Seven-level diffraction grating structure and its preparation method, wafer lithography alignment method

Abstract

The invention discloses a seven-grade diffraction grating structure, a preparation method thereof and a wafer photoetching alignment method. The seven-grade diffraction grating structure comprises a wafer and a grating graph structure formed on the wafer. The grating graph structure is composed of grating fine structure units. The width of each grating fine structure unit is a grating period. The grating fine structure units are equally divided into 28 regions in the width direction. Each region is provided with a first graphic structure 1st or a second graphic structure 2nd. Different grating fine structure units are formed because the first graphic structures 1st and the second graphic structures 2nd are distributed in the width direction of the grating graphic structure in different sequences. The grating fine structure units are any one of a first grating fine structure unit, a second grating fine structure unit, a third grating fine structure unit, a fourth grating fine structure unit, a fifth grating fine structure unit, a sixth grating fine structure unit and a seventh grating fine structure unit. The grating structure can effectively improve diffraction light intensity of a grating, the selective range of coating materials on the alignment grating and the thickness of the alignment grating is widened during photoetching, the alignment uncertainty range is reduced, and alignment precision is improved.

Description

technical field [0001] The invention relates to the technical field of integrated circuit manufacturing, in particular to a seven-level diffraction grating structure for improving wafer lithography alignment and a preparation method thereof. In addition, the invention also relates to a wafer lithography alignment method. Background technique [0002] High-precision photolithographic alignment is an important problem that continues to be faced in the manufacture of micro-nano devices. The commonly used precise alignment structure is a grating pattern structure. There are different levels of diffracted light at different angles, and the light intensity of different diffraction orders is separated through a specific optical structure, which can achieve precise grating positioning that is much smaller than the size of the alignment structure. [0003] At present, the grating pattern structure commonly used by integrated circuit chip manufacturing companies in the 193nm lithograp...

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Problems solved by technology

At the same time, its maximum diffracted light WQ is the 0th order diffracted light, because the 0th order diffracted light will interfere with the light intensity of other diffraction orders, therefore, the stronger 0th order diffracted light in the AH74 structure will cause the contrast of other diffraction orders to be relatively low. low, reducing the alignment accuracy of the AH74 structure

In some specific photolithography processes, such as etching or chemical mechanical polishing, etc., the AH74 alignment mark is partially damaged and the 7th-order diffraction light intensity is very weak. At this time, it is possible to use the 3rd-order and 5th-order diffraction The light is finely aligned, but the WQ of the 3rd and 5th order diffracted light of AH74 is only 2.8 and 1 respectively, which is not conducive to the lithography alignment in this case

Under certain application conditions, for example, when the grating pattern structure is coated with a high light-absorbing material coating, the diffraction light intensity reflected into the detector will be very low, and even a strong enough diffraction light intensity cannot be collected in the detector. In this case, in order to achieve wafer alignment, opening operations such as partial removal of the high-absorbing coating on the top layer of the wafer covering the grating pattern structure need to be performed during the photolithography process, resulting in the use of an additional mask, or Adverse effects such as having to replace the top coat material

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