PGSD is one of the solutions as a developer of 70 nm node generation mask fabrication. To make 55 nm node generation mask, CD error induced by loading effect (loading-effect-induced CD error) must be reduced. As is generally known, primary cause of loading effect is dissolution products that hinder the progress of development.
We think that it is the key in development technology to control movement of dissolution products and to disperse dissolution products uniformly for minimizing the loading-effect-induced CD error.
In this paper, we propose a new concept and procedure to optimize the movement direction and the amount of dissolution products.
CD error caused by loading effect is becoming a significant issue in mask fabrication. At the same time, quantification method of CD error caused by loading effect has not been established in many cases because it is very difficult to measure the error according to various coverages. In previous studies, we presented the development equipment named PGSD (Proximity Gap Suction Development). PGSD can reduce loading error of development process by using of nozzles to spout developer and suck in dirty developer. However, in the case of using PGSD for development process, CD error caused by loading effect seems to still remain.
In this paper, we propose a new method to quantify the error caused by loading effect, and estimate the development-induced error out of total CD error. We evaluated 70 nm NAND mask by investigating the correlation between CD and coverage. Moreover, we discuss the residual CD error excluding the loading effect.
In recent years, more precise pattern dimension control (CD control) on a photomask has been required than ever as finer-line of IC pattern progresses. In the case of the conventional development (spray-development, puddle-development), CD control is difficult due to loading and micro-loading effect. The "loading and micro-loading effect" refers to the differences of exposed area around the pattern.
The low pattern density generates numerous dissolution products and decreases the concentration of developer. This phenomenon changes resist dissolution rate and causes difficulties in controlling the CD. To solve this problem, we have been developing a new type of developer, called "Proximity Gap Suction Development (PGSD)." Nozzle of PGSD has five slits; opening for supplying developer is in the center, two suction slits are on the both sides, and two slits for rinse are on the very end. The proximity gap is kept between the nozzle surface and resist during development. Contaminated developer is immediately sucked/removed and stable development can be achieved by the continuous dispense of fresh developer at high speed. Thus, a desired pattern size can be obtained without loading and micro loading effect. We reported the principle of PGSD at BACUS in 2002. In this thesis, we would like to report the following topics.
(1) System overview of α machine, which we are currently developing.
(2) Effect of the PGSD on CD uniformity and the number of defects.
CDs of photomasks include errors caused by photomask-making processes, namely, writing process, baking process in chemically amplified resist, resist development process, and etching process. Recently, the conventional resist develop methods, such as spray development, have raised issues concerning uneven pattern density on photomasks. Dependency of resist coverage is caused by low solubility of developer containing dissolved resist. In the ideal development process, only fresh developer would be on the resist surface at all times. To realize this ideal development process, we propose a development method, Proximity Gap Suction Development (PGSD), based on a new concept. PGSD involves the use of a scanning nozzle having five slits located in its surface facing the resist surface, a scanning mechanism keeping proximity gap between resist surface and the nozzle surface with slits, and a photomask holder. The nozzle is scanned from end to end of photomask on the holder. Developer spouts from a center slit of the nozzle. Slits at both sides of the center slit suck developer on resist surface with rinse fluid spouting from slits located outside of suction slits on the nozzle. Because proximity gap is kept between resist surface and the nozzle surface, spouted fresh developer reaches resist surface directly and it runs over resist surface at high speed. Then, developer on resist surface is excluded immediately with rinse fluid by suction slits. PGSD can produce CDs of resist pattern controlled precisely on photomask having uneven pattern density. We report details of the PGSD system, and compare the results for CDs obtained by PGSD with those obtained using the conventional method.
The loading effect is becoming a great issue in mask fabrication. To reduce CD error due to resist load, we have developed a developer based on a new concept, Proximity Gap Suction Development (PGSD), involving the use of a nozzle to spout developer and suck in dirty developer. In this paper, the performance of PGSD is reported.
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