One or more techniques or systems for forming a pattern during semiconductor fabrication are provided herein. In some embodiments, a photo resist (PR) region is patterned and a spacer region is formed above or surrounding at least a portion of the patterned PR region. Additionally, at least some of the spacer region and the patterned PR region are removed to form one or more spacers. Additionally, a block co-polymer (BCP) is filled between the spacers. In some embodiments, the BCP comprises a first polymer and a second polymer. In some embodiments, the second polymer is removed, thus forming a pattern comprising the first polymer and the spacers. In this manner, a method for forming a pattern during semiconductor fabrication is provided, such that a width of the spacer or the first polymer is controlled.