The field of the invention is plating substrates such as semiconductor material wafers.
Microelectronic devices such as semiconductor devices are generally fabricated on and/or in substrates or wafers. In a typical fabrication process, one or more layers of metal or other conductive materials are formed on a wafer. A large number of variables can affect the quality, uniformity and other characteristics of the plated metal layer, which in turn influences the yield, or the amount of good micro-scale devices obtained from the wafer. These variables may include plating time, plating current profile, electrolyte quality and additives, wafer surface and wetting characteristics, and others. As the size of micro-scale devices continue to get smaller, improved electroplating processors and methods are needed.
In the drawings, the same element number indicates the same element in each of the views.
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Alternatively, the backing plate or other components of the rotor may be heated using hysteresis and/or eddy current heating. In this case, the backing plate material may be selected to provide preferred heating characteristics, without use of individual discrete heating components. In an alternative design the heaters 60 may be replaced by coolers, for example thermoelectric coolers. In this design, the backing plate is cooled in turn cooling the wafer.
Alternatively the backing plate 30 may have through openings to allow the lamps 70 to shine directly onto the back side of the wafer. In another design, the backing plate 30 may have built in windows adapted to allow the heating radiation to pass through. In another design, the back side of the wafer may be heated by supplying a heated liquid or gas to the backing plate 30, or onto the back side of the wafer 50, optionally via the shaft 22, with a back side seal sealing the heated liquid within the rotor. Chilled liquid or gas may also be used to cool the back side of the wafer.
In an example of use, the front side of the wafer is moved into contact with the bath of electrolyte in the bowl 16. Electrical current is supplied to one or anodes in the bowl 16. The wafer is electrically connected to a cathode via the contact ring 42. The current flows through the electrolyte causing metal ions to plate out on the front side of the wafer, creating a metal layer. The heaters 60, lamps 70 and/or heating liquid may be used to heat the back side of the wafer. Since certain chemical reactions increase with temperature, certain plating characteristics may be improved. Specifically, heating the back side of the wafer may allow for better control of the plating reaction kinetics and mass transfer of metal ions onto the wafer, without changing the electrolyte bath. The wafer may optionally be heated or cooled to a temperature different from the temperature of the bath. In some methods, a temperature gradient may be maintained in the wafer. Heating the wafer during plating may also improve the plated metal film grain structure.
Heating the wafer may improve metal ion diffusion for high aspect ratio features. Mass transfer within vias of high aspect ration features is often limited to diffusion as the dominant mechanism. By increasing the temperature within the via, mass transfer may be improved because diffusion is temperature dependent. By heating the back side of the wafer, the bottom of a trench, via or other feature may be raised to a temperature slightly higher than the front side surface temperature, because the bottom of the trench is closer to the heat source. The temperature can therefore be used to affect diffusion and reaction kinematics at the bottom of the feature.
Heating may improve plating in areas that are denser or more open, which have more seed layer exposed to plating, and less photoresist. If photoresist is more insulative, more heat may be channeled to the more open areas. The increased temperature may increase the layer thickness in a dense region, which may improve within die (WID) uniformity. Heating also reduces surface tension, which may improve wetting during dwell steps. Heating may also improve mixing of the bath solution with water from a pre-wet step, to improve plating uniformity.
In some applications, the amount of heating may be limited by the thermal budget of the front side of the wafer. The methods described may optionally be used in face-up or face-down plating. In face-up plating, warmer electrolyte rising from the bottom of a via may aid in mixing and diffusion. The methods described may be used in bumping, RDL (redistribution layer) as well as TSV (through silicon via) plating.
The term wafer as used here means a substrate or workpiece on which microelectronic, micro-mechanical, micro-electromechanical, and/or micro-optical devices are formed. The methods described here may also be performed using other types of processors different from the processors shown in
Thus, novel methods and apparatus have been shown and described. Various changes and substitutions may of course be made without departing from the spirit and scope of the invention. The invention therefore should not be limited except by the following claims and their equivalents.