Harald Okorn-Schmidt

Behaviour of a Well-Designed Megasonic Cleaning System

In this paper, we will demonstrate the performance of a new generation of megasonic systems. It has been improved beyond the state-of-the-art through a thorough, space resolved study and correlation of cavitation events coupled with multi-bubble-sonoluminescence (MBSL) [1], particle removal efficiency (PRE) and device damage creation. Minimizing “killer particles” becomes extremely critical as feature sizes of semiconductor devices continue to shrink. Wet processing has been fulfilling these stringent requirements to control particulate contamination in the sub-micron size range through the introduction of megasonic systems. By doing this, the chemical activity is supported through additional mechanical forces. However, recent reports are giving significant hints that current megasonic systems are creating too much device damage and paying a price for highparticle removal efficiency [2].

Single Bubble Cleaning and Vortex Flow

Ultrasonic cleaning is a well proven technique in many industrial, laboratory and even household applications. It is known that cavitation bubbles can induce fast microscale flows and thus are responsible for cleaning and even corrosion [1,2]. Nevertheless there are numerous effects that can have a potential role in cleaning processes, as the behavior of an acoustic bubble is very complex: radial oscillations, surface oscillations, leading sometimes to the disintegration of a bubble, collapses, rebounds and subsequently shockwaves, liquid jets and vortex flows can be observed. But as bubbles in sound fields typically appear in a random fashion and in complicated interactions, it is very hard to identify the processes and their effects with respect to cleaning. To isolate the various ongoing processes and to study them in detail, single cavitation bubbles and their interaction with a surface are examined in this work. The single bubbles are of sizes around 500 μm in radius and are produced by a pulsed laser that is focused into water, which allows creating bubbles of a repeatable size at a defined position.

Process Parameter Control for BEOL TiN Hard Mask Etch-Back

In this paper we demonstrate an effective process control mechanism to significantly improve on the process performance of a BEOL post-etch cleaning process with an integrated partial or complete removal of the TiN HM (hard mask) layer by so called formulated chemistries on a single wafer processing tool. The novel process control mechanism enables a 50% reduction in chemical consumption while achieving an at least equivalent TiN etch uniformity.

Tris(Trimethylsilyl)Germane (Me3Si)3GeH: A Molecular Model for Sulfur Passivation of Ge(111) Surfaces

Tristrimethylsilylgermane, (Me3Si)3GeH, was employed as a molecular model compound for hydrogen terminated Ge(111) surfaces. Time and temperature dependent NMR spectroscopy yielded rate constants for the reaction between (Me3Si)3GeH and elemental sulfur and allowed for the determination of the activation energy for this molecular model reaction to mimic germanium surface passivation.

The Risk of Pattern Collapse for Structures in Future Logic Devices

Pattern collapse has long been known in photoresist patterning where the resist patterns merge or collapse during rinsing and drying steps [. The forces responsible for this collapse were identified as capillary forces during the drying process. Structures such as titanium nitride DRAM cylinders [ and silicon Flash shallow trench isolation (STI) lines have also been observed to be pattern collapse sensitive due to increase in aspect ratio of the features. Micro-electromechanical systems (MEMS) devices also show a similar phenomenon, but on a larger length scale, and is referred to as stiction [. For the technology nodes <14 nm, back-end-of-line (BEOL) low-k structures are also on the verge to show pattern collapse behavior. Whether a structure is sensitive to pattern collapse or not depends on several parameters, which will be analyzed in this paper.

Cleaning of semiconductor substrates by controlled cavitation

The continuing downscaling of device geometries in the semiconductor industry is driving the requirements for both process and contamination control. Historically, the physical and the chemical processes required for contamination control were evolutionarily scaled with device geometry. However, todays tailored wet‐chemical cleaning approaches must strive to meet stringent requirements to assure a minimal material loss and no damage to extremely fragile structures. While chemical solutions exist for the control of molecular‐organic and metallic ion contamination, the physico‐chemical solutions for the removal of nanosized particulate contamination to critical diameters below 20 nm are still undetermined. Therefore, the potential and the limitations of megasonic cleaning, which is mainly based on cavitation, are carefully balanced and a detailed understanding of the ongoing physical mechanisms is necessary to maintain a stable window of operation. The relevant active mechanisms present in such a cavitatio...

The Active Role of Etch Products in Particle Removal by SC-1 Solutions

The following experiments were carried out with silicon nitride (Si3N4) particles (high-purity product SN-E10, donated by UBE) on silicon wafers with native oxide. The Si3N4 powder was dispersed in ultra pure water and used as a parent solution. Silicon nitride particles were chosen, because they are widely used for cleaning efficiency tests in the semiconductor industry. Solid State Phenomena Online: 2007-11-20 ISSN: 1662-9779, Vol. 134, pp 181-184 doi:10.4028/www.scientific.net/SSP.134.181

Electrophoretic Studies on Silicon Nitride: Traces of Silicates in UPW Shift Zeta Potential Similar to SC-1

In this paper we report on a new method of controlling the zeta potential of Si3N4 particles by addition of silicate traces to neutral ultra pure water (UPW). The positive zeta potential of Si3N4 at neutral pH shifts to negative values similar in alkaline pH solutions (e.g. with ammonia).