Method for overlay metrology of low contrast features
AssigneeInfineon Technologies AG
InventorShoaib Hasan Zaidi
Life of this patent
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Abstract
A wavefront sensing tool, such as a Shack-Hartmann detector, detects alignment features in a semiconductor wafer that might otherwise be undetectable using conventional optical tools, such as a microscope. This is particularly advantageous for alignment features formed in photoresist with a height that is less than one fourth the illuminating light's wavelength. The wavefront sensing tool can be used in conjunction with conventional optical tools and a composite alignment image can be formed from the two tools. For higher sensitivity, the light reflected off the wafer can be magnified, with e.g. a telescopic lens, prior to impinging upon the wavefront sensing tool. The composite image can be generated by one or both of the tools or by a computer coupled to the tools.
Claims22
A method of detecting the alignment of two layers in an integrated circuit comprising multiple stacked layers of material, one underlying layer having a first alignment mark and one overlying layer having a second alignment mark, the method comprising:
- detecting the first alignment mark and a reference mark using a wavefront sensing tool and forming thereof a first image;
- detecting the second alignment mark and the reference mark using a second alignment tool and forming thereof a second image;
- and
- forming a composite image from the first and second image by aligning the reference mark in the first and second image.
An alignment detection apparatus comprising:
- a stage having a surface for receiving thereon a semiconductor wafer;
- a light source directed to illuminate a wafer when placed upon said stage with a light having a predetermined wavelength;
- a beam splitter located to intercept light from said light source reflected off a wafer placed upon said stage and to split said reflected light into a first light path and a second light path;
- an optical tool in the first light path, configured to detect an alignment mark in a layer on the semiconductor wafer;
- a wavefront sensing tool in the second light path;
- and
- a computer coupled to the optical tool and the wavefront sensing tool and receiving there from alignment detection data and outputting an alignment image.
A method for measuring the overlay alignment of at least two layers of a semiconductor wafer using a wavefront sensing tool comprising:
- generating a reference signal by observing a flat reference surface with the wavefront sensing tool and storing the resulting signal;
- aligning at least a portion of the semiconductor wafer containing a first and second alignment mark with the wavefront sensing tool;
- illuminating the portion of the wafer and detecting a wavefront of light reflected from the portion of the wafer and from the first and second alignment marks;
- magnifying the reflected wavefront of light;
- generating a wavefront slope signal by observing the magnified reflected wavefront of light with the wavefront sensing tool;
- determining the location of the first and second alignment marks by comparing the wavefront slope signal with the reference signal;
- and
- calculating a distance between the first and second alignment marks based upon the results of the step of determining the location of the first and second alignment marks.
A method of detecting the alignment of two layers in an integrated circuit comprising:
- detecting a first alignment feature in a first layer of an integrated circuit using a wavefront sensing tool and forming thereof a first image;
- detecting a second alignment feature in a second, underlying layer of the integrated circuit using a microscope and forming thereof a second image;
- forming a composite image from the first and second image;
- and
- measuring from the composite image overlay between the first and second layer.
Dependencies are inferred from the claim text.