Carola Blaesing-Bangert

Next-generation mask metrology tool

For next generation photo mask lithography the tolerance range for pattern placement and critical dimensions (CD) is further shrinking. Improved optical resolution and precision of a metrology system are required to qualify the lithography tool and monitor the photo mask process. Edge detection methods in transmitted light mode for pattern placement and CD measurements are advantageous if the tightened resolution and precision requirements can be met. The new LMS IPRO2 using an illumination wavelength range of 360 to 410 nm has a significantly enhanced resolution for registration and CD measurements in both, transmitted and reflected light. A new laser interferometer with an enhanced resolution of 0.3 nm contributes to the overall improved system performance. The stage is designed to measure on quartz substrates and next generation lithography (NGL) reticles up to 230 mm square in transmitted light as well as in reflected light on 200 mm and 300 mm wafers for stepper qualification.

Performance data obtained on a new mask metrology tool

A new mask and wafer metrology tool is under final development at Leica to be launched in 1996. Recent performance data on the LMS IPRO system at Leicas development center shows precision and accuracy performance required for the 0.18 micrometers design rule device generation.

First performance data obtained on next-generation optical mask metrology tools

To keep pace with continuously shrinking design rules for masks and reticles Leica Microsystems has developed two new mask metrology tools. The LWM 250 DUV is designed to measure Critical Dimensions (CD) on mask in transmitted light at 248nm illumination. The LMS IPR02 is designed to measure pattern placement and CDs in transmitted light at I- line (365nm) illumination. System overview and first performance data are presented for both tools. The step to a shorter illumination wavelength leads to a better optical resolution power resulting in an improved edge detection and CD linearity compared to systems using white light or I-line illumination for imaging.

Performance data obtained on a next-generation mask metrology tool

A new mask and wafer metrology tool is under final development at Leica and will be launched in 1996. The new technical concept is discussed. Recent performance data on the LMS IPRO system at Leicas development center shows precision and accuracy data required for the 0.18 micrometer design rule device generation.

Using the Leitz LMS 2000 for monitoring and improvement of an e-beam

Kaizen--a continuously improving--is a philosophy lived in Japan which is also becoming more and more important in Western companies. To implement this philosophy in the semiconductor industry, a high performance metrology tool is essential to determine the status of production quality periodically. An important prerequisite for statistical process control is the high stability of the metrology tool over several months or years; the tool-induced shift should be as small as possible. The pattern placement metrology tool Leitz LMS 2000 has been used in a major European mask house for several years now to qualify masks within the tightest specifications and to monitor the MEBES III and its cassettes. The mask shops internal specification for the long term repeatability of the pattern placement metrology tool is 19 nm instead of 42 nm as specified by the supplier of the tool. Then the process capability of the LMS 2000 over 18 months is represented by an average cpk value of 2.8 for orthogonality, 5.2 for x-scaling, and 3.0 for y-scaling. The process capability of the MEBES III and its cassettes was improved in the past years. For instance, 100% of the masks produced with a process tolerance of +/- 200 nm are now within this limit.

Metrology on phase-shift masks

In the evaluation of new manufacturing processes, metrology is a key function, beginning with the first step of process development through the final step of everyday mass production at the fabrication floor level. RIM-type phase shift masks are expected to be the first application of phase shift masks in high volume production, since they provide improved lithography process capability at the expense of only moderate complexity in their manufacturing. Measurements of critical dimension (CD) and pattern position (overlay) on experimental rim-type and chromeless phase shift masks are reported. Pattern placement (registration) was measured using the Leitz LMS 2000. The overall design and important components were already described. The pattern placement of the RIM type phase shift structures on the photomask described above was determined within a tolerance of 25 nm (3s); nominal accuracy was within 45 nm (3s). On the chromeless phase shift mask the measurement results were easily obtained using a wafer intensity algorithm available with the system. The measurement uncertainties were less than 25 nm and 50 nm for precision and nominal accuracy respectively. The measurement results from the Leitz CD 200 using transmitted light were: a CD- distribution of 135 nm (3s) on a typical 6 micrometers structure all over the mask; the 0.9 micrometers RIM structure had a distribution of 43 nm (3s). Typical long term precision performance values for the CD 200 on both chrome and phase shift structures have been less than 15 nm.