Plasma Etching of Polysiloxane Based SOG Films
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PLASMA ETCHING OF POLYSILOXANE BASED SOG FILMS NICOLE M. RUTHERFORD AND SATISH K. GUPTA Allied-Signal Inc., Planarization and Diffusion Products, Milpitas, CA 95035 ABSTRACT We have studied the plasma etch behavior of four different SOG materials which range from 0 to 14% in their organic content A number of gas chemistries were (weight percent of -CH 3 ). Etch investigated, including SF 6 /He, CF4/He, CZF 6 , and CHF 3 /He. rates of SOG films were determined relative to that of thermal SiO as a function of the partial pressure of the fluorinecontaining gases. In general, at low partial pressures of the etch gas, where no polymer formation occurs, the SOG films etch faster than thermal oxide. Also, the etch rates increase with an increase in the overall organic content (Si-CH3 ) of the SOG. While higher SOG etch rates relative to that of thermal Si0 2 are attributable to the lower SOG densities, the increase in SOG etch rates with increasing Si-CH3 content probably reflects the effect of decreasing Si-O bond density. Under conditions favoring polymer formation, the SOG etch rates are suppressed relative to that of oxide indicating enhanced polymerization rates Preliminary data obtained using gas on a siloxane SOG surface. chemistries with high F/C ratios suggest that the relative contributuion by F atoms to etching is larger in a siloxane SOG than in Si02 . INTRODUCTION In integrated circuit fabrication, the use of spin-on glass (SOG) films for dielectric planarization is becoming widespread. In applications where dielectric planarization between multilevel metal interconnects is desired, CVD/SOG/CVD sandwich structures are common, either with total etch back (TEB) or partial In both processes, the planetch back (PEB) of the SOG layer. arized profile of the SOG layer is transferred to the underlying CVD layer by plasma etching the SOG and the CVD oxide silmutaneously. In the final structure, the SOG may completely etched away (TEB), or it may be left in the spaces between the metal lines (PEB). In both of these schemes a etch ratio of 1:1 CVD oxide to SOG is desirable. For a given set of plasma etching conditions, however, the etch rate of an SOG film is likely to be different from that of a conventional oxide film due to As a result, differences in density and chemical composition. it has become important to understand the plasma etch characteristics of SOG's relative to other dielectric materials such as Si0 2 in order to devise optimal etch processes. To understand how the SOG films might interact with various reactive species present in a plasma, it is useful to consider that SOG solutions consist of Si-O network polymers dissolved in Typically, the polymers are prepared through organic solvents. acid catatyzed hydrolysis/condensation reactions of tetraethyl When the SOG solution is spun onto a orthosilicate, Si(OEt) 4 . substrate and cured, the low molecular weight polymers in solution undergo further condensation and crosslinking to form solid sio 2 -like films (silicate SOG). The film properties can be modif
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