Patent Grant
8852679
The present invention relates generally to semiconductor and solar processing. More specifically, an apparatus for high throughput combinatorial dip-coating of varied thin films and the methods of combinatorial testing are described.
Combinatorial processing enables rapid evaluation of semiconductor, solar, or energy processing operations. The systems supporting the combinatorial processing are flexible to accommodate the demands for running the different processes either in parallel, serial or some combination of the two.
Some exemplary processing operations include operations for adding (depositions) and removing layers (etch), defining features, preparing layers (e.g., cleans), doping, etc. Similar processing techniques apply to the manufacture of integrated circuit (IC) semiconductor devices, flat panel displays, optoelectronics devices, data storage devices, magneto electronic devices, magneto optic devices, packaged devices, and the like. As feature sizes continue to shrink, improvements, whether in materials, unit processes, or process sequences, are continually being sought for the deposition processes. However, semiconductor and solar companies conduct research and development (R&D) on full wafer processing through the use of split lots, as the conventional deposition systems are designed to support this processing scheme. This approach has resulted in ever escalating R&D costs and the inability to conduct extensive experimentation in a timely and cost effective manner. Combinatorial processing as applied to semiconductor, solar, or energy manufacturing operations enables multiple experiments to be performed at one time in a high throughput manner. Equipment for performing the combinatorial processing and characterization must support the efficiency offered through the combinatorial processing operations.
Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings:
A detailed description of one or more embodiments is provided below along with accompanying figures. The detailed description is provided in connection with such embodiments, but is not limited to any particular example. The scope is limited only by the claims and numerous alternatives, modifications, and equivalents are encompassed. Numerous specific details are set forth in the following description in order to provide a thorough understanding. These details are provided for the purpose of example and the described techniques may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the embodiments has not been described in detail to avoid unnecessarily obscuring the description.
Embodiments of the current invention describe a high performance combinatorial apparatus for the combinatorial development of coatings by a dip-coating process. The dip-coating process may be used for multiple applications, including forming coatings from varied sol-gel formulations, coating substrates uniformly with particles to combinatorially test particle removal formulations, and the dipping of substrates into texturing formulations to combinatorially develop the texturing formulations.
Sol-Gel Coating Application
Sol-gel processes are those where a wet formulation (the “sol”) is dried to form a gel coating having both liquid and solid characteristics. The gel coating is then treated to form a solid material. The gel coating or the solid material may be formed by applying a thermal treatment to the sol. This technique is valuable for the development of coatings because it is easy to implement and provides films of uniform composition and thickness. Therefore, sol-gel processes are valuable for development as combinatorial processes to develop coatings for various applications such as for materials used in semiconductor device manufacturing, solar cell manufacturing, glass manufacturing, or energy cell manufacturing.
The coatings formed by sol-gel processes may be developed using combinatorial methods of optimizing the sol-gel formulations and conditions used to create those coatings. Combinatorial processing may include any processing that varies the processing conditions in two or more substrates or regions of a substrate. The combinatorial methodology, in embodiments of the current invention, includes multiple levels of screening to select the coatings for further variation and optimization.
As indicated by the funnel, the primary screening 102 includes the largest number of samples of coatings formed by a sol-gel process. During the secondary screening 104, a smaller number of samples are tested, while the tertiary screening 106 involves testing the least number of coatings. Thus, the funnel-like shape of the diagram indicates that fewer and fewer samples are used at each step. The number of samples used at any of the screening levels may be dependent on the substrate or tools used to process the samples.
The screening at the different levels of the funnel is designed to identify and to optimize a coating having predetermined qualities. Combinatorial processing includes performing a large number of processes and materials during a first screen, selecting promising candidates from those processes, performing the selected processing during a second screen, selecting promising candidates from the second screen, and so on. In addition, feedback from later stages to earlier stages can be used to refine the success criteria and provide better screening results.
For example, thousands of materials are evaluated during the primary screening, or materials discovery stage, 102. Promising candidates selected based on the results of the materials discovery stage 102 are advanced to the secondary screening, or materials and process development stage, 104. Evaluation of the materials may then be performed using metrology tools such as physical and electronic testers and imaging tools. The materials and process development stage 104 may evaluate hundreds of materials (i.e. a magnitude smaller than the number of materials during the materials discovery state 102) and may focus on the processes used to deposit or develop those materials. Based on the results of the materials and process development stage 104, promising materials and processes are again selected and advanced to the tertiary screening, or process integration stage, 106, where tens of materials and/or processes and combinations are evaluated. The process integration stage 106 may focus on integrating the selected processes and materials with other processes and materials into structures.
The most promising materials and processes from the process integration stage 106 are advanced to the device qualification stage 108. During the device qualification stage 108, the materials and processes selected are evaluated for high volume manufacturing, which may be conducted on full wafers within production tools. The results are evaluated to determine the efficacy of the selected materials, processes, and integration. If successful, the use of the screened materials and processes can proceed to the manufacturing stage 110. The schematic diagram 100 shown in
In one embodiment of the present invention, during the primary screening 102, coating materials formed by a dip-coating sol-gel process are combinatorially screened in a high throughput manner to identify coatings that have predetermined qualities. Dip-coating is one method of sol-gel processing. Other methods of sol-gel processing include spin coating, curtain coating, or spray coating. It has been determined that dip-coating can be correlated to the other methods of sol-gel processing and thus serve as a primary screen for coatings formed by sol-gel processing. Dip-coating may be chosen as the primary screening process because it can be adapted to process large numbers of coatings for high throughput combinatorial screening.
The fluid supply system 214 may include one or more supplies of the various processing fluids (i.e., liquids, gases, etc.) used in the methods and processes described herein. The control system 212 may include a processor and memory (i.e., a computing system) in operable communication with the other components of the dip-coating tool 200 and be configured to control the operation thereof in accordance with the methods and processes described herein.
It should also be understood that although not shown as a separate component, the dip-coating tool 200 includes a variation generating system (or subsystem) capable of creating variations between at least two of the formulations, substrates, coatings, or portions of a single substrate, as described in greater detail below. These variations may relate to specifications such as temperatures, exposure times, layer thicknesses, chemical compositions, humidity, etc. of the formulations and/or the substrates at various stages of the screening processes described herein. It should be understood that these variations are intentionally created for the purposes of evaluating the characteristics of specific materials and processing techniques in order to identify those that are best suited for particular uses.
The dispense arm 206 (and/or dispense head 220) is used to dispense varied formulations, such as sol-gel formulations, into the wells 218 which are held by the well holders 204. The dispense arm 206 can have any configuration of dispensers 224. In another embodiment, the dispense arm 206 includes one row of dispensers 224 to fill one row of wells 218 at a time.
The test substrates 234 may be formed of many types of materials, but in some embodiments may be glass or silicon. In an embodiment in which the test substrates 234 are glass, the glass may be, for example, float glass or a treated glass. The size of the test substrates 234 may be any size compatible for use in the combinatorial dip coating tool. In one particular embodiment, the test substrates 234 are coupons having dimensions of approximately 1 cm×10 cm. The size of the test substrates 234 may be decided based on the size limitations imposed by various characterization techniques for the subsequent films. Examples of test substrates 234 that may be used in embodiments of the current invention include, but are not limited to, soda-lime glass, borosilicate glass, single or multi-crystal silicon wafers, or photovoltaic cells with multiple device layers. The test substrates 234 may be optically flat, textured, or patterned.
Referring again to
The speed of the withdrawal is controlled to provide a particular thickness of the coating applied to the substrates. The draw speed can be determined based on the desired thickness of the coating. The dip coating can also be correlated to other types of coating processes such as spin coating, curtain coating, or spray coating.
In an alternate embodiment, the substrate holders 210 and/or the dip-coating arm 208 may be designed to clamp the same number of test substrates 234 as a single row or column of the well holder 204 so that the draw speed of the coatings may be varied between rows or columns. In such an embodiment, the dip-coating apparatus 200 may include more than one dip-coating arm 208 to simultaneously dip the rows or columns in the formulations and draw them from the formulations at different speeds.
The formulations themselves may be varied by varying the chemical composition of each of the formulations. For example, the composition of the formulation may be varied by varying one or more of the components based on the material itself or the ratios of the components. Examples of components commonly found in sol-gel formulations are monomers, solvents, surfactants, viscosity modifiers, cross-linking agents, accelerators, catalysts and porogens, although this list is not meant to be limiting. Alternatively, the individual substrates may be varied to determine the effects of coating on different types of materials. Examples of the substrates include glass, silicon, metallic coated materials, or plastics. The substrate could be optically flat, textured, or patterned. Also, different types of substrates may be used at different levels of screening. The library may be formulated using the dispensers 224 of the dispense arm 206. In another embodiment, the dispensers 224 may be used to retrieve formulations from the wells 218 of one well holder 204 and dispense them into the wells 218 of another one of the well holders 204, as opposed to receiving the formulations from the fluid supply system 214, thereby creating a library of combinatorially varied sol-gel formulations.
At step 320 in
The dried coatings formed of the combinatorially varied sol-gel formulations are characterized at step 350 in
Still referring to
At step 370, the performance of each of the annealed coatings formed from the combinatorially varied sol-gel formulations is characterized. The characterization of the coatings may occur while the substrates 234 remain clamped to the substrate holder 210. Thus, it is possible that the dip-coating in step 320, the drying in step 340, the characterizing of the dried coatings in step 350, the annealing of the coatings in step 360, and the characterizing of the annealed coatings in step 370 may all be performed while the substrates 234 remain clamped to the substrate holder 210. Performing all of these processes while the substrates 234 remain clamped to the substrate holder 210 may allow for high processing throughput. The coatings may be characterized by many methods based on visual methods, the measurement of thickness and refractive index, the contact angle of the coating, the surface topography of the coating measured by AFM and SEM, the optical transmission and reflectance of the coating, the film composition may be measured by XRD (X-Ray Diffraction) or XRF (X-Ray Fluorescence), and the detection of organic molecules in the film by FTIR (Fourier Transform Infrared) spectroscopy. The characterization of the annealed coatings may be compared to the dried coatings to determine the effects of the components on the coatings. Different types of components will have different effects on the properties of the coatings after drying vs. after annealing.
The substrates 234 may still remain clamped to the substrate support 210 during the characterization of the annealed coatings. Doing so may improve the efficiency of the characterization as the characterization may be automated. Improvements in efficiency are valuable to high throughput combinatorial processing. The data obtained during characterization, and particularly during automated characterization, may be fed to a computer program capable of rapidly screening the data.
After characterization of the coatings, a subset of the varied sol-gel formulations that had been used to form the coatings are selected for further varying at step 370. The selection criteria for the screening may include sol stability, thickness and refractive index, and film uniformity. The further varying may occur by a feedback loop to another primary screening of the sol-gel formulations or coating conditions to further narrow down the candidates.
The further varying may also occur by proceeding to the secondary screening of the selected sol-gel formulations. The combinatorial methodology then funnels down to the secondary screening 104 of
The tertiary screening 106 of
Anti-Reflective Coatings
Coatings that give a low reflectivity over a broad wavelength range of light (e.g., anti-reflective coatings) are desirable in many applications. These coatings have an optimized refractive index in between air (n=1) and a substrate such as glass (n≈1.5). Low refractive index (low RI) coatings are thus of great interest. These low RI films may have many applications including solar and energy applications. The dip-coating/screening process described above may be applied to the screening and development of coatings having a lower refractive index (RI) than glass. The screening process depicted in
In particular, at step 310, a library of combinatorially varied sol-gel formulations to form low RI films is formulated. The number of combinatorially varied sol formulations screened during the primary screening may be on the order of 1000's of variations. Low RI films may be formulated of multiple components. The components of the sol-gel formulation used to form low RI coatings may include a precursor molecule, a solvent, additives and an accelerator. The precursor molecule is the component that will form the primary structure of the gel and of the resulting solid coating. Additives may be included for many purposes, for example, to tailor the refractive index of the coating, to modify the viscosity of the sol formulation, or to improve bonding of the coating with the substrate. An accelerator may be added to accelerate the cross-linking of the precursor molecules in the sol formulation. The solvent is added to solvate the components and to form the liquid solution that can be dip coated onto substrates during the combinatorial processing. The sol-gel formulations for the low RI films may be varied by varying any of the components concentrations, relative amounts, or the type of compound used.
In one embodiment, at step 310, the varied sol formulation for a low RI film involves use of tetraalkylorthosilicate, where the alkyl may be for example a methyl, an ethyl, or a propyl as the precursor molecule. The solvent is a mixture of alcohol and water, and either an acid or base as the accelerator. In this embodiment, the varied component of the formulation is a surfactant that acts as a porogen. The surfactant may be varied by type of surfactant or by the concentration of the surfactant. In one embodiment, the surfactants may be cationic. The combination of these components forms a sol, which is a dispersion of silica nano-particles stabilized in the solvent system. In one particular embodiment, the sol may be a solution of tetraethylorthosilicate (TEOS) as the precursor, a mixture of ethanol and water as the solvent, and hydrochloric acid (HCl) as the accelerator, and cetyltrimethylammonium bromide (CTAB) as the surfactant. The surfactant may be varied by adding mass fractions of CTAB ranging from approximately 1.5% to approximately 5%.
These varied low-RI sol formulations may be dip coated (in a manner similar to that described above) at step 320 onto substrates (e.g., substrates 234) processed by the combinatorial dip coating tool 200 illustrated in
The coatings are then annealed at step 360 at a temperature high enough to form a solid coating. In the TEOS and CTAB formulation example, the annealing temperature may be 500° C. for 30 minutes.
The annealed low-RI film is then characterized at step 370 to determine the effect of the components on the refractive index of the low-RI film. The total reflection, the total transmission, and the thickness are measured and the refractive index is calculated. This information can be compared to the pre-annealing characterization to determine whether the variation in the sol formulation had an effect on any of the relevant properties. The porosity may also be quantified by measuring the roughness to establish a relationship between the surfactant (porogen), the porosity, and the refractive index of the low-RI coating. The roughness may be measured by AFM and SEM images. After performing the data analysis the coatings that meet the predetermined requirements for refractive index and porosity may be selected at block 380 for further variation and processing. Alternatively, porosity can also be measured by spectroscopic ellipsometry.
In an alternate embodiment, multiple layers of coatings may be deposited during the dip-coating, drying, and annealing cycle. This is possible when the coatings within the multi-layer film may all be deposited by a sol-gel method. The use of a combinatorial dip-coating tool to form the multiple coatings allows for high throughput processing and screening of the coatings. As such, combinatorial processing and tools provide a method of quickly testing and screening multiple layer coatings. Coatings with multiple layers may be used for multi-layer anti-reflective coatings. Multiple layers may be used to maximize anti-reflective properties and a combination of properties such as anti-reflective properties and passivation properties. For example, the multi-layer may be a gradient of low-RI coatings where the refractive index of the first coating deposited on the substrate is a material having a refractive index close to that of the substrate and ending with a top layer that is a material having a refractive index close to that of air. Any number of coatings may be used to create this gradient. The coating that is varied may be one or more of the coatings in the multi-layer.
In one particular embodiment the multi-layer may be formed of three coatings over a silicon substrate. The coating formed directly on the silicon substrate may be titanium dioxide (RI=1.9), the coating formed over titanium dioxide may be a mixture of titanium dioxide and silicon dioxide in a proportion that creates a refractive index of approximately 1.7, and the third and uppermost coating is formed of silicon dioxide (RI=1.45). Silicon dioxide provides good passivation for a silicon substrate but does not provide a good refractive index as an anti-reflective coating for the silicon substrate. Titanium dioxide has a good refractive index as an anti-reflective coating for silicon, but does not provide good passivation for silicon. In this embodiment the best qualities of both silicon dioxide and titanium dioxide may be employed by creating a multi-layered gradient starting with silicon dioxide formed over the silicon substrate and ending with a layer of titanium dioxide. The gradient in between these two layers may be formed of any number of layers. The combinatorial screening process described by the flowchart of
At step 380 in
The secondary screening process follows the same process as described in the flowchart of
In the tertiary screening of the anti-reflective coatings formed by the sol-gel process, the process is scaled up to a production process. For example, the production process could be spin coating, curtain coating, or spray coating of the process onto a substrate. The tertiary screening would test the subset of formulations under process conditions to determine the optimal formulation for the formation of an anti-reflective coating having predetermined properties. The subset may be on the order of tens of formulations, or even less than ten. The anti-reflective coatings formed during the tertiary screening may include an adhesion test (e.g. a tape test), a stress test, a humidity test, and a visual test of whether there is any color variation across the substrate. The identified formulation may then be further scaled up to manufacturing where the anti-reflective coating may be integrated into a product, such as a solar cell.
Particle Removal Applications
The sol-gel combinatorial methodology and tool described above may also be used to identify particle removal formulations having optimized particle removal capabilities. In this application, the sol-gel technique is used to form a uniform coating of particles having a known particle density and distribution on substrate coupons. A uniform coating of particles is identified using the combinatorial sol-gel tool and the identified coating will subsequently be used to test particle removal formulations using the combinatorial sol-gel tool. This methodology may be used to develop cleaning formulations for semiconductor or solar processing. Obtaining contaminated semiconductor or solar substrates from between process steps is difficult and the particle density and distribution may vary greatly from one substrate to the next. Therefore, a process where contaminated substrates may be simulated and controlled may have value for the development of particle removal formulations that may be used in production.
At step 401, a plurality of substrates (e.g., the substrates 234 in
At step 402, the coatings are characterized to select a coating having a known particle count. The particle count will be a combination of the particle distribution and density over the surface of the substrate. The distribution and density of the particles may be measured by testing multiple positions on the substrate by taking pictures of those positions. The testing may be automated and the particle distribution, density, and count may be determined by analysis of those pictures by software developed for such a purpose. The predetermined particle distribution, density, and count may be based on information obtained from actual substrates analyzed during a production process. The particle contamination information obtained from the actual processing may be mirrored or modified in a known manner to test a particle cleaning formulation. Particle coatings are selected after characterizing the plurality of substrates based on the selected predetermined contamination information.
The coatings selected at step 402 are then dip-coated onto a plurality of substrates to form coatings having a known particle count. The coated substrates may be created using the same combinatorial dip-coating tool and method described above. Alternatively, a single substrate may be coated with a single selected coating and then tested using a combinatorial processing tool similar to that described above.
The plurality of substrates having coatings with known particle counts are then dip-coated into a plurality of varied cleaning solutions at step 404. The coated substrates may remain clamped to the substrate holder 210 during the processes of steps 403 and 404.
Alternatively, if a single substrate is coated with the coating having known particle count, density, and distribution, a plurality of cleaning solutions may be applied to site-isolated regions of the substrate using the combinatorial wet processing tool 250 illustrated in
The combinatorial wet processing tool 250 includes a housing (and/or processing chamber) 252, a well holder 254 holding wells 256, and a dispense arm 258 having a dispense head 260, similar to the dip-coating combinatorial apparatus 200 described above. The wet processing tool 250 also includes a reactor assembly 262 having an array or reactors (or fluid containers) 264 positioned over a substrate support 266. A substrate 268 is placed on the substrate support 266 and positioned relative to the reactors 264 such that bottom edges of the reactors contact the substrate 268 and form seals around the respective portions of the substrate 268. In a manner similar to that described above, the dispense arm 258 may retrieve cleaning solutions from the wells 254 and dispense them into the reactors 264. Because of the seals formed between the reactors 264 and the substrate 268, the cleaning solutions remain within the reactors 264 and are isolated from the other cleaning solutions. The cleaning solutions may be varied by varying the chemical composition or temperature. The time of application of the cleaning solutions may also be varied. It should be understood that although the wet processing tool 250 in
Referring again to
At step 406, a subset of the cleaning solutions may be selected for further variation during another iteration of primary screening or secondary screening. The secondary screening may focus on another aspect of the cleaning formulation composition or the conditions under which the cleaning formulation is applied to the substrate. Another iteration of primary screening or secondary screening may repeat steps 403 though 406 in
In an alternate embodiment, the combinatorial dip-coating tool 200 of
In another alternate embodiment, the combinatorial dip-coating tool 200 may be used for the dipping of substrates into texturing formulations to combinatorially develop the texturing formulations. In such an embodiment, the test substrates may be developed for use in solar applications. For example, the substrates may be silicon (monocrystalline, polycrystalline, or amorphous) to develop a silicon texturing formulation. Alternatively, the substrates may be glass that has been coated with a transparent conductive oxide (TCO) to develop a TCO texturing formulation. In the TCO embodiment, the substrates may be coated with the TCO before or after being cut into coupons for combinatorial testing. The use of the dip-coating tool for the combinatorial evaluation of texturing formulations may provide the advantages of maintaining the texturing formulations at a constant temperature and of visual observation of the texturing process. The well holder in which the texturing formulations are held may include conduits for flowing liquid therethrough to maintain the formulations at a particular temperature. Additionally, because the well holder is open from above, an observer or a camera may visually assess the progress of the texturing process. Visual observation may be valuable because as most texturing processes proceed the color of the substrate will change, providing an observer with valuable information on the progress of the texturing reactions. This information may be recorded digitally with a video recorder for processing of the information by an observer or by a computer to gain an understanding of the different texturing formulations.
These texturing formulations may be varied by varying the chemical compositions thereof. The textured substrates may then be characterized and a subset may be selected for further varying by either primary or secondary combinatorial screening. Experiments may be designed based on the predetermined properties required for the textured substrate. Once the texturing formulations have been narrowed down to the order of tens of formulations, the tertiary screening of the texturing formulation may occur on a production scale process.
In one embodiment of the present invention, a method for testing coating formulations is provided. A plurality of coating formulations are provided. A plurality of test substrates are simultaneously dip coated in the plurality of coating formulations to generate a plurality of coated substrates. A variation between at least two of the plurality of coated substrates is generated. The plurality of coated substrates are characterized to obtain characterizing results. A subset of the plurality of coating formulations is selected based on the characterizing of the plurality of coated substrates.
In another embodiment, a method for testing sol-gel coating formulations is provided. A first screening is performed to identify a subset of sol-gel coating formulations having predetermined characteristics. In the first screening, a plurality of sol-gel coating formulations are provided within a housing of a coating formulation apparatus. A plurality of test substrates are simultaneously dip coated in the plurality of sol-gel coating formulations to generate a plurality of coated substrates. A variation between at least two of the plurality of coated substrates is generated. A subset of the plurality of sol-gel coating formulations is selected based on characterization results. A second screening is performed by coating a second plurality of test substrates with the selected subset of the plurality of sol-gel coating formulations, wherein the coating is performed using spin coating.
In a further embodiment, an apparatus for testing coating formulations is provided. The apparatus includes a housing enclosing a testing chamber, a plurality of vessels coupled to the housing and positioned within the testing chamber, each of the plurality of vessels being configured to hold one of a plurality of coating formulations, a dip coating assembly coupled to the housing and configured to hold a plurality of test substrates, simultaneously dip each of the test substrates into one of the plurality of coating formulations, and draw the test substrates from the plurality of coating formulations to form a plurality of coated substrates. The apparatus also includes a variation generating system coupled to the housing and configured to generate a variation between at least two of the coated substrates.
Although the foregoing examples have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed examples are illustrative and not restrictive.
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| Number | Date | Country | |
|---|---|---|---|
| 20120156498 A1 | Jun 2012 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12970638 | Dec 2010 | US |
| Child | 13160732 | US |
