Patent Application
20080081114
In the following detailed description of the present invention, numerous specific embodiments are set forth in order to provide a thorough understanding of the invention. However, as will be apparent to those skilled in the art, the present invention may be practiced without these specific details or by using alternate elements or processes. In other instances, well-known processes, procedures and components have not been described in detail so as not to unnecessarily obscure aspects of the present invention.
Introduction
As indicated, the present invention provides an apparatus and associated method for conducting a chemical deposition. The apparatus and method are particularly applicable to use in conjunction with a semiconductor fabrication based dielectric deposition process that requires separation of self-limiting deposition steps in a multi-step dielectric deposition process (e.g., pulsed layer deposition (PDL) processing for catalyst and silicon precursor deposition), however they are not so limited and can be used with other chemical deposition techniques and in other application where uniform delivery of a fluid (in a gaseous or liquid state) to a substrate surface is desired. In some instances, the apparatus and process of the invention are described below with reference to PDL embodiments. However, it should be understood that the invention is not necessarily so limited.
Generally, a PDL process involves sequentially depositing a plurality of atomic-scale films on a substrate surface by sequentially exposing and removing reactants to and from the substrate surface. An exemplary case of PDL processing using reactant gases A and B will now be used to illustrate principle operations of a PDL process in accordance with the present invention. First, gas A is injected into a chamber and the molecules of gas A are chemically or physically adsorbed to the surface of a substrate, thereby forming a “saturated layer” of A. Formation of a saturated layer is self-limiting in nature and represents a thermodynamically distinct state of adsorbed A on a surface. In some cases, a saturated layer is only one monolayer. In other cases, a saturated layer is a fraction of a monolayer, or some multiple of monolayers.
After a saturated layer of A is formed, typically, the remaining gas A in the chamber is purged using an inert gas and/or pumped using a vacuum pump. Thereafter, the gas B is injected so that it comes in contact with the adsorbed layer of A and reacts to form a reaction product of A and B. Because the saturated layer of A is nominally thin and evenly distributed over the substrate surface, excellent film step coverage (i.e., conformal films) can be obtained. B is flowed over the substrate for a period of time sufficient to allow the reaction between A and B to preferably go to completion; i.e., all of the adsorbed A is consumed in the reaction. In a PDL process, B is flowed over the substrate for a period of time sufficient for a large enough quantity of B to be exposed to the substrate, resulting in a film formation in excess of one monolayer. After a desired quantity of B is delivered, the flow of B is stopped. There may be an optional soak time after stopping the delivery of B, to allow enough time to fully complete the reaction. At this point, residual gas B and any byproducts of the reaction are purged and/or pumped from the chamber. Further PDL cycles of substrate exposure to A, followed by exposure to B, can be implemented and repeated as needed for multiple layers of material to be deposited. Another deposition technique related to PDL is atomic layer deposition (ALD). PDL and ALD are both surface-controlled reactions involving alternately directing the reactants over a substrate surface. Conventional ALD, however, depends on self-limiting typically monolayer-producing reactions for both reactant gases. As an example, if reactants C and D are first and second reactant gases for an ALD process, after C is adsorbed onto the substrate surface to form a saturated layer, D is introduced and reacts only with adsorbed C. In this manner, a very thin and conformal film can be deposited. In PDL, as previously described using exemplary reactants A and B, after A is adsorbed onto the substrate surface, B reacts with adsorbed A and is further able to react to accumulate a self-limiting, but much thicker than one monolayer film. Thus, as stated previously, the PDL process allows for rapid film growth similar to using CVD methods but with the conformality of ALD methods.
PDL methods are related to the well-established chemical vapor deposition (CVD) techniques. However, in CVD, the chemical reactant gases are simultaneously introduced in a reaction chamber and allowed to mix and chemically react with each other in gas phase. The products of the mixed gases are then deposited on the substrate surface. Thus, PDL processing methods differ from CVD since in PDL the chemical reactant gases are individually injected into a reaction chamber and not allowed to mix prior to contacting the substrate surface. That is, PDL is based on separated surface-controlled reactions.
The station 100 generally includes a seal 105 at the point of engagement of the pedestal 103 and showerhead 106 modules to facilitate station closure. While closed, there can be a separate flow of precursors to and a separate vacuum evacuation from the deposition region, the microvolume 102. Fluid chemical reactants, such as precursors or catalysts for dielectric or other films, are introduced into the microvolume from a source (or sources) via an injection inlet 109. An advantage of this configuration is that the total volume inside the station 100 is much smaller than the main reactor volume. For example, using a 2-3 mm gap between the wafer and the lower surface of the showerhead and a 300 mm wafer, the total volume of the station may be less than about 0.25 L.
In accordance with the present invention, a diffuser 110 is located at the distil end of the fluid injection inlet 109 relative to the fluid source. The diffuser 110 is an apparatus having a plurality of fluid passages between the distil end of the fluid injection inlet 109 and the microvolume 102 where the substrate 101 to which fluid reactants are to be delivered resides. In specific embodiments, the substrate 101 is a semiconductor wafer and the fluids reactants are precursor gases for a film to be formed on the substrate, such as a dielectric film in a blanket dielectric deposition or gap fill operation. The fluid passages of the diffuser 110 connect one or more injection points to a greater number of exit points (X injection points to Y exit points where Y>X). The plurality of fluid passages have substantially equal effective flow resistance. That is, the plurality of fluid passages are configured such that fluids (gases or liquids) entering the diffuser 110 have the same residence time; fluids entering the diffuser together are evenly distributed across the plurality of passages and exit the diffuser together with the substantially same mass flux at each exit point. This is the case under all flow conditions, including subsonic, transient, and supersonic. In this way, the diffuser 110 uniformly distributes materials, in the process chamber of the integrated circuit manufacturing equipment for example.
In operation of a chemical deposition (film deposition) system, the diffuser 110 is engaged with the showerhead module 106 and above the substrate (e.g., wafer) 101, which is located in the pedestal module 103. The showerhead module 106 may also optionally include a faceplate 112 located between the diffuser 110 and the pedestal module 103/wafer 101. The faceplate 112 has uniformly distributed holes configured to enhance uniform flux of fluid exiting the diffuser exit holes. Both the diffuser 110 and the optional faceplate 112 optimally configured so that their diameters match the diameter of the wafer 101. This facilitates uniform material delivery throughout the microvolume 102 and thus to the wafer surface, although it may not always be the case
The diffuser 110, optional faceplate 112 and other components of the apparatus and system may be made of any suitable material(s), such as are known in the art. In particular, the diffuser 110 and faceplate 112 may be made of metal, ceramic or polymeric materials with physical and chemical properties suitable for the chemical deposition environment. Aluminum is one such suitable material.
Fluid material, such as a dielectric precursor gas, enters the showerhead 106 though the injection inlet 109 and flows into the diffuser 110, spreading between multiple passages. As the fluid progresses through the diffuser passages the pressure gradually decreases. This gradual reduction in fluid material pressure from stage to stage renders the apparatus less susceptible to the material passage cross-talk (material leakage from a high pressure fluid passage to a low pressure fluid passage) and facilitates uniform distribution of the fluid exiting the diffuser 110 which leads to uniform mass flux to the microvolume 102 above the substrate target area. The diffuser may comprise one (a single layer) or multiple (a plurality of stacked layers) layers of material to form the passages.
In the embodiment illustrated in
Stage 1, the high-pressure stage, has a fluid material injection point 305 common to all the passages that ultimately exit through the exit holes 350 of low pressure stage 3 and several different passages 310 emanating from it. There are three different passage sizes to source flow to three effective areas, as shown in stages 2 and 3. The passage widths are different to accommodate a different amount of flow so that the flow to each of the different regions is substantially the same. Stage 2, the mid-pressure stage, has passages 320 that link the passages 310 of stage 1 to those 330 of stage 3, the high pressure stage. Stage 3 also has the distribution holes 350 from which the fluid exits the diffuser.
In this embodiment, the low-pressure stage 3 is designed to have substantially identical passage geometry to insure equal flow distribution under any flow conditions. To insure the material uniform flow distribution, all passages on this stage have equal shape, equal cross-section and equal length. The passages are straight (without bends and curves). In some embodiments, straight passages are preferred since this makes their conductance less susceptible to variations under all flow conditions. Straight passages are easier to design and cheaper to manufacture in comparison with bended and curved ones. Additionally, they may have more predictable flow characteristics. The distribution holes at the end of the passages have equal diameter. In other embodiments, the passage may have different geometry and the distribution holes may have different diameters as long as they have substantially equal effective flow resistance and deliver substantially equal mass flux.
The arrows illustrate the flow of fluid material through the stages of the diffuser in operation to show how the material is evenly distributed. A fluid material, such as a precursor gas, flows from the injection point 305 into inlets to each of the passages 310 in the high pressure stage 1. The fluid flows into the passages 310 through to the outlet holes at the end of the passages on that stage. When the material reaches the outlet hole of the passage in one stage (e.g., stage 1, high pressure), it flows through the hole into the next diffuser stage (e.g., stage 2, mid pressure), spreads between two or more passages and through holes into next diffuser stage (e.g., stage 3, low pressure). Ultimately, the fluid material exits the diffuser through distribution holes of the final stage (e.g., stage 3) equally spaced to insure the uniform material flux towards the substrate. The effect of the diffuser is that material entering the diffuser at the single injection point 305 in stage 1 cascades through the passages and leaves the diffuser at stage 3 uniformly distributed through the 54 distribution holes.
In the previously illustrated embodiments, the distribution holes in the low-pressure stage have a cylindrical shape. Such a geometry is acceptable in accordance with the present invention, particularly when a faceplate is used in conjunction with the diffuser. However, these holes may also be conically or otherwise shaped to minimize a jet effect of the exiting material and create a flow smoothing effect equivalent to the effect of a faceplate.
As noted previously, a diffuser in accordance with the present invention may be optionally supplemented with a faceplate to smooth out the jet effect of the diffuser exit holes and further facilitate uniform fluid distribution from the diffuser. Such a faceplate has a large number of holes, much larger than the number of distribution holes exiting the diffuser (e.g., thousands of holes). Use of a faceplate can improve performance in some circumstances, but may not be necessary in others, such as where the jet effect of the distribution is addressed by tailoring the shapes of the holes (e.g., making them conical).
A diffuser in accordance with the present invention can be integrated into a film deposition system having a substrate for film deposition, for example a PDL system for depositing silicon-containing dielectric for gap fill in semiconductor processing. The fluid passage configuration is such that during operation of the system the substrate surface is exposed to a substantially uniform mass flux. In this embodiment, and others of this sort, the fluid flux can be a dielectric film precursor gas flux. In some implementations, the region of substantially uniform fluid flux may extend beyond the substrate surface, for example to address edge effects.
The present invention provides a diffuser and associated apparatus and method of use that enables uniform fluid delivery to a substrate. The invention has particular benefit in chemical deposition applications where deposition is extremely rapid, and therefore the transient flux when a fluid reactant is first introduced is important to the uniformity of the deposition process. In such cases it is generally optimal for all parts of the wafer to be exposed to equal quantities of fluid reactant (e.g., dielectric precursor gas), especially during the initial filling of the deposition chamber (e.g., microvolume). Use of the apparatus and method of the present invention achieves this goal, thereby improving the quality of the resulting deposited film.
Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing both the process and apparatus of the present invention. For example, while the invention has been described primarily in terms of preparing integrated circuits, it is not so limited. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.
All documents cited herein are hereby incorporated by reference in their entirety and for all purposes.
