US20170016117A1

US20170016117A1 - Scalable triode pecvd source and system

Info

Publication number: US20170016117A1
Application number: US14/900,502
Authority: US
Inventors: William E. Quinn; Ruiqing Ma; Siddharth Harikrishna Mohan
Original assignee: Universal Display Corp
Current assignee: Universal Display Corp
Priority date: 2013-06-21
Filing date: 2014-06-21
Publication date: 2017-01-19
Also published as: WO2015006034A1; US9738976B2; US20140377592A1

Abstract

Plasma deposition systems and techniques are provided that use plasma generating units having one horizontal dimension at least three times as long as the other horizontal dimension. Plasma sources as disclosed herein thus have non-uniformly scaled dimensions in the x and y directions, to facilitate uniform deposition. Sources as disclosed herein may reduce heating of the substrate due to substrate cooling between plasma sources. They also may provide improved particle coverage when the film deposited is a barrier film due to plasma and gas flow divergence at the edges of the plasma source.

Description

PRIORITY

This application claims priority to U.S. Provisional Application No. 61/837,681, filed Jun. 21, 2013, the disclosure of which is incorporated by reference in its entirety.
The claimed invention was made by, on behalf of and/or in connection with one or more of the following parties to a joint university corporation research agreement: Regents of the University of Michigan, Princeton University, The University of Southern California, and the Universal Display Corporation. The agreement was in effect on and before the date the claimed invention was made, and the claimed invention was made as a result of activities undertaken within the scope of the agreement.

FIELD OF THE INVENTION

The present invention relates to organic light emitting devices (OLEDs) and, more specifically, to techniques and systems for fabricating OLEDs and similar devices using plasma generating units.

BACKGROUND

Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.
OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.
One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.
One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)₃, which has the following structure:
In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.
As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.
As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.
As used herein, “solution processible” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.
A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.
As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level.
As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions.
More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.

SUMMARY OF THE INVENTION

In an aspect of the invention, a plasma deposition system includes a plasma generating unit having an upper electrode, a lower electrode, and a gas inlet. The plasma generating unit may have a first horizontal dimension W and a second horizontal dimension L, where L is at least 3W, at least 10W, at least 20W, or any intermediate multiple of W. The plasma generating unit may include a central electrode, which may be perforated, disposed between the first upper electrode and the first lower electrode. A first electrical power supply may be electrically connected to the first upper electrode, and a second electrical power supply, electrically separate from the first electrical power supply, may be electrically connected to the first lower electrode. Alternatively, a common electrical power supply may be electrically connected to the first upper electrode and the first lower electrode. The system may include a gas distributor having a first horizontal dimension X and a second horizontal dimension M>X. The gas distributor may be disposed adjacent to the plasma generating unit with an edge having length M about parallel to an edge of the plasma generating unit having length L. The gas inlet may be disposed closer to an outer edge of the plasma generating unit than to the center of the plasma generating unit. The system may include additional plasma generating units, each of which may have a configuration similar to that of the first. An insulator may be disposed between adjacent plasma generating units to prevent movement of plasma between regions defined by the electrodes of each unit. Each unit may be operated by a separate power supply, or a common power supply may be used to power multiple units. The plasma generating units may be arranged at different angles, such as relative to the substrate, such that the upper or lower electrode of one unit is not parallel to the upper or lower electrode of another unit. The total length of N multiple plasma generating units in the W dimension may be at least Z, and the total length of the plurality of plasma generating units in the L dimension may be at least NW. Cooling regions may be disposed between adjacent plasma units, which may include active cooling systems and/or gas outlets.
In an aspect of the invention, a deposition system may include a plasma deposition system previously described, and a moveable substrate holder, such as a roll-to-roll mechanism, configured to translate a substrate between the first upper electrode and the first lower electrode.
In an aspect of the invention, a method of depositing a layer on a substrate includes obtaining a substrate, placing the substrate between the electrodes of a first plasma generating unit having a horizontal dimension W and a horizontal dimension L of at least L 3W, 10W, 20W, or any intermediate multiple of W, introducing a first gas into the region between the electrodes, and activating the plasma generating unit to generate a plasma adjacent to the substrate. The substrate may be placed non-parallel to the electrodes, for example, at any angle greater than 0 degrees. The substrate may be placed between the electrodes by translating the substrate between the first upper electrode and the first lower electrode. The substrate may be placed within multiple plasma generating units, each of which has one horizontal dimension at least three times the other horizontal dimension. The substrate may be placed in each unit at a different angle relative to the electrodes of the unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer.

FIGS. 3A-3B show a related, conventional parallel plate PECVD system, with FIG. 3A showing a cross-sectional view of the system, and FIG. 3B showing a top view.

FIG. 4A shows a cross-section view of a small scale triode plasma system used to deposit single layer barrier films as disclosed herein.

FIG. 4B shows a top view of the system shown in FIG. 4A.

FIG. 4C shows a system as illustrated in FIG. 4A, with two RF sources.

FIGS. 5A and 5B show cross section views along the x and y axes of an example of a scalable triode plasma enhanced CVD system as disclosed herein.

FIG. 6A shows a cross-section view along the x axis of a scalable triode PECVD system as disclosed herein.

FIG. 6B shows a top-down view of a scalable triode PECVD system as disclosed herein.

FIG. 7 shows top and cross-section views of an example configuration of a roll to roll triode PECVD system as disclosed herein.

FIG. 8 shows a side view of an example roll to roll PECVD system with additional substrate cooling stations as disclosed herein.

FIG. 9 shows an example of side wall coating of particles due to plasma and gas flow with a horizontal component in a system as disclosed herein.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an “exciton,” which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non-radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable.
The initial OLEDs used emissive molecules that emitted light from their singlet states (“fluorescence”) as disclosed, for example, in U.S. Pat. No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds.
More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated. Baldo et al., “Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices,” Nature, vol. 395, 151-154, 1998; (“Baldo-I”) and Baldo et al., “Very high-efficiency green organic light-emitting devices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporated by reference in their entireties. Phosphorescence is described in more detail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporated by reference.
FIG. 1 shows an organic light emitting device 100. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, a cathode 160, and a barrier layer 170. Cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers described, in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporated by reference.
More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. Examples of emissive and host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety.
FIG. 2 shows an inverted OLED 200. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an “inverted” OLED. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of device 100.
The simple layered structure illustrated in FIGS. 1 and 2 is provided by way of non-limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer, or may further comprise multiple layers of different organic materials as described, for example, with respect to FIGS. 1 and 2.
Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed in U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in FIGS. 1 and 2. For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated by reference in their entireties.
Unless otherwise specified, any of the layers of the various embodiments may be deposited by any suitable method. For the organic layers, preferred methods include thermal evaporation, ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. Pat. No. 7,431,968, which is incorporated by reference in its entirety. Other suitable deposition methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink-jet and OVJP. Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processibility than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing.
Devices fabricated in accordance with embodiments of the present invention may further optionally comprise a barrier layer. One purpose of the barrier layer is to protect the electrodes and organic layers from damaging exposure to harmful species in the environment including moisture, vapor and/or gases, etc. The barrier layer may be deposited over, under or next to a substrate, an electrode, or over any other parts of a device including an edge. The barrier layer may comprise a single layer, or multiple layers. The barrier layer may be formed by various known chemical vapor deposition techniques and may include compositions having a single phase as well as compositions having multiple phases. Any suitable material or combination of materials may be used for the barrier layer. The barrier layer may incorporate an inorganic or an organic compound or both. The preferred barrier layer comprises a mixture of a polymeric material and a non-polymeric material as described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos. PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporated by reference in their entireties. To be considered a “mixture”, the aforesaid polymeric and non-polymeric materials comprising the barrier layer should be deposited under the same reaction conditions and/or at the same time. The weight ratio of polymeric to non-polymeric material may be in the range of 95:5 to 5:95. The polymeric material and the non-polymeric material may be created from the same precursor material. In one example, the mixture of a polymeric material and a non-polymeric material consists essentially of polymeric silicon and inorganic silicon.
Devices fabricated in accordance with embodiments of the invention may be incorporated into a wide variety of consumer products, including flat panel displays, computer monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfinders, micro-displays, 3-D displays, vehicles, a large area wall, theater or stadium screen, or a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 degrees C. to 30 degrees C., and more preferably at room temperature (20-25 degrees C.), but could be used outside this temperature range, for example, from −40 degree C. to +80 degree C.
The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures.
Plasma Enhanced Chemical Vapor Deposition (PECVD) is used to deposit a number of thin films for the electronics and opto-electronics industries. PECVD is used in applications where use of CVD would require substrate temperatures that would cause damage to the substrate. Many variants of PECVD exist, and each has advantages for different applications. Triode PECVD is one variant that is used for dielectric and barrier film deposition. The triode plasma system employs a flat center driven electrode and two plasma regions surrounding the center electrode. Gas enters the system on one side of the center electrode and the substrate is located on the opposite side of the electrode. Electrodes in this system are round, which is good for small scale depositions and for round wafers, but, this configuration is difficult to scale to large area deposition, such as large area glass, or roll-to-roll systems due to plasma instabilities in large area electrodes and difficulty in maintaining a consistent precursor and by product concentration across the area of deposition.
Increasing the size of the system for commercial manufacturing by simple scaling of the length and width of the system is not possible due to gas flow non-uniformity and plasma instability. No commercial triode system capable of use in large scale manufacturing is available. The large scale system described here also provides better particle coverage and better thermal control of the substrate than a system made by simple scaling of a small area system.
Plasma sources currently used for large area deposition are diode type systems, where the precursors are injected through a planar porous electrode, and substrates are placed on another planar electrode that is located parallel to the first electrode. One of the electrodes is attached to a power supply, which creates a plasma between the electrodes. The power supply can be DC, low frequency AC, or high frequency RF. This type of system is shown in FIG. 3. Such systems are described in further detail in, for example, in Glow Discharge Processes by Brian Chapman (John Wiley and Sons, N Y, 1980). Another type of PECVD system that has been used to deposit films is a triode system, an example of which is shown in FIG. 4. Such a triode system has two distinct plasma regions, and an inverted system is shown. Such systems are described in further detail in, for example, Prashant Mandlic, “Thesis from Princeton University “A Novel Hybrid Inorganic-Organic Single Layer Barrier for Organic Light Emitting Diodes”, 2009).
In contrast, embodiments of the invention described herein provide a scalable, triode-type plasma source, which can be used for large area deposition. A plasma source as described herein includes a linear triode source with two plasma zones. The source has the same parallel electrode configuration, and dimensions in the vertical (z) direction, but the dimensions are scaled non-uniformly in the x and y directions, i.e., parallel to the electrodes, to facilitate uniform deposition. Thus, generally, systems disclosed herein may include a plasma generating unit that includes an upper electrode, a lower electrode, and a gas inlet, where the plasma generating unit has one horizontal dimension that is at least three times the length of the other horizontal dimension. As used herein, a “horizontal” direction refers to one that is generally parallel to the electrodes. Thus, when such a system is oriented vertically, the “horizontal” directions may be within a vertical plan as viewed from outside the system. The directions parallel to the electrodes are referred to as “horizontal” directions herein for ease of description, regardless of whether the system is oriented and/or used in a vertical configuration.
The linear source has two additional advantages to conventional broad area sources. The first is that heating of the substrate may be minimized due to substrate cooling between plasma sources. The cooling can occur by radiation and convection from the substrate in the area with no plasma, or active cooling can be added between plasma sources to cool the substrate. Another advantage includes improved particle coverage when the film deposited is, for example, a barrier film. The plasma and gas flow diverge at the edges of the plasma source and may no longer be entirely or primarily vertical, i.e., perpendicular to the substrate. The diverging angle may provide better particle coverage than flow normal to the surface by minimizing shadowing caused by the particles. Embodiments of the systems and techniques disclosed herein may be used for the production of layers for organic electronic and optoelectronic devices, such as OLED displays and lighting deposited on rigid and flexible substrates, organic electronic devices, organic solar cells and flexible solar cells.
FIGS. 3A and 3B show a conventional parallel plate or capacitively coupled Plasma Enhanced Chemical Vapor Deposition (PECVD) system. In such a system, a substrate 5 is placed on the lower electrode 3, usually through a gate or slit valve (not shown) located in the side of the vacuum chamber 1. Precursor or reactive gas is introduced to the upper electrode 2 through the gas inlet 6. The upper electrode 2 typically has a porous lower surface to distribute gas uniformly over the wafer 5. Gas is evacuated through an exhaust port 4 which is connected to a pumping system used to evacuate the chamber and maintain a pressure in the milli-torr range. The electrodes 2, 3 are connected to an alternating current power supply 7, creating a plasma. The precursor gas is decomposed in the plasma and a film is deposited on the substrate 5. The lower electrode 3 can be heated to improve film quality. FIG. 3B shows a top view of the system described with respect to FIG. 3A, showing the generally circular shape of the electrode and chamber.
FIGS. 4A and 4B show side and top views of a conventional triode PECVD system. In such a system, a substrate 15 is attached to the upper electrode 12. The substrate 15 may be attached to a holder (not shown) that fits into the upper electrode 12 to facilitate transfer of substrates into and out of the chamber. The lower electrode 13 contains a gas inlet 16 and a gas distribution system to uniformly distribute gas over the surface of the electrode. The reactant gas is contained by an insulating ring 19 and a perforated electrode 18 is placed on the insulating ring 19. Reactant gas is pumped from the chamber through port 14, which is connected to a vacuum pumping system capable of maintaining a pressure in the milli-torr range when gas is flowing into the chamber 11. The perforated electrode 18 is connected to one leg of an alternating current power supply, the other leg of the power supply 17 is connected to the lower electrode 13 and upper electrode 12 and the vacuum chamber 11. When the power supply 17 is powered on, a plasma is struck between the perforated electrode 18 and the bottom electrode 13 and between the perforated electrode 18 and the upper electrode 12. The reactant gas is decomposed in the two plasma regions and a film is deposited on the substrate. FIG. 4C shows a variant of the triode system that uses separate ac power supplies for the lower and upper electrodes. This two-power supply variant can be applied to all subsequent figures. As shown in the top overhead view of the triode PECVD system in FIG. 4B, such systems use a circular geometry. The plasma region closest to the gas inlet is shown as a capacitatively coupled plasma. Those skilled in the art will recognize that this could also be an inductively coupled plasma by wrapping a high frequency inductive coil around the insulating ring 19 of the lower electrode assembly.
FIGS. 5A-5B show an example of a scalable triode system as disclosed herein. FIG. 5A shows the shows the short end of the system, which has an arrangement similar to the conventional system described with respect to FIG. 4. FIG. 3B shows a 90 degree rotation of FIG. 2A. The horizontal dimension (“scaling direction” in FIG. 5B) of the electrodes 32 and 33 may be from 3 to 20 times longer than the horizontal dimension in FIG. 5A.
Referring to FIG. 5A, the number and general function of the components are similar to the components shown in FIG. 4. In FIG. 5B, a view rotated 90 degrees from the view in FIG. 5A, it is apparent that in the presently-disclosed system the components are elongated compared to the round geometry of FIG. 4. As previously described, he vacuum chamber 31 may have an aspect ratio of from 3:1 to 20:1 (length:width) or more, although other ratios can be used, including any ratio in between. More generally, a plasma generating unit as disclosed herein may have one horizontal dimension that is 3, 10, or 20 times the other horizontal dimension, or any intermediate multiple of the other horizontal direction. Thus, the electrodes 32, 33, 38 have an elongated shape with an aspect ratio similar to the vacuum chamber 31. The pumping ports 34 are rectangular rather than round so that reacted gas can be removed from the chamber along each side of the electrode structure. The central electrode 38, which may be perforated, may allow for the creation and use of two plasma regions. In a first of the plasma regions in which the gas is injected, a high-concentration plasma may be formed. In the region on the opposite side of the electrode, the plasma may be of a lower concentration, and thus may behave more like a drift plasma.
FIG. 6 shows comparative vertical views of the standard and scalable triode systems. In the example shown, the length of the scalable system is 3 to 20 times longer than the diameter of the small system. There are advantages of scaling in one dimension rather than in both directions, or simply increasing the diameter of the small system. As the diameter of a round plasma system increases, the velocity of the gas at the outer edge of the electrode increases compared to a smaller diameter system. The residence time of gas increases for gas injected in the center, which can change the gas and film composition. The gas is pumped at the circumference of the electrode. Scaling the system in one dimension keeps the surface area to perimeter ratio approximately constant by pumping only along the long edges of the electrode. Referring to FIG. 6B, the top down view of the chamber shows that the electrode assembly 32, pumping ports 34 and the gas distributor 36 are elongated compared to the small research system shown for reference in FIG. 6A. Generally, a system as disclosed herein may include a gas distributor having one horizontal dimension greater than the other. The gas distributor may be disposed adjacent to a plasma generating unit as previously described and as shown in FIG. 6, with the longer edge disposed parallel to a long edge of the plasma generating unit. Similarly, the gas inlet may be disposed closer to an outer edge of the plasma generating unit than to the center of the unit.
In some embodiments, multiple plasma generating units may be used, such as multiple triode PECVD sources. Each plasma generating unit may include an upper electrode, a lower electrode, and a gas inlet as previously described. An insulator may be disposed between adjacent plasma generating units to prevent movement of plasma beyond the region defined by the electrodes of each plasma generating unit. Each unit may have an independent power supply, i.e., a power supply that is electrically separate and isolated from the power supply of the other. More generally, any number N of plasma generating units may be used. In some configurations, the units may be placed end-to-end. The general geometry of the overall system may be maintained. For example, where each of N PECVD sources has a shortest horizontal dimension W, the total length of the sources in the longest horizontal dimension may be at least NW. FIG. 7 shows a PECVD system as disclosed herein that includes multiple triode PECVD sources. As shown, such a system may be capable of processing rolled material such as thin metal sheet stock or polymeric materials. The plasma generating components includes the upper electrode assembly 42, the lower electrode assembly 44, and the gas injection 47. Any number of plasma generating components can be arranged in a vacuum chamber 41 depending on the thickness of the film to be deposited, the deposition rate and the speed of the material through the system. The shape of the system is shown as flat along the path of the roll, but circular (along an arc) or other geometries are also possible.
In configurations that use multiple plasma generating units, cooling regions may be disposed between them to allow for cooling a substrate in between processing by each unit. FIG. 8 shows additional cooling regions 47, 48 added between plasma sources 42. The cooling regions can be active cooling systems, such as cooled rollers 47 or a larger belt-type chiller 48, which provides longer contact with the moving substrate.
In some configurations, divergent plasma flows may be used to provide better coverage of features or particles on a surface. FIG. 9 is a schematic diagram of particles 53 on the surface of a substrate 51. The scale of the particles is greatly enlarged to illustrate the mechanism of improved coverage. One issue with covering particles with a barrier film in conventional systems typically is that the particle masks or shadows area 56 between the widest part of the particle and a substrate, illustrated by the insert in FIG. 9, where arrows indicate the direction of flow. This masking prevents coverage of the area which is masked, and the area becomes a point of failure for barrier coatings. To overcome the masking issue, barrier films are normally deposited with thickness greater than the largest particles to achieve complete coverage. The divergent gas flow and plasma at the edge of the plasma sources eliminates the shadowing effect. As a particle on a moving substrate enters the leading edge of the plasma zone, the leading side of the particle 53 may be coated by the incoming divergent flow. In the center of the source, the gas flow is normal to the substrate and masking occurs as in a standard source 54. At the trailing edge of the source, the trailing side of the particle 53 is coated by the film. Although the coating under the particle may not be as thick as in the particle free areas of the substrate, there may be no area left uncovered to become a source of barrier failure. Thus, such an arrangement may be preferable for deposition of barrier films and the like in comparison to conventional sources.
Divergent plasma flow may result from the specific geometries described herein, i.e., as a result of the elongated shape of the plasma generating units. An example technique to achieve or increase divergent plasma flow is to orient the plasma generating system such that it is not normal to the substrate, i.e., so that the electrodes are not parallel to the substrate. As another example, multiple plasma generating units may be used, such as described with respect to FIG. 7, and oriented at different angles relative to the substrate. For example, each plasma generating unit may be oriented such that the electrodes of one unit are non-parallel to another. One or more units may be oriented such that the electrodes are parallel to the substrate, or each unit may be oriented such that the electrodes are not parallel to the substrate. As a specific example, three plasma generating units may be used, corresponding to the three directions of flow shown in FIG. 9. That is, a first unit may be oriented such that the electrodes cause flow in the upper-left direction shown in FIG. 9, a second unit such that the electrodes cause flow directly toward the substrate, and a third such that the electrodes cause flow in the upper-right direction shown in FIG. 9. More generally, any number of plasma generating units may be used and placed in varying orientations to achieve divergent plasma flow and allow for improved coating of features or particles as described and shown in FIG. 9.
Generally, each system disclosed herein may be operated by placing or moving a substrate within the plasma generating unit, such that it is disposed between the electrodes. The unit may then be activated to produce a plasma, resulting in deposition on the substrate as previously described. The substrate may be placed on a substrate holder within a vacuum chamber, or may be placed on a moveable substrate holder that translates the substrate between the electrodes of each plasma generating unit. Such a substrate holder may be a roll-to-roll mechanism or any other suitable translation system as previously described.
Each system described herein may use one or more power supplies, electrically connected to one or more of the electrodes in each plasma generating unit. Each electrode or set of electrodes may be connected to a power supply that is electrically isolated from a power supply connected to another electrode or set of electrodes, or a single power supply may be used to provide power to multiple electrodes or sets of electrodes.
Although described and shown herein with substrates oriented horizontally orientated with the deposition side facing down for ease of illustration, embodiments disclosed herein are not so limited. That is, the substrate also may be horizontally orientated with the deposition side facing up, vertically orientated, or any other orientation.
It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. The present invention as claimed may therefore include variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art. It is understood that various theories as to why the invention works are not intended to be limiting.

Claims

1. A plasma deposition system comprising:

a first plasma generating unit comprising:

a first upper electrode;

a first lower electrode; and

a first gas inlet;

wherein the first plasma generating unit has a first horizontal dimension W and a second horizontal dimension L, and L is at least 3W.

2. The system of claim 1, wherein the first plasma generating unit further comprises a first central electrode disposed between the first upper electrode and the first lower electrode.

3. The system of claim 2, wherein the first central electrode is perforated.

4. The system of claim 2, further comprising:

a first electrical power supply electrically connected to the first upper electrode; and

a second electrical power supply, electrically separate from the first electrical power supply and electrically connected to the first lower electrode.

5. The system of claim 2, further comprising a first electrical power supply electrically connected to the first upper electrode and the first lower electrode.

6. The system of claim 1, wherein L is at least 10W.

7. The system of claim 1, wherein L is at least 20W.

8. The system of claim 1, further comprising a first gas distributor having a first horizontal dimension X and a second horizontal dimension M>X, the first gas distributor disposed adjacent to the first plasma generating unit with an edge having length M about parallel to an edge of the plasma generating unit having length L.

9. The system of claim 1, wherein the first gas inlet is disposed closer to an outer edge of the first plasma generating unit than to the center of the first plasma generating unit.

10. The system of claim 1, further comprising a second plasma generating unit comprising:

a second upper electrode;

a second lower electrode; and

a second gas inlet.

11. The system of claim 10, further comprising an insulator disposed adjacent to the second plasma generating unit and configured to prevent movement of a plasma beyond a region defined by the second upper electrode and the second lower electrode.

12. The system of claim 10, further comprising:

a first electrical power supply electrically connected to the first plasma generating unit; and

a second electrical power supply, electrically separate from the first electrical power supply, electrically connected to the second plasma generating unit.

13. The system of claim 10, wherein the second upper electrode is not parallel to the first upper electrode.

14. The system of claim 10, wherein the second lower electrode is not parallel to the first lower electrode.

15. The system of claim 1, further comprising a plurality N of plasma generating units, each of the plurality of plasma generating units comprising:

an upper electrode; and

a lower electrode.

16. The system of claim 15, wherein the total length of the plurality of plasma generating units in the W dimension is at least Z, and the total length of the plurality of plasma generating units in the L dimension is at least NW.

17. The system of claim 15, further comprising a cooling region disposed between the first plasma generating unit and the second plasma generating unit.

18. The system of claim 17, further comprising an active cooling system disposed in the cooling region.

19. The system of claim 17, further comprising a gas outlet disposed in the cooling region.

20. The system of claim 15, wherein at least a first of the N plasma generating units is disposed such that the upper electrode of the at least a first of the N plasma generating units is not parallel to an upper electrode of at least a second of the N plasma generating units.

21. A deposition system comprising:

a plasma deposition system as recited in claim 1; and

a moveable substrate holder configured to translate a substrate between the first upper electrode and the first lower electrode.

22. The system of claim 21, wherein the moveable substrate holder comprises a roll-to-roll substrate mechanism.

23. A method of depositing a layer on a substrate, comprising:

obtaining a substrate;

placing the substrate between a first upper electrode and a first lower electrode of a first plasma generating unit having a horizontal dimension W and a horizontal dimension L, wherein L is at least 3W;

introducing a first gas into the region between the first upper electrode and the first lower electrode; and

activating the first plasma generating unit to generate a first plasma adjacent to the substrate.

24. The method of claim 23, wherein the substrate is placed between the first upper electrode and the first lower electrode at an angle greater than 0 degrees.

25. The method of claim 23, wherein placing the substrate between the first upper electrode and the first lower electrode comprises translating the substrate between the first upper electrode and the first lower electrode.

26. The method of claim 23, further comprising:

placing the substrate between a second upper electrode and a second lower electrode of a second plasma generating unit having a horizontal dimension X and a horizontal dimension M, wherein M is at least 3X;

introducing a second gas into the region between the second upper electrode and the second lower electrode; and

activating the second plasma generating unit to generate a second plasma adjacent to the substrate.

27. The method of claim 26, wherein the substrate is placed between the first upper electrode and the first lower electrode at a first angle relative to the first upper electrode, and the substrate is placed between the second upper electrode and the second lower electrode at a second angle, different than the first angle, relative to the second upper electrode.