Large Area Direct write lithography

Atomic Layer Deposition (ALD) is similar to CVD except that the ALD reaction occurs at lower temperature and it is broken into two half-reactions, keeping the precursor materials separated during the reaction. The separation of the precursors is important to achieve a self-limiting surface reaction to enable precise thickness control and ensure uniform coatings and compactness even in complicated 3D structures.

The present implementation of the technique is suitable for mm to cm-size samples as those typically studied by spectroscopy and microscopy.

ALD has a rich history in microelectronics. It is studied as a potential technique to deposit high-k (high permittivity) gate oxides, high-k memory capacitor dielectrics, ferroelectrics, and metals and nitrides for electrodes and interconnects.

The number of materials that can be prepared by ALD has tremendously increased in the past decade. Notably, it can deposit a wider variety of materials, including important functional oxides like Al₂O₃, MoO₃, SiO₂ and HfO₂.

Dicing is typically used to separate die from a wafer to be mounted in a package or on a PC board. Some users dice a wafer into smaller pieces to process individually. It can be used to cut a wide range of materials and devices including Semiconductor devices, Ceramic Substrates, Thick-film Devices, Sensors, MEMS, Opto-electronic Components, IC Wafers.

Some tools are optimized for multi-angle dicing of thin, tight tolerance products up to 150 mm or 6" diameter and capable of more complex patterns such as multiple indexes and varying cut depths.

Wafers are typically mounted on dicing tape which has an adhesive backing that holds the wafer on a metal frame. The frame with the wafer on it is placed on the chuck of the dicing saw. The wafer is moved into an abrasive blade, usually diamond, rotating at typically 15,000 to 30,000 RPM. The abrasive chips away at the wafer as the blade rotates. Water is supplied to the blade to remove cutting residue and enhance cut quality.  

The cut depth is a function of the substrate thickness and could be optimized depending on the cut quality and blade loading. A good rule of thumb is to cut no more than about 500 µm of material per pass. Harder materials should be cut with shallower cuts and more passes to minimize blade wear. Deeper cuts require a thicker blade to minimize blade flexing or deflection.

AFM is a surface sensitive technique permitting to obtain a microscopic image of the topography of a material surface. Typical lateral image sizes are within a range of only a few Nanometers to several 10 Micrometers, whereas height changes of less than a Nanometer may be resolved.

A fine tip attached to a cantilever is scanned across the material surface and enables to measure height changes exploiting an optical beam deflection system (a laser that is reflected from the rear side of the cantilever onto a segmented photodiode). The position of a laser spot on the photodiode permits to track height changes as e.g. due to a nano-particle on the surface or an atomic terrace of a single crystal surface. A feedback loop controls the tip-surface distance and therefore ensures stable imaging conditions.

Different operation modes like contact or non-contact mode can be used to optimize the imaging conditions with highest lateral resolution on one hand and least sample interaction on the other hand. Measurements in different environmental conditions (liquid, gas,...) on a broad class of samples (smooth, rough, insulating, conductive, soft, stiff, wet, dry...) can be performed.

Choosing suitable tips and imaging modes, additional surface properties can be mapped together with the topography, with similar spatial resolution, like friction force, magnetization and surface potential, surface charge density and electrical resistance, as well as elastic modulus and adhesion of heterogeneous sample surfaces can be obtained.