surfaces curved surfaces or inclined surfaces in embodiments the head section is cone shaped to facilitate insertion of the chuck assembly into the substrate in embodiments the space defined by the head section ranges from about 20 to about 90 of the volume of the head section the present invention may be advantageous in embodiments the presence of space 40 in the head section increases the volume of the closed area i e the trapped air volume within the substrate interior between the coating solution and the chuck assembly such an increased volume of the closed area decreases the buildup of pressure caused by vapor e g solvent evaporation from the coating solution thereby reducing the occurrence of the u201c burping u201d phenomenon in addition the space 40 reduces the thermal mass of the chuck assembly to produce uniform coatings it is advantageous for the substrate to have uniform temperature profiles throughout all the processing steps since the chuck assembly acts as a heat sink it is desirable to minimize the thermal mass of the chuck assembly thus reducing its effect on temperature uniformity additionally this reduction of thermal mass will reduce the transfer of heat to the entrapped gas which will reduce the gas expansion burping operation of the chuck assembly depicted in fig1 proceeds as follows the width changing apparatus 8 is depressed downwards via pressure on top cap.