Process of patterning photo resist layer extending over step of underlying layer without deformation of pattern

A process of patterning a photo resist layer, comprising the steps of:

• a) preparing an underlying layer having an upper portion and a lower portion on both sides of a step and a characteristic curve representative of relation between a critical dimension of a pattern formed in a sample photo resist layer and a thickness of said sample photo resist layer to be required for said critical dimension;
• b) determining a first target thickness of a thick portion of a photo resist layer extending over said lower portion and a second target thickness of a thin portion of said photo resist layer extending over said upper portion in such a manner that a difference between said first target thickness and a certain thickness at an extreme value of said critical dimension on said characteristic curve is approximately equal to a difference between said second target thickness and said certain thickness;
• c) covering said underlying layer with said photo resist layer having said thin portion and said thick portion;
• and
• d) forming said photo resist layer into a photo resist pattern having said critical dimension.