Cavity structure using patterned sacrificial layer

A method includes forming a sacrificial layer over a bottom substrate. The sacrificial layer is patterned based on a desired etching distance. A top layer is formed over the sacrificial layer. At least one release hole is formed through the top layer. The sacrificial layer is etched through the at least one release hole.

TECHNICAL FIELD

The present disclosure relates generally to an integrated circuit and more particularly a cavity structure using patterned sacrificial layer.

BACKGROUND

For some semiconductor devices, a cavity structure needs to be supported by an isolated anchor structure with precise dimensions. Some methods included using release holes for etching around the anchor structure. Etching time is determined by relative distance from release holes to anchors. Sometimes the release holes are limited to certain locations, which may lead to a longer process time or excessive undercut from etching at some sites. The shape of the anchor structure is easily affected by locations of the release holes.

DETAILED DESCRIPTION

FIGS. 1A-8Bare top and cross-section views of intermediate fabrication steps of an exemplary patterned cavity structure according to some embodiments.FIG. 1Ais a top view of a bottom substrate102.FIG. 1Bis a cross-section view ofFIG. 1Aalong the line103. The bottom substrate can comprise silicon, silicon dioxide, aluminum oxide, sapphire, germanium, gallium arsenide (GaAs), an alloy of silicon and germanium, indium phosphide (InP), silicon on insulator (SOI), or any other suitable material. In some embodiments, the bottom substrate102may have other structures including devices and components such as transistors, resistors, inductors, capacitors, etc. The followingFIGS. 2A-8Bare similarly arranged, each top view with a corresponding cross-section view.

InFIG. 2A, a sacrificial layer104is formed over the bottom substrate102. In some embodiments, the sacrificial layer104comprises SiO2, metal, polymer, or any other suitable material. In some embodiments, the thickness of the sacrificial layer104is in the range of 10 nm-100 μm. In one example, the sacrificial layer104comprising SiO2is deposited by chemical vapor deposition (CVD) or physical vapor deposition (PVD).FIG. 2Bis a cross-section view ofFIG. 2A.

InFIG. 3A, the sacrificial layer104is patterned to make at least one channel or cavity106based on a desired etching distance. The sacrificial layer104will be etched later in the process (e.g., inFIG. 7A) and the etching distance depends on the specific process and etching time. The sacrificial layer104can be patterned by photolithography process and wet/dry etching, for example. One or more channel or cavity106is patterned around an anchor structure105in some embodiments.FIG. 3Bis a cross-section view ofFIG. 3A.

InFIG. 4A, a top layer108is formed over the sacrificial layer. In some embodiments, the top layer108comprises silicon. In some embodiments, the top layer108is formed by bonding a top substrate over the sacrificial layer104, and the top substrate is bonded by fusion bonding or direct bonding. Any other suitable bonding method can be used. In some embodiments, the top layer108may have other structures including devices and components such as transistors, resistors, inductors, capacitors, etc. In some embodiments, the top layer108has a thickness ranging from 1 μm to 1000 μm.

InFIG. 5A, release holes110aand110bare formed through the top layer108. In some embodiments, circular release holes110aare distributed around the anchor structure105. A release hole110bis formed in the shape of a rectangular closed loop channel around another anchor structure107. The illustrated release hole110ofFIG. 5Bdoes not correspond directly to either release holes110aor110bofFIG. 5A, but rather is intended to generically represent in a simplified fashion any and all release holes that are formed in top layer108. Both anchor structures105and107are in the sacrificial layer104. The release holes110aand110bcan have different shapes, locations, and dimensions depending on the layout.

The release holes110aand110b, and the patterned channel/cavity106are designed according to the desired final structure of the sacrificial layer104inFIGS. 8A-8B. The release holes110aand110bcan be formed by deep reactive-ion etching (DRIE), for example. In some embodiments, the release holes110aand110bhave a width or diameter ranging from 1 μm to 100 μm.

FIG. 6Ashows the locations of the release holes110aand110brelative to the sacrificial layer104. The followingFIGS. 7A-8Bshow the sacrificial layer104to illustrate how the etching process changes shapes in the sacrificial layer104.

InFIG. 7A, the sacrificial layer104is etched through the release holes110aand110band an etched out cavity area112ais formed and enlarged. For example, dry etching, wet etching, or vapor etching process can be used. The pre-patterned sacrificial layer104structure inFIG. 6Awith channel or cavity106reduces etching amount and allows better etching distance control, based on etching time and the specific etching process. TheFIGS. 7A-7Billustrate the etched area112abeing enlarged from the release holes110aand110bby the etching process.

The patterned sacrificial layer104structure also provides the functionality of support and structural interconnection in locations that are not etched out. The anchor structure105in the sacrificial layer104provides structural support, for example.

InFIG. 8A, the etched out sacrificial layer104is shown with the cavity112bformed from the etching process. The shape, distance, and speed of formation of the cavity112binFIG. 8AandFIG. 8Bcan be controlled by the location and size of the release holes110aand110b, the sacrificial layer104material, the size and shape of cavity(ies)106, and selected etching time and method. The density of the channel or cavity106in the patterned sacrificial layer104structure inFIG. 6Acan be uniform or non-uniform over a wafer depending on the desired etching speed and distance at different locations.

In some embodiments, the top layer108and the bottom substrate102can have electrical connections and routings separately or connected together by vias and/or metal layers comprising electrically conductive material such as metal, polysilicon, or any other suitable material.

By designing the pre-patterned channel/cavity106in the sacrificial layer104and the locations of the release holes110aand110bin the top layer108, the etched structure of the sacrificial layer104inFIG. 8Ahas the desired etching distance and shape. For example, the anchor structure105is defined by generally straight lines with a rectangular shape, and an appropriate etching distance111around the anchor structure107is obtained without etching a longer (or larger) undercut than desired or planned.

In other embodiments, the anchor structure105may have a different shape such as circle, oval, or other polygon. Using the method described above, the anchor structure105will be defined by generally straight lines or generally smooth curves using pre-patterned sacrificial layer104. In comparison, some other methods using release holes only will result in multiple arc shapes with sharp connecting points by etching at the multiple release holes, similar to the etched line114.

The etching distance can be controlled with etching time of the specific etching process. In some other methods different from the method described above, while trying to obtain the desired etching distance around the anchor structure105, the etched distance111around the anchor structure107can be greater than what is desirable, for example.

By using the method described with respect toFIGS. 1A-8Bwith the pre-patterned sacrificial layer104and the release holes110aand110b, the etched distance can be controlled better and the shape of the anchor structures105and107are less affected by the location of release holes110aand110b, compared to a different method using only the release holes110aand110b.Also, the different shapes and different numbers of channels/cavities106and release holes110a/110bcan be designed to obtain the final structure with a planned etching distance. Thus, the etching can be performed under relatively uniform conditions without the need to etch different distances at different locations.

FIGS. 9A-9Eare top views of various exemplary patterned structure layouts according to some embodiments. The release holes110are distributed the same inFIGS. 9A-9E, but the channel or cavity106is patterned differently in the sacrificial layer104. InFIG. 9A, two rectangular closed loop channels are formed around the anchor structure105.

InFIG. 9B, one rectangular closed loop channel is formed around the anchor structure105and multiple circular channels are formed around the release holes110. InFIG. 9C, the patterned channel or cavity106is similar toFIG. 9B, and an additional rectangular closed loop channel is formed around the outside of the release holes110.

InFIG. 9D, the patterned channel or cavity106is similar toFIG. 9A, and additional cavities are formed at the release hole110locations. InFIG. 9E, the patterned channel or cavity106is similar toFIG. 9D, and an additional rectangular closed loop channel is formed connecting the release hole locations110.

The locations, shapes, and dimensions of the patterned channel or cavity106in the sacrificial layer104can be designed to obtain the desired structure of the sacrificial layer104after the etching inFIGS. 7A-7Band reduce undesired under cut at different locations when the etching process is performed simultaneously.

Etching time can be controlled by the density of patterns (e.g., multiple parallel channels inFIG. 9A, or distributed circular channels inFIG. 9B) in addition to relative distance between release holes110and the anchor structure105. The location of release holes110can be limited in the layout depending on the available chip area, but the sacrificial layer104can be patterned to save etching time and/or undesired undercut. This method is to not only reduce etching amount of sacrificial layer104by pre-patterning the sacrificial layer104, but also guide the etchant to desired locations for etching.

FIGS. 10A-10Care top views of various exemplary patterned structure layouts according to some embodiments. The pattern of the channel or cavity106can be a closed loop or an open loop. The channels/cavities106in the sacrificial layer104can be a closed loop, an open loop, rectangular, circular, or any other shape. InFIG. 10A, the parallel channels106in the sacrificial layer104have a rectangular closed loop shape around the anchor structure105.

InFIG. 10B, the two parallel channels106in the sacrificial layer104have different shapes, with a rectangular closed loop shape inside and a broken (open) loop shape outside. InFIG. 10C, the parallel channels106in the sacrificial layer104ofFIG. 10Aare connected at the corners of the rectangular shape and the inner channel has openings. Any suitable shape and pattern can be used in other embodiments.

According to some embodiments, a method includes forming a sacrificial layer over a bottom substrate. The sacrificial layer is patterned based on a desired etching distance. A top layer is formed over the sacrificial layer. At least one release hole is formed through the top layer. The sacrificial layer is etched through the at least one release hole.

According to some embodiments, an integrated circuit includes a bottom substrate and a sacrificial layer over the bottom substrate. The sacrificial layer includes at least one cavity and an anchor structure. A top layer is disposed over the sacrificial layer. The top layer includes at least one release hole formed through the top layer. The at least one release hole is used for etching the sacrificial layer to form the at least one cavity and the anchor structure, and the anchor structure is defined by generally straight lines or generally smooth curves.

The above method embodiment shows exemplary steps, but they are not necessarily required to be performed in the order shown. Steps may be added, replaced, changed order, and/or eliminated as appropriate, in accordance with the spirit and scope of embodiment of the disclosure. Embodiments that combine different claims and/or different embodiments are within the scope of the disclosure and will be apparent to those skilled in the art after reviewing this disclosure.