Method for controlling etching in pitch doubling

[0001] This application is related to and claims priority to U.S. Provisional Application No. 62/056,263, filed Sep. 26, 2014, the entire contents of which are herein incorporated by reference.

[0002] The present invention generally relates to etching in semiconductor manufacturing, and more particularly to a method of controlling etching in pitch doubling.

[0003] Pitch multiplication is a class of technologies for manufacturing integrated circuits (ICs), developed for photolithography to enhance the feature density. Pitch doubling or double patterning techniques where a conventional lithography process is enhanced to produce double the expected number of features is the simplest case of pitch multiplication. One problem that arises during etching of a substrate using pitch doubled patterns is how to control difference in etch rate between different regions on a substrate.

[0004] According to embodiments of the invention, a method of forming semiconductor structures by Self-aligned Double Patterning (SADP) is described.

[0005] According to one embodiment, the method includes receiving a substrate having a pattern thereon defined by spacers formed on sidewalls of a plurality mandrels, and transferring the pattern defined by the spacers into the substrate using a plasma etch process that etches the plurality of mandrels and the substrate, the transferring forming first recessed features in the substrate below the mandrels and second recessed features in the substrate between the mandrels, where the plasma etch process utilizes an etching gas containing O₂ gas, and the relative amount of O₂ gas in the etching gas is selected to control the depth of the first recessed features relative to the depth of second recessed features.

[0006] According to another embodiment, the method includes receiving a substrate having a mask layer thereon and a pattern on the mask layer, the pattern defined by spacers formed on sidewalls of a plurality mandrels, and transferring the pattern defined by the spacers into the substrate using a plasma etch process that etches the mandrels, the mask layer, and the substrate, the transferring forming first recessed features in the mask layer and in the substrate below the mandrels and second recessed features in the mask layer and the substrate between the mandrels, where the plasma etch process utilizes an etching gas containing O₂ gas, and the relative amount of O₂ gas in the etching gas is selected to control the depth of the first recessed features relative to the depth of second recessed features.

[0013] Embodiments of the invention are described below in reference to the Figures. According to one embodiment, a method is provided for forming a semiconductor device. The method includes receiving a substrate having a pattern thereon defined by spacers formed on sidewalls of a plurality mandrels, and transferring the pattern defined by the spacers into the substrate using a plasma etch process that etches the mandrels and the substrate, the transferring forming first recessed features in the substrate below the mandrels and second recessed features in the substrate between the mandrels, where the plasma etch process utilizes an etching gas containing O₂ gas, and the relative amount of O₂ gas in the etching gas is selected to control the depth of the first recessed features relative to the depth of second recessed features.

[0014] Self-aligned Double Patterning (SADP) is a patterning technique that uses spacers formed adjacent to a template pattern (mandrels) that is defined by conventional lithography. After stripping the template material, the spacers serve as a hardmask with double the line density of the original lithographically defined template. Embodiments of the invention describe a method to control difference in etch rate between different regions on a substrate during etching of a substrate using SADP.

[0015] FIG. 1 schematically shows a cross-sectional view of a layered structure 1 on a substrate 10. The layered structure 1 includes an oxide layer 16 that is conformally deposited on mandrels 14. The mandrels 14 are formed on a mask layer 12 on the substrate 10. According to some embodiments, the mask layer 12 may be omitted and the mandrels 14 formed directly on the substrate 10. In one example, the substrate 10 can contain an amorphous carbon layer (ACL), but other substrate materials may be used. The mandrels 14 can include a patterned photoresist (PR) layer, the mask layer 12 can include a silicon anti-reflective coating (SiARC, an organic bottom ARC that contains Si), and the oxide layer 16 can include SiO₂. The layered structure 1 can be fabricated using well known lithography and film deposition methods in semiconductor manufacturing. For simplicity, FIG. 1 only shows two (2) mandrels, but semiconductor manufacturing commonly uses a large number of such mandrels.

[0016] FIG. 2 schematically shows a cross-sectional view of a layered structure 2 following a spacer etch of the layered structure 1 in FIG. 1. The spacer etch process forms a pattern defined by the spacers 18 on the sidewalls of the mandrels 14. The spacer etch can utilize a capacitively coupled plasma (CCP) reactor or other types of plasma reactors, for example an inductively coupled plasma (ICP) reactor, or a microwave plasma reactor. In one example, a CCP reactor was used where 600 W at 60 MHz was applied to the upper electrode and 50 W at 13.56 MHz was applied to the lower electrode (substrate holder). The reactor pressure was 100 mTorr, the etch time was 90 seconds, and the substrate temperature was about 40-80° C. The etch gas contained CF₄ (150 sccm) and CHF₃ (100 sccm).

[0017] According to embodiments of the invention, the pattern defined by the spacers 18 may be transferred into the mask layer 12 and into the substrate 10 by an etching process, thereby forming recessed features in the mask layer 12 and in the substrate 10 below and/or between the mandrels 14. According to one embodiment, an etching gas can include O₂ and a halogen-containing gas. The halogen-containing gas can, for example, include a silicon-halogen-containing gas. The silicon-halogen-containing gas can, for example, be selected from the group consisting of SiF₄ and SiCl₄. According to one embodiment, the etching gas may be pulsed during the etching process to further control the etch rate in the recessed features.

[0018] FIG. 3 schematically shows a cross-sectional view of a layered structure 3 on the substrate 10. In one example, the layered structure 3 was formed using a selective etch that utilized a CCP reactor where 600 W at 60 MHz was applied to the upper electrode and 200 W at 13.56 MHz was applied to the lower electrode (substrate holder). The reactor pressure was 40 mTorr, the etch time was 60 seconds, and the substrate temperature was about 40° C. The etching gas contained SiF₄ (20 sccm), O₂ (10 sccm), and Ar (300 sccm). The selective etch process transferred the pattern defined by the spacers 18 into the mask layer 12 and into the substrate 10 below the mandrels 14, thereby forming first recessed features 20 in the mask layer 12 and in the substrate 10 below the mandrels 14. However, little or no etching of the mask layer 12 was observed in the open areas between the mandrels 14.

[0019] FIG. 4 schematically shows a cross-sectional view of a layered structure 4 on the substrate 10. The layered structure 4 was formed using a selective etch that utilized a CCP reactor where 600 W was applied to the upper electrode and 200 W was applied to the lower electrode (substrate holder). The reactor pressure was 40 mTorr, the etch time was 45 seconds, and the substrate temperature was about 40° C. The etching gas contained SiF₄ (20 sccm), O₂ (5 sccm), and Ar (300 sccm). The selective etch process transferred the pattern defined by the spacers 18 into the mask layer 12 and into the substrate 10, thereby forming first recessed features 20 in the mask layer 12 and in the substrate 10 below the mandrels 14, and forming second recessed features 22 in the mask layer 12 and in the substrate 10 between the mandrels 14.

[0020] The first recessed features 20 may be referred to as being in PR open regions or mandrel open regions, and the second recessed features 22 may be referred to as valley open regions, indicating the regions between the mandrels 14. Those skilled in the art will readily realize that these different regions can have very different etch rates and that successful double patterning manufacturing schemes will require good control over the depth of the first and second recessed features 20, 22. In particular, for some semiconductor devices, forming recessed features with the same or substantially the same depth will be required. The inventors have discovered that the relative amount of O₂ gas in the etching gas may be selected to achieve this. It is speculated that the amount of O₂ in the etching gas compensates for an aspect ratio effect and other differences between the first and second recessed features 20, 22.

[0021] FIG. 7 schematically shows the depth of the first and second recessed features 20, 22 for the two different O₂ gas flows in FIGS. 3 and 4. The curve 50 shows the depth of the first and second recessed features 20, 22 for an O₂ gas flow of 10 sccm in FIG. 3, and the curve 52 shows the depth of the first and second recessed features 20, 22 for an O₂ gas flow of 5 sccm in FIG. 4. FIG. 7 shows that an etching recipe may readily be selected where the curves 50 and 52 are substantially horizontal, which provides first and second recessed features 20, 22 with the same or substantially the same depths.

[0022] Thus, as schematically shown in FIG. 5, an etching recipe may be selected that achieves first and second recessed features 20, 22 having the same or substantially the same depth. The selected etching recipe can contain less O₂ in the etching gas than the etching recipe in FIG. 3, but contain more O₂ in the etching gas than the etching recipe in FIG. 4. In some embodiments, the first and second recessed features 20, 22 may have different widths and/or aspect ratios.

[0023] The layered structure 5 in FIG. 5 may be further processed and the spacers 18 removed as schematically shown in FIG. 6. Thereafter, the recessed features 20, 22 in the substrate 10 may be used as a mask to etch a layer or multiple layers underneath the substrate 10.

[0024] A plurality of embodiments for controlling etching in pitch doubling 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. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.