Thomas Marschner

Determination of best focus and exposure dose using CD-SEM sidewall imaging

We use CD-SEM side-wall imaging using the Applied Materials VeraSEM 3d system as a destruction free and quick method to determine side-wall profiles. The system allows the reconstruction of profiles by tilting the SEM beam up to 6 degrees. Using two different tilt angles the reconstruction of side-wall profiles is possible in a quick and destruction free way even for negatively sloped profiles. The use of the profile analysis utility is believed to reduce cycle time significantly especially for process development and troubleshooting in production. We compare profiles obtained from the profile analysis utility of the VeraSEM 3D to X-SEM measurements to qualify this method for use in development and high volume production. For selected examples containing resist lines we investigate process windows determined from topdown CD measurements, X-SEM measurements and the profile analysis utility and compare the best stepper focus and exposure dose values obtained from these methods. It is shown how the results from the profile analysis utility can be used for process monitoring by comparing the obtained data to reference data from FEM wafers.

193-nm resist roughness characterization and process propagation investigation using a CD-SEM

We use the LER measurement capabilities of the Applied Materials NanoSEM 3D CD-SEM for the determination of LER for different manufacturing steps of the DRAM gate layer for the 90 nm technology node and below (after develop, after hard mask-open and final inspection steps). The system allows the fully automatic measurement of the LER as a 3 sigma value for top as well as bottom LER and yields also information about the spatial frequency along the line edge. We demonstrate precision of LER measurements (3 sigma) of less than 10% of the LER for resist structures as well as for etched structures with random or artificial LER within a range from 4 to 20 nm LER. The results agree with the requirements of the ITRS roadmap for structures down to 70 nm. We show on etched poly wafers containing artificial LER that the identification of discrete frequencies is possible down to LER values of below 5 nm (3 sigma). Based on these result we investigate LER on product wafers and show that the LER of left and right line edge, repsectively, are independent of each other. Additionally, no significant discrete frequencies are detected for all process steps under investigation, although the LER amplitude varies significantly in dependence of process conditions.

Spectroscopic Ellipsometry based Scatterometry enabling 193nm Litho and Etch process control for the 110nm technology node and beyond

In the production of sub 140nm electronic devices, CD metrology is becoming more critical due to the increased demands placed on process control. CD metrology using CD-SEM is approaching its limits especially with respect to precision, resolution and depth of field. Potentially, scatterometry can measure structures down to 50nm with the appropriate precision. Additionally, as scatterometry is a model based technique it allows a full reconstruction of the line profile and the film stack. In this work we use SE based scatterometry in the control of a 110nm DRAM WSix Gate process at the Litho and the Mask Open step. We demonstrate the use of a single trapezoid as a basic shape model in FEM and field mapping applications as well as in a high volume production test. The scatterometry results are compared to CD-SEM data. We show that for the GC Litho application, n&k variations in some of the stack materials do not affect the scatterometry CD measurement significantly.

Automatic CD-SEM offline recipe creation for OPC qualification and process monitoring in a DRAM pilot-fab environment

In our work we discuss two approaches of offline CD-SEM recipe creation for both OPC qualification wafers and the introduction of new products to the manufacturing line using the Applied Materials OPC Check and Offline Recipe Editor (ORE) applications. We evaluate the stability of the offline created recipes against process variations for different OPC test layouts as well as for production measurements on multiple lots per week and compare the results to the performance of recipes created directly on the tool. Further, the success rate of recipe creation is evaluated. All offline recipes have been generated in advance of wafer availability using GDS data. The offline created recipes have shown pattern recognition success rates of up to 98% and measurement success rates of up to 99% for line/space as well as for contact-hole (CH) measurements without manual assists during measurement. These success rates are in the same order of magnitude as the rates typically reached by an experienced CD-SEM engineer creating the recipes directly on the tool.

Qualification of an integrated scatterometer for CD measurements of sub-100nm resist structures in a high-volume 300mm DRAM production environment

In our work, Tokyo Electrons iODP103 (integrated Optical Digital Profilometry) technology is used for integrated measurements on a next-generation Lithius Clean Track on after develop inspect (ADI) 300mm wafers. We show that single tool precision and tool-to-tool matching of three integrated systems fulfill the precision requirements of the 70nm DRAM technology node. Further results from a long-term pilot test using integrated scatterometry in a full-volume DRAM production of the 110nm technology node on 300mm wafers are also discussed. The data from our experiment is collected and charted in fab monitored statistical process control (SPC) charts, and compared to the charts from the POR CD-SEM measurements. The sampling plans are optimized in such a way as to perform fully integrated measurements on all wafers per lot, without throughput loss of the litho cluster. We demonstrate that the possibility of measuring all wafers per lot directly after development, in combination with the sensitivity of the method, allows the identification of effects that could not previously be identified by CD-SEM measurements alone.

Impact of averaging of CD-SEM measurements on process stability in a full volume DRAM production environment

In our work we investigate the influence of averaging varying numbers of measurement structures on process stability and CD uniformity. Measurements are performed on an Applied Materials VeritySEM CD-SEM system which provides the possibility to measure several lines or contact hole structures and to yield the average and 3 sigma value of all measured structures. We show that averaging significantly improves the single tool precision up to 30%. Additionally, a long term pilot test has shown that the range of the CD distribution of selected production layers is significantly decreased reducing the contribution of the measurement to the total CD budget resulting in a yield enhancement. Further, we discuss the influence of averaging on the contribution of short-range random CD variations for CD uniformity measurements. This is done by investigating the distribution of the CD difference between adjacent structures across the wafer. We show that increased averaging significantly reduces the contribution of random CD variations to the CD budget.

Characterization of 193-nm resist layers by CD-SEM sidewall imaging

In this work the profile reconstruction capability of the Appplied Materials NanoSEM 3D CD-SEM is evaluated. The system allows the fully automatic reconstruction of profiles by evaluating profiles measured at two different beam tilt angles. From two different tilt angles up to 15 degrees the reconstruction of side-wall profiels is possible in a quick and non-destructive way even for negatively sloped profiles. The sensitivity of profile reconstruction especially with respect to height and undercut detection in dependence of structure height and beam tilt angle is discussed. We investigate precision and accuracy of profile reconstruction by comparing results from profile reconstruction to AFM and X-SEM results. We show that the side-wall angle can accurately be detected for 193nm resist structures even for negatively sloped profiles. This enables the system for the production use especially for monitoring of such profiles which cannot be detected by top-down CD-SEM so far.

Application of integrated scatterometry measurements for a wafer-level litho feedback loop in a high-volume 300 mm DRAM production environment

With critical dimensions in microelectronics devices shrinking to 70nm and below, CD metrology is becoming more and more critical, and additional measurement information will be needed, especially for sidewall profiles and profile height. Integrated scatterometry is, on the one hand, giving the needed measurement precision, and on the other hand, it enables more measurements than stand-alone metrology. Both high precision and large sampling are needed for future technology nodes. This paper shows results from several full volume DRAM applications of state-of-the-art technology nodes on 300 mm wafers. These applications include critical line/space (L/S) layers as 2D applications and contact-hole (CH) layers consisting of elliptical CH-like structures as critical 3D applications. The selected applications are significantly more challenging with respect to scatterometry model generation than the applications presented in previous papers [1, 2]. Simultaneously, they belong to the most critical lithography steps in DRAM manufacturing. In the experiments, the influences of both pre-processes and the litho cluster on Critical Dimension Uniformity (CDU) have been investigated. Possible impacts on Run-to-Run systems like Feed-back and Feed-forward loops will also be discussed. We show that using integrated scatterometry can significantly increase the productivity of lithography clusters.

Characterization of 193-nm resist layers by critical dimension-scanning electron microscopy sidewall imaging

In this work, the profile reconstruction capability of the Applied Materials NanoSEM 3-D critical dimension-scanning electron microscopy is evaluated. The system allows the fully automatic reconstruction of profiles by evaluating profiles measured at two different beam tilt angles. From two different tilt angles up to 15 deg, the reconstruction of sidewall profiles is possible in a quick and nondestructive way, even for negatively sloped profiles. The sensitivity of profile reconstruction, especially with respect to height and undercut detection in dependence of structure height and beam tilt angle, is discussed. We investigate precision and accuracy of profile reconstruction by comparing results from profile reconstruction to AFM and cross-sectional (X-SEM) results. We show that the sidewall angle can accurately be detected for 193-nm resist structures even for negatively sloped profiles. This enables the system for production use especially for monitoring of such profiles. As the profile reconstruction is done with nearly the same speed as regular top-down measurements, a clear advantage over existing monitoring techniques is obvious.

In line measurements of the side wall angles for litho process tool monitoring using profile reconstruction capabilities of a CD SEM

In our work the Applied Materials NanoSEM 3D CD-SEM is used for in-line monitoring of profile height and side wall angle on product wafers. The system allows the fully automatic reconstruction of profiles using the built in beam tilting capability. From these measurements an immediate status of the focus of the litho tool is obtained. The side wall information in combination with the CD allows to distinguish between focus and exposure excursions, respectively. The side wall angle of an isolated line on a focus sensitive backend product layer within the Infineon 140 nm technology has been monitored over a period of 3 months in a full volume DRAM manufacturing environment. The selected structure has been identified being much more sensitive to focus variations than dense lines. The changes in the side wall angle have been found to cover a side wall angle range from 80/spl deg/ up to 93/spl deg/ allowing a successful monitoring of the focus of the litho tool. This sensitivity of the side wall angle to focus changes is expected to enable an earlier warning than from top-down CD measurements only, if the focus drift of the litho tool passes a predefined limit. During the evaluation period, one minor focus excursion could be identified which was not detected by top-down CD-SEM data only.