The present disclosure relates to method and apparatus for depositing thin sputtered film, and in particular, for depositing nanoscale thin layer on a flexible substrate.
A reel-to-reel sputtering apparatus is widely used as a thin film deposition. One of the reasons for the widespread use is a high productivity with a low running cost. In general, a reel-to-reel plasma sputtering system enables manufacturing various devices by depositing thin film layers onto a substrate as the substrate moves through a high vacuum plasma sputtering chamber. The microstructure and morphology of growing film may be determined by certain factors of energy and direction of sputtered atoms. Sputtered atoms from a sputtering target collide with gas particles present in the vacuum chamber during transport to the substrate, and the collisions can change the atomic energy, direction, and momentum. Thus, the flux distribution of sputtered atoms is nonuniform. As such, it is crucial to develop a new technique or apparatus for achieving highly uniform thin film growth by a reel-to-reel sputtering system.
Generally speaking, the term sputtering is often referred to one of physical vapor deposition methods, in which the deposition process starts with ejection of atoms by bombardment between energetic ions and the surface of a sputtering target. All sputtered atoms leaving the target surface are enabled to collide with the gas atoms present in a vacuum chamber while moving to the substrates. The collisions change the atom direction, energy, and momentum, thereby affecting the microstructure and morphology of growing films. Hence, the important parameters determining the microstructure and morphology of the growing film include energy of bombarding ions and gas pressure.
To explain the energy and angular distribution of sputtered atoms leaving the target, Sigmund-Thompson theory is utilized because nearly all other analytical models of the sputtering process are dependent on the Sigmund-Thompson theory. Based on Sigmund-Thompson theory, it is available to separate the collision cascade into three regimes: the single-knock-on regime, the linear cascade regime, and the spike regime, which are determined by the incident energy of bombarding ions. For example, the single-knock-on regime, the linear cascade regime, and the spike regime are characteristic of the lowest incident energy, several hundreds to KeV energy, and MeV energy, respectively. In the single-knock-on regime, the energy is transferred from ions in the plasma to target surface when the ions are bombarded to the target atoms. A small number of one-to-one collisions are possibly generated. In the linear and the spike regime, the recoiled target atoms are vigorous enough to produce secondary and higher generation recoils.
In this regard, a cascade of recoils is produced, and some atoms at the target surface may be escaped. This regime is named linear because the sputter yield is proportional to the applied power on the target material. In the spike regime, the density of recoiled atoms is sufficiently high to generate collisions between two moving atoms. In a quantitative respect, the regimes can be distinguished by the range of bombarding particle's energy. The single-knock-on regime, the linear cascade regime, and the spike regime are characteristic for bombarding particles with the lowest incident energy, several hundreds to KeV energy, and MeV energy, respectively. Since the bombarding particles in the magnetron sputtering consist of the range of several hundreds' eV energy, the linear cascade regime has been the main concern.
The sputtering yield may be expressed as the number of sputtered atoms per bombarding ions. In case for low energy ion bombardment (hundreds' eV), the sputter yield may be expressed as shown below:
where E is the energy of bombarding ion, and M1 and M2 are the masses of the ion and the target atom. α is a dimensionless parameter associated with the ion energy and mass ratio between the ion and the target atom. Us is the surface binding energy of the target. Based on the equation, M1=M2 means the bombarding ions transfers its maximum momentum to the target atoms. This momentum transferred from ion bombardment should overtake the surface barrier (Us) to sputter an atom from the target.
In the magnetron sputtering system, ejection positions of the sputtered atoms are according to a racetrack of a magnetron. The sputtered atoms are ground-state atoms, and these are elastically collided with neutral gas atoms because of two reasons. The first reason for the collision is the very low ionization degree. The number of ionized atoms per total gas atom in the chamber is ˜0.1%. The second reason for the collision is that the density of the sputtered atoms is much less than the neutral gas density. Based on these reasons, the passage of sputtered atoms through the plasma and neutral gas atoms can be considered as a sequence of straight trajectories, which may be stopped by a binary elastic collision with a gas atom. As such, the free path length until the next collision depends on the velocity of the sputtered atoms V.
However, the existing technology has many shortcomings and challenges. By way of example, among many other challenges, it is often difficult to achieve highly uniform ultra-thin film deposition with a controlled deposition rate on a flexible substrate. Many others have tried to overcome this film non-uniformity problems using a hybrid of alternating current (AC) and radio frequency (RF) combination power, a specially shaped linear magnetron sputtering target, or a continuously rotating sputtering target, all of which result in increases in the manufacturing costs as well as decreases in the production throughput because of issues relating to equipment reliability, equipment maintainability load/unload times, and production yield. As such, there is still a need for advanced methods and techniques for overcoming these challenges relating to the reel-to-reel sputtering deposition of ultra-thin films on a flexible substrate.
The present technology disclosed herein overcomes the challenges in a cost-effective manner as well as provides advanced features for a reel-to-reel sputtering system. In view of the challenges of the existing technology, the present technology eliminates one or more major hurdles relating to the existing reel-to-reel sputtering deposition of ultra-thin films on a flexible substrate during the plasma deposition process, in various aspects of the present disclosure.
In an aspect of the present disclosure, an apparatus for depositing a thin sputtered film in a deposition chamber is provided. By way of example, the apparatus includes a processing chamber, one or more sputtering devices in the processing chamber, a mask device disposed in the processing chamber, mask supporters coupled to the mask device, a first roller set, a second roller set, and a flexible substrate. The flexible substrate may be configured to move from the first roller set to the second roller set.
In an aspect of the present disclosure, the apparatus may further include a first vacuum chamber and a second vacuum chamber, wherein the first roller set is disposed in the first vacuum chamber. Further, the flexible substrate is configured to move from/to the first roller set to/from the second roller set, while the one or more sputtering devices are activated to sputter atoms on the substrate through the mask device.
in an aspect of the present disclosure, the one or more sputtering devices include either a direct current (DC) power sputtering device or a radio frequency (RIF) power sputtering device.
In an aspect of the present technology, the one or more sputtering devices include a dual-purpose sputtering device configured to provide a DC power sputtering and/or RF power sputtering.
In an aspect of the present technology, the one or more sputtering devices are coupled to the processing chamber via one or more rotary mechanisms.
In an aspect of the present disclosure, the mask device is configured to include two sliding doors and wherein the two sliding doors are in an open position such that sputtered atoms arrive at the flexible substrate through an opening, forming a deposition film having a uniform thickness.
In an aspect of the present disclosure, the opening is formed by the two sliding doors of the mask device and the two sliding doors are separated a distance of 9 cm apart from each other.
In an aspect of the present disclosure, the one or more sputtering devices are disposed to have a distance of 2 cm-6 cm away from the flexible substrate disposed in the processing chamber.
In another aspect of the present disclosure, the apparatus further includes one or more target materials coupled to the one or more sputtering devices.
In another aspect of the present disclosure, wherein the second vacuum chamber is disposed in a glove box coupled to the processing chamber of the reel-to-reel sputtering system.
In another aspect of the present disclosure, the apparatus further includes a real-time monitoring system, an automatic deposition control system, and a user interface.
In another aspect of the present disclosure, the automatic deposition control system in configured to: receive a target type and a desired film thickness, and determine a discharge power, a chamber pressure, and a speed of the flexible substrate.
A more detailed understanding may be obtained from the following description in conjunction with the following accompanying drawings.
The detailed description of illustrative examples will now be set forth below in connection with the various drawings. The description below is intended to be exemplary and in no way limit the scope of the claimed invention. It provides detailed examples of possible implementation(s), and as such they are not intended to represent the only configuration(s) in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts, and it is noted that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts and like reference numerals are used in the drawings to denote like elements and features.
It is also noted that in some instances while the methodologies are described herein as a series of steps or acts, for the purpose of simplicity it is to be understood that the claimed. subject matter is not limited by the order of these steps or acts, as some steps or acts may occur in different orders and/or concurrently with other acts from that shown and described herein. Further, not all illustrated steps or acts may be required to implement various methodologies according to the present technology disclosed herein. Also, it should be appreciated that the apparatus and methods described herein may be utilized separately or in combination with other aspects of the present disclosure, or in combination with conventional technology, without departing from the teachings of the present disclosure.
The present disclosure relates to an apparatus and reel-to-reel antioxidation sputtering method for growing one or more highly uniform thin films on a flexible substrate. The target materials may include metals and transition metal dichalcogenides (TMDs), and substrates are flexible metals.
In an aspect of the present disclosure, by way of example,
By way of example, in an aspect of the present disclosure,
In the example, the deposition chamber 102 may include a direct current (DC) power sputtering device 106 and/or a radio frequency (RF) power sputtering device 107 disposed in the deposition chamber 102. The deposition chamber 102 of the reel-to-reel sputtering system 100 may further include a mask device 108 and substrate supporters 112. The mask device 108 is configured to be a size adjustable aperture 108 and positioned between sputter targets such as a first sputter target 109 and a second sputter target 110 and a flexible substrate foil 111 in the deposition chamber 102. In the example, the first sputter target 109 is coupled to the DC power sputtering device 106 and a second sputter target 110 is coupled to the RF power sputtering device 107. Also, the substrate supporters 112 are disposed below the substrate foil 111.
In an aspect of the present disclosure, in preparation for operation of the apparatus 130, sputter target materials such as target materials 109, 110 may be installed in each target holder or sputtering devices 106, 107 inside the deposition chamber 102. Further, the substrate foil 111 may be installed between the first roller set 113 and the second roller set 114, prior to the operation of the apparatus 130. For example, a rolled substrate foil may be prepared in advance and placed on the second roller set 114 through a third vacuum chamber door (not shown) and then on the first roller set 113 through a second vacuum chamber door (not shown) and the glove box. Further, before installation of the substrate foil 111, two dummy foils such as thin copper dummy foils may be rolled up both the first winding/unwinding roller set 113 and the second winding/unwinding roller set 114, separately. Also, the edge of the substrate foil 111 may be bound to an edge of the dummy foil which is rolled up the first roller set 113, and the other edge of the substate foil 111 may be bound to the edge of the dummy foil rolled up on the second roller set 114.
In an aspect of the present disclosure, as shown in
In another aspect of the present disclosure, for the operation of the reel-to-reel sputtering system 100, a process gas for creating plasma may be filled in the processing chamber 102 and a negative bias may be applied to the sputtering devices disposed inside the processing chamber, for a deposition process of a thin film or film growth on a flexible substrate. By way of example, in one implementation, the negative bias may be applied to the first sputtering device 106 for metal film growth and to the second sputtering device for ceramic film growth. When the substrate foil 111 (including a first dummy substrate, a substrate foil, and a last dummy substrate) is moved toward the third vacuum chamber 104 from the second vacuum chamber 103, atoms are sputtered and the sputtered atoms may arrive at the first dummy substrate, the substrate foil 111, and the last dummy substrate, through the mask device 108, as the substrate foil 111 is moved from the first roller set 113 to the second roller set 114.
In the example, the speed of the substate foil 111 may be controlled by the first motor 116 coupled to the first roller set 113 and the second motor 117 coupled to the second roller set 114. In another aspect of the present disclosure, for the deposition of a composite film, negative biases may be applied to both the first sputtering device 106 and the second sputtering device 107 simultaneously. Further, in another aspect of the present disclosure, for the deposition of a multi-stacked film, the negative bias may be applied to the first sputtering device 106 as the substate foil 111 moves in the direction towards the third vacuum chamber 114 for a first film growth, and then a negative bias may be applied to the second sputtering device 107 as the substate foil 111 moves in the direction towards the second vacuum chamber 103 for a second film growth. That is, the substrate foil 111 may move back and forth between the first and second roller sets as different sputtering devices are engaged. Further, after the completion of the deposition process of thin films, the substrate foil 111 may be rolled in the second vacuum chamber 103 and moved to the inside of the glove box 101 from the second vacuum chamber 103 after argon gas is filled in the deposition chamber 102 and the vacuum chambers 103 and 104.
In another aspect of the present disclosure, the size dimension of the main sputtering chamber may include a dimension of 45 cm (width) by 60 cm (height). Further, the two target holders may be disposed on a ceiling portion of the deposition chamber 102, and targets 109, 110, for example, ceramic or metal targets may be disposed on the target holders of the respective magnetron devices for operation of depositing a single layer, multi layers, or co-sputtered layers on the flexible substrate 13. Further, in another aspect of the present disclosure, the magnetron devices may be disposed such that a distance of about 4 cm˜5 cm is maintained between the targets and the mask device 108. Also, in the example, the flexible substrate 13 may be disposed a distance of 2 cm-3 cm away from the mask device 108 as the flexible substrate 13 moves from the second chamber to the third chamber, or in a forward direction. Also, as mentioned above, the flexible substrate 13 may move in a backward direction from the third chamber to the second chamber. Further, the apparatus 100 may include two substrate supports 21 under the foil substrate 13 to prevent forming of a convex down shape (e.g., sagging) of the flexible substrate 13. In the example, when the flexible substrate 13 is not flat, it is noted that a thickness of the deposited films may be non-uniform and thus may be out of a desirable range of a film thickness variance.
In another aspect of the present disclosure, two parameters are relevant to the design of the present technology. The first parameter is the energy distribution of emitted atoms from a sputtering target. A conventional magnetic plasma sputtering system includes ring-shaped magnets under its target holder as shown in
In an aspect of the present disclosure, to obtain desired sputtering outcomes, these two parameters (e.g., energy distribution of emitted atoms and the distance between the substate and the sputtering target) need to be taken into consideration and controlled. In the example, and in an aspect of the present disclosure, a mask device may be designed and disposed to block the high energy atoms from the sputtering target and to allow the atoms having low energy for depositing on the flexible substrate without bouncing out or moving through the surface. The hole or opening size of the mask device may be in various design and be controlled, depending on the distance between the flexible substrate and the sputtering target.
In another aspect of the present disclosure,
In another aspect of the present disclosure,
In another aspect of the present disclosure,
Further,
In another aspect of the present disclosure, the present technology may include or combined with one or more of the conventional reel-to-reel techniques. By way of example, in a conventional reel-to-reel sputtering system, the two representative ways are useful for enhance the sputtered film uniformity. First, heat may be used to increase the uniformity of the deposited film thickness. In one example, the heat may be generated to a flexible substrate after the sputtering process is started. A substrate heater that can sustain the substrate at a high temperature may be essential. In such a case, in a vacuum sputtering system, a heating lamp or a heater coil may be used for a heating element. Also, the effect of having an increase in the substrate temperature has been theoretically and experimentally proved that the crystallite size increases with increasing the substrate temperature. Since thermal energy is transferred from the heater to the arriving atoms on the substrate surface, the atoms have enough energy to move until the grain boundaries in the film. The other way to enhance the film uniformity is rotating the target holder. The angular distribution of the atoms leaving the target is highly directional. In addition, in the center part of the target, the largest atoms are emitted with the highest energy than the edge part. All emitted atoms from the target may be capable to collide with gas particles present in the deposition chamber during transport to the substrate. However, in case of the distance between the substrate and the target is close to each other, the emitted atoms may be still directional after colliding with other particles. As such, the rotating target holder during the deposition process of thin films may be helpful to make the deposition of films more uniform by reducing the angular and energy distribution within the target area.
Further, generally, the influence of deposition parameters on morphology and. microstructure of the sputtered film depends on the energy flux sputtered atoms. At low energy of ions, the sputtered atoms will stick to the surface of the substrate and stay in the position because the mobility of sputtered atoms is low to overcome the existing diffusion barrier. Thus, formation of only small crystalline island enables to grow. The grown films have porous structure and reduced density. Hence, overhang structures can be formed. When the energy of the sputtered atoms increases, the mobility also increases, and the film density can be enhanced. The voids in the film begin to be filled with the target atoms and then become a denser film. The mobility of sputtered atoms also affects to grain size and morphology. If the high mobility sputtered atoms arrive to surface of the substrate, the atoms can move to the edge of the crystal or grain due to the high diffusion length; thus, a high mobility result in a lateral growth, whereas a low mobility helpful to a normal growth of the crystal plane. Further, increasing the mobility of sputtered atoms is conducive to the film consisting of straight columns, and then the columns forming the film will enlarge their diameter. In addition, when the energy flux of sputtered atoms surpasses 10 eV, the incident atoms can penetrate into a substrate and form some atomic size voids. Meanwhile, some incident atoms bounce out after a collision with a substrate and then bump against other incident atoms or gas atoms. Therefore, a higher energy flux can form a film having a rough surface and straight column structure.
In still another aspect of the present disclosure, an investigation is carried out as to how sputtering conditions affect grain structure variations in the deposited MoS2 film layers on the substrates. By way of example, while a thickness of deposited MoS2 layer on Li-metal is set to about 25 nm (±1.5 nm) and the speed of the flexible substrates was set to 10 mm/min, sputtering conditions such as discharge power and chamber pressure are varied from 125 \'V to 250 W and 5 mTorr to 25 mTorr, respectively. Based on the above operational parameters, the surface morphology measurements were investigated using Atomic Force Microscope (AFM) to determine how the grain structure is affected by the varying operational parameters during the sputtering process. The results are shown
In another aspect of the present disclosure,
As shown above, various methods, techniques, arrangements or their variants may be implemented for artificial trees or plants with capability of producing scent or other features. Other embodiments of the present technology may be possible and are not limited to the disclosed embodiments herein.
Further, as mentioned above, it is noted that as used in the specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents or one or more items, unless the context clearly indicates otherwise. Also, no element, act, step, or instruction used in the present disclosure should be construed as critical or essential to the present disclosure unless explicitly described as such in the present disclosure. As used herein, except explicitly noted otherwise, the term “comprise” or variations of the term, such as “comprising,” “comprises,” and “comprised” are not used to exclude other additives, components, integers or steps. The term “first,” “second,” and so forth used herein may be used to describe various components, but the components are not limited by the above terms. The above terms are used only to discriminate one component from other components, without departing from the scope of the present disclosure. Also, the term “and/or” as used herein includes a combination of a plurality of associated items or any item of the plurality of associated items. Further, it is noted that when it is described that an element is “coupled” or “connected” to another element, the element may be directly coupled or directly connected to the other element, or the element may be coupled or connected to the element through a third element. Also, the term “include” or “have” as used herein indicates that a feature, an operation, a component, a step, a number, a part or any combination thereof described herein is present. Furthermore, the term “include” or “have” does not exclude a possibility of presence or addition of one or more other features, operations, components, steps, numbers, parts or combinations. It is also noted that the foregoing relates only to exemplary embodiments of the present invention or technology and that numerous modifications or alternations may be made therein without departing from the spirit and the scope of the present disclosure as set forth in this disclosure.
Although the exemplary embodiments of the present disclosure are provided herein, the present disclosure is not limited to these embodiments. There are numerous modifications or alternations that may suggest themselves to those skilled in the art. It is appreciated by one skilled in the art that a wide variety of alternate and/or equivalent implementations may be substituted for the specific examples shown and described without departing from the scope of the present disclosure. As such, the exemplary embodiments should not be construed in any way as imposing limitations upon the scope thereof. On the contrary, it is understood that various other embodiments, modifications, and equivalents thereof which, after reading the description herein, may suggest themselves to those skilled in the art without departing from the spirit of the present invention or disclosure and/or the scope of the appended claims.
This application claims the benefit of U.S. Provisional Patent App. No. 63/113178, filed Nov. 12, 2020, which is incorporated by reference herein in its entirety.
Number | Date | Country | |
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63113178 | Nov 2020 | US |