A holistic study on metal pitch uniformity control in the scheme of self-aligned double patterning

The chip size progressive shrinkage imposes more stringent requirement on the fine geometry processing with the technology revolution in the semiconductor industry. Until EUV mass production is available, Selfaligned double patterning (SADP), as well as self-aligned quadruple patterning (SAQP), is the dominate technique applied to achieve smaller Bit Line/Word Line (metal pitch) profile beyond lithography limitation. Conventional metal pitch is formed through Tungsten (W) deposition in the trench after SADP flow, however, the process variation in SADP scheme worsens the metal pitch length uniformity due to Aspect-ratio dependent etching (ARDE) effect. Such metal pitch length nonuniformity directly affects the resistance in the circuit as well as the device performance. Firstly, this paper starts with a deep investigation on the Critical dimension (CD) variation in the traditional SADP scheme from analytical study, followed by the conventional CD control mechanism for individual step. Secondly, it highlights current CD tuning limitation and introduces a novel tuning method. Lastly this paper describes the procedure to build up the new tuning mechanism conceptually and provides applicable suggestions for the industry implementation. Such novel tuning mechanism achieved 32% CD variation reduction.