The ammonia durability of the 157-nm lithography resists is still unclear due to the smaller target dimensions, thinner resist films, and variations in base polymer compared to those of 193-nm and 248-nm resists. It has not been determined what ammonia concentrations must be achieved in order to successfully process 157-nm resists. Until now, the ammonia durability of initial 157-nm resists during post exposure delay (PED) and during post coating delay (PCD) was compared to those of 193-nm and 248-nm resists. It was confirmed that all initial 157-nm resists had low ammonia durability. In this paper, the ammonia durability of newly developed 157-nm resists, that have improved transmittance and resolution, was evaluated during PED and PCD. Then, we found that the ammonia durability of these resists were not enough and that the ammonia concentration from exposure to development should be kept under 0.1 ppb. Thermal desorption spectroscopy results showed that resists with lower ammonia durability tended to have more amount of adsorbed ammonia than other resists. Furthermore, the ammonia durability of 157-nm resist couldn’t be improved to the level of that of 193- and 248-nm resist by the adjustment amount of resist additives. Due to the low ammonia durability, it will be necessary to control the ammonia concentration below 0.1 ppb in processing equipment used in 157-nm lithography.
This paper describes the investigation on the feasibility of current coater/developer processes to the 157-nm lithography from the viewpoint of critical dimension (CD) control. The effect of coating, bake, and development process on the CD of a 157-nm resist, where fluorine is introduced in the side chain, is studied. A KrF and ArF resist is also used for comparison. Firstly, as for the coating process, the coverage performance and the film thickness uniformity of the 157-nm resist shows that the current coating methods are feasible to 157-nm resist, even though the 157-nm resist is highly hydrophobic. Secondly, as for the bake process, the post exposure bake (PEB) temperature dependence of CD for the 157-nm resist is found to be lower than that for 248 and 193-nm resist. This means that our current PEB temperature control system, which is suitable for 248 or 193-nm resist, is also effective for the 157-nm resist. Thirdly, as for the development process, it is found that a static puddle formation process shows a smaller line edge roughness (LER) than a dynamic puddle formation process. Therefore, the static puddle formation process, with the use of linear drive (LD) developer nozzle for instance, is attractive for the 157-nm resist process. Lastly, from the viewpoint of contamination control, it is found that the amine level should be controlled to be less than 0.1ppb in order to prevent the CD change during post exposure delay (PED) for the 157-nm resist.
In a photolithography process, it is vital to control Critical Dimension (CD) within wafer. In the current process, although parameters are controlled during post-exposure bake (PEB) and development, only film thickness is checked before exposure for the CD control. However, as the fine patterning by using chemically amplified resist (CAR) has progressed, CD control within wafer has been affected by very small changes of protecting groups; distribution of additives (PAG, quencher etc.) concentrations, and solvent concentrations, thus it has become more important to control film compositions = film properties before exposure. Following by CD variations within wafer caused by air flow in Post applied Bake (PAB) chamber, we examined evaluation methods of KrF resist film properties and made various evaluations of unexposed film after PAB. This paper describes correlation between CD and PAG, quencher, and solvent concentration; consideration of CD variations mechanism based on the correlation data; and problems when shifting to the next generation process.