichloroethylene (DCE) and oxalyl chloride (OC). Different parameters were evaluated including: metal removal efficiency, poly-silicon haze, Fe bulk incorporation, carrier lifetime and Cl-incorporation in the oxide. C12 was identified as the active component in Cl-oxidation. As a consequence, OC was identified as being the most efficient Cl-source. In particular, OC is the most suited Cl-source for applications requiring reduced oxygen concentration, such as the manufacturing of ultra thin gate oxides. INTRODUCTION Historically C1 has been introduced in the oxidation ambient mainly in order to improve the gate oxide quality [1-3]. Particularly the reduction of electronic instabilities, attributed to the presence of mobile ions, mainly from Na, has been emphasized. The beneficial effect of Cl on the mobile ion instabilities was attributed to a "passivation" of the mobile ions by Cl [1-4]. In addition, the use of Cl during gate oxidation was also found to result in a
reduction of the density of dielectric breakdown defects [3, 5]. Over the past years, it has been demonstrated that metallic contamination on the wafer surface prior to gate oxidation has a distinct negative effect on the dielectric integrity of thin gate oxides [6,7]. Particularly Ca has been identified as one of the most detrimental metals in that respect [6,7]. Ca is also relatively commonly present on wafers. Even after state of the art wet cleaning the surface concentration of Ca ranges typically from 1x 1010 to 5x 1010 at./cm 2 [8]. The introduction of Cl in the oxidation ambient was found to be very efficient in removing metals, in particular for Ca [9-12]. The beneficial effect of the use of C1 during oxidation on gate oxide integrity (GOI) was therefore primarily attributed to the removal of Ca [9, 11]. In order to meet the stringent future gate-oxide defect density requirements, as projected by the SIA roadmap [13], the residual concentration of metals and of Ca in particular, will have to be further reduced. It is the believe of the authors that a well optimized (wet) cleaning process [8] should be used in combination with the in situ use of a small amount of C1 during oxidation. The C1 during the oxidation is required to remove the eventual small traces of metal contamination, left after the pre-gate cleaning process and the potential recontamination from the wafer storage ambient (e.g. clean room air). Furthermore the in situ use of Cl protects against Ca contamination during the oxidaton, e.g. resulting from the quartz of the furnace wall. Various Cl-containing molecules have been used
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