The uniformity of large area thin films deposition is a crucial process as we widely apply electron cyclotron resonance chemical vapor deposition (ECR-CVD) in solar industry. In this work, we installed sub-magnetic (auxiliary) fields for inner and outer coils under ECR-CVD process chamber to improve the deposition uniformity of a-Si solar thin films. Next, we measured the distribution of magnetic field along the central axis of chamber and the diameter of substrate surface. By this approach, we investigated the effect of sub-magnetic field to the uniformity of electron cyclotron resonance a-Si solar thin films deposition. We succeeded in obtaining an excellent deposition uniformity of a-Si solar thin films over 150mm diameter on glass substrates by adjusting the magnetic field distribution from inner and outer magnetic coils. The uniformity is within 10%. Moreover, We obtained optimal conditions for solar cell fabrication between the rapid process deposition rates (>10 Å/sec) and magnetic parameters.