# Patent

## Title
Method of patterning semiconductor structure and structure thereof

## Abstract

Method of patterning a semiconductor structure is disclosed. The method involves crystallographic etching techniques to enhance a patterned monocrystalline layer as a hard mask. In one embodiment, the method includes bonding a monocrystalline silicon layer to a non-crystalline protective layer; patterning the monocrystalline layer to form a hard mask; enhancing the pattern of the hard mask; stripping the hard mask after conventional etching of protective layer; and forming a gate oxide thereon. The enhanced patterning of the hard mask is performed with crystallographic etching to replace optical effects of rounding and dimension narrowing at the ends of a defined region with straight edges and sharp corners. A resulting structure from the use of the enhanced patterned hard mask includes a layer of composite materials on the substrate of the semiconductor structure. The layer of composite materials includes different materials in discrete blocks defined by straight edges within the layer.

## Background
BACKGROUND
1. Technical Field
The disclosure relates generally to patterning of semiconductor structure in complementary metal oxide semiconductor (CMOS) circuits fabrication, and more particularly, to method of enhancing a patterned hard mask.
2. Background Art
In the current state of the art, continued complimentary metal oxide semiconductor (CMOS) scaling has resulted in high density CMOS circuitry. Optical effects in the printing of patterns onto substrates of semiconductors for CMOS circuitry fabrication lead to rounding and dimensional reduction at the ends of printed lines. Often, the rounding and dimensional reduction exacerbates the effectiveness of device and circuit operations in a densely packed circuitry. This is demonstrated in 45 nm static random access memory (SRAM) designs at the active area (RX) and polycrystalline layers.
Crystallographic etching has been recognized as a means for enhancing printed patterns at the RX level. The use of this type of etching technique requires a monocrystalline layer. However, as most semiconductor structures involve non-crystalline and polycrystalline layers, the use of crystallographic etching for such enhancement purposes cannot be applied directly to every level of semiconductor fabrication.
SUMMARY
Method of patterning a semiconductor structure is disclosed. The method involves crystallographic etching techniques to enhance a patterned monocrystalline layer as a hard mask. In one embodiment, the method includes bonding a monocrystalline silicon layer to a non-crystalline protective layer; patterning the monocrystalline layer to form a hard mask; enhancing the pattern of the hard mask; stripping the hard mask after conventional etching of protective layer; and forming a gate oxide thereon. The enhanced patterning of the hard mask is performed with crystallographic etching to replace optical effects of rounding and dimension narrowing at the ends of a defined region with straight edges and sharp corners. A resulting structure from the use of the enhanced patterned hard mask includes a layer of composite materials on the substrate of the semiconductor structure. The layer of composite materials includes different materials in discrete blocks defined by straight edges within the layer.
A first aspect of the disclosure provides a method for patterning a semiconductor structure comprising: bonding a monocrystalline layer to a protective layer disposed on the semiconductor structure; lithographically patterning the monocrystalline layer to form a hard mask; applying crystallographic etching to enhance the patterned hard mask; and etching the protective layer according to the enhanced patterned hard mask.
A second aspect of the disclosure provides a semiconductor structure comprising: at least one composite layer formed on a substrate, the composite layer including discrete blocks of different materials, wherein the discrete blocks are defined by straight edges.
A third aspect of the disclosure provides a semiconductor structure comprising: a substrate; and multiple composite layers, wherein at least one of the multiple composite layers is disposed on the substrate, wherein each of the multiple composite layers includes a plurality of discrete blocks of different material, wherein each discrete block is defined by straight edges.
These and other features of the present disclosure are designed to solve the problems herein described and/or other problems not discussed.



BRIEF DESCRIPTION OF THE DRAWINGS
Various aspects of the disclosure will be more readily understood from the following detailed description taken in conjunction with the accompanying drawings that depict different embodiments of the disclosure, in which:
FIGS. 1A, 2A, 3A, 4A, 5A and 6A are top views of various embodiments of a semiconductor structure according to a method of the disclosure.
FIGS. 1B, 2B, 3B, 4B, 5B and 6B are cross-sectional views of the various embodiments of the semiconductor structure, taken along the line A-A, in corresponding FIGS. 1A, 2A, 3A, 4A, 5A and 6A, respectively.
FIG. 7A is a top view of an embodiment of a semiconductor structure resulting from the method of FIGS. 1A-6B.
FIG. 7B is a cross-sectional view of the embodiment of the semiconductor structure taken along the line A-A in corresponding FIG. 7A.
FIG. 8 is a cross-sectional view of an embodiment of a semiconductor structure illustrating multiple composite layers formed by the method of the disclosure.



It is noted that the drawings of the disclosure are not to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.
DETAILED DESCRIPTION
Embodiments depicted in the drawings in FIGS. 1A-8 illustrate the method and various resulting structures of the different aspects of fabricating a patterned semiconductor structure 10.
FIG. 1A is a top view of a semiconductor structure 10 illustrating a monocrystalline layer 130 disposed thereon. Monocrystalline layer 130 may include, for example, but not limited to: crystalline silicon (Si) of a single orientation (i.e., monocrystalline silicon). Monocrystalline layer 130 may have a thickness ranging from approximately 10 nm to approximately 1000 nm, and preferably within a range of approximately few hundred nanometers. In FIG. 1B, monocrystalline layer 130 is bonded to a protective layer 120 using currently known or later developed processes. Protective layer 120 may be formed from a non-crystalline or polycrystalline insulating material that may be suitably integrated into a fabrication scheme. Protective layer 120 may include, for example, but is not limited to: silicon nitride, doped oxide, silicon-germanium, borosilicate glass (BSG), borophosphosilicate glass (BPSG), and any combination thereof. Protective layer 120 is disposed on substrate 110 using currently known or later developed techniques. Substrate 110 is formed, by currently known or later developed techniques, from a dielectric material 112 with shallow trench isolation regions (STI) 114 and pad oxide regions 116 incorporated therein. Substrate 110 may incorporate critical threshold voltage (Vt) implants (not shown).
FIG. 2A illustrates a top view of semiconductor structure 10 where a lithographic mask 140 is formed over bonded monocrystalline layer 130. FIG. 2B is a cross-sectional view of semiconductor structure 10 taken along line A-A in FIG. 2A, showing lithographic mask 140 on bonded monocrystalline layer 130. Lithographic etching, for example, but not limited to, reactive ion etching (RIE), transforms bonded monocrystalline layer 130 into hard mask 132 (FIG. 3A) having the same pattern as lithographic mask 140, which is removed concurrently.
The top view illustrated in FIG. 3A shows patterned hard mask 132 of single or mono crystalline orientation over protective layer 120. FIG. 3B is an alternative view showing the cross-section of semiconductor structure 10 taken along line A-A in FIG. 3A. The pattern on hard mask 132 is enhanced by currently known or later developed crystallographic etching techniques, for example, but not limited to wet etching with ammonium hydroxide in a protic solvent, to form enhanced patterned hard mask 136 (FIG. 4A). The single crystalline orientation of monocrystalline silicon layer 130 provides for crystallographic etching to remove any rounding and dimensional narrowing of curved surfaces 134.
As shown in FIG. 4A, enhanced patterned hard mask 136 includes straight edges 162, 164 that meet at sharp corners 138. Straight edges 162 that are parallel keeps a substantially constant spacing; while straight edges 162 and 164 that meet are substantially perpendicular to each other. In an alternative view illustrated in FIG. 4B, monocrystalline layer 130, which is bonded to protective layer 120 is converted into enhanced patterned hard mask 136 following crystallographic etching.
FIG. 5A illustrates a top view of an embodiment of semiconductor structure 10 after further processing of protective layer 120. Protective layer 120 is etched by currently known or later developed etching techniques, for example, but not limited to, RIE, according to enhanced patterned hard mask 136 (FIG. 4A-4B). Patterned protective layer 120 exposes regions 118 of substrate 110, which includes portions of STI 114 and pad oxide regions 116.
In FIG. 6A, regions 118 (FIG. 5A) are covered by an oxide layer 150 deposited on substrate 110. Oxide layer 150 may include any material suitable for use as a gate conductor, for example, but is not limited to, silicon dioxide (SiO2), silicoxynitride, hafnium dioxide (HfO2), aluminum oxide (Al2O3) and zirconium dioxide (ZrO2). Oxide layer 150 is formed by currently known or later developed techniques, including for example, but not limited to deposition and chemical mechanical polishing (CMP). Oxide layer 150 may have a thickness ranging from approximately 1 nm to approximately 10 nm.
As shown in FIGS. 6A and 6B, oxide layer 150 is incorporated as part of the protective layer 120 covering exposed region 118 of substrate 110 to form a composite layer 170 of different materials on substrate 110. Composite layer 170 includes different materials in discrete blocks 160, defined by straight edges 162, 164 therein.
FIGS. 7A and 7B illustrate an embodiment of a resulting semiconductor structure 10 with further processing from the structure from FIG. 6B. When remaining protective layer 120 (FIG. 6A and FIG. 6B) is stripped using currently known or later developed processes, oxide layer 150 that remains (FIG. 7A) presents a better defined gate conductor in discrete block 160, defined by straight edges 200, as compared to a gate conductor created without enhanced patterned hard mask 136 (FIG. 4A-4B).
The method according to the disclosure may be repeated to form a semiconductor structure 20 (FIG. 8) with multiple composite layers 170i, where i=1, 2, 3, . . . n and n is an integer. FIG. 8 illustrates semiconductor structure 20 with multiple composite layers 170i built on a substrate 110. Substrate 110 may include features (not shown) including, for example, but not limited to, deep trench isolations (not shown), STI (not shown), pad oxide regions (not shown), high aspect ratio via/contacts (not shown). Composite layers 1701, 1702, . . . 170n, may be interspersed with non-composite layers, for example, a single monocrystalline layer, an oxide layer, a nitride layer, a polysilicon layer or a metal layer. Each of the composite layers 1701, 1702, . . . 170n includes one or more discrete blocks 180j, 190k of different materials therein, where j and k=1, 2, 3, . . . n, and n is an integer. The thickness of each composite layer 170i may vary according to a desired requirement in the fabrication process. Each discrete region 180j within a composite layer 170i interfaces an adjacent discrete region 190k at straight edges 200 that define that region. Straight edges 200 meet at specific angles according to the crystalline characteristic of a material used in the enhanced patterning process of the disclosed method. For example, the specific angle may be selective to a monocrystalline material where crystallographic etching would result in, for example, an angle of 45°, 60° or 90° in the enhanced patterned hard mask. In the case where the specific angle is 90°, the edges are perpendicular and do not taper towards each other.
The foregoing description of various aspects of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the scope of the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of the invention as defined by the accompanying claims.

## Claims

1. A method for patterning a semiconductor structure comprising:
bonding a monocrystalline layer to a protective layer disposed on the semiconductor structure, wherein the monocrystalline layer is formed from crystalline silicon of a single crystalline orientation and the protective layer is selected from a group consisting of non-crystalline and polycrystalline materials;
lithographically patterning the monocrystalline layer to form a hard mask;
applying crystallographic etching to enhance the patterned hard mask;
etching the protective layer according to the enhanced patterned hard mask;
removing the enhanced patterned hard mask;
filling the etched protective layer with an oxide layer; and
removing any remaining material of the protective layer,
wherein the protective layer is selected from a group consisting of: silicon nitride (Si3N4), doped oxide, silicon-germanium (SiGe), borosilicate glass (BSG), borophosphosilicate glass (BPSG), and a combination thereof.