Sandra Malhotra

Analysis of thin film stress measurement techniques

Abstract Residual stresses in several magnetron sputtered Mo thin films, with thicknesses from 100 nm to 1.60 μm, were determined using double-crystal diffraction topography (DCDT), sin 2 ψ , and the high-resolution X-ray diffraction technique (HRXRD). The Mo films had a range of microstructures that included random and polycrystalline, textured out-of-plane, and textured in-plane. When the average biaxial stresses over the entire film thickness were determined for the films using the aforementioned techniques, the results were comparable in magnitude. However, the stresses determined with the substrate curvature technique, DCDT, were consistently smaller than those obtained with the sin 2 ψ and HRXRD techniques. The difference may arise for several reasons. For example, the HRXRD and sin 2 ψ measurements of a textured film may not be indicative of the mean film stress, and thus may differ from the curvature measurement. Also, substrate curvature techniques measure extrinsic stresses, or stresses that arise solely from the presence of the substrate. The techniques which analyze the film directly, such as sin 2 ψ and HRXRD, measure the extrinsic stresses and the intrinsic stresses that arise from defects or morphology changes within the film. The additional information that can be obtained from the depth-sensitive HRXRD technique concerning stress variations within thin films was also highlighted.

Depth dependence of residual strains in polycrystalline Mo thin films using high-resolution x-ray diffraction

The magnitude of the stress in a thin film can be obtained by measuring the curvature of the film–substrate couple. Crystal curvature techniques yield the average stress throughout the film thickness. On a microscopic level, the details of the strain distribution, as a function of depth through the thickness of the film, can have important consequences in governing film quality and ultimate morphology. A new method, using high‐resolution x‐ray diffraction to determine the depth dependence of strain in polycrystalline thin films, is described. The technique requires an analysis of the diffraction peak shifts of at least six independent {hkl} scattering vectors, at a variety of penetration depths from the free surface of the film. The data are then used to determine the magnitude and directions of the strain eigenvalues in a laboratory reference frame for each penetration depth from the free surface of the film. A linear elastic model was used to determine the strains in successive slabs of the film. Result...

STRAIN GRADIENTS AND NORMAL STRESSES IN TEXTURED MO THIN FILMS

The high-resolution x-ray-diffraction technique was used to explore strain variations in sputtered Mo films with thicknesses of 170, 260, and 800 nm that possess a (110) out-of-plane texture. The strains in crystallographic planes perpendicular to the surface of each film were found to be nominally constant and compressive at all x-ray penetration depths. Near the surface of each film, the inclined-plane strains were compressive, and then relaxed as the penetration depths approached each entire film thickness. The strain tensor in a laboratory reference frame for each film, as a function of penetration depth, revealed that the normal strain ezz was tensile near the surface of each film, and then relaxed to a nominally constant value as the penetration depths approached the entire film thickness. The penetration depth over which the normal strain decayed to a nominally constant value increased as the total film thickness increased. A consequence of the large normal strains near the free surface of each fil...

High-Productivity Combinatorial PVD and ALD Workflows for Semiconductor Logic & Memory Applications

With materials innovation driving recent logic and memory scaling in the semiconductor industry, High-Productivity Combinatorial™ (HPC) technology can be a powerful tool for finding optimum materials solutions in a cost-effective and efficient manner. This paper will review unique HPC wet processing, physical vapor deposition (PVD), and atomic layer deposition (ALD) capabilities that were developed, enabling site-isolated testing of multiple conditions on a single 300mm wafer. These capabilities were utilized for exploration of new chalcogenide alloys for phase change memory, and for metal gate and high-K dielectric development for high-performance logic. Using an HPC PVD chamber, a workflow was developed in which up to 40 different precisely controlled GeSbTe alloy compositions can be deposited in discrete site-isolated areas on a single 300mm wafer and tested for electrical & material properties, using a custom in-situ high-throughput sheet-resistance measurement setup, to get very accurate measurements of the amorphous – crystalline transition temperature. We will review how resistivity as a function of temperature, crystallization temperature, final and intermediate (if any) crystalline phases were mapped for a section of the GeSbTe phase diagram, using only a few wafers. Another area where HPC can be very valuable is for finding optimum materials for high-k dielectrics and metal gates for high-performance logic transistors. Assessing the effective work-function (EWF) for a given high-k dielectric metal-gate stack for PFET and NFET transistors is a critical step for selecting the right materials before further integration. One way to obtain EWF is by using a terraced oxide wafer with different SiO2 thickness bands underneath the high-k dielectric. We report a HPC workflow using our wet, ALD & PVD capabilities, to quickly assess EWF for multiple different high-k dielectrics and metal gate stacks. This workflow starts with a HPC wet etch of thermal silicon oxide, creating different oxide thicknesses 1–10nm in select areas of the same substrate. This is followed by atomic layer deposition of a high-k dielectric film such as HfO2. Next, a metal e.g., TaN is deposited through a physical mask or patterned post-deposition to complete the formation of MOS capacitors. The final step is C-V measurements and C-V modeling to extract Vfb, high-k dielectric constant, EOT, and EWF from Vfb vs EOT plot. This workflow was used to extract EWF for a TaN metal gate with an ALD HfO2 high-k dielectric using a metal-organic precursor. We will discuss how EWF for this system was affected by annealing post-dielectric deposition & post-metallization, different annealing temperatures & ambients, Hf pre-cursors and interfacial cap layers e.g., La2O3 & Al2O3. Finally, we will also discuss more advanced versions of this workflow where the ALD high-k dielectric and PVD metal gate is also varied on the same wafer using HPC versions of ALD & PVD chambers.

Depth Profiling of Molybdenum Thin Films Using Grazing Incidence X-Ray Scattering

It is important that inherent strains (or stresses) be controlled during thin film processing. This study used grazing incidence x-ray scattering (G1XS) to determine the strain gradient present in a ∼1700 A sputtered molybdenum thin film. In particular, the gradient in the hydrostatic strain was Measured. This observation corresponded to assessing the average change in the lattice parameter as a function of depth throughout the thickness of the film. In addition, the strain ellipsoids, which represent the state of strain in three dimensions, were calculated as a function of film depth. It was shown that the strain varied throughout the ∼1700 A Mo film thickness and that the principal strains were anisotropic, with one principal strain much larger than the others in Magnitude.