Methods and apparatus for displacing fluids from substrates using supercritical CO2

The production of semiconductor products often requires wet etching or some other form of wet processing of substrates that involves exposing the substrates to an aqueous-based liquid. After wet processing, the processing fluid and/or any aqueous-based rinsing fluid that remains on the surface of the substrate typically needs to be removed in order to prepare the substrate for the next processing step.

Generally speaking, the wet processing fluid and/or rinsing fluid may be removed by saturating the substrate with a drying fluid (DF) to displace the wet processing fluid. The drying fluid may be alcohol-based, for example, and may include surfactants and/or other adjuncts to maximize displacement efficiency. In order to avoid collapse of fragile structures on the substrate due to capillary forces, additional post-wet-processing step(s) may be performed to dry the substrate in a satisfactory manner.

As semiconductor features become smaller and smaller to accommodate higher device density requirements, there is a critical need for DF removal techniques that will prevent collapse of fragile structures and can satisfactorily dry out the wafer in as short a time as possible.

Supercritical CO 2 has been investigated and employed to facilitate DF removal and avoid collapse of fragile structures on the substrate. CO2 at supercritical conditions (Tc=31 C, Tp=1070 psi) has no surface tension to initiate collapse from capillary forces, and good solubility for several potential drying fluids.

Existing DF removal processes utilizing supercritical CO 2 have shown promising results toward preventing collapse of fragile structures, but often been time consuming, requiring a long time for DF agents and any other remaining residues to be satisfactorily removed. Existing DF removal processes using supercritical CO2 also require a large number of chamber turnovers to satisfactorily flush DF agents and any other remaining residues from the substrate surface, thereby undesirably increasing the total process time and volume of CO2 required, and reducing manufacturing productivity.

In view of the foregoing, improved supercritical CO2-based DF removal processes and apparatuses are desired.

The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

FIG. 1 shows, in accordance with an embodiment of the invention, an example overall view of the DF removal technique employing supercritical CO 2 .

FIG. 2 shows, in accordance with an embodiment of the present invention, a side view of a chamber for efficiently removing drying fluid from substrate surfaces.

FIG. 3 shows, in accordance with an embodiment of the present invention, an exploded side view of a portion of a processing chamber employing nozzles for supercritical CO 2 delivery.

FIG. 4 shows, in accordance with an embodiment of the present invention, an exploded side view of a portion of a processing chamber employing slits for supercritical CO 2 delivery.

The present invention will now be described in detail with reference to a few embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. Many of the descriptions are relevant to a mini-batch drying process, in which multiple wafers are stacked above each other in the pressure chamber, but the principles described are applicable to a single wafer process as well. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention.

The invention relates, in one or more embodiment, to an innovative substrate processing chamber design that employs either a plurality of nozzles or slits arranged such that supercritical CO 2 is flowed across the wafer surfaces with minimum recirculation loops and/or vortices. The innovative processing chamber design, in one or more embodiments, enables DF agents and any other remaining residues to be removed by the supercritical CO 2 in less time and with greater fluid rinsing efficiency.

The features and advantages of embodiments of the invention may be better understood with reference to the figures and discussions that follow.

FIG. 1 shows, in accordance with an embodiment of the invention, an example overall view of the DF removal technique employing supercritical CO 2 . In step 102 , the substrate undergoes wet processing. The particulars of the wet processing step, such as wet etch, will not be described here, but step 102 may represent any wet process in which a substrate is required to be cleaned/dried in subsequent steps 104 and 106 .

Step 104 represents the exposure of the post-wet-process substrate to a drying fluid to aid in the removal of the wet processing fluid and/or an aqueous-based rinse solution. Generally speaking, the drying fluid employed in step 104 may be, for example, alcohol-based although any suitable agent for displacing the wet processing fluid from the substrate may be employed.

Step 106 represents the DF removal step using supercritical CO 2 in accordance with aspects of the present invention. In step 106 , the absence of surface tension and solvent properties of supercritical CO 2 are taken advantage of to remove the DF agent employed in step 104 as well as any etchant residue of step 102 that may be remaining on the substrate surface. In one or more embodiments, both steps 104 and 106 may be performed in the same innovative chamber (discussed below) to minimize substrate transfer and total processing time.

As the term is employed herein, supercritical CO 2 refers to CO 2 that is simultaneously above both its critical temperature (Tc=31.1 C) and critical pressure (Pc=1070 psi) For example, CO 2 will be in its supercritical state at 35 degree Celsius and 1,100 PSI. In one or more embodiments of the invention, the CO 2 pressure is between about 2,000 PSI and about 4,000 PSI. In an embodiment of the invention, the CO 2 pressure is about 3,000 PSI.

As will be discussed later herein, the supercritical CO 2 of step 106 is delivered to the substrate via innovative arrangements that substantially minimize vortices and recirculating loops to improve fluid rinsing efficiency and to reduce the time and CO2 volume required to satisfactorily remove the DF agent and any other remaining residue from the substrate.

To elaborate, vortices and recirculation loops represent stagnant areas of supercritical CO 2 , wherein the fluid velocity of the supercritical CO 2 is substantially reduced. Since the goal is to replace as much of the DF agent with the supercritical CO 2 as quickly as possible, vortices and recirculation loops disadvantageously increase the chamber transient time, thereby increasing the time required and CO2 volume required to dry out the substrate with the supercritical CO 2 .

FIG. 2 shows, in accordance with an embodiment of the present invention, a side view of a chamber 202 that includes a vertical plenum 210 coupled with a plurality of horizontal manifolds 212 , such as horizontal manifolds 212 a , 212 b , 212 c , and 212 d . Although only four horizontal manifolds are shown to facilitate discussion, any number of horizontal manifolds may be employed. As the term is employed herein, horizontal refers to the plane that is parallel to the substrate when the substrate is disposed within the processing volume of the processing chamber. On the other hand, vertical refers to the plane that is perpendicular to the horizontal plane.

Each of horizontal manifolds 212 a , 212 b , 212 c and 212 d is coupled to a plurality of nozzles disposed annularly about the processing volume within which the substrates are disposed for DF agent removal. Thus, there are rows of nozzles connected to the plurality of horizontal manifolds. Each nozzle is connected at one end to its respective horizontal manifold. For example, nozzle 222 is shown coupled to horizontal manifold 212 a , while nozzle 224 is shown coupled to horizontal manifold 212 b . At least one nozzle outlet is disposed at the other end of the nozzle and points inward toward the processing volume within which the substrates are disposed for DF agent removal.

It should be understood that the purpose of the rows of nozzles is to deliver supercritical CO 2 to the surfaces of substrates. In an embodiment, each row of nozzles is disposed such that a flow of supercritical CO 2 is directed in between a pair of substrates that are adjacent (but kept in a spaced-apart relationship). Thus, a single row of nozzles may be employed to clean two surfaces of the two adjacent-but-spaced-apart substrates. However, it may also be possible to dedicate one or more rows of nozzles to each substrate surface.

Supercritical CO 2 enters vertical plenum 210 and then flows to horizontal manifolds 212 a , 212 b , 212 c and 212 d . Each horizontal manifold serves as a conduit to allow supercritical CO 2 under pressure to flow into the row of nozzles connected to it. The nozzle and nozzle outlet sizes are dimensioned appropriately to enable steady streams of supercritical CO 2 to flow across substrate surfaces.

The supercritical CO 2 generally flows across the substrate surface from the nozzle outlets toward an exhaust port of the chamber (typically disposed on the other side of the nozzle). In one or more embodiments, some or all individual nozzles of a nozzle row may be disposed parallelly relative to one another. That is, some or all individual nozzles and/or nozzle outlets may be pointed, in one or more embodiments, such that the streams of supercritical CO 2 emitted by the nozzle outlets flow substantially parallelly across the substrate surface toward the exhaust port of the chamber while minimizing recalculating loops and vortices over the substrate surface. In another embodiment, some or all individual nozzles of a nozzle row may be disposed non-parallelly relative to one another such that the supercritical CO 2 may exit individual nozzle outlets at different angles relative to the center-of-horizontal-manifold-to-exhaust port vector.

In one or more embodiments some or all nozzles of a nozzle row may be pointed such that the supercritical CO 2 is directed in a plane that is parallel to the surface of the substrate or may be directed toward or away from the substrate surface. In one or more embodiments, the nozzle row may comprise different segments and/or the nozzles in a nozzle row may be non-planar when viewed in the direction from the substrate center toward the horizontal manifold. Given the system proposed herein, the optimization of the nozzle size, nozzle outlet size, the direction pointed by individual nozzles may be performed using empirical data to ensure that supercritical CO 2 is delivered with minimal vortices and recirculating loops.

Generally speaking, the total flow mass of supercritical CO 2 is governed approximately by Eq. 1 below.

TMF=( C )×( N )×( a )  Eq. 1

where C is a constant that is specific to the supercritical CO 2 in the application, N is the number of nozzles, and (a) is the cross-section area of each nozzle. Total mass flow (TMF) is a product of C, N, and a.

Furthermore, it has been found that fluid rinsing efficiency tends to be improved when N is large and a is small for any given total mass flow. Considerations such as uniformity of supercritical CO 2 delivery by the nozzles arranged along a nozzle row needs to be taken into consideration. In an embodiment, the nozzle outlets may have different sizes or the horizontal manifolds may have non-uniform cross-sections from one end to another and/or from horizontal manifold to horizontal manifold to minimize pressure gradients in the nozzle outlet pressures among nozzle outlets of a particular nozzle row or from nozzle row to nozzle row. The goal is to deliver uniform supercritical CO 2 flow to/over/across all relevant areas of all substrate surfaces with minimal circulation loops or vortices and minimal differences from substrate surface to substrate surface in a batch.

FIG. 3 shows, in accordance with an embodiment of the present invention, an exploded side view of a portion of a processing chamber, including a chamber wall 302 , a vertical plenum 304 , and a plurality of horizontal manifolds 306 , 308 , and 310 . Each horizontal manifold, e.g., horizontal manifold 306 , is coupled to a plurality of nozzles forming a nozzle row. For illustration purposes, nozzle 320 is shown coupled to horizontal manifold 306 .

Nozzle 320 also includes a nozzle outlet 322 for ejecting supercritical CO 2 into the processing volume within which the set of substrates (either single substrate or a batch of substrates stacked parallelly in a spaced-apart relationship) is disposed. The nozzle outlets are sized to produce high impinging velocities and to reduce residence time of fluids. In one or more embodiments, the nozzle outlets are set flush with the interior surface of the chamber walls to simplify maintenance/cleaning and to reduce particulate contamination concerns.

As discussed earlier, improved DF agent flushing, reduced vortices, reduced recirculation loops, reduced DF agent removal time, and reduced CO2 usage may be achieved when the number of nozzles is large (see Eq. 1). In one or more embodiments, individual nozzles of a nozzle row are replaced by a slit that is configured to eject supercritical CO 2 as a sheet instead of as individual streams as in the case with nozzles. FIG. 4 shows, in accordance with an embodiment of the present invention, an exploded side view of a portion of a processing chamber employing slits for supercritical CO 2 delivery, including a chamber wall 402 , a vertical plenum 404 , and a plurality of horizontal manifolds 406 , 408 , and 410 . Each horizontal manifold, e.g., horizontal manifold 406 , has at least two openings: an opening toward the processing volume within which the set of substrates are disposed to function as a slit from which supercritical CO 2 can be ejected, and one or more openings that couple the horizontal manifold to the vertical plenum to permit supercritical CO 2 to flow from the vertical plenum to the horizontal manifold to be discharged toward the processing volume via the slit.

For illustration purposes, slit 420 is shown coupled to or formed integrally with horizontal manifold 406 for ejecting supercritical CO 2 into the processing volume within which the set of substrates (either single substrate or a batch of substrates stacked parallelly in a spaced-apart relationship) is disposed. In one or more embodiments, the slits are set flush with the interior surface of the chamber wall to simplify maintenance/cleaning and to reduce particulate contamination concerns.

When a slit is employed, the number of nozzles may be thought of as being infinite between two ends of the slits. As a result of a high N value (see Eq. 1), it has been found that the slit design tends to result in high fluid rinsing efficiency, low chamber turnovers, and reducing or eliminating vortices and recirculation loops in the supercritical CO 2 flow. In one or more embodiment, the slits may be about 0.005″ wide although this is not an absolute requirement or a limitation of the present invention.

As can be appreciated from the foregoing, embodiments of the invention result in a highly uniform flow of supercritical CO 2 with low or no recirculation loops and/or vortices. The result is more efficient chamber turnovers and reduced time required for satisfactory DF flushing. In turn, the overall substrate process time may be reduced, leading to improved productivity for semiconductor manufacturers.

Having disclosed exemplary embodiments and the best mode, modifications and variations may be made to the disclosed embodiments while remaining within the subject and spirit of the invention as defined by the following claims.