Photomask features with chromeless nonprinting phase shifting window

Abstract

Aspects of the present invention provide for a novel photomask for patterning features for an integrated circuit, the photomask including a first area transmitting light in a first phase surrounded by second area, the second area transmitting light in a second phase, the second phase opposite the first phase. No blocking material separates the first area from the second area. After development of photoresist, the transition between the first and second area causes formation of a residual photoresist feature on the photoresist surface due to phase canceling of light. If the first area is small enough, it is nonprinting, ie., the opposite sides of the residual photoresist feature formed at its perimeter merge, forming a contiguous photoresist feature, and thus a corresponding patterned feature after etch.

Description

BACKGROUND OF THE INVENTION [0001] The invention relates to a method for patterning fine features for semiconductor devices using a phase shifting mask with no blocking material separating the opposite phases. [0002] Patterned features making up integrated circuits are conventionally formed using photolithography and etch techniques. A photomask, which transmits light in some areas and blocks it in others, is formed, the blocking areas corresponding to the pattern to be formed on the wafer surface (or its inverse.) The surface to be patterned, for example a semiconductor or dielectric layer, is covered with a layer of photoresist, a photoreactive material. Light is projected onto the photoresist surface using the photomask, selectively exposing areas of photoresist. The wafer is then subjected to a developing process, in which exposed photoresist (or unexposed photoresist, in the case of negative photoresist) is removed, leaving patterned photoresist behind. [0003] The remaining pat...

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Benefits of technology

[0008] The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on tho

Problems solved by technology

As projected features become smaller, the limits of resolution are reached and it becomes more difficult to project patterns with sharp edges.

Poor resolution can lead to incomplete patterning and to incomplete etching or overetching, causing device flaws.

The use of alternating phase shifters in photomasks, however, has disadvantages.

The configuration of some patterns leads to phase conflicts, in which rules dictate that the same area must see light of opposite phases.

To date, this has meant that use of alternating phase shifters has been limited to only certain types of patterns.

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