Carlos L. Ygartua

Characterization of epitaxial silicon germanium thin films by spectroscopic ellipsometry

Abstract In this work we will present the results of spectroscopic ellipsometry measurements (SE) for determination of the Ge concentration (atomic percent) and thickness of relaxed epitaxial SiGe films (on Si) with thicknesses in the range of 900–2500 A for films with 1–35 atomic percent Ge. The Ge concentration is found by measuring the peak value of the real part of the refractive index (RI) which is correlated with Rutherford backscattering (RBS) measurements of atomic percent of SiGe. Conventional tools such as FTIR are not sufficient for accurate measurement of the thickness of SiGe films, which can be thinner than 1000 A. Also, previously there have been no in-line tools in production use for measuring the Ge concentration in SiGe films.

Characterization of copper oxidation and reduction using spectroscopic ellipsometry

The success of advanced IC interconnect schemes using copper depends on control of CU surface oxidation, since even a few monolayers of CuxO can dramatically increase Cu via resistance and reduce Cu-to-dielectric film adhesion. This level of control requires an accurate, in-line method of determining Cu oxidation state and CuxO film thickness. In this paper, we apply spectroscopic ellipsometry to characterize Cu films that were oxidized and then reduced under controlled thermal and plasma conditions representative of IC processing. Oxidation and reduction was carried out on single layers of sputter-deposited Cu as well as on Cu films deposited as part of multilayer thin film stacks. Ellipsometer models were developed and optimized for application to both Cu and copper oxide films. The correlation of ellipsometric data with Rutherford backscattering spectroscopy and x-ray fluorescence analysis of similar films is also discussed.

Production metrology and control of color filter array photolithography for CMOS imagers

The color filter array (CFA) for an image-producing semiconductor device is composed of patterned red-, and green- and blue-colored photoresist structures. CFA photolithography is rather different from that of most semiconductor process levels.

Addressing thin film thickness metrology challenges of 14nm BEOL layers

In this paper we discuss the impact of these two effects on the film thickness measurement and describe our approach to develop a film stack model and recipe which accounts for the underlying stack as well as Chemical Mechanical Planarization (CMP) variation. We also describe the verification and production implementation of this model using mass production data.

Composition measurement of tri-layer SiGe stack using broadband spectroscopic ellipsometry

This paper discusses the development and implementation of a Broadband Spectroscopic Ellipsometry (BBSE) composition measurement to characterize a tri-layer stack consisting of 2 SiGe layers of different Germanium concentrations topped by an epitaxial Si layer. The designed experiment wafer set and the composition model development based on AES and XRD reference data are discussed. The spectral sensitivity of the composition model and the correlation to reference metrology are shown. Wafer to wafer and within wafer variation, stability and tool to tool matching performance are quantified based on the implementation of the composition model as an inline measurement for a 20nm development vehicle. The paper arrives at the conclusion that BBSE is a feasible high throughput metrology option for this application, while leaving room for improvement in future revisions of the model.

Analysis of low dielectric constant and Cu-based single- and multilayered films using spectroscopic ellipsometry

Many materials are being considered as candidates for Low Dielectric Constant, InterLayer Dielectric (ILD) applications. It is expected that some users will introduce Low K ILD materials in Aluminum based processing. Simultaneously, considerable process development is underway worldwide for Copper based Dual Damascene structures and integration of Low K ILD materials in such structures. Spectroscopic Ellipsometry (SE) is widely used in the Integrated Circuit (IC) industry for routine production monitoring. The dispersion information (variation of refractive index with wavelength) from SE can also be correlated to the microstructure and chemical composition of thin films. This provides a powerful, non-destructive and rapid method of analysis and process characterization. In this review, we discuss the application of this technique to the characterization of single and multilayered thin films based on Low Dielectric constant materials. Results of SE analysis of copper films copper oxides and dielectric multilayered films on copper are also presented.

Optical Characterization and Process Control of Top Surface Imaging

The use of selectively silylated resists to facilitate top surface imaging offers the potential for nanoscale lithography using both deep ultra violet (DUV) illumination and electron beam techniques. In this process, an exposure-generated crosslinking prevents silicon incorporation from silylating agents. In the non-crosslinked regions, a silylation agent reacts with OH groups in the resist to form silicon-oxygen bonds. During subsequent dry development in an oxygen plasma, the incorporated silicon attracts oxygen to form silicon dioxide, protecting the resist underneath. The adjacent un-silylated resist erodes (develops) anisotropically 25–100 times faster than the silylation-protected resist. The key to this process is the chemical formation of a silylated region at the top of the resist. A challenge associated with the silylation process, however, is lateral swelling of the silylated layer, which can lead to difficult dimensional control. The amount of swelling depends on the amount of incorporated silicon. Therefore, the uniformity and repeatability of the silylation process must be controlled. This paper will describe how spectroscopic ellipsometry has been used to characterize and monitor the resist silylation process in a non-destructive manner. The simultaneous characterization of the thicknesses and optical properties of a series of silylated resists will be presented. Optical metrology of the thickness of the silylated resists will be correlated with SEM cross-sectional analyses, and process uniformity will be quantified using 49-site wafer maps.

Process monitoring of hemispherical-grained silicon thin films for dynamic random access memory applications

Spectroscopic ellipsometry is employed to correlate the effective thickness of hemispherical-grained silicon (HSG-Si) films on underlying Si capacitor plates to final device capacitance. The fabrication of HSG-Si was developed to increase the storage plate surface area, and hence the capacitance, of dynamic random access memory devices. In this article, a novel combination of modeling techniques is employed to calculate the effective thickness of the HSG-Si film, together with the thickness and degree of crystallinity of the underlying Si capacitor plate. Seven HSG-Si films were fabricated using the “seed and anneal” process. By utilizing a range of seeding temperatures, the morphology and surface area enhancement of the films were deliberately varied. Using broadband spectroscopic ellipsometry, combined with a harmonic oscillator model for the HSG-Si film, a correlation of >95% is demonstrated between the effective thickness of the as-deposited HSG-Si films and the completed device capacitance enhancemen...