Method for processing photoresist materials and structures

Techniques herein include methods of processing photoresist patterns and photoresist materials for successful use in multi-patterning operations. Techniques include combinations of targeted deposition, curing, and trimming to provide a post-processed resist that effectively enables multi-patterning using photoresist materials to function as mandrels. Photoresist patterns and mandrels are hardened, strengthened, and/or dimensionally adjusted to provide desired dimensions and/or mandrels enabling straight sidewall spacers. Polymer is deposited with tapered profile to compensate for compressive stresses of various conformal or subsequent films to result in a vertical profile despite any compression.

BACKGROUND OF THE INVENTION

This relates to microfabrication including fabrication of semiconductor devices.

Continuous micro-miniaturization of digital semiconductor devices has been the engine for economic growth for past three decades. The number of transistors being fabricated on chips approximately doubles every few years. This micro-miniaturization has continued from planar devices into three dimensional space. Continued scaling, however, has come at a cost. Patterning the progressively smaller dimensions at advanced technology nodes has grown in complexity. Starting with simple direct print using 193 nm dry lithography at relatively larger technology nodes, patterning for advanced nodes has moved into complicated multi-patterning schemes using 193 nm-immersion lithography. Some common multi-patterning techniques employed in industry include double and/or triple litho-etch (LELE or LELELE (LEx)), self-aligned double patterning (SADP), self-aligned quadruple patterning (SAQP), etc.

SUMMARY

Some efforts for continued scaling involve using extreme ultraviolet (EUV) lithography using 13.5 nm photons in the hope of providing a simple direct print approach. There are, however, significant challenges to successfully implementing EUV lithography. Not only are there complex technical challenges in providing a reliable functional EUV system, there is a cost challenge that can make using EUV patterning essentially prohibitive. As such, self-aligned multi-patterning is a working solution for continued scaling.

Self-aligned multi-patterning, however, has some cost-based challenges. One conventional approach for self-aligned quad patterning includes executing two self-aligned double patterning operations. Such a patterning flow conventionally uses two hard mandrels and corresponding etch stop layers and also hardmasks for making two layers of hard mandrels. Such an approach can be expensive because of the accompanying etch steps, wet cleans, and sacrificial layer depositions.

Using photoresist materials for defining critical dimensions and/or as mandrels would be beneficial and reduce multi-patterning costs. Photoresist materials, however, are “soft” materials compared to hardmask materials. Using photoresist as mandrels has historically been challenging because of pattern collapse. Conventionally, a photoresist pattern is used to create mandrels in an underlying hardmask layer with the underlying hardmask layer having mechanical properties sufficient to function as mandrel material. For example, when attempting to form sidewall spacers on photoresist mandrel, a photoresist mandrel is first conformally coated with a spacer material, such as an oxide. This conformally deposited material can exert a relatively enormous compressive stress on photoresist mandrels, which can cause such photoresist mandrels to deform. For example, a photoresist mandrel having a rectangular cross-section can become deformed resulting in a bell-shaped profile or trapezoidal profile. In other words, a photoresist mandrel can result in a positive vertical taper in that upper portions of the photoresist mandrel are collapsed together making a mandrel cross section narrow on top while essentially keeping an initial width at the base (wide base and narrow top). The result is severe leaning (inward leaning) of sidewall spacers, which frustrates use of sidewall spacers for continued patterning.

Another challenge with using photoresist mandrels and patterns for self-aligned double patterning is that of precisely controlling critical dimensions (CDs), critical dimension uniformity (CDU), line edge roughness (LER) and line width roughness (LWR). Precise control is beneficial because any percentage dimensional variation in mandrel CD/CDU results in three times the percentage dimensional variation after final patterning. For example, at 7 nm node fabrication, angstrom level control over the CD, CDU and LER/LWR is desired for mandrel etch.

Techniques herein include methods of processing photoresist patterns and photoresist materials for successful use in multi-patterning operations. Techniques include combinations of targeted deposition, curing, and trimming to provide a post-processed resist that effectively enables multi-patterning. Photoresist patterns and mandrels can be hardened, strengthened, and/or dimensionally adjusted to provide desired dimensions and/or mandrels enabling straight sidewall spacers. One embodiment includes a method for processing a substrate. A substrate is received having a first relief pattern. The first relief pattern is comprised of a photoresist material. The first relief pattern includes structures having vertical sidewalls. The first relief pattern is positioned on an underlying layer. A deposition process is executed that deposits an organic polymer on the first relief pattern. The deposition process includes a plasma-based deposition process that includes a curing agent. The curing agent generates VUV (vacuum ultraviolet) light during plasma-based deposition. The deposition process is controlled such that more organic polymer is deposited on upper portions of the structures of the first relief pattern as compared to organic polymer deposited on lower portions of the structures of the first relief pattern resulting in a reverse taper profile on vertical sidewalls of the structures in that the upper portions of the structures have wider cross-sections as compared to cross-sections of corresponding lower portions. Controlling the deposition process includes maintaining an isotropic deposition during plasma-based deposition.

DETAILED DESCRIPTION

Techniques herein include methods of processing photoresist patterns and photoresist materials for successful use in multi-patterning operations. Techniques include combinations of targeted deposition, curing, and trimming to provide a post-processed photoresist that effectively enables multi-patterning. Photoresist patterns and mandrels can be hardened, strengthened, and/or dimensionally adjusted to provide desired dimensions and/or mandrels enabling straight sidewall spacers.

One embodiment includes a method for processing a substrate. The method includes receiving a substrate having a first relief pattern. Referring toFIG. 1, the first relief pattern131is formed of a photoresist material. The first relief pattern includes structures130having (approximately) vertical sidewalls. The first relief pattern131is positioned on an underlying layer110. This first relief pattern131can be formed using, for example, photolithography. A layer of photoresist can be exposed to a pattern of actinic radiation, and then developed to reveal a relief/topographic pattern. Note that any number of underlying layers can be included such as layer107and layer105. Various layers can be labeled as target layers, memorization layers, etc.

A deposition process is executed that deposits an organic polymer135on the first relief pattern131. An example result is shown inFIG. 2. The deposition process includes using a plasma-based deposition process that includes a curing agent. The curing agent generates vacuum ultraviolet (VUV) light during plasma-based deposition. VUV light is typically between about 10 nm to 200 nm. Exposing photoresist material to VUV light is beneficial because such radiation can harden a given photoresist by interacting with the carbon-oxygen bonds. These bonds and or lactone groups and other constituents can absorb VUV light.

The deposition process is controlled such that more organic polymer135is deposited on upper portions of the structures130of the first relief pattern131as compared to organic polymer135deposited on lower portions of the structures130of the first relief pattern resulting in a reverse taper profile on vertical sidewalls of the structures130in that the upper portions of the structures130have wider cross-sections as compared to cross-sections of corresponding lower portions. In other words, more material is deposited on top of structures130or mandrels as compared to an amount of material deposited on the bottom of structures130, as can be seen in the illustration ofFIG. 2. Controlling the deposition process can include maintaining an isotropic deposition during plasma-based deposition. An isotropic deposition can be maintained by not using a substrate bias that would accelerate ions toward the substrate. Instead, essentially a line-of-sight deposition condition is created which results in more deposition on tops of features.

Substrate or photoresist processing can also include executing a trim process that etches a portion of the organic polymer. The trim process is a plasma-based process that includes a trim agent selected from the group consisting of oxygen-containing gas, hydrogen-containing gas, and nitrogen-containing gas. For example, CO2can be used as a trim agent. Some deposition gasses can be included for passivation. The trim process can include clearing organic polymer135from surfaces of underlying layer110. An example result is shown inFIG. 3. A directional (anisotropic) etch or partially-directional etch can be used to clear organic polymer135from the substrate. In some embodiments, organic polymer135can be cleared from top surfaces of structures130, or partially removed from such top surfaces. With isotropic deposition, more organic polymer135can be deposited on such top surfaces of structures130as compared to exposed surfaces of underlying layer110. As can be seen inFIG. 3, a result is that the structures130now have a profile with a reverse taper, that is wider on top and narrower on the bottom. Such a reverse taper will function to compensate for compressive stresses of subsequent conformal layer(s).

In some embodiments, the deposition process and the trim process can be cycled until a predetermined critical dimension of the structures is achieved. The deposition process and the trim process can also be cycled to create a predetermined amount of reverse taper on vertical sidewalls of the structures130. Executing the deposition process can include flowing a process chemistry into a plasma processing chamber with the process chemistry including CxHyin an amount that is greater than 20% by volume of total process gas flow into the plasma processing chamber. In some embodiments the deposition process and the trim process are both executed in a same plasma processing chamber. The curing agent can be selected from any of argon, helium, hydrogen bromide, hydrogen, CxFy, xenon, neon, or combinations thereof.

In one embodiment, the method includes forming sidewall spacers on the first relief pattern131. Such spacer formation can include depositing a conformal film140on the substrate.FIG. 4illustrates conformal film140having been deposited on the substrate. Note inFIG. 4that although the structures130have been compressed to be narrower at the top of the structure cross section, the combination of the organic polymer135and the structures130provide a straight sidewall or a sidewall that is vertical (approximately vertical). In other words, as the mandrels were compressed on top, the reverse taper provided by the organic polymer135was also moved inwardly with the result being a vertical interface between the conformal film140and the combination of the organic polymer135and the structures130. The organic polymer135deposited with a reverse taper profile provided a bias to each cross-section so that after compression a desired profile results. The amount of reverse taper profile can be adjusted based on type of photoresist, organic polymer, spacer material, scaled, etc., so that the conformal film140creates a compressive stress sufficient to cause the reverse taper profile to become a vertical profile.

InFIG. 5, a spacer open etch step can be executed to remove conformal material from tops of horizontal surfaces. The result is sidewall spacers141having a vertical profile. The mandrel materials (organic polymer135and structures130) can then be removed or pulled, leaving sidewall spacers141on the underlying layer110. This essentially creates a second relief pattern145as illustrated inFIG. 6. The second relief pattern145can be used as an etch mask when etching into the underlying layer110, or as mandrels for an additional sidewall image transfer step, or for other fabrication processes. Accordingly, sidewall spacers can be pattern transferred without needing an additional hardmask layer and accompanying sacrificial layers. Using photoresist for mandrels, as enabled herein, can significantly reduce costs associated with self-aligned multi-patterning operations. Accordingly, in other words, techniques herein can address deformation of photoresist material during spacer formation. First, VUV curing can help harden the photoresist material itself for improved mechanical strength. Secondly, depositing a reverse taper profile polymer can compensate for mandrel deformation so that even with deformation from spacer material, a final orientation of spacer material is a vertical orientation, thereby enabling accurate pattern transfer.

In addition to such profile engineering embodiments, CDs can be targeted for correction or improvement. Techniques can include cycling the deposition process and the trim process until a predetermined critical dimension (target CD) of the structures is achieved. The deposition process and the trim process can be executed in a same plasma processing chamber. Such a cyclic deposition and trim process can be used to achieve any CD without regard to that printed at lithography, while simultaneously improving LER/LWR and CDU. With each consecutive cycle, an increased CD trim amount can be achieved.

Another embodiment includes a method for processing a substrate. Referring now toFIG. 7, a substrate is received having a first relief pattern131. The first relief pattern131is formed of a photoresist material. The first relief pattern131includes structures130having vertical sidewalls. The first relief pattern131is positioned on an underlying layer110, such as, for example, an anti-reflective coating layer, memorization layer, etc.

A deposition process is executed that deposits an organic polymer135on the first relief pattern131. A result is shown inFIG. 8. The deposition process includes a plasma-based deposition process that includes a curing agent. The curing agent generates VUV light during plasma-based deposition. The deposition process is controlled such that a same amount of organic polymer135is deposited on upper portions of the structures130of the first relief pattern131as compared to organic polymer135deposited on lower portions of the structures130of the first relief pattern131resulting in a straight profile on vertical sidewalls of the structures130. Controlling the deposition process can include maintaining an isotropic deposition during plasma-based deposition. In other words, deposition is controlled to provide a generally uniform thickness deposition on sidewalls of a VUV-hardened resist.

A trim process can be executed that etches a portion of the organic polymer135. The trim process is a plasma-based process that includes a trim agent selected from an oxygen-containing gas, a hydrogen-containing gas, or a nitrogen-containing gas. Executing the trim process can include clearing organic polymer from surfaces of the underlying layer110. A result is illustrated inFIG. 9. As described above, sidewall spacers141can be formed on the photoresist structures, and both the deposition and trim processes can be executed in a same plasma processing chamber.FIG. 10shows deposition of conformal film140, andFIG. 11, shows the substrate with sidewall spacers141after a spacer open etch is executed.

Cycling the deposition process and the trim process can be executed until a predetermined critical dimension (target CD) of the structures is achieved. Executing the deposition process can include flowing a process chemistry into a plasma processing chamber, the process chemistry including CxHyin an amount that is between 5% to 10% by volume of total process gas flowed into the plasma processing chamber. Such a flow rate can be used for substantially conformal deposition on vertical surfaces of the relief pattern. The curing agent can be selected argon, helium, hydrogen bromide, hydrogen, CxFy, xenon, neon, etc.

FIG. 12shows the substrate segment after mandrel material has been removed, leaving sidewall spacer pairs on the substrate for further fabrication steps.

Another embodiment for processing a substrate includes receiving a substrate having a first relief pattern. The first relief pattern being formed of a photoresist material. The first relief pattern including structures having vertical sidewalls. The first relief pattern is positioned on an underlying layer. A plasma-based curing process is executed that uses a curing agent. The curing agent generates VUV light during plasma-based curing. Any of the previously-listed curing agents can be used. A trim process is executed that etches a portion of the photoresist material. The trim process is a plasma-based trim process that includes a trim agent such as an oxygen-containing gas, a hydrogen-containing gas, and/or a nitrogen-containing gas. The trim process can be controlled such that more photoresist material is etched from upper portions of the structures of the first relief pattern as compared to photoresist material etched from lower portions of the structures of the first relief pattern. This results in a positive taper profile on vertical sidewalls of the structures in that the upper portions of the structures have smaller cross-sections as compared to cross-sections of corresponding lower portions. Controlling the trim process can include maintaining an isotropic trim during the plasma-based trim process. In other words, a given photoresist CD can be reduced using this combination trim and curing step which reduces a CD as well as creates a positive taper photoresist cross section. This trim process can be continued until structures of the first relief pattern achieve a predetermined critical dimension. In other embodiments, sidewall spacers can be formed thereon as described previously.

Accordingly, techniques herein can enable photoresist profile engineering to eliminate spacer leaning thereby reducing edge placement error. CD targeting capability is also enabled to achieve any CD target without regard to lithography. Improved control over CD can also minimize pitch walking. Another benefit of techniques herein is improved CDU, LER/LWR as compared to lithography alone. Accordingly, techniques herein enable photoresist to be used as mandrels for lower cost SAQP schemes and other patterning schemes.