Method for detecting a particle in a nanoimprint lithography system

A method for detecting a particle between a nanoimprint mold assembly and a substrate in a nanoimprint lithography system, said method comprising:

• positioning said nanoimprint mold assembly and said substrate in a desired spatial relationship using an imprint head and a stage, said nanoimprint mold assembly and said substrate being spaced-apart to define a desired distance and desired volume therebetween, said distance having an expected value and said volume substantially filled by polymerizable material;
• measuring said distance between said nanoimprint mold assembly and said substrate employing encoder signals produced by said imprint head, defining a measured value of said distance, wherein measuring occurs after fluid has filled the volume between said nanoimprint mold assembly and said substrate;
• comparing said measured value of said distance with said expected value of said distance, defining a difference between said measured value and said expected value;
• and
• determining a presence of said particle between said nanoimprint mold assembly and said substrate based on said difference.