Patent Application
20090026912
The invention described herein relates generally to the formation of multi-exposure dense lithographic patterns using new approaches and methodologies. In particular, the invention relates to an apparatus and method of operating a controllable electron beam projection device. Also the inventors contemplate systems and methods for generating densely patterned images having a resolution beyond that of existing technologies and as such embodiments of the invention enable increased effective resolution beyond that generally possible using existing tools and technologies. Inventive embodiments enable control of the potential in an electron beam directed onto a digital pattern generator to enable the fabrication of high definition photoresist patterns and/or resultant high definition substrate patterns.
As the density and complexity of microcircuits continue to increase, the photolithographic processes used to print circuit patterns become more and more challenging. Previous technologies and thinking in the art has required denser and more complex patterns to achieve the formation of the denser circuits consisting of smaller pattern elements packed more closely together. Such patterns push the resolution limits of available lithography tools and processes and place serious burdens on the design and quality of the devices used to fabricate such patterns.
In one prior art approach an electron beam is used to write a pattern onto a photoimageable surface to enable patterning. One such approach relies upon an extremely high voltage cathode set at a high voltage to produce an electron beam that is directed through an aperture to produce a beam that writes the desired pattern on a target (that lies in the path of the beam).
Such a high voltage cathode produces the electron beam directed to an aperture. But, when the pattern requires that no beam be directed onto the target, the beam must be impeded. Some manufacturers (for example, Applied Materials, Inc. of San Jose, Calif.) have attempted to achieve this by applying an appropriate voltage at the aperture in order to deflect the beam off of the target. A voltage sufficient to establish a deflecting electrical field must be applied at the aperture in order to deflect the flow of electrons at the aperture. The problem with this process is that the beam deflection is difficult to actuate at a very high rate of speed. Systems having switching speeds of on the order of 50 picoseconds or less and having a repetition rates on the order of 100's of megahertz (MHz) are difficult to implement using existing technologies. Existing systems capable of applying a 50 volt potential within 50 (or less) picoseconds in a duty cycle of 100 or 200 MHz are, at this date, simply not effective. Moreover, in the time the beam is deflected, a residual beam artifact remains as the beam moves. This artifact produces numerous difficulties that have proven difficult to solve and result in unsatisfactory patterns being formed. Furthermore, such systems produce a resultant electron beam having substantial residual beam energy impinging on the target resulting from the finite time it takes to effectively deflect an electron beam. This has proven unworkable.
Moreover, when a beam is deviated from the aperture by a magnetic field many other detrimental effects are observed. For example, the switching speeds of such deviated beams do not operate efficiently at the required frequencies (hundreds of MHz) and, as explained previously, the motion of the beam as it is deviated generates numerous artifacts that result in pattern errors that are difficult, if not impossible, to correct for.
The inventors postulate that a system that does not demonstrate some or all of these drawbacks would be helpful and present a significant advance over the current state of the art. Accordingly, the embodiments of invention present substantial advances over the existing methodologies and overcome many limitations of the existing electron beam blanker arts. These and other inventive aspects of the invention will be discussed herein below.
In accordance with the principles of the present invention, methods and apparatus for achieving high-speed blanking and dynamic pattern generation in reflection electron beam lithography are disclosed.
Numerous aspects of the present invention are described in detail in the following description and drawings set forth hereinbelow.
In one embodiment, the invention teaches a blanker apparatus including a cathode for generating an electron beam having a cross-section. A cathode activation source is arranged to controllably cause the cathode to produce an electron beam that is directed through an aperture in a focusing electrode. A cathode control amplifier regulates the voltage at the cathode to regulate the potential of the electron beam. Cathode control circuitry adjusts the cathode control amplifier to enable regulation of the potential of the electron beam.
In another embodiment, the blanker above is configured to direct an electron beam onto a dynamic pattern generator to produce a patterned electron beam that is projected onto a target to achieve pattern transfer.
In another embodiment, the invention discloses a cathode system configured for blanking. The system includes a cathode that emits electrons when exposed to radiation and a cathode activation source for controllably activating the shaped cathode to produce the electron beam. Control circuitry is configured to adjust the cathode activation source to regulate the electron beam produced by the shaped cathode.
In another embodiment, the invention discloses another cathode system configured for blanking. The system includes a cathode that emits electrons in an electron beam when exposed to radiation. A cathode activation source is used to controllably activate the cathode to produce the electron beam. Control circuitry adjusts the cathode activation source to regulate the electron beam produced by the cathode.
In a method embodiment of the invention, high speed blanking in a reflection electron beam lithography device is performed as follows. A cathode is activated to generate a continuous electron beam that is directed onto a digital pattern generator, having an array of programmable elements configured to selectively imprint patterns onto the continuous electron beam to form patterned electron beam. The elements of the array are adjusted to selectively imprint patterns onto the continuous electron beam to form the patterned electron beam. A voltage level is modulated at the cathode to controllably adjust the potential of the continuous electron beam such that when the voltage level is biased to a first voltage level no patterned electron beam is produced and such that when the voltage level is biased to a second voltage level the patterned electron beam is produced. This patterned electron beam can be directed onto a target to achieve electron beam pattern transfer.
In another embodiment, the invention teaches a method for performing high speed blanking in a reflection electron beam lithography device, the method comprises activating a photo cathode with a laser to generate an intermittent electron beam and directing the intermittent electron beam onto a digital pattern generator. Programmable elements of the digital pattern generator are configured to selectively imprint patterns onto the intermittent electron beam to form patterned electron beam. The laser output is modulated to controllably gate the production of electrons by the photo cathode such that when the laser is off the intermittent electron beam is off and no patterned electron beam is produced and such that when the laser is on the intermittent electron beam is on and the patterned electron beam is produced.
These and other aspects of the present invention are described in greater detail in the detailed description of the drawings set forth hereinbelow.
The following detailed description will be more readily understood in conjunction with the accompanying drawings, in which:
a) & 1(b) are schematic depictions of an embodiment of an electron beam and electron blanker device.
c) depicts an example of an on/off cycle and its relationship to “repetition rate” and duty cycle in accordance with the principles of the invention.
a) is schematic diagram depiction of a REBL device employing a blanker cathode embodiment of the invention.
b) & (c) are block diagrams illustrating alternative embodiments of cathode activation sources and cathodes in accordance with embodiments of the invention.
d) is schematic diagram depiction of a REBL device employing a photoemissive cathode embodiment of the invention.
a) is a simplified depiction of a dynamic pattern generator utilized in some embodiments of the invention.
b) & 5(c) are simplified illustrative depictions of a selectively biased cathode interacting with the dynamic pattern generator utilized in some embodiments of the invention.
It is to be understood that, in the drawings, like reference numerals designate like structural elements. Also, it is understood that the depictions in the Figures are not necessarily to scale.
The present invention has been particularly shown and described with respect to certain embodiments and specific features thereof. The embodiments set forth herein below are to be taken as illustrative rather than limiting. It should be readily apparent to those of ordinary skill in the art that various changes and modifications in form and detail may be made without departing from the spirit and scope of the invention.
The following detailed description describes various embodiments of a method and approach for obtaining a highly controllable electron beam. Additionally, disclosure of many embodiments of a highly effective electron beam blanker are disclosed. In one approach an electron beam is used to write a pattern onto a photoimageable surface to enable patterning. As depicted in
As illustrated in
The inventors have provided
In the proposed variable speed, variable duty cycle system embodied in aspects of the present invention, Tfull (113) and Ton (116) can be varied on a pulse-to-pulse basis. This grants extraordinary flexibility and utility to embodiments of the present invention. Accordingly, the quantities “repetition rate” and “duty cycle” can be varied on a pulse-to-pulse basis and defined as instantaneous quantities which that can be varied over time.
The following detailed description describes various embodiments of a method and approach for obtaining a highly controllable electron beam produced by a blanker.
These embodiments are explained in greater detail as follows.
An advantage of such thermionic heating is that it can be arranged such that the distribution of the electrons 401e is generally equal across the entire cathode 402. This enables relatively uniform heating distribution across the electrode which in turn enables a relatively even distribution of produced electrons 406. And another advantageous feature of this direct thermionic heating (with the electrons 401e) is that the energy spread for the electrons produced by the cathode 402 by such heating have a narrow energy distribution. By this, the inventors mean that the voltage range for the electrons produced at 402 is not subject to much energy variance. For example, in one embodiment, the energy spread (range of voltages) in the produced electrons varies by less than 0.25 V. Additionally, prior art electrically activated cathodes also experience marked voltage gradients across the cathodes. This commonly results in a substantial gradient in the voltages imparted to the produced electrons. Accordingly, in prior art systems large voltage variances are experienced by the produced electrons (e.g., tens of volts). Moreover, the energy spread suffers from a physical dimension wherein the spread has a geometric distribution based on the shape of the electrode and the physical characteristics of the electrical gradient across the electrode. State of the art electron beam “optics” are hard pressed to obtain suitable focus of the resultant electron beam across such a large voltage gradient/energy spread. Accordingly, the discussed thermionic heating approach (e.g., with an electron beam) has some advantages over prior approaches.
Additionally, the voltage of the produced electron beam 406 is modulated at the electrode 402 by using a controllable amplifier system (for example 204, 205 or 304, 305) 430. Such a system 430 typically includes an amplifier 431 and circuitry including a biased amplifier power source 432 and control “circuitry” (that may include, optical elements, or RF communication elements, as well as a wide range of other control elements) 433. In one example implementation, the amplifier 431 can comprise a high frequency 5V RF amplifier biased, for example, to a negative 2.5 volts (e.g., using a microwave amplifier). This enables the amplifier to be modulated by an amplifier power source 432 in a range between, for example, about −2.5 volts and +2.5 volts. Other voltage ranges can be used, but ranges that can be modulated between ±1.5-2.5 volts are preferred. In one implementation, the amplifier is controlled by circuitry 433 arranged to enable the amplifier 431 to operate with a pulse frequency of at least 100 mega hertz (MHz) (but preferably in the range of about 200-400 MHz with most preferred embodiments having a duty cycle modulated from 0-100% and having voltage modulation from about −2.5 volts to +2.5 volts with switching speeds in the range of 40 picoseconds (ps) or less (in a selected example a rise time (an example switching speed) ranges between about 25 to 35 ps)). Square wave patterned voltage signals are preferred due to their ability to obtain quick rise and fall times which accordingly result in very small amounts of intermediate voltages (i.e., such square waves generate effectively on and off states with very little intermediate voltage between the “on” and “off” states).
The inventors point out that such embodiments can enable a pulse repetition frequencies of in the range of 200-400 MHz. In fact, embodiments of the type disclosed herein, enable a great degree of flexibility of selecting repetition rates that enable extremely high repetition rates (e.g., on the order of 100's of MHz using embodiments that employ thermionic cathodes with voltage regulation or even higher repetition rates (up into several GHz to tens of GHz) using the laser or optical beam controlled embodiments described below) as well enable extremely high switching rates (short rise and fall times) and enable arbitrary duty cycles. Thus, embodiments of the invention enable the easy adjustment of the repetition rates to enable variable repetition rates as well as very high repetition rates and variable duty cycles.
In one embodiment, the circuitry 433 includes a pulse generator which is configured to control the blanking frequencies of the electrode (via modulating the amplifier 431) and communication circuitry configured to control the amplifier. Due to the very high potentials of the system such control circuitry is chosen with some care. In one example, the inventors contemplate the control circuitry being “photonic” in nature. For example, a pulse generator can be used to operate a laser (or an optical beam such as generated by an LED or other convenient source) which emits a control beam that can be transmitted through a fiber optic line to an optical receiver which receives the optical signal and communicates electrical signals to the amplifier 431 which is then used to modulate the cathode 402. Other optical configurations or layouts can be employed. However, the circuitry 433 is not limited to optically based systems. The inventors point out that all that is necessary is that modulation instructions be provided to the amplifier 431 by the circuitry 433. In another embodiment, the control circuitry can employ radio frequency or microwave devices. The inventors further contemplate that other signal transmission schemes compatible with high potential systems can be employed.
The electron beams 406 so created and modulated are directed through an aperture 403 (similar to 203, 303) and then onto a dynamic pattern generator 407 (or other suitable target substrate) where a pattern is impressed upon the beam as needed and then directed onto a subject 408 (which can be a wafer, a mask substrate, or any other substrate including patternable substrates) where a pattern can be transferred using the beam 406. Implementations of this invention can be used to accomplish for example, without limitation, patterning of a semiconductor wafer, patterning of a mask substrate to form mask reticles, and numerous other pattern transfer processes. Many details of such pattern transfer are well explained in pending patent applications and patents. Examples of certain Dynamic Pattern Generators (DPG's) which embody Direct Write (DW) e-beam lithography are discussed briefly as follows. In one example, the dynamic pattern generator 407 is used as in reflective electron beam lithography (REBL). One such new device is described in the U.S. Pat. No. 6,870,172 entitled “Maskless Reflection Electron Beam Projection Lithography” dated Mar. 22, 2005 which is hereby incorporated by reference for all purposes, including, a specific illustration of a REBL device. Further DPG embodiments are depicted in the U.S. patent application Ser. No. 10/851,041, entitled “Reflective Electron Patterning Device and Method of Using Same” by Harald F. Hess et al, filed on May 21, 2004 and also U.S. patent application Ser. No. 11/391,976, entitled “Dynamic Pattern Generator for Controllably Reflecting Charged-Particles” by Vincenzo Lordi, filed on Mar. 28, 2006 both of which incorporated by reference for all purposes. Additionally, as pointed out above with respect to DPG 307, embodiments of the invention can employ targets 407 that do not impress a pattern onto the beam, but merely operate as an “on/off” switch.
Continuing with description of
a) is a simplified depiction of one example implementation of a dynamic pattern generator (DPG) 500 constructed in accordance with the principles of the invention. The depicted DPG 500 includes a pattern generation array 501 including a multiplicity of pattern generation elements 501e. As is extensively described in the forgoing applications and patents, each of these elements 501e comprises a conductive surface configured such that a voltage can be applied individually to each element as needed to establish a desired pattern in a resultant beam. Typically, a negative bias is applied to obtain reflection in electrons directed onto the pattern generation elements 501e and a positive bias is applied to elements 501e that will absorb electrons (thus, subtracting them from the resultant electron beam). In this way an electron beam projected onto the pattern generation array 501 has a pattern impressed thereon by the configuration of the pattern generation elements 50e. Typically, various control circuitries 502 can also be included on the DPG 500. Such circuitry 502 can optionally be formed on layers beneath the pattern generation array 501 to form a more compact structure if desired.
Referring to the simplified illustrations of
Moreover, referring to
An alternative cathode activation source/cathode arrangement (420) is depicted in
In yet another alternative embodiment, the combination 420 of cathode activation source and cathode is depicted in
In yet another alternative embodiment depicted in
It should be pointed out that in many of the above applications it is advantageous to employ a shaped cathode (which is useful in generating an electron beam having cross-sectional dimension that generally matches the shape of the cathode). The cathode activation source activates the cathode to produce an electron beam that is similar in cross-sectional area to the cathode. For example, a circular cathode will produce an electron beam with a circular cross-section, a rectangular cathode will produce an electron beam with a rectangular cross-section, and so on.
The present invention has been particularly shown and described with respect to certain preferred embodiments and specific features thereof. However, it should be noted that the above-described embodiments are intended to describe the principles of the invention, not limit its scope. Therefore, as is readily apparent to those of ordinary skill in the art, various changes and modifications in form and detail may be made without departing from the spirit and scope of the invention as set forth in the appended claims. Other embodiments and variations to the depicted embodiments will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims. Further, reference in the claims to an element in the singular is not intended to mean “one and only one” unless explicitly stated, but rather, “one or more”. Furthermore, the embodiments illustratively disclosed herein can be practiced without any element, which is not specifically disclosed herein.
