Application of CMP to the Cladding Layer of MRAM

Inhalt:
Although the Magnetoresistive Random Access Memory (MRAM) claims to be one of the non-volatile memories of the next generation for its non-volatility, high speed and high endurance, the high current required to generate a magnetic field for programming the MTJ (Magnetic Tunneling Junction) device represents a limit to practical applications. A cladding layer made of magnetic materials (Ta/NiFe/Ta) surrounding the write word line to enhance the magnetic efficiency of the passing current has been deployed to effectively reduce the write current by ~ 50%. This cladding layer, however, imposes a challenge to the CMP process because of its relatively chemically reactive nature. In this work we study the variation of dishing phenomenon in different loading areas for polishing the cladding layer along with the Cu line. Different recipes of slurry are compared and an optimal solution is suggested. A possible mechanism for the dishing is also proposed.