Resist pump buffer tank and method of resist defect reduction

A method of dispensing a resist material on a wafer, the method comprising:

• flowing the resist material from a resist supply through a resist filter to a resist tank structure;
• flowing the resist material from the resist tank structure through a resist pump device to a resist dispensing nozzle;
• dispensing a first portion of the resist material through the resist dispensing nozzle on the wafer;
• generating a circulating flow by directing a second portion of the resist material from the resist pump device back to the resist tank structure via the resist filter;
• and
• continuously flowing from the resist tank structure to the resist pump device and, via the resist filter between the resist supply and the resist tank structure, back to the resist tank structure;
• wherein the resist tank structure is substantially L-shaped and includes a taper-shaped upper tank that is substantially vertically oriented and a taper-shaped lower tank that is oriented at angle θ to the upper tank, wherein an internal width of the upper tank at an upper tank inlet is greater than an internal width of the upper tank at an upper tank outlet, wherein the upper tank outlet and a lower tank inlet are connected each other and have a same cross-sectional area, and wherein an internal width of the lower tank at the lower tank inlet is greater than an internal width of the lower tank at a lower tank outlet.

A method of dispensing a resist material, the method comprising:

• flowing a resist material from a resist supply through a resist filter to a resist tank structure;
• flowing the resist material vertically in the resist tank structure, wherein the resist material continuously flows downward from where the resist material enters the resist tank structure until the resist material exits the resist tank structure;
• flowing the resist material downstream from the resist tank structure through a resist pump device to a resist dispensing nozzle;
• dispensing a first portion of the resist material through the resist dispensing nozzle on a surface of a wafer to form a resist layer;
• generating a continuous circulating flow of the resist material in the resist tank structure and from the resist tank structure to the resist pump device and, via the resist filter between the resist supply and the resist tank structure, back to the resist tank structure;
• and
• determining a number of defects in the resist layer,
• wherein the resist tank structure is substantially L-shaped and comprises a substantially vertically oriented upper tank and a lower tank oriented at angle θ to the upper tank, wherein the resist material continuously flows in the upper tank having an internal portion that is tapered such that an internal width of the upper tank at an upper tank inlet is greater than an internal width of the upper tank at an upper tank outlet,
• wherein the upper tank outlet and a lower tank inlet are connected to each other and have a same cross-sectional area, and wherein an internal width of the lower tank at the lower tank inlet is greater than an internal width of the lower tank at a lower tank outlet.