Patent Application
20160074968
The present disclosure relates to laser-based etching techniques, and more specifically, to a mask reticle configured to control etching depths during laser-based etching processes.
Various materials such as, for example, semiconductor and/or etching materials, can be etched using laser etching tools configured to generate high-energy laser pulses that pattern the workpiece. Conventional laser-based etching processes achieve a desired pattern depth by controlling the fluence of the laser pulses, the amount of time a patterned area of the workpiece is exposed to the laser pulses, and/or the amount of pulses delivered to the patterned area. In order to etch patterns having varied depths, conventional laser-based etching processes require multiple etching passes combined with multiple mask reticles to achieve a respective depth. Consequently, the laser etching tool must perform multiple passes corresponding to each mask.
According to at least one embodiment a laser etching system includes a laser source configured to generate a plurality of laser pulses during an etching pass. A workpiece is aligned with respect to the laser source. The workpiece includes an etching material that is etched in response to receiving the plurality of laser pulses. A mask reticle is interposed between the laser source and the workpiece. The mask reticle includes at least one mask pattern configured to regulate the fluence or a number of laser pulses realized by the workpiece such that a plurality of features having different depths with respect to one another are etched in the etching material following a single etching pass.
According to another embodiment, a method of etching a workpiece comprises generating a plurality of laser pulses having a fluence during an etching pass. The method further includes aligning a workpiece with respect to the plurality of laser pulses, the workpiece including an etching material that is etched in response to receiving the plurality of laser pulses. The method further includes regulating at least one of the fluence and a number of laser pulses realized by the workpiece using at least one mask pattern such that a plurality of features having different depths with respect to one another are etched in the etching material.
Additional features are realized through the techniques of the present invention. Other embodiments are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the features, refer to the description and to the drawings.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing features are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
Various embodiments of the present disclosure provide a mask reticle configured to pass laser fluences therethrough and toward a workpiece to etch a pattern having multiple different depths. In this manner, the mask reticle provided by at least one embodiment provides greater cost savings, while also decrease processing time, wear on the tool, and the use of consumables required to operate the laser.
With reference now to
The laser source 102 may include any commercially available laser source such as one capable of generating one or more ultra violet (UV) laser pulses 108 having a wavelength of, for example, approximately 308 nanometers (nm). A representative high energy UV pulse 108 may include fluences ranging, for example, from approximately 0.05 joules (J) to approximately 1.0 J per square centimeter (cm), and a pulse duration of approximately 1 nanosecond(ns) to approximately 100 ns, for example. The wavelength of the UV pulse 108 may include all wavelengths produced by an excimer laser such as, for example, approximately 126 nm to approximately 351 nm, and/or other wavelengths, without limitation.
The workpiece 104 includes an etching material 110 formed on an etch-resistant base 112. The etching material may be formed from, for example, a dielectric material. The dielectric material includes, but is not limited to, photodefinable polymers, polyimides (PI), polybenzobisoxazole (PBO), epoxies, and bisbenzocyclobutene (BCB).
The mask reticle 106 includes a transparent layer 114 having a reflective layer 116 formed on an upper surface thereof. The transparent layer 114 is formed from various laser transparent materials including, but not limited to, quartz. The reflective layer 116 is formed from various reflective materials including, but not limited to, aluminum. According to an embodiment, a first opening 118a has a first critical dimension and a second opening 118b has a second critical dimension that is less than the first critical dimension. The mask reticle 106 can be interposed between the laser source 102 and the workpiece 104. Although the masking reticle 106 is illustrated with the openings 118a, 118b, etc., disposed below the transparent layer 114, it is appreciated that the masking reticle 106 can be formed such that the openings 118a, 118b, etc., are disposed above the transparent layer 114.
According to an embodiment, laser pulses 108 generated by the laser source 102 are directed toward the mask reticle 106 during a single etching pass. The reflective layer 116 prevents the laser pulses 108 from penetrating therethrough and reaching the workpiece 104. The openings 118a/118b, however, allow portions of the pulses 108 to pass through the transparent layer 114 and reach the workpiece 104 disposed beneath the mask reticle 106 to form corresponding openings 120a/120b. The size of the openings 118a/118b limits the area where energy is applied to the workpiece 104. If the applied area is sufficiently small, the sloping of sidewall features will intercept one another and self-limit the ablation process. For example, the applied area can have a dimension that is, for example, less than the thickness of the layer being etched.
Turning to
Various examples of a feature 120 etched in a workpiece 104 are illustrated in
In
Turning to
Referring again to
In response to increasing the fluence, the additional energy introduced to the etching material 110 improves the ability to overcome the etching threshold (i.e., the threshold at which the etching material begins to breakdown due to exposure from the pulses 108) such that one or more second features 120b are formed as self-limiting features 120b. In cases where the fluence is remains constant, the self-limiting features 120b are formed having approximately identical sidewalls, while lower fluences will produce a termination depth that is shallower. Additional pulses 108 at a low fluence will not help overcome the etching threshold of the side walls.
Turning now to
The etched features 120a-120c are formed with a depth and size that are proportional to the size of the openings 118a-118c. For example, a first opening 118a having the smallest size among the openings 118a-118c facilitates the formation of a first feature 120a having the shallowest depth among the etched features 120a-120c, while a third opening 118c having the largest size among the openings 118a-118c facilitates the formation of a third feature 120c having the deepest depth. Accordingly, the variation in sizes of the openings 118a-118c facilitates the formation of respective self-limited features 120a-120c having different depths with respect to one another.
With respect to
A first portion of mask reticle 106 is patterned to form a first opening 118a that extends through both the partially-reflective sub-layer 122 and the fully-reflective sub-layer 124. A second portion of the mask reticle 106 is patterned to form a second opening 118b that extends through only the fully-reflective sub-layer 124 to expose an underlying portion of the partially-reflective sub-layer 122. The first opening 118a allows the full fluence of the laser pulses 108 to pass through the transparent layer 114 while the second opening 118b allows only a partial fluence of the laser pulses 108′ to pass through the transparent layer 114. Accordingly, the full-fluence laser pulses 108 form a fully-etched feature 120a into the etching material 110 while the partial-fluence laser pulses 108′ form a partially-etched feature 120b into the etching material 110. In addition, the fluence of the laser pulses 108 and the number of laser pulses 108 can be adjusted to control the dimensions of the etched features 120a/120b. For example, increasing the fluence of the laser pulses 108 and the number of laser pulses 108 directed toward the mask reticle 106 increases the depth of the etched features 120a/120b. It is appreciated that a change to the fluence that etches 120a, however, may have no impact in the etch depth. Increasing or decreasing the fluence of the laser pulses 108 also increases or decreases, respectively, the angle of the sidewalls defined by each feature 120a/120b. To this end, by decreasing the laser fluence, the etched feature 120a may only extend partially through the etching material 110 (similar to feature 120b), or the partially etched via 102b (and possibly the fully etched via 102a) and may become self-limiting as the wall angle/slope decreases due to the fluence reduction.
Referring now to
According to at least one embodiment, the stacked reflection layer is patterned such that a single isolated partially-reflective sub-layer 122′ is interposed between the first and second openings 118. Stacked reflection layers are formed on the transparent layer 114. The stacked reflection layers include a fully-reflective sub-layer 124 stacked directly on a partially-reflective sub-layer 122 as described above. Each opening 118 separates a respective stacked reflection layer from the isolated partially-reflective sub-layer 122′. The openings 118 extend through the partially-reflective sub-layer 122 and the fully-reflective sub-layer 124 and expose the transparent layer 114. Accordingly, full-fluence laser pulses 108 pass through the openings 118 to reach the etching material 110 and etch a first feature 120 therein.
The first feature 120 is, for example, a fully-etched feature 120 that exposes a portion of the underlying base 112. The isolated partially-reflective sub-layer 122′, however, reduces the fluence of the laser pulses 108 without completely blocking the laser pulses 108 from passing through the transparent layer 114. Accordingly, partial-fluence laser pulses 108′ impinge on the etching material 110 and form a partially-etched isolated feature 126 that is interposed between the fully-etched features 120. In this manner, the fully-etched features 120 and the partially-etched isolated feature 126 can enable the formation of electrically conductive interconnects, for example, which connect one or more vias using various plate up and dual-damascene fabrication processes as understood by those having ordinary skill in the art. It is appreciated that similar sets of features can be formed in a single pass utilizing varied etch feature openings and the techniques described above with respect to
Turning to
The position of the mask reticle 106 is adjustable with respect to one or more laser pulses 108. According to an embodiment, the mask reticle 106 may be supported by a moveable mask stage (not shown in
A sequence of alignment operations that align the masking patterns 128a-128c with respect to a plurality of laser pulses 108 and a workpiece 104 is illustrated with reference to
In
In
With reference still to
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one more other features, integers, steps, operations, element components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the inventive teachings and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated
The flow diagrams depicted herein are just one example. There may be many variations to this diagram or the operations described therein without departing from the spirit of the invention. For instance, the operations may be performed in a differing order or operations may be added, deleted or modified. All of these variations are considered a part of the claimed invention.
While various embodiments have been described, it will be understood that those skilled in the art, both now and in the future, may make various modifications which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.
