US-20260126587-A1 - NESTED WAVEGUIDE FAN-OUT STRUCTURE AND METHODS FOR FORMING THE SAME

Abstract

An optical beam splitter includes a multi-stage nested network of waveguide bifurcation branches, which includes: first-stage waveguide bifurcation branches each including a pair of first-stage waveguide segments, and second-stage waveguide bifurcation branches each including a pair of second-stage waveguide segments. Each pair of first-stage waveguide segments includes a first common end and a pair of first split ends and a pair of first interconnection portions. Each first common end points toward a first widthwise direction. Each pair of second-stage waveguide segments includes a second common end and a pair of second split ends and a pair of second interconnection portions. Each second common end and each second split end of the optical beam splitter point toward a second widthwise direction which is an opposite direction of the first widthwise direction.

Inventors

• Chun-Hao Fann
• Ming Lee
• Wei-Heng Lin
• Hsing-Kuo Hsia
• Chen-Hua Yu

Assignees

• TAIWAN SEMICONDUCTOR MANUFACTURING COMPANY LIMITED

Dates

Publication Date

20260507

Application Date

20260102

Claims (20)

1. 1 . A method of forming a semiconductor structure, the method comprising: forming a waveguide material layer overlying a dielectric material layer; and patterning the waveguide material layer into a multi-stage nested network of waveguide bifurcation branches, the multi-stage nested network of waveguide bifurcation branches comprising: first-stage waveguide bifurcation branches, wherein a first-stage waveguide bifurcation branch comprises a pair of first-stage waveguide segments, the pair of the first-stage waveguide segments comprising a first common end, a pair of first split ends, and a pair of first interconnection portions connecting the first common end to a respective first split end of the pair of first split ends, the first common end and the respective first split end pointing toward a first widthwise direction of an optical beam splitter, and a first interconnection portion of the pair of first interconnection portions comprising a respective first outer convex sidewall segment generally facing a second widthwise direction that is an opposite direction of the first widthwise direction; and second-stage waveguide bifurcation branches, wherein a second-stage waveguide bifurcation branch comprises a pair of second-stage waveguide segments, the pair of the second-stage waveguide segments comprising a second common end, a pair of second split ends, and a pair of second interconnection portions connecting the second common end to a respective second split end of the pair of second split ends, the respective second split end being connected to a respective first common end of the first-stage waveguide bifurcation branch, and the respective second common end and the second split end pointing toward the second widthwise direction of the optical beam splitter.
2. 2 . The method of claim 1 , wherein forming the waveguide material layer comprises depositing the waveguide material layer overlying the dielectric material layer as a blanket material layer having a uniform thickness throughout and comprising silicon or silicon nitride, and wherein the dielectric material layer comprises silicon oxide.
3. 3 . The method of claim 1 , further comprising: forming a photoresist layer overlying the waveguide material layer; lithographically patterning the photoresist layer into a pattern of optical beam splitters; and anisotropically etching the waveguide material layer using the patterned photoresist layer as an etch mask to form the multi-stage nested network of waveguide bifurcation branches.
4. 4 . The method of claim 1 , wherein an entirety of the multi-stage nested network of waveguide bifurcation branches is formed as a single continuous waveguide structure having a uniform height throughout.
5. 5 . The method of claim 1 , wherein a total angular propagation direction change within each of the first interconnection portions is not greater than 180 degrees in a plan view, and a total angular propagation direction change within each of the second interconnection portions is 180 degrees in the plan view.
6. 6 . The method of claim 1 , wherein: the first interconnection portion comprises a first inner convex sidewall segment having a first radius of curvature R 1 in a range from 2 microns to 5 microns; the second interconnection portion comprises a second inner convex sidewall segment having a second radius of curvature R 2 in a range from 2 microns to 5 microns; and the first radius of curvature R 1 equals the second radius of curvature R 2 .
7. 7 . The method of claim 1 , wherein: a width WW of the first-stage waveguide segment and the second-stage waveguide segment is in a range from 100 nm to 500 nm; a spacing WS between adjacent ones of the first-stage waveguide segments and the second-stage waveguide segments is in a range from 100 nm to 500 nm; and a sum (WW+WS) is less than a minimum radius of curvature of inner convex sidewall segments of the multi-stage nested network of waveguide bifurcation branches.
8. 8 . A method of forming a semiconductor structure, the method comprising: forming a waveguide material layer overlying a dielectric material layer; and patterning the waveguide material layer into an optical beam splitter comprising a multi-stage nested network of waveguide bifurcation branches, the multi-stage nested network of waveguide bifurcation branches comprising: a first-stage waveguide bifurcation branch comprising a pair of first-stage waveguide segments having a first common end, a pair of first split ends, and a pair of first interconnection portions connecting the first common end to a respective first split end; a second-stage waveguide bifurcation branch comprising a pair of second-stage waveguide segments having a second common end, a pair of second split ends, and a pair of second interconnection portions connecting the second common end to a respective second split end, a second split end of the pair of second split ends being connected to a respective first common end; a third-stage waveguide bifurcation branch comprising a pair of third-stage waveguide segments having a third common end, a pair of third split ends, and a pair of third interconnection portions connecting the third common end to a respective third split end, the respective third split end being connected to a respective second common end; and a fourth-stage waveguide bifurcation branch comprising a pair of fourth-stage waveguide segments having a fourth common end, a pair of fourth split ends, and a pair of fourth interconnection portions connecting the fourth common end to a respective fourth split end, the respective fourth split end being connected to a respective third common end.
9. 9 . The method of claim 8 , wherein: the first common end and the respective first split end point toward a first widthwise direction of the optical beam splitter; the second common end and the respective second split end point toward a second widthwise direction of the optical beam splitter that is an opposite direction of the first widthwise direction; the third common end and the respective third split end point toward the first widthwise direction; and the fourth common end and the respective fourth split end point toward the second widthwise direction.
10. 10 . The method of claim 8 , wherein the pair of first interconnection portions, the pair of second interconnection portions, the pair of third interconnection portions, and the pair of fourth interconnection portions comprises a respective outer convex sidewall segment generally facing one of the first widthwise direction and the second widthwise direction and a respective inner convex sidewall segment generally facing the other one of the first widthwise direction and the second widthwise direction.
11. 11 . The method of claim 8 , wherein a total number N of optical channels at the first split ends is 16 and a number K of stages of waveguide bifurcation branches is 4 such that N=2 K .
12. 12 . The method of claim 8 , further comprising forming optical devices that are optically connected to the first split ends, wherein optical ports associated with the optical devices are nested within the multi-stage nested network of waveguide bifurcation branches in all horizontal directions in a plan view.
13. 13 . The method of claim 8 , wherein the pair of first interconnection portions, the pair of second interconnection portions, the pair of third interconnection portions, and the pair of fourth interconnection portions comprises a respective pair of inner convex sidewall segments connected to each other by a straight waveguide segment, and each of the inner convex sidewall segments has a total azimuthal extension angle of 90 degrees around a respective center of radius.
14. 14 . The method of claim 8 , wherein all radii of curvature of inner convex sidewall segments of the multi-stage nested network of waveguide bifurcation branches are equal to one another and are in a range from 2 microns to 5 microns.
15. 15 . A device structure comprising an optical beam splitter, wherein: the optical beam splitter comprises a multi-stage nested network of waveguide bifurcation branches including at least a first-stage waveguide bifurcation branch, a second-stage waveguide bifurcation branch, a third-stage waveguide bifurcation branch, or a fourth-stage waveguide bifurcation branch; and a total number N of optical channels connected to first split ends of the first-stage waveguide bifurcation branches is at least 16 and a number K of stages is at least 4 such that N=2 K .
16. 16 . The device structure of claim 15 , wherein: a common end and a split end of odd-stage waveguide bifurcation branch point toward a first widthwise direction of the optical beam splitter; a common end and a split end of even-stage waveguide bifurcation branch point toward a second widthwise direction of the optical beam splitter that is opposite to the first widthwise direction; and an interconnection portion comprises an outer convex sidewall segment generally facing one of the first widthwise direction and the second widthwise direction and an inner convex sidewall segment generally facing the other of the first widthwise direction and the second widthwise direction.
17. 17 . The device structure of claim 15 , further comprising optical devices optically connected to the first split end of the first-stage waveguide bifurcation branch, wherein optical ports associated with the optical devices are entirely nested within the multi-stage nested network of waveguide bifurcation branches in all horizontal directions in a plan view.
18. 18 . The device structure of claim 15 , wherein radii of curvature of inner convex sidewall segments of the multi-stage nested network of waveguide bifurcation branches are equal to one another and are in a range from 2 microns to 5 microns.
19. 19 . The device structure of claim 15 , wherein the device structure further comprises a photonic die including: first dielectric material layers; the optical beam splitter formed within the first dielectric material layers; optical devices optically connected to the first split end of the first-stage waveguide bifurcation branch; first metallic bonding pads electrically connected to the optical devices through first metal interconnect structures formed within the first dielectric material layers; and a semiconductor die bonded to the photonic die and including control circuits configured to control operation of the optical devices.
20. 20 . The device structure of claim 19 , wherein: the semiconductor die comprises second metallic bonding pads bonded to the first metallic bonding pads; and the control circuits comprise field effect transistors electrically connected to the second metallic bonding pads through second metal interconnect structures.

Description

This application is a continuation application of U.S. application Ser. No. 18/463,522 entitled “Nested Waveguide Fan-Out Structure and Methods for Forming the Same,” filed on Sep. 8, 2023, the entire contents of which are incorporated herein by reference for all purposes. BACKGROUND Waveguide fan-out structures for optical devices may occupy a large portion of a device's overall footprint. Reduction of footprint for waveguide fan-out structures is desirable in order to reduce the device's overall footprint. BRIEF DESCRIPTION OF THE DRAWINGS Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. FIGS. 1A-1C are vertical cross-sectional views that illustrate a manufacturing process for forming first dies according to an embodiment of the present disclosure. FIG. 1D is a top-down view of the structure of FIG. 1A. FIGS. 2A and 2B are vertical cross-sectional views that illustrate a manufacturing process for forming second dies according to an embodiment of the present disclosure. FIG. 3 is a vertical cross-sectional view of a bonded assembly according to an embodiment of the present disclosure. FIGS. 4A-4D are sequential vertical cross-sectional views of a region that corresponds to region M in FIG. 3 during a manufacturing process. FIGS. 5A-5C are various top-down views of a portion of an optical beam splitter after the processing steps of FIG. 4B. The vertical cross-sectional plane X-X′ in FIG. 5A corresponds to the plane of the vertical cross-sectional view of FIG. 4B. FIG. 6 is a flow chart that illustrates a sequence of processing steps that may be used to manufacture a device structure according to an embodiment of the present disclosure. DETAILED DESCRIPTION The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. Elements with the same reference numerals refer to the same element, and are presumed to have the same material composition and the same thickness range unless expressly indicated otherwise. As used herein, an element or a system “configured for” a function or an operation or “configured to” provide or perform a function or an operation refers to an element or a system that is provided with hardware, and with software as applicable, to provide such a function or such an operation as described in the present disclosure, and as known in the art in the event any details of such hardware or such software are not expressly described herein. Embodiments of the present disclosure provide a high channel density waveguide fan-out structure using nested enveloping bifurcation structures. The waveguide fan-out structure may provide optical connection between optical devices and/or optical input/output ports in a configuration in which the waveguide paths envelop connection points with the optical devices and/or the optical input/output ports. Bifurcation structures connected to a lesser number of optical ports or optical devices may be nested within bifurcation structures connected to a greater number of optical ports or optical devices to provide enveloping configurations and to reduce the overall footprint of the waveguide fan-out structure. Various embodiment waveguide fan-out structures