The present invention relates generally to a system and method for adjusting or moving a sample upon whose surface a material is to be deposited or removed. More particularly, the present invention relates to a system and method for using a system that removes or ablates material or adds material from a sample surface by use of a lasing device wherein the sample is positioned in multiple dimensions with a high degree of accuracy.
The prior art details the use of translation stages for moving samples in and around a laser beam or other radiated beam such that the beam is used for the removal or addition of material from or to a sample. Such systems may use the beam to remove material from the sample or to modify the surface of the sample. These stages typically use lead screws or linear motors to move a carriage on which the sample is mounted.
The sample is placed onto a mounting surface that is attached to a bearing mounted on rails. Some of these systems may use combinations of stages that move the sample itself and separate stages that are used to modify the direction of the laser beam. This is accomplished by moving various components in the beam delivery path to steer the beam to different locations on the sample surface. Such systems as described in U.S. Pat. No. 6,605,799 to Brandinger et al. use an X, Y stage to position the sample and additional motion control devices to move components in the optical column.
One inherent and serious problem with the prior art involves the well know positional inaccuracies due to Abbe errors when moving in the sample and stages linear directions. Stages are known to have small non-orthogonalities in X, Y and Z that create location errors if moving in any one of these linear axis. When attempting to produce laser induced surface changes in the nanometer range, the resulting Abbe offsets can produce significant errors in position even when the stage makes small changes in X, Y and Z. The offsets can result in significant errors in the location of material removed or surface modifications made on the sample surface. The prior art has no adequate solution for correcting these errors.
In addition, the prior art systems suffer from a second problem in the form of parasitic errors. These errors are a result of undesirable cross coupling of motion from one axis to another. If motion is commanded to the stage in the X direction, for example, in addition to a resulting motion in X, an undesirable motion in translational Y, Z or in the rotational roll, pitch, or yaw axis may occur. This results in a positional error. This cross-coupled or parasitic motion may occur in any of the other degrees of freedom either in one or more of the translational or rotational axis. In all, the present invention may include correction in each of the three translational axes and the three rotational axes for correction in all six degrees of motion.
U.S. Pat. No. 6,656,539 and U.S. Pat. No. 6,333,485 to Haight et al. describes a piezo electric stage for moving the sample that moves approximately orthogonal to an optical axis in two directions. The use of piezo electric stage motion can minimize some of the Abbe error effects inherent in the majority of the prior art. However, none of the prior art inventions provide a means to control errors in orthogonal and rotational motions (i.e., parasitic motion errors). This is also true for parasitic motions relative to the optical axis. As the focal depth of field is reduced by the use of high numerical aperture objective lenses, the dependence of the focal spot positioning relative to the target surface becomes more critical.
The prior art does not have the ability to introduce an intentional tilt of the sample surface plane in a roll, pitch, and yaw direction while also creating linear motion in X, Y and Z to the optical axis. Control in the rotational axis is highly desired for accurate positioning in all three linear axes. It can also be useful for ablating or adding material in other than approximately round shapes.
As a consequence of the above, the prior art has specific and inherent limitations in ability to compensate for the described motion errors resulting from mechanical construction tolerances and separated motion control. Accordingly, it is desirable to provide a method and apparatus that enables a sample to be positioned on a surface such that any errors inherent in a system are minimized.
The foregoing needs are met, to a great extent, by the present invention, wherein in one aspect an apparatus is provided that in some embodiments, the present invention corrects for undesirable position errors whether such errors are caused by Abbey errors, cross coupling errors, or other positional errors.
The present invention provides a system including a lasing device or other type of beam removal and additive device and a device for moving a target sample relative to a beam generated by the lasing device. In combination with sample movement, the beam also contains sufficient energy that, when the beam is focused to a small diameter spot, the beam causes the surface material on a sample to be ablated. Alternatively, if the beam is a laser beam, the laser energy can be chosen such that, in the presence of selected gases or liquids, material deposition occurs on the surface. In the present invention the laser beam may be either continuous or pulsed. In applications where nanometer range surface modifications are desired, the beam must be focused to the smallest possible spot diameter. This invokes certain optical principles. The wavelength of the laser beam should be short and the included angle of the beam, as it exits the final focusing lens, must be as wide as possible. In combination, these attributes will make the diffraction limit of the focused image small. In such instances, the depth of field will necessarily be very short. Consequently, along the axis of the beam, the spatial positioning of the sample surface and the final focusing lens must be precisely controlled.
The laser beam energy may be pulsed to control the amount of material removed and to control the mechanism by which the material is removed. In this embodiment, the pulse duration may include pulse durations in the femto-second range.
The present invention uses an apparatus with stable optical mechanical design for high precision laser machining or deposition. The apparatus utilizes piezo driven stages to move the sample (with minimal parasitic errors) in the X, Y, and Z directions while holding the critical optical components fixed relative to the sample. The result is that the laser focus point can be fixed in space during the process of removing material from the sample. The present invention also may include piezo actuators to rotate the stage in a roll, pitch, and yaw direction.
Further, the present invention includes sensing devices that provide information about the actual cross coupled errors in translational and rotational axis. This information may then be used to instruct the actuator components in the stage to offset or correct for the undesired parasitic or cross coupled translations and rotations. Under appropriate conditions, parasitic motion corrections can be made “real-time”, thereby, maintaining the desired motion with minimal error.
An advantage of this method and apparatus is that precise positioning of the target material, especially in the direction of beam axis, is maintained relative to the focal volume of the laser without parasitic errors or backlash. The same advantage results in the X and Y direction. Accurate positioning in all directions is obtained with minimal Abbe errors and minimal parasitic motion. Small movement is especially accurate and placement of the target relative to the laser beam focal point is highly repeatable. Further, by adjusting the energy levels of the laser beam, a region of energy density that is smaller than the diffraction limited beam diameter can be achieved. By carefully positioning the target sample in the beam, a region of ablation of the target sample can be also made smaller than the diameter of the beam at the focus position. In the present invention, it is the extreme precision and the six axis of motion control, resulting from the piezo driven stages that make nanometer range sample surface modifications possible. In addition, the piezo stages can position the target sample such that its surface is at an angle to the axis of the beam. This allows for different shaped ablation regions.
The present invention may also include the use of a multi-axis stage with correction for Abby and parasitic motions in combination with an atomic force microscope when such microscope is used to remove or add material to a sample surface. Alternatively, other energy sources could be used for adding or removing material, including, FIB and electron beam. These same sources could also be used for measuring the locations of created features as well as preexisting features on the sample surface.
There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. An embodiment in accordance with the present invention provides precision positioning of a sample in six axis of motion. This precise positioning is made enabled by including precision measurements and by combining coarse and fine motion stages. By using a combination of stages and precise measuring means according to the present invention, normal and typical errors in positioning encountered with prior art systems and devices may be significantly reduced and an improved position capability provided that is not present in prior art systems.
An embodiment of the present inventive apparatus and method is illustrated in
The lasing device 20 preferably emits a wavelength in the range of 180 nanometers to 300 nanometers with beam 28 having a diameter in the range of 2 millimeter to 10 millimeters. Beam 28 enters the final focusing lens 22 and the lens 22 may have an entry diameter of 2.5 to 3 millimeters. If the beam diameter overfills the focusing lens entry diameter, the lens 22 will vignette beam 28. In this case, the effective numerical aperture of the lens is limited by the diameter of lens 22 and not by the diameter of beam 28 since the exit diameter is fixed by lens 22.
Further, the lasing device 20 preferably is pulsed with pulse durations less than ten picoseconds. Pulse durations in this region have the advantage of cleanly removing material from the sample, and producing surface affected areas smaller than the diffraction limited beam spot size.
The alignment of the lasing device 20 with the focusing lens 22 is critical and it is desirable that this alignment not be disturbed during ablation of material from the target sample 32. Since a volume of material is typically removed from the target sample 32, one advantage is achieved by the precise movement of the sample 32 relative to laser beam focal point 34. This precise movement is accomplished by the multi-axis stage 24. The multi-axis stage 24 can move the sample in three translational axes X, Y and Z and rotated in the roll, pitch, and yaw axes. Any non orthogonalities or parasitic errors are measured and compensated for by actuating one or more of the other translational or rotational axes with complex errors possibly requiring adjustment of up to all six axes.
In order to remove material from the target sample 32, the target sample 32 is precisely positioned such that the location on sample 32, that is to be ablated, is positioned in X, Y, and Z relative to a point is space at which the laser beam 30 is at its smallest diameter. The laser 20 is then pulsed and a portion of the sample 32 is ablated.
Referring to
Where D is the diameter of the beam γ is the wavelength of the beam and N.A. is the numerical aperture.
Additionally in
The per pulse energy of the lasing device 20 may be reduced and therefore the closed line of constant energy density 68 needed to create ablation will change to closed line 67. The closed line 67 is smaller and therefore causes a smaller area of ablation. The importance of this feature is described in more detail in
Referring to
An additional embodiment of the invention may be understood by referring to
Another alternate embodiment of the invention is shown with reference to
In order to compensate for the errors generated by non-orthogonal motion, the present invention employs an observation and control system 90 as shown in
Another feature of the present invention is that lens 22 serves a dual purpose. One feature used to measure the ablation results with the second one being to focus the beam of laser 20 on the surface as described in
As may be appreciated by studying
The present invention may include a device 126 to also move the beam or mechanical machining device in combination with the sample motion device.
A flexure 130, which may be actuated by a piezo device, may be used for creating motion in the multi-axis stage 24. Capacitive sensor or sensors 132 may be used for sensing motion or motions of the multi-axis stage 24. In this case, the signal detector 134 senses changes in the capacitive sensor 132 via the signaling wires 136. An interferometer or plurality of interferometers 138 generating a beam 140, with the return beam 142 reflecting from a mirror 131, may be used for sensing motion of the multi-axis stage 24 in one or more axes. Other sensing mechanisms may also be used and may be employed to sense motion in any or all of the axes of multi-axis stage 24.
The system 114 additionally may be placed under humidity control, temperature control, and or vibration isolation. Such single or multiple controls may be accomplished with a device or devices 144, which are able to track the above listed capabilities.
As the process of the embodiment of the invention just describe progresses, it is important to note that each ablation step must be properly registered with the previous step. This can be accomplished with very high accuracy utilizing the current invention, because Abbe errors are minimized. This is also true for the Z-axis steps described above, because the X and Y parasitic motion during Z moves can be compensated.
It is also important that the ablation steps be properly registered to features on the target surface. This can be best achieved when the observing device 94 and focusing lens 22 are the same. In the case of a mechanical material removal method, again best registration is achieved when the probe microscope 124 is used to both observe and remove material. In the case of an electron or particle beam device, the best registration is obtained when the ablating beam is also the observing device. The X and Y positioning accuracy must be maintained as each subsequent material removal step is accomplished.
The piezo actuators 174, 176, 178 can be actuated individually or as a whole set or subset. By allowing individually movement of the actuators, the multi-axis stage is able to be moved and rotated in any number of directions as desired in order to reduce or substantially reduce the unintended errors in the system.
The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.