Patent Application
20150211126
The present invention relates to methods and systems for delivering and vaporizing solution based precursors for use in atomic layer deposition processes.
Moore's law predicts the long-term trend whereby the doubling of the number of transistor that can he inexpensively on an integrated circuit occurs approximately every two years. The capabilities of digital electronic devices, e.g. processing speed, memory capacity, etc. have been strongly linked to Moore's for the last half century and is expected to continue for several more years.
However, as semiconductor devices continue to get more densely packed with devices in accordance with Moore's law, channel lengths have to he made smaller and smaller and chip performance will have to he enhanced while reducing unit costs. To meet these needs, new materials for use in conjunction with silicon-based IC chips will need to be developed and used. For example, the use of transition metals and lanthanide metals has been suggested for USC in critical functionalities of electronic devices. Oxides of these metals may he used to replace the current SiO2 and SiON gate dielectrics as they can he deposited as ultra thin, effective oxide thickness less than 1.5 nm, high-k oxides. Examples of high-k materials that have acceptable properties, such as high band gaps and band offsets, good stability on silicon, minimal SiO2 interface layers, and high quality interfaces on substrates, are described in published U.S. patent application 20100055321 and issued U.S. Pat. No. 7,514,119, each incorporated herein by reference. More specific examples of precursors that are useful for depositing such high-k materials are described in published U.S. patent application 20090305504, published U.S. patent application 20090117274, published U.S. patent application 20100290945, published U.S. patent application 20100290963 and published PCT patent application 2011005653, each incorporated herein by reference.
Atomic layer deposition (ALD) is the enabling deposition technology for the next generation conductor barrier layers; high-k gate dielectric layers for silicon, germanium and carbon based group IV elemental semiconductors; high-k gate dielectric layers for InGaAs and other III-V high electron mobility semiconductors; high-k gate dielectric layers for carbon based electronics, such as carbon nanotube and graphene applications; high-k capacitor layers for DRAM; high-k dielectric layers for flash and ferroelectric memory devices; Magnetic junction layers for STT-MRAM, function layers in phase-change memory and resistive RAM memory; metal-based catalyst layers for gas purification, organic synthesis, fuel cell membranes and chemical detectors; metal-based surfaces for electrode materials in fuel cells; capping layers; metallic gate electrodes, etc. However, many of the precursors noted in the references above can he difficult to use in vapor phase deposition processes such as ALD, because these precursors have generally low volatility and exist as solids at room temperatures. Therefore as noted in the above references the precursor materials must be combined with suitable solvents to create solution-based precursors prior to use in the deposition process. ALD processing is the most beneficial technology for deposition of such solution-based precursors because ALD is used to build ultra thin and highly conformal layers of metal, oxide, nitride, and others one monolayer at a time in a cyclic deposition process. ALD processes can be also used in the manufacturing of flat panel displays, compound semiconductors, magnetic and optical storage devices, solar cells, nanotechnology and nanomaterials.
A typical ALD process uses sequential precursor gas pulses to deposit a film one layer at a time. In particular, a first precursor gas is introduced into a process chamber and produces a monolayer by reaction at the surface of a substrate in the chamber. A second precursor is then introduced to react with the first precursor and form a monolayer of film made up of components of both the first precursor and second precursor, on the substrate. Each pair of pulses (one cycle) produces exactly one monolayer of film allowing for very accurate control of the final film thickness based on the number of deposition cycles performed.
As set out in the references noted above, for ALD processes, the precursors should have good volatility and be able to saturate the substrate surface quickly through chemisorptions and surface reactions. The ALD half reaction cycles should be completed within 5 seconds, preferably within 1 second and exposure dosage should be below 108 Langmuir (1 Torr*sec=106 Langmuir). The precursors themselves should also be highly reactive so that the surface reactions are fast and complete, as complete reactions yield good purity in the films produced. Because of the important controls needed for the deposition parameters of these solution-haled precursors, the delivery and vaporization mechanism is important. The equipment and techniques used must be capable of maintaining stability of the solution-based precursor material within the deposition temperature window in order to avoid uncontrolled CVD reactions from occurring.
In general, the standard commercial delivery and vaporizer systems are not suitable for solution-based precursors. This is in part because it is difficult to deliver a small enough dose of precursor needed to limit monolayer coverage of the substrate. In particular, the pulse width of the vapor phase reactant is 1 second or less and the shape of the vaporized liquid pulse may be distorted with sharp leading and tailing edges of the liquid pulse being lost after vaporization. It is very difficult to synchronize two well separated reactants to perform the desired self-limiting and sequential ALD growth.
For example, the Savannah™ Series ALD system from Cambridge NonoTech, is representative of available ALD systems. This system provides means to deposit ALD films on 200 mm wafer surfaces using static one-end source containers. Neat precursor vapor that has higher pressure than chamber operating pressure is delivered by ALD pulse valves from Swagelok. To obtain high enough precursor vapor pressure, the one-end source containers may be heated by electrical heating jackets with temperature controls. However, the use of solution-based precursors in the standard Savannah ALD tool is difficult, because solvent and solute in the solution-based precursors are separated in the vapor phase during pulse at the control temperature. Higher volatile components, generally the solvents, are therefore enriched on the head space of the source container, causing deposition inconsistencies.
Direct liquid injection methods can be used to control the vaporization and pulse of precursor materials. U.S. published patent application 2003/0056728 discloses a pulsed liquid injection method in an atomic vapor deposition (AVD) process using a precursor in liquid or dissolved form. However, the liquid dose is too large to meet ALD growth requirements. Min, et al., “Atomic layer deposition of Al2O3 thin films from a 1-methoxy-2-methyl-2-propoxide complex of aluminum and water”, Chemistry Materials (2005), describes a liquid pulsing method for solution precursors, where the liquid dose is again too large for ALD growth to occur, Neither of these liquid pulse methods provide ALD growth, but instead represent variants of CVD processes and result in uncontrolled CVD layer growth.
Methods and apparatus related to the vaporization and delivery of solution-based precursors in ALD processes are described in published U.S. patent application 20100036144 and published U.S. patent application 20100151261, both incorporated herein by reference.
There remains a need in the art for improvements to the delivery and vaporization of ALD solution-based precursors. In particular, the ability to use local vaporizers that fit into existing commercial ALD wafer tools is needed.
The present invention provides methods and systems for the delivery of solution-based precursors to local vaporizers that are integral with standard ALD wafer tools, More particularly, the present invention provides method and systems wherein the delivery and vaporization of solution-based precursors is precisely controlled by liquid pulses of the precursors into the local vaporizers, full vaporization of the liquid pulsed into the local vaporizer, vapor phase ALD pulses of the fully vaporized precursor into the deposition chamber, and similar pulsing of cleaning inert gas pulses into the chamber. This process achieves true controlled ALD film growth. The liquid pulse can be either solution-based precursor or cleaning solvent from a dual source Flex-ALD container without any dead volumes.
The present invention provides methods and systems for the precise control of the delivery of solution-based precursors for use in ALD processes. By using direct liquid injection of the precursor solution to a local vaporizer, the vaporization of the solution-based precursors and delivery of the vaporized precursor can be precisely controlled in order to achieve true ALD film growth.
The system of the present invention provides a means of introducing solution-based liquid precursors by direct liquid injection to a local vaporizer on a standard ALD wafer tool. The solution-based precursor is transported by liquid mass flow control at room temperature so that the precursor material has a low thermal budget and to prevent any thermal degradation of the precursor. The solution-based precursor is then vaporized inside the local vaporizer to provide a gas phase precursor and solvent vapor for the ALD operation. The system according to the present invention can he a drop-in replacement of a standard static heated source container and requires no modification of the deposition chamber or precursor manifold.
The system of the present invention be described in greater detail with reference to the drawing figures. In particular,
The solution-based precursor delivery system 100 operates according to the following process. Solution-based precursor material is prepared, such as the precursor materials described in the several published patent applications and issued patents noted in the background section of this application. The prepared solution based precursor is filled into an inner vessel of container 10, that can be a dual ALD bubbler container, such as that described in published U.S. patent application 2010/0140120, incorporated herein by reference. Pure solvent, such as octane is filled into the outer vessel of the container 10. Using such a container 10 allows for delivery of ether pure solvent or precursor solution to be switched for delivery to the vaporizer 20 without line break. The solvent or precursor solution delivered to the vaporizer is carefully controlled using the liquid mass flow controller 40 and liquid pulse valve 50. The mass flow controller 40 is preferably a low delta T liquid mass flow controller, wherein the temperature increase or decrease of delivered material is less than 5° C. and preferably less than 3° C. This control avoids the formation of bubbles and also avoids component separation of the delivered material as well as reducing bubble formation in the liquid delivery lines. The liquid pulse valve 50 delivers a precisely controlled amount of liquid at room temperature into the vaporizer 20. The vaporizer 20 may be constructed of stainless steel and may include VCR connections as well as a built-in liquid injection nozzle. The liquid precursor solution delivered to the vaporizer 20 is then fully vaporized without phase separation by the vaporizer 20 at temperatures up to 250° C., preferably at temperatures from 100° C. to 200° C. If it is desired to pressurize the vaporized precursor, inert gas from inert gas from inert gas source 60 can be delivered to the vaporizer 20 along with the precursor solution. The inert gas is delivered in a controlled amount through gas mass flow controller 70 and gas pulse valve 80 and hack pressure is regulated by regulator 85. Once the precursor material has been vaporized, the precursor material is delivered in a precisely controlled manner to the wafer deposition chamber 30 through vapor pulse valve 90. This precise control allows the precursor vapor to be delivered without leading and trailing edge formation. Following deposition, the wafer chamber can be purged with inert gas.
One operation sequence for the ALD system 200 comprises delivering the first precursor material to the first local vaporizer 220 to be vaporized and then delivered as a precisely controlled pulse to the deposition chamber 230 through the first vapor pulse valve 225. In order to complete the ALD cycle, the second precursor material is then delivered to the second local vaporizer 250 to be vaporized and then delivered as a precisely controlled pulse to the deposition chamber 230 through the second vapor pulse valve 255. Purge steps may be added before, between and after the two precursor deliveries. In one alternative, instead of a second solution based precursor being used, a neat liquid precursor can be substituted and delivered for example from a container 260 or 270. A further embodiment provides for the addition of a third solution based precursor material to be delivered to through a third vaporizer to the deposition chamber. Alternatively, a third precursor material could be a neat liquid precursor delivered from a standard container.
The invention provides for very precise control of the ALD deposition process. Table 1 sets forth two examples of films obtained using the system of the invention.
It is anticipated that other embodiments and variations of the present invention will become readily apparent to the skilled artisan in the light of the foregoing description, and it is intended that such embodiments and variations likewise be included within the scope of the invention as set out in the appended claims. For example, many different piping and valve arrangements can be utilized without departing from the invention. Further, virtually any arrangement of the container and chambers within the container is possible. For example, a cylinder within cylinder arrangement that requires only a single inert gas feed for pressurization of the head space for both chambers is possible.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US13/58122 | 9/5/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61697940 | Sep 2012 | US |
