Recently, interest in the research and applications of diamond has increased significantly due to the development of the Chemical Vapor Deposition (CVD) technique for producing diamond films. Since diamond has the highest thermal conductivity of all known substances, it has numerous potential applications. However, this high thermal conductivity creates a problem in measuring the thermal conductivity of diamond materials 1,2 . Numerous techniques exist for measuring the thermal conductivity of solid materials3~6. This study proposes a two layer model based on the principle of heat diffusion to determine the thermal conductivity for various CVD diamond thin films based on the effective thermal diffusivity of a diamond film on a silicon substrate measured by using a holographic interferometric technique7. The main sources of distortion for soft pellicle systems include temperature changes and the attachment of curved frames to non-flat reticles, with the latter being the inevitable consequence of the stressed chrome pattern8,9. According to the research by A. Mikkelson in 200110, the reticle oxide layer thickness may reach 20nm, adding 5nm to the wafer, if optical reducing ratio is used.
Wafer throughput in micro-lithography depends on the sensitivity of the resist film to radiation. A lower exposure time required to produce a latent Image in the resist corresponds to a higher throughput11. The focus affects line-width: a focus of 0μm yields the lowest line-width, the width increases
with the focus distance. Positive and negative foci yield symmetrical results12. The primary factor that dominates the gradient of the exposure/line-width relationship is the resist’s internal chemical composition13.
Resist spin coating has been successfully modeled using a detailed non-Newtonian analysis, which allows local fluid viscosity to vary with concentration and shear rate14. The cleavage of a butylester is acid-catalyzed and yields carboxcylic acid and isobutene after exposure to the PAC (Photo Active Component) and PEB (Post-Exposure Back)15. When an acid generator is present in a CAMP (Chemically Amplified) resist formulation, the mechanism for producing a lithographic pattern is simple. The strong acid formed causes deprotection at a relatively low temperature with an activation energy of around 11 to 14 kcal/mol16.
Wafer throughput in micro-lithography depends on the sensitivity of the resist film to radiation. A lower exposure time required to produce a latent Image in the resist corresponds to a higher throughput17 . The designed by
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Watanabe et al.18 showed that the focus margin for 0.3µm lithography with a KrF excimer stepper is ±0.08µm for DOF (Depth of Focus) of ±0.5µm. It is possible for an ArF excimer laser stepper to achieve 0.13µm lithography with a DOF of ±0.5µm by using the recently developed technique of super resolution.
The wafer surface profile is structure of the device and has irregularities of 0.3 to 1µm. As optical lithography will not reach the necessary resolution for future demands in microengineering. Now lithographic techniques have to be ready to produce nanostructures in a parallel way. Atoms with thermal kinetic energies have de Broglie wavelengths in the picometer regime and so they do not suffer from diffraction when focused down to a nanometer scale spot size.
In the last decade the investigation of atom light interaction has shown, that the trajectories of neutral atoms can be efficiently manipulated with laser light and that optical elements for neutral atoms can be built using the resonant interaction with laser light 18 −21 .
Chapter 3
The traditional reticle level detects the method
Introduction
In an apparatus for monitoring any deviation of a planar surface from its desired position, a light source and a light detector are positioned so that when the surface is at the desired position a beam of light projected by the light source is reflected by the surface and fully registers on the light detector causing the light detector to generate a peak output signal. When the surface deviates from its desired position, the reflected beam of light does not fully register on the light detector, causing the light detector to generate less than peak output signal.
Summary of the reticle level detects the method
According to an embodiment of the present invention, depicted in Figure 3.1 is an optical level detector configured for monitoring whether a planar surface has deviated from its desired position, represented by a reference plane. Reference plane only represents a desired position for the planar surface and does not represent a physical surface. Optical level detector is
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positioned at a known distance X from the reference plane . The absolute value of the distance X is not important but it is important that the distance X
be fixed and does not change once the optical level detector is set up.
Associated with the reference plane is an incidence axis and a reflection axis . The incidence axis represents the path of an incident light beam from a light source incident to the reference plane and defines a refe rence incidence angle ?1 between the reference plane and the incidence axis. When a planar
surface is placed at the reference plane, the incidence beam will be reflected by the planar surface and returned towards the optical level detector as a reflected beam. The reference reflection axis represents the path of the reflected light beam when the planar surface is placed at the position defined by the reference plane, i.e. the desired position for the planar surface. The reference reflection axis defines a reference reflection angle ?2, which is equal to the incidence angle ?1, between the reference plane and the reference reflection axis. Therefore, by positioning a light detector in line with the
reference reflection axis, one may detect whether the planar surface has deviated from the reference plane.
In the embodiment of the present invention illustrated in Figure 3.1, the light source is provided in the optical level detector for projecting a narrow beam of
light, the incidence beam, on to the planar surface. The light source is preferably a laser or a light emitting diode but any other light source may be adopted for this purpose. The light source projects the incidence beam along its projection axis. In this embodiment of the present invention, the light
source is positioned such that the projection axis is coincident with the incidence axis. Thus, the incidence beam propagates along the path defined by the incidence axis and on to the planar surface. The incidence beam is reflected by the planar surface and travels back to the optical level detector as a reflected beam. The optical level detector is provided with a light detector for receiving this reflected beam.
The light detector is positioned with its viewing axis coincident with the reference reflection axis so that when the planar surface is in its desired position, the reflected light beam falls squarely on the light detector. The light detector is preferably a device such as a photocell that converts the light energy of the reflected beam into an electrical signal that can be readily detected and monitored. The voltage level of a typical photocell’s output signal will vary proportionally with the intensity or the amount of light shone on the photocell. Thus, when the reflected beam falls completely on the light detector (i.e. fully registers with the light detector), the output signal of the light detector
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will be at the peak voltage value possible with the reflected beam. If the reflected beam falls on the light detector only partially (i.e. does not fully register with the light detector), the output signal of the light detector will be at some voltage value less than the peak value.
This ensures that when a planar surface is in its desired position, i.e. at the position represented by the reference plane, the reflected beam will be coincident with the viewing axis and the reflected beam will completely register with the light detector. In this scenario, the output signal of the light detector will exhibit a peak voltage value for the given planar surface and its light reflecting characteristics. It should be noted that the peak voltage value of the light detector in this context does not necessarily mean the absolute peak voltage value that the light detector is capable of producing. It refers to the peak voltage value that the light detector will produce in the given configuration of the optical level detector.
If the planar surface deviates from its desired position, the reflected beam will not be coincident with the reflection axis and, in turn, not coincident with the viewing axis of the light detector. Thus the reflected beam will not completely register with the light detector. Depending on the degree of the deviation, the reflected beam could completely miss the light detector or only
partially register with the light detector. In either case, the resulting output signal of the light detector will exhibit a voltage value that is less than the peak value.
The exemplary configuration of Figure 3.1 represents the situation where the planar surface is in its desired position. Thus, the angle of incidence for the incidence beam with respect to the planar surface is same as the reference incidence angle ?1. And, correspondingly, the angle of reflection for the
reflected beam with respect to the planar surface is same as the reference reflection angle ?2.
Thus, the optical level detector of the present invention can be used to determine whether a planar surface has deviated from its desired position, represented by the reference plane by monitoring the output signal of the light detector. The output signal can be monitored using any suitable circuits or devices that can measure the voltage level of the output signal. Such circuits or devices are well known to one of ordinary skill in the field and they need not be discussed in detail here. Figures 3.2 and 3.3 illustrate some examples of a number of different situations in which a planar surface may deviate from the reference plane which can be detected by the optical level detector.
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In Figure 3.2, the planar surface has deviated from the reference plane by an angular translation represented by angle ß . The incidence beam will strike the planar surface at a n incidence angle a1 and the reflected beam leaves the planar surface at a reflected angle a2. As illustrated, the resulting reflected
beam also has been angularly translated from the viewing axis of the light detector by the angle ß . The reflected beam is not coincident with the viewing
axis and no longer registers with the light detector. The resulting output signal of the light detector will be zero volts, signifying that the planar surface has deviated from the reference plane. If the translation angle ß is sufficiently
small, the reflected beam may register partially with the light detector. The output signal of the light detector, then, will not be zero volts but it will be something less than the peak value, still signifying that the planar surface has deviated from the reference plane.
In Figure 3.3, the planar surface has deviated from the reference plane by a linear translation represented by Y. The incidence beam will strike the planar surface at an incidence angle a1 and the reflected beam leaves the planar surface at a reflected angle a2. The planar surface is parallel to the reference plane and the incidence angle a1 and the reflected angle a2 are same as the reference incidence angle ?1 and the reference reflected angle ?2,
respectively. However, the reflected beam will be translated accordingly as represented by Y’ and thus the reflected beam will not be coincident with the
viewing axis of the light detector. Again, the reflected beam will not fully register with the light detector and the outp ut signal of the light detector will be some value less than the peak value, signifying that the planar surface has deviated from the reference plane.
In another embodiment of the present invention, the light source and the light detector may be mounted in the optical level detector such that they are not coincident with the projection axis and the viewing axis, respectively, to accommodate different mounting configurations. For example, in Figure 3.4, the light source and the light detector are mounted in horizontal configuration, but by employing reflectors and respectively, the incidence beam and the reflected beam are made to travel along the desired paths. The reflectors may be mirrors, prisms or other suitable reflectors. The light source and the light detector may be configured in many different orientations as long as the reflectors are used to direct the incidence beam and the reflected beam to propagate along the desired paths.
In certain applications, a plurality of the optical level detector may be utilized to monitor positions of a plurality of surface regions on a planar surface.
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For example, as illustrated in Figure 3.5, a planar surface may have a surface region A that is on the reference plane but the remainder of the planar surface represented by surface region B may be deviated from the reference plane. If one optical level detector was monitoring the surface region A, the planar
surface may seem as though it is on the reference plane. Thus, two or more optical level detectors may be utilized to monitor a plurality of surface regions on the planar surface to better detect any deviations from the reference plane.
The inventor has applied the optical level detector of the present invention in such a manner in detecting out-of-level reticles (or photo lithographic masks) during the photolithography processes in semiconductor wafer manufacturing.
In one application, illustrated in Figure 3.6, four optical level detectors similar to the embodiments described herein may be mounted on a reticle stage of a stepper tool. The reticle stage has a reticle holding well for holding a reticle in place. Each of the four optical level detectors may be positioned near each of the four corners of the reticle holding well, as identified by the reference numbers. The optical level detectors are used to monitor whether
or not a reticle (not shown) placed on the reticle holding well is properly leveled.
Each of the four optical level detectors may be configured, for example, so that their light detectors generate peak output signal values when the reticle is
properly leveled in the reticle holding well. The output signals of the light detectors may be monitored individually. Alternatively, the optical level detectors may be connected in series and monitor the total voltage of the output signals.
Figure 3.7 illustrates a sectional view of an optical level detector as implemented by the inventor on the reticle stage according to another embodiment of the present invention. The light source is attached to the optical level detector by a light source holding plate. The light from the light source passes through a pin hole in the optical level detector and emerges as the incidence beam. The incidence beam is reflected by the planar surface (representing a reticle surface) and if the planar surface does not deviate from the reference plane, the reflected beam will be coincident with the reference reflection axis. In this example, the light detector is positioned in the optical level detector in a configuration similar to that discussed in reference to Figure 3.4. The light detector is provided such that its viewing axis is horizontally oriented and not coincident with the reference reflection axis. A reflector is provided at an appropriate orientation so that when the planar surface is at the desired location and does not deviate from the reference plane, the reflected beam will be deflected towards the light detector and fully register with the light
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detector through the hole provided in the optical level detector. As with the other embodiments of the present invention discussed herein, when the planar surface deviates from the reference plane, the reflected beam will no longer be in proper alignment with the reference reflection axis and the reflected beam will no t fully register with the light detector. By monitoring the electrical output signal of the light detector, one can thus detect whether or not the planar surface is at the desired location represented by the reference plane.
In the particular configuration implemented by the inventor, the optical level detector is mounted on to the reticle stage by a set of connecting hardware that allows the height of the optical level detector to be adjusted relative to the reticle surface (the planar surface). The set of connecting hardware comprises a vertically actuating guide bearing that allows the height of the optical level detector to be adjusted and an L-bracket for attaching the whole assembly on to the reticle stage. The guide bearing is a standard slide/bed type comprising a slide and a bed. To adjust and control the height of the optical level detector attached to the guide bearing, a worm gearing set up is used. The slide is provided with wormgear teeth and a worm is situated in the bed. The worm has a thumb screw to enable a human operator to adjust the height of the optical level detector buy turning the thumb screw. These connecting hardware may
be viewed in more detail in the exploded view of the assembly illustrated in Figure 3.8. As discussed in reference to Figure 3.6, four of the optical level detector may be installed near the four corners of the reticle holding well using the connecting hardware described herein to verify that the reticle is properly leveled in the reticle holding well before the stepper is operated. The vertically actuating guide bearing may be of other types of guide bearing well known in the art and not necessarily limited to the slide/bed type described herein.
The use of the optical level detector of the present invention has simplified the stepper tool operator's task of verifying that the reticle is properly level in the reticle stage. While the foregoing invention has been described with reference to the above embodiments, various modifications and changes can be made witho ut departing from the spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope of the appended claims.
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Chapter 4
The traditional thermal of slightly out of shape reticle detects the method Introduction
The present invention relates to reticles used in the formation of integrated circuit (IC) patterns or dies on semiconductor wafer substrates. More particula rly, the present invention relates to a thermal detector which determines whether a reticle is thermally distorted to an excessive degree prior to exposure of a wafer through the reticle in photolithography.
Summary of the reticle thermal detects the method
The present invention contemplates a novel reticle thermal detector which is suitable for determining whether a reticle is distorted typically due to thermal effects from an exposure light source in a stepper or scanner prior to exposure of a semiconductor wafer through the reticle. The reticle thermal detector alerts personnel to the distorted condition of a reticle as the reticle lies on a reticle stage in a stepper or scanner preparatory to a photolithography process.
Therefore, the distorted reticle can be removed and a replacement reticle placed on the reticle stage to ensure that a circuit pattern of high integrity is
Therefore, the distorted reticle can be removed and a replacement reticle placed on the reticle stage to ensure that a circuit pattern of high integrity is