The use of immersion tank processes in photolithography has decreased due to excessive material consumption, non-uniform resolution, and poor clearing from high-aspect-ratio features. Spin developing has become the more popular method for development of features in photolithography, with three main methods emerging: puddle/stream dispense, side spray dispense, and direct spray dispense. The side spray dispense has become the most popular option, as it allows for a variety of wafer sizes, materials, and feature sizes, while direct spray dispense is useful for continuous-spray applications and accelerated development of thick films with high aspect ratios.
Development of features is a critical process step in photolithography. There are several processes to perform this step such as tank (bath) immersion and spin developing.
The use of immersion tank processes has steadily declined in MEMS fabrication and advanced lithography over the past decade due to excessive material consumption, non-uniform resolution, and poor clearing from high-aspect-ratio features. Additionally, increased throughput requirements and smaller features have further shifted mainstream applications to spin developing. As the popularity of the spin developing has grown, three main methods have emerged.
The most common and oldest process is the stream/puddle dispense. Developer is dispensed into a puddle at the center of the wafer. The wafer is then spun at low speed (0-50 rpm) long enough for the developer to cover the entirety of the wafer. The rotation is then stopped allowing the chemical reaction to dissolve the soluble areas of the patterned film. This process is very popular for thin films ≤ 1 µm thick and/or for small wafer applications. For thick films and/or high-aspect-ratio features, the stream puddle step may be repeated over several iterations to reapply fresh developer. However, this method is problematic for many of today’s process requirements. Often features along the wafer perimeter are underdeveloped, and center features are over-developed due to the inherent over exposure of a puddle dispense.
Side Spray Dispense
The use of side-angle spray nozzles (45º) significantly enhances fluid deposition uniformity. The standard configuration utilizes two side-spray nozzles to evenly apply developer solution across the substrate. These nozzles are positioned to spray from the center of the wafer out. The side spray nozzles are factory positioned outside the wafer plane and ensure uniform deposition for many substrate sizes. Cee® recommends the side spray dispense option for aspect ratios up to 5:1.
Direct Spray Dispense
Direct-angle nozzles (90º) are often used for continuous-spray applications and allow accelerated development of thick films (5-100 µm) with features having high aspect ratios greater than 5:1. The direct angle provides sufficient agitation to penetrate the film and remove soluble material.
Over the years, the direct spray dispense has become the most popular option as it allows for a variety of wafers sizes, materials, and feature sizes. Cee® Developers use direct spray dispense as the standard setup configuration.
The Cee® Apogee® Spin Developer can be configured to accommodate process techniques including stream, spray, or direct spray dispense. As the predominant lab-scale equipment supplier for advanced R&D and prototyping, the Cost Effective Equipment product team is eager to meet your specific application needs. Contact us today for more information!