Chemical mix and delivery systems and methods thereof

#The present invention relates generally to systems and methods for mixing and/or delivering of liquid chemical(s), and more particularly, to systems and methods for mixing and delivering liquid chemicals in precise amounts using logic devices and multi-reservoir load cell assemblies.

#The present invention has many applications, but may be explained by considering the problem of how to deliver photoresist to silicon wafers for exposure of the photoresist in the process of photolithography. To form the precise images required, the photoresist must be delivered in precise amounts on demand, be free of bubbles, and be of precise uniform thickness on the usable part of the wafer. The conventional systems have problems as discussed below.

#As shown in FIG. 1, a representative conventional photoresist delivery system includes supply containers 100, 102, typically bottles, which supply photoresist to a single-reservoir 104 by line 117, which is connected to supply lines 106, 108 monitored by bubble sensors 110,112 and controlled by valves V1 and V2. The bottom of the reservoir is connected to a photoresist output line 114 to a track tool (not shown), which dispenses photoresist on the wafer. The space above the photoresist in the reservoir 104 is connected to a gas line 118 which, based on position of a three-way valve V3, either supplies nitrogen gas to the reservoir 104 from a nitrogen manifold line 126, regulated by needle valve 1, or produces a vacuum in the reservoir 104. To sense the level of the photoresist in the reservoir 104, the system employs an array of capacitive sensors 122 arranged vertically on the walls of the reservoir 104. A two-way valve V4, located between the nitrogen gas manifold and the inlet of a vacuum ejector 124, supplies or cuts off flow of nitrogen to the vacuum ejector 124.

#FIG. 1 illustrates a chemical delivery system using a single-reservoir and bubble sensors on the supply lines leading to the single-reservoir.

#FIG. 2A is a front cross-section of a first embodiment of the multi-reservoir load cell assembly of the present invention.

#FIG. 2B is a top view of the first embodiment of the multi-reservoir load cell assembly.

#In the first embodiment, the present invention includes a multi-reservoir load cell assembly 200 as shown in FIGS. 2A-2B. The assembly 200 can be part of the system shown in FIG. 3, and can replace the problematic single-reservoir 104 and bubble sensors 110, 112 of FIG. 1.

#In this embodiment, the assembly 200, constructed of Teflon, SST, polypropylene or any chemical compatible material, includes an upper compartment 202, a main reservoir 206, and a buffer reservoir 208, all in an outer housing 212. The buffer reservoir 208 is sealed from the main reservoir 206 by a separator 209, and an o-ring seal 211 seals the perimeter of the separator 209 to the outer housing 212. The separator 209 uses a center conical hole 250 that allows an internal sealing shaft 204 to form a liquid and gas-tight seal with the separator 209. The separator 209 forms a liquid and gas-tight seal to the pneumatic tube 215 with an o-ring seal 210. The main reservoir 206 contains a middle sleeve 214 that forms a rigid separation between the separator 209 and the reservoir cap 205. O-ring 203 seals the perimeter of the reservoir cap 205 seals against the internal surface of the outer housing 212. The reservoir cap 205 seals against the internal sealing shaft 204, the chemical input tube 217, and the pneumatic tubes 215 and 218 with a set of o-ring seals 207, 220, 222, and 224 (hidden, but location shown in FIG. 2B), respectively. Mounted to the reservoir cap 205 is a spacer 244, which also mounts to the pneumatic cylinder 226. The reservoir cap 205 is held in position by the upper sleeve 233 and the middle sleeve 214. The outer Teflon reservoir top 201 is bolted to the outer housing 212 and forms a mechanical hard stop for the upper sleeve 233 and the pneumatic cylinder 226. Pneumatic airlines for the pneumatic cylinder 226 penetrate the outer Teflon reservoir top 201 through the clearance hole 260.

#It should be clear that the present invention is not limited to the delivery of CMP slurries or photoresist on silicon wafers. For example, although the invention shows advantages over the conventional system in this environment, the systems of the present invention can deliver other liquid chemicals for other types of processes. Because the novelty of the present invention extends beyond the nature of the chemical being delivered, the following description refers to the delivery of chemicals to avoid a misunderstanding regarding the scope of the invention.