Study of BEOL Process Induced High Resistance in IC's Manufacturing
|關鍵字:||製程誘發;後段製程;高阻抗;Process Induced Effects;BEOL|
Abstract In this thesis, there are two topics of BEOL (Back End of Layers) process to be studied. One is the study of process-induced high via contact resistance problem. The other is the study of process-induced abnormal interconnection line sheet resistance. On the first topic about the via hole contact resistance, it was interesting to find that the via hole contact resistance was not simply related to the contact area on the base of the same process conditions. It was found that all the Ar (argon) sputtering etch (before plug deposition), the via hole profile (taper angle) and the damaged TiN ARC (anti-reflective coating) layer of the bottom metal line would affect the via hole contact resistance. During argon sputtering process, the accelerated argon ions will sputter the sidewall of the via holes to cause chipping oxide drop on the bottom of the via hole. The chipping sidewall oxide will shrink the contact area, and impact the contact interface quality and finally increase the contact resistance. The taper angle of the via hole profile also affects the contact resistance. The more taper the via profile is, the larger the acceptance area of via sidewall is. Therefore, the chipping oxide effect increases and influences the contact resistance. The surface condition of the ARC layer of the bottom metal line is also an important factor. The damaged ARC layer surface during via etching will cause extremely high contact resistance. It was concluded that the incomplete titanium-oxide removal by argon sputtering is the dominant factor. Titanium contained polymers generated during via etching are also a key factor which impacts the via resistance. It was proved that nitrogen gas added in the via etching process would improve the Ti-polymer problem. It is also effective to adopt a Ti softened etching process to remove Ti polymers. According to the results of the study, to obtain a stable contact resistance is to get a more vertical via profile, an optimized argon sputtering condition, a non-damaged contact surface, and polymers free via holes. The other topic in this thesis is the study of process induced abnormal sheet resistance of interconnection lines. Circular defects resulting from the attack of the developer will cause high sheet resistance and short circuit of the interconnection lines. It is found that to get thicker ARC TiN, to adopt ozone treatment after metal film deposition, and to insert a stress relief layer of Ti all would improve the circular defects problem. Metal residues resulting from the rework process of photo resist also impact sheet resistance of the interconnection lines. The oxidation of the ARC titanium may be served as the hard mask during etching the line pattern. This hard mask is an etching obstacle which causes incomplete etching and results in metal residues. It was proved effectively to eliminate metal residues by controlling ashing temperature and with wet stripper. The disadvantages of these strategies are impacts on throughput and lots of cost.