METHOD OF FORMING A SEMICONDUCTOR DEVICE WITH AIR GAPS FOR LOW CAPACITANCE INTERCONNECTS

A method of forming a semiconductor device with air gaps for low capacitance interconnects. The method includes providing a substrate containing raised metal features with a top area and a sidewall, and a void between the raised metal features, filling the void with a sacrificial fill material, and selectively depositing a blocking layer on the sacrificial fill material. The method further includes depositing a cap layer on the top area of the raised metal features, where the cap layer has an overhang that extends past the sidewall, removing the blocking layer and the sacrificial fill material between the raised metal features, and depositing a dielectric film, where the dielectric film forms an air gap between the raised metal features below the overhang.

FIELD OF INVENTION

The present invention relates to the field of semiconductor manufacturing and semiconductor devices, and more particularly, to a method of forming a semiconductor device with air gaps for low capacitance interconnects.

BACKGROUND OF THE INVENTION

As device feature size is scaled, interconnects are becoming a significant problem in performance improvement. This is in part due to an increase in electrical resistivity (Rs) with ever decreasing device feature sizes and detrimental capacitance between adjacent features. One way of reducing capacitance is using ultra low-k dielectric materials, but air gaps offer the lowest dielectric constant (k) value of approximately 1. As a result, device manufacturers are adding air gaps to critical layers in advanced metallization schemes.

SUMMARY OF THE INVENTION

This disclosure describes a novel method of fabricating air gaps in advanced semiconductor devices. According to one embodiment, the method includes providing a substrate containing raised metal features with a top area and a sidewall, and a void between the raised metal features, filling the void with a sacrificial fill material, and selectively depositing a blocking layer on the sacrificial fill material. The method further includes depositing a cap layer on the top area of the raised metal features, where the cap layer has an overhang that extends past the sidewall, removing the blocking layer and the sacrificial fill material between the raised metal features, and depositing a dielectric film, where the dielectric film forms an air gap between the raised metal features below the overhang.

According to another embodiment, the method includes providing a substrate containing raised metal features with a top area and a sidewall, and a void between the raised metal features, depositing a cap layer on the top area of the raised metal features, wherein the cap layer has an overhang that extends past the sidewall, and filling the void with a sacrificial fill material. The method further includes depositing a dielectric film on the sacrificial fill material and the cap layer, decomposing the sacrificial fill material into one or more gaseous decomposition products, and removing at least one of the one or more gaseous decomposition products by diffusion through the dielectric film, where the decomposition of the sacrificial fill material forms an air gap between the raised metal features below the overhang.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

A method of fabricating air gaps in advanced semiconductor devices is described. The method includes using mushrooming during selective film deposition to facilitate formation of air gaps in a dielectric material.

FIGS.1A-1Hschematically show through cross-sectional views a method of processing a substrate according to an embodiment of the invention. The method includes, providing a substrate100containing a base film105and a metal layer110on the base film105. This is schematically shown inFIG.1A. Examples of the metal layer110include metals commonly found in semiconductor devices, for example ruthenium metal (Ru), molybdenum metal (Mo), tungsten metal (W), copper metal (Cu), cobalt metal (Co), a binary metal alloy, or a tertiary metal alloy.

The method further includes patterning the metal layer110to form raised metal features106(metal lines) that are separated by voids107. In one example, the patterning can include forming a patterned mask layer on the metal layer110, and performing anisotropic gas phase etching of the metal layer110according to the patterned mask layer to form the raised metal features106. The resulting structure is schematically shown inFIG.1B. The raised metal features106contain a top area108and a sidewall109, and a void107between raised metal features106.

In another example, the structure inFIG.1Bmay be formed using a semi-damascene process that includes patterning via openings in a mask layer and anisotropically etching vias into an underlying dielectric film. Thereafter, the vias are filled with a metal, and the dielectric film removed to form the patterned metal layer with raised metal features106.

The method further includes filling the void107between the raised metal features106with a sacrificial fill material115. For example, the sacrificial fill material115can contain a dielectric material. Examples include silicon-containing dielectric materials such as SiO2and SiOC. The resulting structure may be planarized using a planarizing process (e.g., chemical mechanical polishing) to form the planarized structure schematically shown inFIG.1C, where exposed surfaces of the top area108of the raised metal features106and exposed surfaces of sacrificial fill material115are at least substantially in the same horizontal plane.

The method further includes selectively depositing a blocking layer120on the exposed surfaces of the sacrificial fill material115. This is schematically shown inFIG.1D. In one example, the blocking layer120can include, but is not limited to, a self-assembled monolayer (SAM) that selectively forms on the sacrificial fill material115relative to the top area108of the raised metal features106. In one example, the blocking layer120can contain a bi-layer SAM containing vertically stacked layers of different SAM molecules. In another example, the blocking layer can contain a carbon-based material.

The method further includes selectively depositing a cap layer125on the top area108of the raised metal features106, where the cap layer125has an overhang126that extends horizontally past the sidewall109. The blocking layer120on the sacrificial fill material115facilitates high deposition selectivity of the cap layer125on the top area108of the raised metal features106. The deposition of the cap layer125can be performed until a degree of mushrooming (i.e., lateral growth) above the blocking layer120is reached. In the embodiment shown inFIG.1E, the overhang126covers a portion of the blocking layer120. The cap layer125can contain a dielectric material. The dielectric material can, for example, contain a metal oxide or a silicon-containing dielectric material. Examples include Al2O3, HfO2, and other metal oxides, SiCNx, TiO2, AlONx, AlNx, SiO2, SiOC, SiOCN, and organic layers such as carbon-based layers. According to one embodiment, the cap layer125may include the same material as the sacrificial fill material115. The degree of mushrooming may be tuned by controlling the thickness and the lateral growth of the cap layer125.

The method further includes removing the blocking layer120and the sacrificial fill material115between the raised metal features106. The resulting structure is schematically shown inFIG.1F. In one example, the removing can include one or more a gaseous isotropic etching processes, or a heat-treatment.

The method further includes depositing a dielectric film135over the structure inFIG.1F, where the dielectric film135forms an air gap140between the raised metal features106below the overhang126of the cap layer125. This is schematically shown inFIG.1G. The presence of the overhang126of the cap layer125narrows the opening at the top of the void107between the raised metal features106and this aids in the formation of the air gap140where no dielectric material is formed during the deposition of the dielectric film135. In one example, the dielectric film135may be deposited in two or more steps, for example using a conformal deposition step followed by a non-conformal deposition step, or using a non-conformal deposition step followed by a conformal deposition step. According to one embodiment, the dielectric film135may include a different material than the cap layer125. According to another embodiment, the dielectric film135may include the same material as the cap layer125.

According to one embodiment, following deposition of the dielectric film135, the substrate100may be further processed to form a device. In one example, the method can further include depositing a blanket dielectric film145over the film structure inFIG.1G. This is schematically shown inFIG.1H. The blanket dielectric film145can, for example, include a silicon-containing dielectric material such as SiO2, SiOC, or SiOCN. The blanket dielectric film145may, for example, be used as an etch stop layer during subsequent metallization processing.

FIGS.2A-2Eschematically show through cross-sectional views a method of processing a substrate according to an embodiment of the invention. The substrate100inFIG.1Ehas been reproduced as substrate200inFIG.2A. The method further includes selectively removing the blocking layer120from the sacrificial fill material115. The resulting structure is schematically shown inFIG.2B. In one example, a SAM blocking layer may be removed by heat-treating.

The method further includes performing an anisotropic etching process that removes a portion of the sacrificial fill material115from the void107but leaves a spacer layer117(sidewall spacer) on the sidewall109of the raised metal features106. The presence of the overhang126aids in the formation of the spacer layer117. The resulting structure is schematically shown inFIG.2C.

The method further includes depositing a dielectric film136over the structure inFIG.2C, where the dielectric film136forms an air gap141between the raised metal features106below the overhang126. The resulting structure is schematically shown inFIG.2D. The presence of the overhang126narrows the opening at the top of the void107between the raised metal features106and this aids in the formation of the air gap141during the deposition of the dielectric film136. In one example, the dielectric film136may be deposited in two or more steps, for example using a conformal deposition step followed by a non-conformal deposition step, or using a non-conformal deposition step followed by a conformal deposition step. According to one embodiment, the dielectric film136may include a different material than the cap layer125. According to another embodiment, the dielectric film136may include the same material as the cap layer125.

According to one embodiment, the method can further include depositing a blanket dielectric film145over the film structure inFIG.2D. This is schematically shown inFIG.2E. The blanket dielectric film145can, for example, include a silicon-containing dielectric material such as SiO2, SiOC, or SiOCN. The blanket dielectric film145may, for example, be used as an etch stop layer during subsequent metallization processing.

FIGS.3A-3Eschematically show through cross-sectional views a method of processing a substrate according to an embodiment of the invention. The substrate100inFIG.1Fhas been reproduced as substrate300inFIG.3A. The method further includes filling the void107between raised metal features106with a sacrificial fill material116. According to one embodiment, the sacrificial fill material116can include amorphous carbon (a-C) that may be deposited by a PECVD process. The resulting structure is schematically shown inFIG.3B. The method further includes depositing a blanket dielectric film114on the sacrificial fill material115and the cap layer125. The blanket dielectric film145can, for example, include a silicon-containing dielectric material such as SiO2, SiOC, or SiOCN. The resulting structure is schematically shown inFIG.3C.

The method further includes heat-treating the film structure inFIG.3Cto remove the sacrificial fill material116. The resulting film structure is schematically shown inFIG.3D. The heat-treating may be performed in an oxidizing atmosphere such as O2and results in decomposition of the sacrificial fill material116into one or more gaseous decomposition products, and removal of the at least one of the one or more gaseous decomposition products by diffusion through the blanket dielectric film145, where the decomposition and removal of the sacrificial fill material116forms an air gap142between the raised metal features106. According to one embodiment, the method can further include depositing a blanket dielectric film145over the film structure inFIG.3D. The resulting structure is schematically shown inFIG.3E.

FIGS.4A-4Eschematically show through cross-sectional views a method of processing a substrate according to an embodiment of the invention. The substrate100inFIG.1Bhas been reproduced as substrate400inFIG.4A. The method further includes filling the filling the void107with a sacrificial fill material116. According to one embodiment, the sacrificial fill material116can include amorphous carbon (a-C). The resulting structure is schematically shown inFIG.4B. The method further includes selectively depositing a cap layer125on the top area108of the raised metal features106, where the cap layer125has an overhang126that extends past the sidewall. The deposition of the cap layer125can be performed until a degree of mushrooming (i.e., lateral growth) is reached. In the embodiment shown inFIG.4C, the overhang126covers a portion of the sacrificial fill material116.

The method further includes depositing a dielectric film130on the sacrificial fill material116and the cap layer125. The dielectric film130can, for example, include a silicon-containing dielectric material such as SiO2, SiOC, or SiOCN. The resulting structure is schematically shown inFIG.4D.

The method further includes heat-treating the film structure inFIG.4Dto remove the sacrificial fill material115. In one example, amorphous carbon may be removed by heat-treating in an oxidizing atmosphere such as O2. The resulting film structure is schematically shown inFIG.4Ewhere air gap143is formed between raised metal features106. The heat-treating results in decomposing the sacrificial fill material116into one or more gaseous decomposition products, and removes at least one of the one or more gaseous decomposition products by diffusion through the dielectric film, where the decomposition of the sacrificial fill material leaves an air gap between the raised metal features below the overhang.

According to one embodiment, the method can further include depositing a blanket dielectric film145over the film structure inFIG.4E. This is schematically shown inFIG.4F.

FIGS.5A-5Eschematically show through cross-sectional views a method of processing a substrate according to an embodiment of the invention. The substrate100inFIG.1Fhas been reproduced as substrate500inFIG.5A. The method further includes depositing a conformal dielectric layer131over the features inFIG.5A, including on the sidewall109of the raised metal features106, on the cap layer125, and optionally on the base film105between the raised metal features106. This is schematically shown inFIG.5B. Examples of the conformal dielectric layer131include SiO2, SiOC, and SiOCN.

The method further includes filling the void107with a sacrificial fill material116. According to one embodiment, the sacrificial fill material can include amorphous carbon (a-C). The resulting structure is schematically shown inFIG.5C. The method further includes depositing a dielectric film130on the sacrificial fill material116and on the conformal dielectric layer131. The dielectric film130can, for example, include a silicon-containing dielectric material such as SiO2, SiOC, or SiOCN. The resulting structure is schematically shown inFIG.5D.

The method further includes heat-treating the film structure inFIG.5Dto remove the sacrificial fill material116. In one example, amorphous carbon may be removed by heat-treating in an oxidizing atmosphere such as O2. The resulting film structure is schematically shown inFIG.5Ewhere air gap142is formed between raised metal features106. According to one embodiment, the method can further include depositing a blanket dielectric film145over the film structure inFIG.5E. The resulting structure is schematically shown inFIG.5F.

A plurality of embodiments for a method of forming a semiconductor device with air gaps for low capacitance interconnects have been described. The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. This description and the claims following include terms that are used for descriptive purposes only and are not to be construed as limiting. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above teaching. Persons skilled in the art will recognize various equivalent combinations and substitutions for various components shown in the Figures. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.