Patent Application
20080142475
The patent relates to the formation of arbitrary three-dimensional (3-D) structures from a solid material.
Prior approaches for forming 3-D structures involve masking at least one surface of a substrate material, patterning the mask, and exposing the substrate to an etchant. The etching may proceed via a wet or dry process and may further be characterized as isotropic or anisotropic. Generally, the etched region is a projection of the masked pattern into the substrate perpendicular to the masked surface. There is limited control of the sidewall slope through the choice of etching process and there is no way to laterally etch regions arbitrarily. The only approach to form such structures involves repetitive deposition and etches cycles which are both complicated and expensive.
When etching a material such as single crystalline silicon in an anisotropic etchant such as potassium hydroxide (KOH), certain crystal planes will typically etch much faster than others. For instance, in silicon the (100) planes etch much faster than the (111) planes. Furthermore, polycrystalline regions etch faster than (100) planes and amorphous regions etch a hundred times faster than the (100) planes in silicon.
Rapidly heating a region of a crystalline silicon followed by a sudden quench to room temperature destroys the crystalline nature of the region causing the crystalline silicon to become amorphous or at least fine grained poly crystalline material. The rapid heating can be accomplished by focusing a pulsed directed energy source into a material such that at the focal point, the power density exceeds a critical value. In doing so, only the region in the immediate vicinity of the focal point will have its crystalline structure altered.
In one previous approach, a laser was used as the directed energy source to create linear regions of altered material across a wafer and through the thickness of the wafer whereby the wafer can be easily broken into many individual die. This approach includes a critical power density for silicon of 108 W/cm2 with a pulse width of less than 1 μS and may be described as multi-photon absorption at the focal point. The wavelength used was typically below the band gap absorption edge thus being only slightly absorbed if at all. The regions below the critical power density therefore are not altered. Adding a masking material in addition to the laser exposure adds another degree of freedom to the process by either blocking the energy or aiding in the coupling of the energy to the material by the selection of appropriate optical properties, i.e. reflective vs. antireflective.
For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein:
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.
While the present disclosure is susceptible to various modifications and alternative forms, certain embodiments are shown by way of example in the drawings and these embodiments will be described in detail herein. It will be understood, however, that this disclosure is not intended to limit the invention to the particular forms described, but to the contrary, the invention is intended to cover all modifications, alternatives, and equivalents falling within the spirit and scope of the invention defined by the appended claims. Like reference numerals are used for like and corresponding elements of the drawings.
It is contemplated that the present approaches are not limited to crystalline materials. Rather, solid materials such as polymers can undergo structural/chemical changes when a critical power density is reached thereby forming altered regions which can be preferentially etched over unaltered regions. Depending on the material and etchant properties, the opposite process is also contemplated in which the unaltered region is preferentially etched over altered regions.
An optional masking material (not shown) being resistant to attack by an etchant (not shown) is applied to at least a portion the material for protecting an underling region of the material 200 and will be discussed in greater detail herein. The fixture 102 for mounting the material 200 can be a motion stage which is controlled and moved by the controller system 104 in an x-direction, a y-direction, an a z-direction, and any combination thereof.
The controller system 104 comprises a computer 112 and a control unit 114. The computer 112 is any type of device capable of processing, transmitting, and receiving data from a user. The computer 112 may provide a Graphical User Interface (GUI) to a user or users. The computer 112 may provide other functions, as well. The computer 112 also controls the operations of the control unit 114. The control unit 114 is a motion stage controller for controlling the movement of the fixture 102. The directed energy source controller 106 for controlling at least one energy source 116, producing at least one energy beam 118 which is reflected by the mirror 110 and is focused into the material 200 by lens 108. The focal point of beam 118 within material 200 may be controlled in the direction normal to the surface (Z axis) by either adjusting the lens 108 or by Z motion of the fixture 102. In one embodiment, the directed energy source 116 is a laser and its wavelength is selected based the optical properties of material 200. In the example of silicon material, the energy source 116 has a wavelength to be approximately 1000 nm and longer so that at low intensities it is not absorbed. Alternatively, the energy source 116 has a wavelength of approximately 1500 nm. In one embodiment, the wavelengths for use with silicon are approximately 1064 nm and approximately 1300 nm. Other examples of energy source are possible. A plurality of energy beams (not shown) may be emitted from the directed energy source 116 to different locations within the material 200, so as to form at least one altered region 210 (See
Referring now to
Another example of applying the present approaches to form a structure in a material is illustrated in
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extend as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.
