Patent Application
20190376184
Chemical Vapor Deposition (CVD) tools are used for depositing thin films on substrates. One type of CVD tool, called a Plasma Enhanced CVD or “PECVD” tool, includes a process chamber, a substrate holder for positioning a substrate in the process chamber, and a shower head. During operation, the shower head distributes a reactant gas above the surface of the substrate to be processed. A Radio Frequency (RF) potential is applied to the shower head, and possibly the substrate holder as well, to generate a plasma. Energized electrons ionize or dissociate (e.g., “crack”) reactant gasses from the plasma, creating chemically reactive radicals. As these radicals react, they deposit and form a thin film on the substrate.
One issue with current shower heads used for PECVD is that the holes provided on the shower head for gas distribution are typically arranged in symmetrical patterns. With symmetrical patterns, macroscopic areas, along the lines of symmetry, tend to form where the velocity vector of the reactant gas exiting the shower head has zero azimuthal velocity and/or stagnate completely. As a result, certain properties of the thin film deposited on the substrate can be non-uniform. In addition, in the locations of stagnant gas flow, the deposited film is susceptible to defects. With certain types of substrates, such as semiconductor wafers, defects are a problem because they may result in non-functioning die, reducing fabrication yields.
An improved shower head design for deposition tools is therefore needed.
A shower head for a Chemical Vapor Deposition (CVD) tool that provides more even gas distribution, resulting in improved uniformity of deposited layers and fewer defects on substrates, is disclosed. The shower head includes a gas dispensing surface having a first set of holes arranged in a first spiral pattern, the first set of holes in fluid communication with a first supply of a first gas and a second set of holes arranged in a second pattern, the second set of holes in fluid communication with a second supply of a second gas, and possibly additional sets of holes in fluid communication with additional supplies of additional gasses. The various patterns reduce or altogether eliminate stagnant or uneven gas flow at the gas dispensing surface of the shower head. Such patterns are preferably, but not exclusively, non-symmetrical patterns that mitigate or eliminate lines or symmetry, allowing for a highly uniform gas flow in the vicinity of the gas dispensing surface of the shower head and above the substrate to be processed. By using non-symmetrical patterns, such as various types of spirals, deposition layers are significantly more uniform, resulting in fewer defects and higher yields.
In non-exclusive embodiments, the patterns of one or more sets of holes are a variety of different types of spirals or close approximations thereof. Examples of such spirals may include, but are not limited to, Archimedean, Vogel, or Fermat spirals.
In yet other embodiments, the various types of spirals may be arranged in a number of different ways on the gas distribution surface of the shower head. Such arrangements may include, but are not limited to, concentric, non-concentric, clock-wise and counter-clockwise spirals, spirals with holes of different sizes, spirals with holes of different densities, three or more spiral patterns, etc.
In yet other embodiments, one or more of the patterns may be spirals, but the remainder of the patterns may be symmetrical. The various patterns may each be supplied by separate plenums.
The present application, and the advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:
In the drawings, like reference numerals are sometimes used to designate like structural elements. It should also be appreciated that the depictions in the figures are diagrammatic and not necessarily to scale.
The present application will now be described in detail with reference to a few non-exclusive embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art, that the present discloser may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present disclosure.
Referring to
During operation, reactant gas(es) are supplied into the process chamber 12 through the shower head 14. Within the shower head 14, the gas(es) is/are distributed via one or more plenums (not illustrated) into the chamber 12, in the general area above the surface of the substrate 18 to be processed. An RF potential, generated by the RF generator 20, is applied to an electrode (not illustrated) on the shower head 14. An RF potential may also possibly be applied to the substrate holder 18 (also not shown) as well. The RF potential generates a plasma 24 within the processing chamber 12. Within the plasma 24, energized electrons ionize or dissociate (i.e., “crack”) from the reactant gas(es), creating chemically reactive radicals. As these radicals react, they deposit and form a thin film on the substrate 18.
In various embodiments, the RF generator 20 may be a single RF generator or multiple RF generators capable of generating high, medium and/or low RF frequencies. For example, in the case of high frequencies, the RF generator 20 may generate frequencies ranging from 2-100 MHz and preferably 13.56 MHz or 27 MHz. When low frequencies are generated, the range is 50 KHz to 2 MHz, and preferably 350 to 600 KHz
The system controller 22 is employed to control operation of the CVD tool 10 in general and process conditions during deposition, post deposition, and/or other process operations. The controller 22 typically includes one or non-transient computer readable medium devices for storing system control software or code computer and one or more processors for executing the code. The term “non-transient computer readable medium” is used generally to refer to media such as main memory, secondary memory, removable storage, and storage devices, such as hard disks, flash memory, disk drive memory, CD-ROM and other forms of persistent memory and shall not be construed to cover transitory subject matter, such as carrier waves or signals. The processor may include a CPU or computer, multiple CPUs or computers, analog and/or digital input/output connections, motor controller boards, etc.
In certain embodiments, the controller 22, running or executing the system software or code, controls all or at least most of the activities of the tool 10, including such activities as controlling the timing of the processing operations, frequency and power of operations of the RF generator 20, pressure within the processing chamber 12, flow rates, concentrations and temperatures of gas(es) into the process chamber 12 and their relative mixing, temperature of a substrate 18 supported by the substrate holder 16, etc.
The controller 22 may also include a user interface (not shown). The user interface may include a display screen, graphical software displays of indicative of operating parameters and/or process conditions of the tool 10, and user input devices such as pointing devices, keyboards, touch screens, microphones, etc., that allow a human operator to interface with the tool 10.
Information transferred between the system controller 22 and the various components of the tool 10 may be in the form of signals such as electronic, electromagnetic, optical, or other signals capable of being transmitted and/or received via any communication link that carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, a radio frequency link, and/or other communication channels.
Referring to
The first gas conduit 44 is in fluid communication with the first plenum 36. In turn, the first plenum 36 is in fluid communication with each of the first set of holes 34. With this arrangement, gas supplied into the first gas conduit 44 flows into the first plenum 36 and then through the first set of holes 34 and through the gas dispensing surface 32 of the shower head 14.
The second gas conduit 46 is in fluid communication with the second plenum 40. In turn, the second plenum 40 is in fluid communication with each of the second set of holes 38. With this arrangement, gas supplied into the second gas conduit 46 flows into the second plenum 40 and then through the second set of holes 38 and through the gas dispensing surface 32 of the shower head.
Referring to
The first gas and the second gas may be different in a number of ways. For instance, the two gases may be entirely different (e.g. one oxygen, the other hydrogen). Alternatively, the two gases may be in fact the same gas, but supplied to the shower head 14 at either (a) different flow rates, (b) different pressures and/or (c) both different pressures and flows rates. The two gases may include the same mixture of two or more gases, but differ in the ratio of the two gases. In various embodiments, the gases may include any gas, including but not limited to reagant gasses, such as silane, dichlorosilane, oxygen, nitrous oxide, hydrogen, tetraethoxysilane, helium, fluorine, nitrogen, argon, acetylene, atomic oxygen, atomic fluorine, and mixtures thereof.
For the first gas, a flow rate controller 54 and a pressure controller 56 are provided between the gas storage device 52 and the first plenum 38. Under the direction of the system controller 22, the flow rate controller 54 controls the flow rate of gas from the storage device 52 via conduit 44 into the plenum 38 and the pressure controller 56 controls the pressure in the plenum 38. For the second gas, flow rate controller 58 and pressure controller 60, also under the direction of the system controller 22, control the flow rate of pressure of the second gas from gas storage device 53 via conduit 46 into the second plenum 40.
The first and second sets of holes 34, 38 may be arranged in various patterns that reduce or altogether eliminate stagnant or uneven gas flow at the gas dispensing surface 32 of the shower head 14. Such patterns are preferably, but not exclusively, non-symmetrical patterns that mitigate or eliminate lines or symmetry, allowing for a highly uniform gas flow in the vicinity of the gas dispensing surface 32 of the shower head 14 and above the substrate 18. By using these non-symmetrical patterns, such as various types of spirals, deposition layers are significantly more uniform, resulting in fewer defects and higher yields.
Archimedean Spirals:
Hole patterns used on the gas distributing surface 32 of showerhead 14 can be described as points located along a generalized Archimedean spiral described by r=c(θ/a)d. The points are chosen such that the azimuthal coordinate θ of each point in this pattern is incremented from the θ coordinate of the preceding point by a certain constant angle a.
The Cartesian coordinates (x, y) for the nth element in the pattern can be described by:
x=x
o
+s
x
r cos θ
y=y
o
+s
y
r sin θ
where:
rn=cnd
θn=θo+na
d∈[0.05, 2.00]. d=½ for a Fermat spiral.
is the θ coordinate increment between successive elements.
The parameter b is an element of the set of all numbers which have a continued fraction representation requiring ≥4 terms. This definition includes irrational numbers. To yield a uniform pattern that maintains uniform element packing and does not develop local structure (such as “spoke” features) over an arbitrarily large number of points, the parameter b is preferred to be the golden ratio
θo∈is the pattern rotation in radians (nominally 0).
xo ∈is the x coordinate offset (nominally 0).
yo ∈is the y coordinate offset (nominally 0).
sx∈ is the x coordinate scale factor (nominally 1).
sy∈ is the y coordinate scale factor (nominally 1).
c∈ is the pattern scale factor.
Varying d changes the radial density gradient of the pattern. The pattern is uniformly dense when d=½. For a continuous curve, the term c/(ad) scales the spiral larger or smaller, and d changes how the spiral is “wrapped”.
It is not necessary for the parameter b to be an irrational number. When b=φ, the elements in the pattern show uniform packing and appear not to exhibit local structures such as spokes. However, patterns may be generated using other values of b in which a ring-shaped subset of the pattern appears uniform and non-structured similar to a pattern generated by b=φ. For example, a pattern with such regions can be generated where b is a rational number such as:
In general, it may be difficult to yield a pattern that is uniform and non-structured when b is a continued fraction representable by less than three terms.
Fermat's Spiral:
A Fermat's spiral is an Archimedean spiral. In the case where d=0.5, the continuous spiral on which the points are located is called Fermat's spiral.
Vogel Spiral:
When d=½ and b=φ, the resulting pattern is known as a Vogel spiral. This pattern is characterized by uniform density, lack of local structure, and even packing of pattern points (where the distance from a given point to its nearest neighbor is very nearly equal to the distance to its fourth-nearest neighbor).
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It should further be understood that implementations of the various embodiments described herein do not require holes to be placed on the gas dispensing surface 32 of the shower head 14 in the exact locations defined by use of any of the equations provided herein to define a given type of spiral. On the contrary, spiral patterns may be used that are merely close approximations of actual spirals defined by using the above equations. By close approximations, it is intended to mean that holes 34 and/or 38 may be offset from their equation defined counter-part points by varying degrees, such as (a) 1/1000th of an inch or less, (b) 1/100 of an inch or less (c) 1/10 of an inch or less. It should be noted that the offset may be intentional, meaning the holes are purposely offset from the hole locations defined by the above-mentioned equations or the offset can be unintentional, meaning within machining tolerances when fabricating the shower head.
Referring to
It should be understood that the embodiments provided herein are merely exemplary and should not be construed as limiting in any regard. In general, the present application is intended to cover any a shower head having at least two set of holes defining two spiral patterns and two plenums for the two patterns respectfully.
Although only a few embodiments have been described in detail, it should be appreciated that the present application may be implemented in many other forms without departing from the spirit or scope of the disclosure provided herein. For instance, the substrate can be a semiconductor wafer, a discrete semiconductor device, a flat panel display, or any other type of work piece.
Therefore, the present embodiments should be considered illustrative and not restrictive and is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.
