This application is a reissue of U.S. Pat. No. 7,537,662, which issued May 26, 2009, from U.S. patent application Ser. No. 10/428,207, filed Apr. 29, 2003.

FIELD OF THE INVENTION

The present invention relates generally to a semiconductor processing apparatus and more particularly, a semiconductor processing apparatus for depositing thin films on a substrate surface.

BACKGROUND OF THE INVENTION

Thin films may be grown on the surface of substrates by several different methods. These methods include vacuum evaporation deposition, molecular beam epitaxy (MBE), different variants of chemical vapor deposition (CVD) (including low-pressure and organometallic CVD and plasma-enhanced CVD), and atomic layer epitaxy (ALE), which has been more recently referred to as atomic layer deposition (ALD) for the deposition of a variety of materials.

In ALD, the sequential introduction of precursor species (e.g., a first precursor and a second precursor) to a substrate, which is located within a reaction chamber is generally employed. Typically, one of the initial steps of ALD is the adsorption of the first precursor on the active sites of the substrate. Conditions are such that no more than a monolayer forms so that the process is self-terminating or saturative. For example, the first precursor can include ligands that remain on the adsorbed species, which prevents further adsorption. Accordingly, deposition temperatures are maintained above the precursor condensation temperatures and below the precursor thermal decomposition temperatures. This initial step of adsorption is typically followed by a first removal (e.g., purging) stage, where the excess first precursor and possible reaction byproducts are removed from the reaction chamber. The second precursor is then introduced into the reaction chamber. The first and second precursor typically tend to react with each other. As such, the adsorbed monolayer of the first precursor reacts instantly with the introduced second precursor, thereby producing the desired thin film. This reaction terminates once the adsorbed first precursor has been consumed. The excess of second precursor and possible reaction byproducts are then removed, e.g., by a second purge stage. The cycle can be repeated to grow the film to a desired thickness. Cycles can also be more complex. For example, the cycles can include three or more reactant pulses separated by purge and/or evacuation steps.

Ideally, in ALD, the reactor chamber design should not play any role in the composition, uniformity or properties of the film grown on the substrate because the reaction is surface specific and self-saturating. However, only a few precursors exhibit such ideal or near ideal behavior. Factors that may hinder this idealized growth mode can include: time-dependent adsorption-desorption phenomena; blocking of the primary reaction through by-products of the primary reaction (e.g., as the by-products are moved in the direction of the flow, reduced growth rate down-stream and subsequent non-uniformity may result, such as when corrosive and less volatile halide products are produced as a byproduct of an ALD process alternating, e.g., TiCl4+NH3to produce TiN); total consumption (i.e., destruction) of the second precursor in the upstream-part of the reactor chamber (e.g., decomposition of the ozone in the hot zone); and uneven adsorption/desorption of the first precursor caused by uneven flow conditions in the reaction chamber.

These problems have been partially alleviated with the use of a showerhead-type apparatus used to disperse the gases into the reaction space, such as disclosed in U.S. Pat. No. 4,798,165. The showerhead-type apparatus, as found in U.S. Pat. No. 4,798,165, may be positioned above a substrate so that the reactants and purge gases flow through apertures that are located on the showerhead and the gas flow may be directed perpendicular to the substrate. However, in such a configuration, in the course of time the reacted gases may form a film in the apertures and the apertures may become blocked. Such blockage may result in uneven deposit of layers onto the substrate.

PCT publication No. WO 00/79019, published Dec. 28, 2000 discloses use of hollow tubes with apertures for ALD deposition. In addition to issues with respect to blockage of the apertures, the disclosed structure contemplates relative rotation of either the substrate or the tubes during deposition. Such a construction leads to the additional issue that, for most efficient saturation of the substrate with reactant, rotation must be calculated to be an integral value in each reactant pulse, limiting flexibility in recipe design and risking non-uniformity. Furthermore, the complexity of rotating elements leads to risks of reactant leakage between rotating parts, consequent particle generation and/or safety hazards.

Thus, there is a need for an improved apparatus and method for depositing thin layers that addresses at least some of the problems described above.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, an apparatus is provided for depositing a thin film on a substrate. The apparatus includes a reaction chamber having a reaction space, a substrate holder, a gas outlet in fluid communication with the reaction space and a gas injector structure positioned with the reaction chamber fixed relative to the substrate during deposition. The gas injector structure includes a first gas injector in fluid communication with a first reactant gas source and a purge gas source, and a second gas injector in fluid communication with a second reactant gas source and a purge gas source. The first and second gas injectors include hollow tubes extending in the reaction space, with a plurality of gas flow apertures spaced along respective tube axes of elongation, where the apertures open to the reaction space.

In one embodiment, the hollow tubes with apertures therein are positioned on opposite sides of the substrate holder. The apertures can face each other or away from one another in different arrangements. A similar third injector can provide a third reactant from a third side of the substrate holder. In another embodiment, the hollow tubes of each injector include tubes branching from distribution tubes on opposite sides of the substrate holder, the branching tubes of the different injectors staggered with one another along an injection plane adjacent a major surface of the substrate. In either of these embodiments, the exhaust can flow through the plane of the injectors. In yet another embodiment, the injectors are hollow tubes extending parallel to one another but stacked upon one another on one side of the substrate.

In accordance with another aspect of the invention, an apparatus is provided for depositing thin films on a substrate. The apparatus includes a reaction chamber, a substrate support and a showerhead rake structure positioned adjacent the substrate support. The showerhead rake structure includes a first gas injector having a first rake in fluid communication with a first reactant source, including a plurality of first fingers extending from and being in fluid communication with a first gas distribution structure. The showerhead rake structure also includes a second gas injector having a second rake in fluid communication with a second reactant source, the second rake including a plurality of second fingers extending from and being in fluid communication with a second distribution structure. Each of the first and second fingers have apertures along a length thereof.

In accordance with another aspect of the invention, a method is provided for depositing a thin layer on a substrate within a reaction space defined by chamber walls. The reaction chamber has a gas feed and removal structure including a first gas injector, a second gas injector, and a gas outlet. The first and second gas injectors comprise elongated tubes disposed within the reaction space and having apertures spaced therealong in fixed relation to the substrate during deposition. The method comprises at least one cycle including the following steps in sequence:a first reactant step including injecting a first vapor phase reactant into the reaction space through the apertures in the first injector while injecting purge gas through the apertures in the second injector;a first purge step including stopping the first reactant injection and injecting purge gas through the apertures in the first and second injectors into the reaction space;a second reactant step including injecting a second vapor phase reactant into the reaction space through the apertures in the second injector while injecting purge gas through the apertures in the first injector; anda second purge step including stopping the second reactant injection and injecting purge gas through the apertures in the first and second injectors into the reaction space.

In one embodiment, gases are exhausted through the elongated tube in route from the substrate to the outlet. Both reactant and purge gas is allowed to diffuse across gaps between the apertures and thereby saturate the substrate in each step. Advantageously, the purge steps can include multiple sequential pulses causing pressure fluctuation, which expedite diffusion between gaps in the apertures, and especially diffusion into deep narrow trenches of the substrate. Similarly, the reactant steps can include multiple sequential pulses causing pressure fluctuations to aid in diffusing reactant across the substrate or into deep, narrow features on the substrate. In one particular arrangement, a booster purge pulse, immediately prior to a standard purge pulse, helps clear reactant from the prior pulse and creates a pressure gradient, while also clearing an inert gas diffusion barrier created by an inert gas valving arrangement.

In accordance with another aspect of the invention, a method is provided for atomic layer deposition. The method includes alternating reactant steps and intervening purge steps in a plurality of cycles, wherein at least some of the purge steps comprise multiple purge pulses. The multiple pulses creating pressure fluctuations within a reaction space.

Further aspects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments.

