A new generation i-line optical stepper utilizing the established benefits of the lx Wynne-Dyson lens design has been developed for mix-and-match lithography. Based on the advantages of cost of ownership and high throughput capability, the Ultratech 2244i was specifically designed as a cost effective approach to complement high NA reduction steppers in a mix-and-match environment, especially for high volume DRAM and ASIC manufacturing. This system features an ultra-large image field of 22 x 44mm with a 0.32 numerical aperture lens with an illumination bandwidth of 20 nanometers (355 to 375nm). As a result, this system provides O.8im manufacturing capability. These features provide improved critical dimension (CD) interference effects and superior depth-of-focus for the 2244i.Applying i-line lithography at lx offers a number of advantages compared to reduction steppers. For example, a critical area of concern in i-line lithography is the impact of thin film interference effects, which typically limits CD control performance. The relatively large bandwidth of the 2244i lx lens suppresses interference effects as compared to narrowband reduction systems. Both lithography simulations and empirical results of linewidth control as a function of resist film thickness variations will be shown in order to depict the relative system immunity to film thickness effects.An additional major challenge associated with increasing numerical apertures of any steppers is limited depth-of-focus. The comparatively low NA of this lx i-line system alleviates this problem, while providing 0.8 micron resolution with greater than 2.0 micron depth-of-focus across the large image field. Excellent critical dimension control for intrafield, interfield, and interwafer conditions will be demonstrated. Swing curves depicting linewidth control through focal plane and resist thickness variations will be shown for both experimental data and lithographic simulations. In addition, simulations of reduction stepper performance will be provided to graphically illustrate the superior CD control of the 2244i.

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As the semiconductor industry moves into deeper sub -quarter micron regime, minimization of post develop process defects is of paramount significance in manufacturing environments. Reduced defect levels can significantly increase the yield in production, resulting in substantial cost savings and also reduce time to market of new devices. Typical approaches to reduce defect levels include extension of the DI (De-lonized water) rinse time immediately after completion of photoresist development, use of multiple rinse steps and variable rinse spin speed. However, many of these penalize the process throughput. The uniqueness of this project was the use of enhanced rinse hardware with a mechanistic understanding and characterization of defect generation for an advanced DUV resist.Numerous studies have identified the development step as the source of the majority of the post-development particles and residues. Thus improving the development-and-rinse step can potentially reduce particle contamination. Defect reduction was accomplished thorough process characterization of defect sources and also through implementation of enhanced rinse hardware. Our enhanced hardware provides an improved rinsing action and a more uniform coverage and reduces the impact forces near each orifice through its optimized geometry. A partial-six factor DOE (Design of Experiment) was implemented with a resolution of first order terms and 2nd factor interactions. Factors examined included rinse spin speed, rinse time, acceleration during dry cycle, nozzle type, rinse time algorithm and chemical injection time The processing system was an advanced SVG Track clustered with a Micrascan II system. This project successfully characterized defect density performance and located the lowest defect level and shortest rinse time from a develop process standpoint, without any impact on CD's. The defect density levels were reduced by a factor of 7 and the develop process time was reduced by 23 %. This was qualified for 0.2-micron defect sizes and larger which is applicable to .25 micron lithography. The yield impact of this defect reduction for killer defects is significant cost savings. In addition, the reduced develop process time can significantly increase the throughput because the develop process is the rate limiting step in a Track system.

Modem package designs generate a large amount of stress on the die which can be controlled using a thick film of polyimide over the passivation layer. Polyimide film thicknesses in excess of twenty microns at exposure are becoming common for very thin packages. The standard polyimide lithographic process frequently utilizes a trilayer film consisting of an adhesion layer, a polyimide film, and photoresist. A major advance in polyimide technology occurred with the introduction of photosensitive polyimide materials. These materials reduce the total number of process steps in the polyimide process. They also offer the opportunity to combine the passivation and polyimide lithography steps into one process level resulting in significant process simplification and manufacturing cost reduction. Consequently, there is a rapid increase in the use of photosensitive polyimides in the semiconductor industry.There are a number of important issues associated with photosensitive polyimide processing. Because most photosensitive polyimides are negative tone, residual film formation has a major impact on resolution and the usable process window. The high exposure doses required for thicker polyimide films exacerbates the residual film problem. Also, resolving small features such as fuse windows in DRAMs is frequently required in thick photosensitive polyimide layers. These small features result in polyimide height-to-linewidth aspect ratios that are comparable to many photoresist applications. Because of these requirements, photosensitive polyimide applications could benefit from detailed process characterization to enhance resolution and increase process latitude. Unfortunately, there is scant literature pertaining to lithographic performance and lithographic process modeling for photosensitive polyimide films.An extension of basic photoresist characterization techniques for thin films can be applied to thick photosensitive polyimide processes. The develop rate characteristics and lithographic performance for several commercial photosensitive polyimide products were studied at a thickness of 12 microns. Cross sectional SEM analysis, Bossung plots, and film retention plots are used to establish relative lithographic capabilities. These experimental results are used to study the effects of polyimide physical and chemical properties on lithographic performance. O-8194-2102-2/96/$6.OO SPIE Vol. 2726 / 169 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/23/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

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