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REDISTRIBUTION LAYER (RDL) VIA ETCH METHODS

IP.com Disclosure Number: IPCOM000240610D
Publication Date: 2015-Feb-12
Document File: 5 page(s) / 163K

Publishing Venue

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Abstract

The objective of this paper is to define methods by which a via etch of polymer or other organic material can be accomplished, a) in parallel with all vias etched simultaneously, b) with a rate sufficient for adequate throughput, c) without the need for vacuum based processing so as to reduce cost, and d) with a process that can scale to very small via diameters of a few microns or lower. A process meeting the above criteria would permit cost effective scaling of RDLs for semiconductor chip packaging to much smaller dimensions and higher densities. To achieve this, a process utilizing a reactive gas, such as ozone at high concentration, elevated temperature for the material to be etched, and the optional addition of ultraviolet light (UV) are combined to remove the polymer material from the via area. The via area being defined by a mask, such as a metal layer with openings defining the via etch.

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Redistribution Layer (RDL) Via Etch Methods

Abstract

    The objective of this paper is to define methods by which a via etch of polymer or other organic material can be accomplished, a) in parallel with all vias etched simultaneously, b) with a rate sufficient for adequate throughput, c) without the need for vacuum based processing so as to reduce cost, and d) with a process that can scale to very small via diameters of a few microns or lower. A process meeting the above criteria would permit cost effective scaling of RDLs for semiconductor chip packaging to much smaller dimensions and higher densities. To achieve this, a process utilizing a reactive gas, such as ozone at high concentration, elevated temperature for the material to be etched, and the optional addition of ultraviolet light (UV) are combined to remove the polymer material from the via area. The via area being defined by a mask, such as a metal layer with openings defining the via etch.

Section 1: Etch process

    The polymer material, composed of carbon, hydrogen and other species, is typically able to be oxidized into volatile species with the exception of an inorganic residue. This residue, for example SiO2, may be wet cleaned from the surface after the oxidation step. Alternatively, the oxidation may be done in liquid phase using an oxidant such as dissolved ozone, but this paper will focus on gas phase oxidation based polymer etch. A potential sequence for processing would be as follows:

1. Substrate is introduced into an atmospheric etch chamber with a mask defining the location of areas to be etched (via locations). The chamber is isolated from external atmosphere.

2. The substrate is heated to a defined temperature, for example 180 deg C, to increase etch rate of the polymer.

3. Oxidizing gas is introduced into the chamber, for example ozone, to react with the polymer material and volatilize it.

4. The process may be accelerated or made anisotropic by the application of UV light to the surface being etched. Such UV light being directed normal to the surface and of a wavelength sufficiently energetic to break bonds in the polymer (ex. < 300 nm). This step is not necessary for etching to occur and may be omitted. The UV illumination may be continuous during the process or pulsed, so that ozone loss by UV reaction is minimized.

5. Process control is achieved by control of the reaction temperature (substrate), ozone (or other oxidant) concentration, flow, and pressure, and optionally by UV illumination intensity, wavelength, and modulation. Control of these parameters defines an etch rate for a planar surface. Duration of etch is also affected by the geometry of the desired via and polymer material used. The via diameter and aspect ratio may dictate a longer etch time than needed for an equivalent planar etch to complete.


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6. Process completion may be determined empirically using test samples with the desired geometry or may be determined in situ using proc...