The invention relates to cleaning processes of the type incorporating soluble oxidants and, in preferred embodiments, relates to removal of photo-resist (PR) and associated by-products during the cleaning stages of integrated circuit manufacture.
It is well known that gas solubilities in liquid media such as water can decrease with rising temperature. In particular, this has been problematic for cleaning systems based on dissolved ozone. When ozone functions as an oxidant in water, e.g., to effect removal of material from a surface, it can be counter productive to increase the intrinsic reaction rate of the ozone by increasing temperature. That is, when the intrinsic rate increases, the overall speed at which the system operates to remove material does not increase and may decrease, due to reduced solubility of the oxidant at elevated temperature.
In the semiconductor industry many manufacturing steps involve photolithography. Photoresist is commonly patterned and etched on an exposed surface of a partially fabricated semiconductor wafer in order to transfer a feature from a photomask to the surface. The feature, defined in the photoresist, is then transferred into the wafer material through, for example, a selective etch process. By way of illustration, this technique is commonly used to define zones for ion implantation, shallow trench isolation, polysilicon interconnect and Damascene trenches for metallization schemes.
After the PR is patterned and etched, and after the patterned photoresist is used to etch the feature, it is necessary to remove photoresist or byproducts of the reactions. Conventionally, this has been accomplished with a cleaning process based on reaction of ozone with the material to be removed. For example, in a batch process, a group of wafers may be dipped in a solution of water and ozone, possibly under agitation, to effect the removal.
It is generally recognized that the reaction rate for ozone removal of PR and associated byproducts from a wafer surface is limited by diffusion of O3 to near the water/PR interface. Recently it has been observed that the rate of removal can be increased by first placing the wafers in a chamber of elevated temperature. With the wafers positioned above a pool of heated water, water vapor condenses upon the wafer surfaces while O3 is introduced into the chamber. In contrast to performing the reaction while the wafers are immersed in a bath of ozonated water, the wafers above the pool have a limited thickness of water on the surfaces. Since the PR strip rate is limited by diffusion of O3 through the DI water, providing a relatively thinner layer of water for a given partial pressure of O3 gas increases the net amount of O3 diffusion to the water/PR interface; and this will result in an increased reaction rate relative to the reaction rate which would result when the ozone diffuses into a bath of water to reach the PR.
Nonetheless, with both the solubility and the diffusion of the reactant species so limited, the approach of placing wafers over a pool of water to diffuse the species through condensate, at best, provides a rate-limited reaction. If the diffusion rate and overall rate of material removal could be further increased, significant economies may be made available. Specifically, PR removal in a single wafer processing system would become more cost effective.
According to one embodiment of the invention, the removal of material in reactions having limited solubility and diffusion of gaseous material can be increased by controlling the thickness of the layer into which the reactant species diffuses. In another embodiment, the thickness of the layer and the diffusion of the gaseous material can be individually controlled. Apparatus and method are provided.
A flow apparatus is provided for removal of material from a work piece having at least one reaction region containing the removable material. The apparatus may include first and second assemblies positionable in spaced-apart relation to form a zone extending between the two assemblies for movement of gaseous material. The first assembly may include a fixture portion positioned to receive the work piece with the reaction region of the work piece disposed in the zone to allow movement of the gaseous material thereover. A flow assembly is configured to transfer into the zone a gas comprising a condensable material and a reacting species.
According to another embodiment a system is provided for removal of material from a workpiece having at least one surface region containing the removable material. The system includes a chamber, a flow component and a support apparatus. The flow component is configured to pass gaseous material into the chamber at a selectable rate and allow exit of liquid and gaseous materials from the chamber. The support apparatus is configured to position the workpiece thereon with the surface region of the work piece oriented for contact with gaseous material passed into the chamber by the flow component. The system may further include a thermal control configured to provide a differential temperature between a portion of a work piece positioned on the support apparatus and gaseous material passed into the chamber by the flow component.
A method for chemical processing is also provided wherein the thickness of a layer of condensate on a surface is actively controlled and a reactant species is diffused from a gaseous region overlying the surface into the layer. According to an exemplary embodiment for removal of material from a work piece having at least one surface region containing the removable material, a workpiece is placed in an atmosphere comprising a condensable gas and a reacting species. The partial pressure of the condensable gas is controlled to limit the formation of liquid condensation on the surface region.
According to a method for removing unwanted material from the surface of a semiconductor wafer, the wafer is placed in a zone having a controllable atmosphere and gaseous materials including a gaseous reactant and a condensing vapor are passed into the zone for contact with a wafer surface having the unwanted material thereon. The partial pressure of the condensing vapor in the zone is controlled to condense the vapor on the wafer surface at a selectable rate and cover the unwanted material with a condensate layer of desired thickness. The gaseous reactant is allowed to dissolve in the condensate.
In another embodiment for removing unwanted material from the surface of a semiconductor wafer, the wafer is placed in a chamber, gaseous materials including an oxidant and a condensing vapor are passed into the chamber for contact with a surface of the wafer having the unwanted material thereon, and vapor is condensed on the wafer surface at a predeterminable rate to cover the unwanted material with a layer of fluid. The oxidant is allowed to diffuse into the fluid at a selectable rate.
The foregoing background and summary have outlined general features of the invention. Those skilled in the art may acquire a better understanding of the invention and the preferred embodiments with reference to the drawings and detailed description which follow.