Patent Application
20090261516
The present invention relates to methods and apparatus for molding of structures on a surface. In particular, these methods and apparatus are useful for forming structures with high aspect ratios and for forming structures from mold materials with low viscosities and/or low thixotropic indices.
The formation of molded structures on substrates may find applications in many fields. In particular, it is desirable to form wafer level molded structures on semiconductor wafers, such as optics lens masters for electrooptical components. Such molded structures may include high aspect ratio or highly aspheric lenses or other optical components. Not only may these structures have high aspect ratios, but they may also require high surface quality.
In order to achieve these high aspect ratios and/or high surface quality, mold materials having high viscosities may be used. These high viscosity mold materials may achieve high aspect ratios without problems due to material flow and wet-out associated with lower viscosity materials. However, it may be difficult to achieve high surface quality with high viscosity mold materials.
One method to improve the surface quality of structures molded from high viscosity mold materials is to increase the pressure at which the structure is molded. This approach may have drawbacks, such as wear on the mold, as well as the possibility that such high pressure molding may damage the potentially fragile substrate on which the structure is molded.
Another method to improve these structures may be to use mold materials that have both a high viscosity and a high thixotropic index. Such materials may have the robustness to hold high aspect ratio forms until cured, and still may potentially be molded with high surface quality at lower pressures.
Embodiments of the present invention provide an approach that allows molding of structures on substrates using mold materials that may have low viscosities and/or low thixotropic indices.
According to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures:
Embodiments of the present invention use molding apparatus to form molded structures on the surface of the substrate. Methods and apparatus of these embodiments use changes in air pressure to draw mold material into features of the molds. This approach allows the production of molded structures with high aspect ratio features. For example, mold features with an aspect ratio greater than or equal to ½ (where the aspect ratio is equal to a maximum vertical dimension of the mold feature divided by its maximum horizontal dimension) may be formed using embodiments of the present invention. Such mold features may include the inverse of: aspherical lenses; high numerical aperture lenses; and lenses of microlens arrays.
Molded structures formed using embodiments of the present invention may exhibit improved fine surface feature quality and/or reduction in defects or voids in the molded structures due to a reduction of gas trapped during the molding process. Additionally, embodiments of the present invention allow for use of mold materials that have low viscosities and/or low thixotropic indices. For example, mold materials with viscosities less than about 1000 Pascal-seconds, or with thixotropic indices less than about 10 may be used. By allowing the use of mold materials with less desirable pre-curing mechanical properties, embodiments of the present invention may allow for use of mold materials with superior post-curing properties, such as more desirable electrical or optical properties.
It is noted that shroud 100 surrounds mold portion 104; however, shroud 100 and mold portion 104 are shown cut-away through the drawings for clarity. The use of cut-away drawings allows mold feature 106 and pins 108 of mold portion 104 to be shown more clearly.
Substrate mount 122 may be any type of mount used to hold substrate 124 during the molding process. Substrate mount 122 is coupled to frame 114 of the pin molding apparatus. As noted above, substrate mount 122 may include a horizontal positioner. It may also include a vertical positioner, in addition to vertical positioner 112 or in place of vertical positioner 112.
Shroud 100 includes a top end and side material extending from the top end to a bottom opening. The material of shroud 100 is substantially impermeable to air so that a pressure difference may be maintained between the interior space formed when the bottom opening of shroud 100 is covered by substrate 124 and the exterior environment. The side material of the shroud 100 may be rigid (as in shroud 100 of the embodiments shown in FIGS. 1 and 2A-D), vertically compressible (as in shroud 304 of the embodiments shown in
In the embodiment of
Once the bottom opening of shroud 100 is sealed against the top surface of substrate 124, vacuum pump 116 may be used to reduce the pressure within the shroud below the ambient pressure, desirably to at least a medium vacuum. Valve 120 may be used to seal the shroud once the desired pressure reduction is achieved (as well as sealing the intake of vacuum pump 116 when the bottom opening of shroud 100 is not sealed) and allow air back into the shroud to raise the pressure back to ambient pressure when desired. Although valve 120, as shown in
Mold portion 104 is coupled below the top end of shroud 100 and is surrounded by the side material of the shroud. In the embodiments of
Mold portion 104 of the pin mold apparatus illustrated in FIGS. 1 and 2A-D, includes pins 108, which extend a predetermined distance below the outer edge of the bottom surface. As illustrated in
As illustrated in
The vertical positioners, horizontal positioners and mold height positioners of the various embodiments of the present invention may include motorized translation stages, kinematic manipulators and/or piezoelectric elements. The vertical positioner(s) and horizontal positioner(s) are coupled to one or both of: substrate mount 122 or shroud 100 (and mold portion 104). The horizontal positioner(s) allow(s) shroud 100 and mold portion 104 to be moved relative to substrate 124 so that molded structure 202 (illustrated in
The mold apparatus is positioned by step 502 over the desired area of the top surface of substrate 124. The control circuitry controls the horizontal and vertical positioners to achieve the desired relative positioning. Using the horizontal positioner(s), the mold apparatus is horizontally aligned over the desired area such that the shroud of the mold apparatus surrounds mold material 126 and mold portion 104 is positioned above the mold material. FIGS. 1 and 3B illustrate mold apparatus according to the present invention that have been aligned over mold material 126, after the mold material is dispensed on the desired area of the top surface of substrate 124. Using the vertical positioner(s), the mold apparatus is vertically aligned such that the shroud forms a seal with the top surface with the top surface of substrate 124. As described above, it may be desirable for the shroud to include a gasket that may be compressed against the top surface of the substrate to form this seal.
The pressure within the shroud of the mold apparatus is reduced in step 504 to below the ambient pressure. This reduction in pressure may be accomplished in a number of different ways. In one embodiment of the present invention (for example, using the mold apparatus of FIGS. 1 and 2A-D), a vacuum pump may be used to pump air out of the shroud and, thus, reduce the pressure within the shroud.
Alternatively, the pressure within the shroud of the mold apparatus may be reduced below the ambient pressure by increasing the volume of the shroud of the mold apparatus. For example, in the embodiment of
While the pressure within the shroud is reduced, mold portion 104 is lowered by step 506 to a predetermined height above the top surface of substrate 124. In the embodiments illustrated in
Although the bottom surface of mold portion 104 is not brought into contact with substrate 124 in step 506, at least an outer edge of mold portion 104 is brought into contact with mold material 126, as illustrated in
Once mold portion 104 is lowered into the desired position, the pressure in trapped pocket 200 is equal at the reduced pressure within the shroud. The pressure within the shroud of the mold apparatus is raised by step 508 back to at least the ambient pressure. Raising the pressure within the shroud pressure does not directly raise the pressure within trapped pocket 200. The difference in the pressure in the shroud and the pressure in trapped pocket 200 causes the mold material to be forced into the mold features of the bottom surface of mold portion 104 to form molded structure 202, as illustrated in
The pressure within the shroud may desirably be raised back to the ambient temperature, or may even be raised above the ambient pressure, i.e. overpressurized. Overpressurizing the air in the shroud may increase the mold quality by further decreasing the volume of any air that was trapped in the pocket in step 506.
Raising the pressure within the shroud may be accomplished in several ways, such as: opening a valve in the shroud; pumping air into the shroud; breaking the seal between the shroud and the top surface of the substrate; reducing the volume of the shroud or a combination thereof. It is noted that opening a valve to the ambient environment or breaking the seal between the shroud and the top surface of the substrate only raise the pressure within the shroud to the ambient pressure. Thus, these methods alone are not sufficient if overpressurization of the shroud is desired.
Both
The mold material is then cured by step 510 to form molded structure 202. The curing process is dependent on the type of mold material used. Depending on the type of mold material used, any method of curing mold material known in the art, however, may be used, such as: irradiating the mold material with UV or IR radiation; heating the mold material; and/or waiting a predetermined period of time.
Once the mold material is sufficiently cured for molded structure 202 to maintain its shape outside of the mold, mold portion 104 of the mold apparatus is raised by step 512 to release the molded structure, as illustrated in
In the method of
A mold is then positioned by step 606 at a predetermined height above the area of the top surface of the substrate with at least the outer edge of the mold in contact with the mold material. The pressure within the vacuum chamber is then raised by step 608 to at least the ambient pressure. As in step 508 of the method of
The mold material is cured by step 610 to form the molded structure, and once the mold material is sufficiently cured for the molded structure to maintain its shape outside of the mold, the molded structure is released by step 612 from the mold.
It is noted that embodiments of the present invention may be used to form a series of molded structures on a substrate in a step-and-repeat process, as well as a single molded structure. After one molded structure is completed, the predetermined volume of the mold material is dispensed onto another area of the top surface of the substrate, the mold apparatus is stepped horizontally to position the mold apparatus over the other area of the top surface of the substrate, and the process is repeated.
Although the invention is illustrated and described herein with reference to specific embodiments, it is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. Specifically, it is contemplated that features of the several disclosed embodiments may be used in different combinations to form further embodiments.
