OmniEtch “36-6” Carrier Medium
De-layering of bare die and packaged die requires the efficacious application of etch chemicals, often combined in incompatible and thus frequently dangerous combinations. The choice of a suitable etch recipe is based upon a number of factors that include:
- Identification and knowledge of components of die stack, including layer thicknesses and method of deposition. In many instances a CVD deposition will etch at a different rate from an electrodeposited layer of comparable thickness and composition
- Specificity of chemical etch
- Relative ease of use of etch
- Standardized and/or specified etch formulae for a given facility
- Local restrictions on use of certain chemicals (e.g. TMAH)
- Experience of Analyst in performing de-layering procedures
Manual Procedures
Manual de-layering is both difficult and time consuming. Sequential layers of a die stack are normally removed by flooding the surface of a die or by immersion of the die in an etch mixture that is chemically specific for the layer to be removed. Depending on the etch recipe, this may or may not require the application of heat.
Chemical de-layering is a trial and error process in which one must balance the removal of a desired layer with chemical specificity of the selected etch mixture. While it is sometimes easy to select an etch recipe that is chemically selective for a given layer composition, it is extremely difficult to prevent the etch chemicals from diffusing into the body of the die stack through the vias to lower layers.
Carrier Medium 36-6
It is possible to eliminate the problems of etchant penetration into the die stack through the vias by attaching the etch medium onto the surface of a Carrier Medium.
36-6 Carrier Medium is a hydrophilic polymer composed of complex polysaccharides, see Technical Bulletins 3102 and 3103. The physical properties of 36-6 are such that this polysaccharide complex can retain water through a combination of hydrogen bonding and/or it can be held captive within the extensive network of inter and intra molecular voids found in the quaternary molecular structure.
Chemical etch recipes typically contain water, or are water-soluble. The presence of water as a constituent of the etch recipe, or the miscibility of a recipe with nascent water bound in the molecule of 36-6 results in the etch formula being absorbed onto the surface of the Carrier Medium particles.
36-6 is chemically inert and is fully compatible with all known etch chemistries. Experiments have shown that this carrier medium is suitable for a wide range of etch chemistries and conditions and is successful from room temperature up to 45°C.
