Patent Application
20090061161
Methods of creating three-dimensional (3D) patterns in photocurable polymers include embossing and photolithography. Embossing has limitations including feature size and topographical feature definition. Photolithographic processes have the disadvantage of being binary, such that material is either removed, or remains, in order to create a two-dimensional (2D) pattern. Photolithography is typically used for creating channels or cavities in the material, but not raised features, such as a 3D stepped feature. To create a 3D stepped feature using photolithography, multiple process steps (coat, expose, develop) are performed.
One embodiment provides a method of patterning a cross-linked polymer layer. The method includes providing a substrate comprising a cross-linked polymer layer. A laser beam is generated. The laser beam is directed onto a first surface of the polymer layer. Relative movement between the laser beam and the first surface is caused, thereby forming at least one feature on the first surface.
In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” etc., may be used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.
In one embodiment, scan mirror assembly 108 scans the laser beam across the substrate 112 in two dimensions (e.g., X and Y dimensions parallel to the plane of the substrate 112), thereby allowing two-dimensional patterns to be traced out on the substrate 112. In one embodiment, controller 102 is also configured to cause movement of stage 114, which allows the system 100 to scan the laser beam over larger substrates 112. In another embodiment, the scan mirror assembly 108 is held in a fixed position or is not used, and relative movement between the laser beam and the substrate 112 is caused solely by movement of the stage 114. In yet another embodiment, system 100 is configured to provide vertical movement (e.g., movement in a Z dimension perpendicular to the plane of the substrate 112) between the stage 114 and the optics (e.g., scan mirror assembly 108 and focus lens 110).
In one embodiment, substrate 112 comprises a cured, cross-linked polymer, such as SU8. SU8 is a negative photoresist material. Uncured SU8 can be in liquid or dry film form. Liquid SU8 is coated onto a substrate by spin, spray, or gravure coating. A dry SU8 film can be laminated onto a substrate. SU8 is typically cured using both UV and thermal curing steps. Cured SU8 is a hardened cross-linked polymer, and has a higher mechanical and thermal stability compared to linear polymers.
In one embodiment, substrate 112 is about five micrometers thick. In other embodiments, substrate 112 is thicker or thinner than five micrometers thick. In one embodiment, laser 104 is an 11 W diode pumped solid state pulsed ultraviolet (UV) laser operating at 60 kHz. Laser 104 generates UV laser light with a wavelength of less than 400 nm, and the wavelength is tied to energies that are equal to or higher than the bond energy of the material to be patterned. In one specific embodiment, laser 104 generates UV laser light with a wavelength of 355 nm and a pulse length of about 40 nanoseconds. The energy of the laser beam generated by laser 104 is controlled by controller 102 by changing the laser current. The interaction between the SU8 polymer and the pulsed UV radiation results in the dissociation of certain chemical bonds in the polymer molecules, fragmenting it into smaller units. This mechanism results in two possible outcomes. Above a specific threshold energy, polymer fragments are ablated from the surface of substrate 112. The amount of material that is ablated increases with increasing laser power. At energies just below the ablation threshold, the SU8 polymer swells, resulting in three-dimensional raised structures or features. At such energies, the structure of the bulk polymer is changed due to the formation of new bonds between fragments with insufficient energy to be ejected. The swelling is due to a thermal effect, and the thermal influence is dependent on the laser pulse length. Longer pulse lengths provide more penetration of the thermal heating into the material, and shorter pulse lengths provide less penetration.
In the illustrated embodiment, controller 102 includes memory 116 for storing pattern information 118, which defines the pattern that controller 102 causes the laser beam to trace out on the substrate 112. In one embodiment, the pattern information 118 also includes laser power information, which defines the laser power that is to be used at the various points in the pattern followed by the laser beam. Based on the stored pattern information 118, controller 102 is configured to cause system 100 to scan the laser beam over the substrate 112 in any desired pattern, and form raised features and cavity features in the substrate 112 in a single process step by modifying the laser power above and below the ablation threshold.
In one embodiment, system 100 is configured to create micro-channels and raised microstructures “simultaneously” (i.e., in one process step), by varying the laser energy above and below the ablation threshold while scanning the laser beam across the substrate 112. The laser patterning performed by system 100 according to one embodiment provides a reduction in process steps, compared to conventional photolithographic processes, as it provides for the patterning of features in cured polymers without the need for photo-masks and the associated develop processes. By using particular photocurable polymer materials, and specific light wavelengths, light intensities, and micropatterning techniques, system 100 creates 3D structures in substrate 112 in a single process step in one embodiment.
When the power of the laser 104 is increased slightly above the ablation threshold of polymer layer 204, material is ablated from the surface of polymer layer 204, resulting in relatively shallow channels or cavities 210 being formed in the polymer layer 204, as shown in
As shown in
Also shown in
One embodiment of system 100 provides direct write patterning of a polymer layer 204 with a process that can be accomplished at low temperatures (e.g., less than 150° C.). The ability to selectively write 3 D structures in a polymer layer 204 provided by system 100 is advantageous to creating customized templated patterns for micro electromechanical systems (MEMS) and macroelectronic applications. One embodiment of system 100 is configured to create 3 D structures in a substrate 112 with fewer and less expensive processing steps compared to traditional photolithographic processes. The patterning process according to one embodiment may also be used in conjunction with other process steps where additional coating layers are not a solution. For example, if the substrate 112 is patterned via a first process, but requires a raised feature, system 100 can provide the raised feature without the need of an additional coating layer being deposited. In one embodiment, system 100 is configured to use direct write patterning to form contact pads between stacked semiconductor chips. The patterning process according to one embodiment is applicable over large areas without the use of a photomask. The patterning process according to one embodiment is also capable of implementation on roll to roll type processing.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.
