Patent Application
20080193643
This invention relates to systems and methods for depositing thin films using Atomic Layer Deposition (ALD).
As dimensions for microelectronics are reduced and the demand for such materials increase, thin semiconductor films having uniform composition and uniform thickness over a larger substrate area are increasingly desirable. A common process used for depositing thin films on a substrate is Chemical Vapor Deposition (CVD), which provides for deposition of relatively uniform films over complex device topography. In a typical CVD process, the substrate is exposed to two or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired thin film.
Despite improvements of CVD over previous deposition techniques, CVD has several disadvantages. For example, because CVD is flux-dependent, deposition conditions such as substrate temperature, pressure, and gas flow rate must be accurately and consistently maintained to produce a desired thin film of uniform thickness. Additionally, CVD tends to incorporate undesired reaction products into the deposited thin film, thereby diminishing the purity of the thin film.
Atomic Layer Deposition (ALD), which represents a variant of CVD, is a contemporary technology for depositing thin films now emerging as a potentially superior method of achieving highly uniform, conformal film deposition. ALD is a process wherein conventional CVD processes are divided into separate deposition steps to construct the thin film by sequentially depositing single atomic monolayers in each deposition step. The technique of ALD is based on the principle of the formation of a saturated monolayer of reactive precursor molecules by chemisorption. A typical ALD process consists of injecting a first precursor for a period of time until a saturated monolayer is formed on the substrate. Then, the first precursor is purged from the chamber using an inert gas. This is followed by injecting a second precursor into the chamber, also for a period of time, thus forming a layer on the wafer from the reaction of the second precursor with the first precursor. Then, the second precursor is purged from the chamber. This process of introducing the first precursor, purging the process chamber, introducing the second precursor, and purging the process chamber is repeated a number of times to achieve a layer of a desired thickness.
ALD thin films may be deposited using single wafer reactors with the reactive gas precursors injected into the process chamber horizontally. The horizontal gas precursor injection directs the gas precursors in a direction parallel to the surface of a stationary substrate. Arrangements in which the reactive gas precursors flow in a direction parallel to the substrate surface are desirable because they result in more uniform thin films than those deposited by gas precursors injected vertically in a direction perpendicular to the substrate surface. Nevertheless, a major disadvantage of a single wafer reactor is that it has a significantly diminished commercial value because of its relatively low throughput. Another disadvantage is that the process chamber must be purged before each individual gas precursor is introduced.
At least in part to overcome the commercial problems associated with single wafer reactors, multi-wafer reactors may be used for ALD processes in which the process chamber is partitioned into a plurality of process compartments. The substrates are rotated relative to the process compartments such that each substrate is sequentially transferred from one compartment to another. In each individual process compartment, each substrate is exposed to either a precursor gas or an inert gas. The rotating substrates are sequentially exposed to the different precursor gases and the inert gas. One characteristic disadvantage of these multi-wafer reactors is that multi-wafer reactors employ showerhead injectors that inject the precursor gases in an axially symmetric direction generally perpendicular to the substrate surface. As a result, although faster process times are achieved, multi-wafer ALD process chambers may produce thin films with reduced thickness uniformity.
Therefore, there is a need for a multi-wafer process chamber in which the reactive gas precursors are injected into each process compartment in a direction parallel to the top surface of the substrates.
One embodiment of the invention provides a deposition system for processing a plurality of substrates. The deposition system comprises a process chamber including a first wall, a second wall spaced apart from the first wall, and a peripheral sidewall connecting the first and second walls to define a processing space. A substrate support is configured to support the substrates between the first and second walls and radially inside the peripheral sidewall. The substrate support is configured to rotate the substrates relative to the peripheral sidewall in a closed path about an axis of rotation. A plurality of partitions extend relative to the axis of rotation toward the peripheral sidewall. The partitions divide the processing space into a plurality of compartments including a first compartment and a second compartment containing an inert atmosphere. A first material injector communicates through the peripheral sidewall with the first compartment and is configured to inject a first process material into the first compartment. A top surface of each of the substrates, during each complete rotation about the axis of rotation, is sequentially exposed to the first process material in the first compartment and the inert atmosphere in the second compartment.
Another embodiment of the invention provides a method for depositing a layer on each of a plurality of substrates. The method comprises arranging the substrates with a spaced circumferential relationship about an axis of rotation and rotating the substrates in a closed path about the axis of rotation. The method further comprises injecting a first process material in a radial direction relative to the axis of rotation and into a first compartment defined by partitions bounding a first included angle about the axis of rotation. During each complete rotation, a top surface of each of the substrates is exposed to the first process material within the first compartment to bond molecules of the first process material and, moreover, to an inert atmosphere within a second compartment defined by partitions bounding a second included angle about the axis of rotation.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention.
With reference to
The load/lock station 14 is adapted to be evacuated from atmospheric pressure to a vacuum pressure and to be vented from vacuum pressure to atmospheric pressure, while the process chamber 16 and transfer chamber 18 are isolated and maintained continuously under vacuum pressures. The load/lock station 14 holds a plurality of the wafer cassettes 20 introduced from the atmospheric pressure environment of the input/output station 12. The load/lock station 14 includes platforms 21, 23 that each support one of the wafer cassettes 20 and that can be vertically indexed to promote wafer transfers to and from the process chamber 16.
A wafer transfer mechanism 22 transfers substrates 15 under vacuum from one of the wafer cassettes 20 in the load/lock station 14 through the transfer chamber 18 and into the process chamber 16. Another wafer transfer mechanism 24 transfers substrates 15 processed in the process chamber 16 under vacuum from the process chamber 16 through the transfer chamber 18 and to the wafer cassette 20. The wafer transfer mechanisms 22, 24, which operate independently of each other for enhancing the throughput of the deposition system 10, may be selective compliant articulated/assembly robot arm (SCARA) robots commonly used for pick-and-place operations. The wafer transfer mechanisms 22, 24 include end effectors configured to secure the substrates 15 during transfers. The process chamber 16 may include distinct first and second sealable ports (not shown) used by wafer transfer mechanisms 22, 24, respectively, to access the processing space 38 (
The wafer transfer mechanism 24 may also transfer processed substrates 15 extracted from the process chamber 16 to a metrology station 26 for examination or to a cool down station 28 used for post-processing low pressure cooling of the substrates 15. The processes performed in the metrology station 26 may include, but are not limited to, conventional techniques used to measure film thickness and/or film composition, such as ellipsometry, and particle measurement techniques for contamination control.
The deposition system 10 is equipped with a system controller 30 programmed to control and orchestrate the operation of the deposition system 10. The system controller 30 typically includes a central processing unit (CPU) for controlling various system functions, chamber processes and support hardware (e.g., detectors, robots, motors, gas sources hardware, etc.) and monitoring the system and chamber processes (e.g., chamber temperature, process sequence throughput, chamber process time, input/output signals, etc.). Software instructions and data can be coded and stored within the memory for instructing the CPU. A software program executable by the system controller 30 determines which tasks are executed on substrates 15 including tasks relating to monitoring and execution of the processing sequence tasks and various chamber process recipe steps.
With continued reference to
A fore line 42, which has the form of a duct or tubular conduit bent at a right angle, is coupled with a port 44 extending through the first wall 32 of the process chamber 16. The fore line 42 couples the processing space 38 in fluid communication with a vacuum system 46, which consists of conventional vacuum pumps of a type used to evacuate gases from an enclosed volume like processing space 38. Although the fore line 42 is depicted as angled with a right angle bend, a person having ordinary skill in the art would appreciate that the fore line 42 may have any desired angular bend or may be straight with no bend at all. The latter configuration is believed to optimize the pumping conductance.
A susceptor having the form of a substrate support 48 is disposed inside the process chamber 16. The substrate support 48 includes a disk-shaped platter 50 and a plurality of circular pockets or recesses 52 defined in a top surface 49 of the platter 50. The top surface 49 of the platter 50 faces toward first wall 32 so that the recesses 52 open toward the first wall 32.
Each of the recesses 52 is configured to hold at least one of the substrates 15 at a location radially within the peripheral sidewall 36 of the process chamber 16. The number of individual recesses 52 may range, for example, from 2 to 7. However, a person having ordinary skill in the art would appreciate that the substrate support 48 may be configured with any desired number of recesses 52 depending on the dimensions of the substrates 15 and the dimensions of the substrate support 48. For example, configuring the platter 50 with between 3 and 6 recesses 52 shaped to receive round substrates 15 may optimize the usable fraction of the surface area of top surface 49. Additionally, although this embodiment of the invention is depicted as having recesses 52 of a circular or round geometrical shape, one of ordinary skill in the art would appreciate that the recesses 52 may be of any desired shape to accommodate an appropriately shaped substrate.
The deposition system 10 may be configured to process 200 mm substrates, 300 mm substrates, or larger-sized round substrates, which dimensioning will be reflected in the dimensions of recesses 52. In fact, it is contemplated that the deposition system 10 may be configured to process substrates, wafers, or liquid crystal displays regardless of their size, as would be appreciated by those skilled in the art. Therefore, while aspects of the invention will be described in connection with the processing of substrates 15 that are semiconductor substrates, the invention is not so limited.
The recesses 52 are distributed circumferentially on the platter 50 about a uniform radius centered on an axis of rotation 54. The recesses 52 have approximately equiangular spacing about the axis of rotation 54, which is substantially collinear or coaxial with the azimuthal axis 40 although the invention is not so limited. As best shown in
With continued reference to
A controller 62, which is electrically coupled to the drive motor 56, operates the drive motor 56 to rotate the platter 50 and drive shaft 58 about the axis of rotation 54. When the substrates 15 are processed in the process chamber 16, the rotation of the platter 50 may be continuous and may occur at a constant angular velocity about the axis of rotation 54. Alternatively, the angular velocity may be varied contingent upon the angular orientation of the platter 50 relative to an arbitrary reference point.
The portion of the processing space 38 between the platter 50 and the second wall 34 includes a pedestal 64 and a heater 66. The heater 66 is coupled to the pedestal 64 such that the heater 66 is at an intermediate location between a bottom surface 51 of the platter 50 and an upper surface 65 of the pedestal 64. When powered, the heater 66 transfers heat energy to the platter 50 for heating the substrates 15 held within the plurality of recesses 52 to a desired processing temperature.
Partitions 68, 70, 72, 74 compartmentalize the processing space 38 of process chamber 16 into a plurality of compartments 76, 78, 80, 82. The partitions 68, 70, 72, 74 extend radially relative to the axis of rotation 54 toward the peripheral sidewall 36. The partitions 68, 70, 72, 74 project upwardly from the top surface 49 of platter 50 towards the first wall 32. Each of the partitions 68, 70, 72, 74 has a height or vertical dimension, d1, approximately equal to the vertical dimension, d2, between the top surface 49 of platter 50 and the confronting surface of the first wall 32. Partition 68 extends between a first end 68a near the peripheral sidewall 36 and a second end 68b proximate to the axis of rotation 54. Partitions 70, 72, 74 have similar first and second ends 70a,b, 72a,b, and 74a,b, respectively.
The respective ends 68b, 70b, 72b, 74b of partitions 68, 70, 72, 74 intersect inside the fore line 42 at the axis of rotation 54, which may further reduce gas exchange among the four compartments 76, 78, 80, 82. The intersecting ends 68b, 70b, 72b, 74b project upwardly such that the vertical dimension, d3, of the partitions 68, 70, 72, 74 is greater within the fore line 42 than the vertical dimension, d1, outside of the fore line 42. However, the invention is not so limited as the partitions 68, 70, 72, 74 may have a uniform vertical dimension, d1, along their entire lengths.
Compartment 76 is defined as a portion of the processing space 38 bounded between the first partition 68, the second partition 70, the first wall 32, the second wall 34, and the peripheral sidewall 36. Compartment 78 is defined as a portion of the processing space 38 bounded between the second partition 70, the third partition 72, the first wall 32, the second wall 34, and the peripheral sidewall 36. Compartment 80 is defined as a portion of the processing space 38 bounded between the third partition 72, the fourth partition 74, the first wall 32, the second wall 34, and the peripheral sidewall 36. Compartment 82 is defined as a portion of the processing space 38 bounded between the first partition 68, the fourth partition 74, the first wall 32, the second wall 34, and the peripheral sidewall 36. Although four partitions 68, 70, 72, 74 are representatively shown, a person having ordinary skill in the art would appreciate that the process chamber 16 may be subdivided with any suitable plurality of partitions to form more or less than four compartments.
With continued reference to
Deposition system 10 further includes a first process material supply system 90 configured to introduce a first process material to compartment 76, and a second process material supply system 92 configured to introduce a second process material to compartment 80. The first and second material supply systems 90, 92 may each include one or more material sources, one or more heaters, one or more pressure control devices, one or more flow control devices, one or more filters, one or more valves, or one or more flow sensors as conventionally found in such process material supply systems.
The first process material can, for example, comprise a precursor, such as a composition having the principal atomic or molecular species found in a film formed on each of the substrates 15. For example, the precursor can originate as a solid phase, a liquid phase, or a gaseous phase, and it may be delivered to compartment 76 in either a gaseous or vapor phase, and either with or without the assistance of a carrier gas. The second process material can, for example, comprises a reactant, which may also have atomic or molecular species found in the thin film formed on substrates 15. For instance, the reactant can originate as a solid phase, a liquid phase, or a gaseous phase, and it may be delivered to compartment 80 in either a gaseous or vapor phase, and either with or without the assistance of a carrier gas.
The first process material supplied by the first process material supply system 90 to process chamber 16 and the second process material supplied by the second process material supply system 92 to process chamber 16 are selected in accordance with the composition and characteristics of a material to be deposited as the thin film on the substrate. For example, the first process material can include a metal organic precursor, such as trimethylaluminum (TMA), and the second process material can include nitrogen (N2) or oxygen (O2). In another example, the first process material can include a precursor, such as tantalum pentachloride (TaCl5), and the second process material can include a reducing agent, such as hydrogen (H2) gas. The temperature and pressure of the first and second process materials are also selected to promote thin film growth.
A first set of injection ports 102 and a second set of injection ports 104 extend through the peripheral sidewall 36 to communicate with compartment 76. The injection ports 102, 104, which collectively define a material injector 100, are coupled by a first manifold 94 with the first process material supply system 90. Injection ports 102, 104 inject the first process material into the compartment 76. A third set of injection ports 108 and a fourth set of injection ports 110 extend through the peripheral sidewall 36 to communicate with compartment 80. The injection ports 108, 110, which collectively define a material injector 106, are coupled by a second manifold 96 with the second process material supply system 92. Injection ports 108, 110 inject the second process material into the compartment 80.
Injection ports 102 of material injector 100 are located proximate to the first partition 68. Injection ports 102 are aligned along a first angular arc 112 extending about the peripheral sidewall 36 in a first plane 114 (
Injection ports 108 of material injector 106 is spatially positioned proximate to the third partition 72. Injection ports 108 are aligned along a third angular arc 120 extending about the peripheral sidewall 36 in a third plane 122. The third plane 122 is located above the second set of injection ports 110 and at a height, h3, above the top surface 49 of the platter 50. The third plane 122 is substantially parallel to the plane containing the top surface 49. Injection ports 110 are spatially positioned proximate to the fourth partition 74. Injection ports 110 are disposed along a fourth angular arc 124 extending about the peripheral sidewall 36 in a fourth plane 126. The fourth plane 126 is at a height, h4, above the top surface 49 of the platter 50 and is parallel to the plane containing the top surface 49. The angular arcs 112, 116, 120, 124 are each measured circumferentially about the peripheral sidewall 36.
In one embodiment of the invention, the first set of injection ports 102 and the third set of injection ports 108 are substantially coplanar, so that height, h1, and height, h3, are substantially equal, and the second set of injection ports 104 and the fourth set of injection ports 110 are substantially coplanar, so that height, h2, and height, h4, are substantially equal. The heights h1-h4 may be adjusted such that planes 114, 118, 122, 126 may have other relative arrangements, as would be appreciated by a person having ordinary skill in the art.
In one specific embodiment of the invention, the first angular arc 112 and the third angular arc 120 may each span an arc angle of about 44°. The second angular arc 116 and the fourth angular arc 124 may each span an arc angle of about 22°. A person of ordinary skill in the art would appreciate that each of the compartments 76, 78, 80, 82 may be independently equipped with any desired number of injection ports 102, 104, 108, 110, respectively, and that the respective angular arcs 112, 116, 120, 124 may each span any desired arc angle. The number of injection ports 102, 104, 108, 110 and the arc angles for the angular arcs 112, 116, 120, 124 are selected to cooperate for optimizing at least one property of the thin film being deposited on each of the substrates 15 and/or for optimizing the flow of the first and second process materials across the top surface of the substrates 15.
The material injectors 100, 106 may be configured to inject the respective first and second process materials in a substantially radial direction away from the peripheral sidewall 36 and toward the axis of rotation 54. In this configuration, process material injection from each of the material injectors 100, 106 in combination with simultaneous evacuation through the fore line 42 creates a gas flow of the respective process materials from the peripheral sidewall 36, across the substrates 15 in a direction substantially parallel to the top surface of each of the substrates 15, and towards the central location of fore line 42. As a consequence, excess process materials and deposition by-products from reactions transpiring at the top surface of the substrates 15 are removed through the fore line 42 as fresh process materials are replenished in the compartments 76, 80.
When the substrate support 48 is rotated about the axis of rotation 54, the arrangement of the recesses 52 about the circumference of the platter 50 allows each substrate 15 to be sequentially exposed to the different environment inside each of the compartments 76, 78, 80, 82. By way of example, upon rotation of the substrate support 48 through a closed path of 27π radians (360°), each of the substrates 15 is serially exposed to first process material in the environment inside the first compartment 76, then to the purge gas comprising the environment inside the second compartment 78, then to the second process material in the environment inside the third compartment 80, and finally to the purge gas comprising the environment inside the fourth compartment 82. Each of the recesses 52 has a desired dwell time in each of the respective compartments 76, 78, 80, 82, as mandated by the characteristics of the thin film to be deposited on each of the substrates 15, sufficient to form the thin film.
The second wall 34 includes a bottom purge opening 130 for introducing a purge gas from a purge gas system 131 into the process chamber 16 beneath or under the substrate support 48. The presence of purge gas under the substrate support 48 may serve to reduce the transfer of the first and second process materials outside of their respective compartments 76, 80.
In use and with reference to
Before and after the exposure to the first process material, each of the continuously rotating substrates is exposed to an inert atmosphere within the second and fourth compartments 78, 82, which respectively bound the second and fourth angular arcs 116, 126 about the axis of rotation 54 during each complete rotation. The second process material is injected in the radial direction relative to the axis of rotation 54 and into the third compartment 80, which is isolated from the first compartment 76 by the second and fourth compartments 78, 82. The layer is incrementally formed as a series of discrete thin film lamina on each of the continuously rotating substrates 15 by chemical reactions of the first and second process materials. By way of example only and not limitation, the vacuum pressures inside the first and second compartments 76, 80 may be on the order of 10 Torr and the substrates 15 may be heated to a process temperature of about 400° C. while exposed to the first and second process materials.
The deposition process form is a conventional deposition technique in which deposition of each atomic layer of the thin film, or a fraction thereof, on the substrates 15 is controlled by alternating and sequential introduction of appropriate gas phase precursors that react in a self-limiting manner to incrementally form or build the thin film. Within the first compartment 76, molecules of the first process material bond (chemically, by absorption, by adsorption, etc.) to the top surface of each of the substrates 15 to form a monolayer or a fraction of a monolayer of the first process material. Within the third compartment 80, the second process material reacts with the molecules of the first process material on each successive substrate 15. As the substrates 15 are rotated through the first and third compartments 76, 80, these steps are repeated with sequential subsequent exposures to the first and second process materials. The environments of first and second process materials in the first and third compartments 76, 80, respectively, are isolated from each other by the chemically non-reactive, purge gas environments inside the second and fourth compartments 78, 82. The environments inside the first and third compartments 76, 80 are not altered to achieve the successive exposure to the first and second materials.
The substrates 15 may be heated to a process temperature to promote the deposition process. In comparison with predominantly thermally driven CVD processes, ALD is predominantly chemically driven. Accordingly, ALD may be conducted at significantly lower substrate temperatures than CVD.
The rotation of the substrates 15 may be regulated such that different substrates 15 are exposed to the first process material when the injection of the first process material is initiated and the injection of the first process material is discontinued. This type of regulation may be effective for controlling the uniformity of deposited layers that are relatively thin. The compartments 76, 78, 80, 82 may be evacuated through the fore line 42 communicating with the first compartment from a location above the substrates. The substrates 15 may be rotated about the axis of rotation 54 with a constant angular velocity.
The invention contemplates that the partitions 68, 70, 72, 74 compartmentalizing the processing space 38 may be adjusted such that the compartments 76, 78, 80, 82 are merged together into a single compartment for depositing layers by CVD processes in the process chamber 16. Specifically, the partitions 68, 70, 72, 74 may be configured to be pivoted, as indicated by reference numeral 135, by a positioning device (not shown) about a radial axis 137 extending generally from the axis of rotation 54 from a vertical orientation (as shown in
With reference to
With reference to
With reference to
The process chamber 16c may be used for plasma-enhanced atomic layer deposition of thin films on the substrates 15. The invention contemplates that, although process chamber 16c includes multiple plasma sources 144, 152, either the first process material or the second process material may be supplied to compartments 76, 80 using injection ports 102, 104, 108, 110 (
With reference to
With specific reference to
With specific reference to
As the platter 50 of substrate support 48 (
With reference to
Although the partitions 68b, 70b, 72b, 74b are arranged such that α1 is about 270° and α2 is about 30°, a person having ordinary skill in the art would appreciate that the partitions 68b, 70b, 72b, 74b can be configured to provide for any desired dwell times within the four compartments 76b, 78b, 80b, 82b. The dwell times may be adjusted to, for example, compensate for first and second process materials having different reaction rates. For example, the dwell time for exposure to the first process material in the first compartment 76b is significantly greater than the dwell time for exposure to the second process material in the second compartment 80b, which would maximize the exposure to the first process material to compensate for a second process material that is fast acting.
While the invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.
