Conducting structures integrated into semiconductor devices needs to be electrically insulated from other parts of the device to ensure reliable functioning of the semiconductor device. Examples of such conducting structures are field electrodes and gate electrodes which are insulated from the semiconductor substrate by insulation layers such as oxide layers. In trench MOSFETs the gate electrodes and source electrodes are usually formed of doped polysilicon. Despite high doping, the resistivity of the electrodes can become very high for small lateral dimensions. The high resistivity may limit the shrink of the trench and cell pitch, and especially for low voltage MOSFETs the RDS(on) reduction
As switching of a potential applied to the conducting structures at high frequency may occur, it may be desirable to form the conducting structures or at least some of the conducting structures of a material having a low resistivity. However, use of a material having a low resistivity may reduce a thermal budget for subsequent processing steps. This may be especially disadvantageous for a field electrode made of metal, since the field electrode is usually formed before forming the gate oxide. The gate oxidation usually has a temperature budget, which is not compatible with the metal electrode being formed before.
In view of the above, there is a need for improvement.