Method and apparatus for the determination of mask rules using scatterometry

Abstract

A method and apparatus for determining optical mask corrections for photolithography. A plurality of grating patterns is printed onto a wafer utilizing a photomask having at least one grating. Each grating pattern within the plurality of grating patterns is associated with known photolithographic settings. Each grating pattern is illuminated independently with a light source, so that light is diffracted off each grating pattern. The diffracted light is measured utilizing scatterometry techniques to determine measured diffracted values. The measured diffracted values are compared to values in a library to determine a profile match. A 2-dimensional profile description is assigned to each grating pattern based on the profile match. A database is compiled of the profile descriptions for the plurality of grating patterns. Photomask design rules are then generated by accessing the database containing the 2-dimensional profile descriptions. In preferred embodiments, the design rules are used to create and correct masks containing OPC corrections, phase-shifting mask corrections and binary masks. In a preferred embodiment the at least one grating is a bi-periodic grating. In a preferred embodiment, the scatterometry technique is optical digital profilometry utilizing a reflectometer or ellipsometer.

Description

[0001] This invention relates to integrated circuit fabrication and in particular to methods for producing precise photolithographic mask patterns.[0002] Computer chips or microcircuits are fabricated using a complex sequence of processing steps consisting of many individual pattern processing steps. As the semiconductor industry continues to shrink the microcircuit designs to create faster microcircuits at lower cost, the semiconductor manufacturing methods have become very complex. The pattern processing sequence typically consists of a photolithographic process and a plasma etch process. Photolithography is the process of creating a 3-dimensional image, using a photomask or reticle pattern, onto a suitable recording media such as a photoresist film on top of a semiconductor substrate or silicon wafer. The process is performed using a photolithographic exposure tool such as a stepper or scanner. Today it takes about 25 pattern processing steps or layers to build-up a modern semico...

AI Technical Summary

Problems solved by technology

A major problem that exists with the prior art lies in the determination of the linewidth of resist lines 60 (shown in FIG. 13) and the profile of 2-D lines 60 and lines 61 (shown in FIG. 14A and FIG. 14B).

The prior art method of making this determination is extremely expensive, time consuming, and destructive. FIG. 13 shows a top view of a portion of a SEM image and FIGS. 14A 14B each show a SEM cross-section view.

The fracturing of the wafer and the CD-SEM preparation procedure is an extremely delicate process that is also time consuming and expensive.

The fracturing of the wafer effectively destroys it.

The problem here is that each wafer has its own unique built-in process variation in that each wafer is processed one at a time.

Additionally, compared with the techniques listed below, because just a single wavelength is utilized, the output data set is rather limited.

The creation of such detailed libraries using standard methods of RCWA would take a very long time.

This technique is not suited for in-situ applications because the machinery involved is rather complex with many moving parts.

Typically some version of RCWA is used to generate the libraries and produce profile results thru optimization routines--however, generally, accurate profile shapes cannot be determined unless account is taken for many diffraction orders in the RCWA calculations.

If many orders are not accounted for, it usually means that a library cannot be created that captures the true details of the feature line images.

Scatterometry techniques that are not sensitive to very small changes in the feature profile are simply not capable of measuring the subtle differences between different OPC test cases.

The problem here is that the library is not robust enough to detect the very small changes 2-D profile changes that usually occur when applying subtle OPC corrections.

However, it is well known that modeling of diffraction of light by corrugated periodic structures is a complex problem that requires sophisticated techniques.

However, unlike in the prior art that typically requires a cross-section CD-SEM analysis, by utilization of the present invention, the user saves considerable time and expense in determining the rules.

Typically, whereas it might take three or four weeks to get the results using the CD-SEM analysis, this technique could shorten this time to a matter of hours.

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