A chemically amplified resist, Poly(4-hydroxystyrene-co-tertiarybutylmethacrylate-co-MethacrylphenylPOSS) with different Polyhedral oligosilsesquioxane (POSS) loading has been synthesized by free radical polymerization. The incorporation of POSS units into the resist matrix has been found to affect their RIE resistance in O2 plasma. The thickness of the films were monitored using ellipsometry at various etch intervals to determine the etch rate and selectivity. It was observed that etch rate of these nanocomposite resists were comparable to the standard PHOST and Novolac based resists. HRTEM and HAADF studies showed that the POSS units exhibit a morphology of rectangular crystallites that are responsible for the plasma etch behavior. We have obtained 120 nm (1:1) (Line/Space) feature using 248 nm lithography. The protecting group, tertiary butyl protecting group exhibits acceptable outgassing. Using e-beam lithography, 70nm pattern feature was obtained.
The electron beam sensitivity of hydrogen silsesquioxane (HSQ) has been enhanced by including sensitizers that decompose to generate nucleophiles which catalyze the conversion of the silicon hydride (Si-H) moieties in HSQ into the insoluble siloxane (Si-O-Si) network. In this study, the consequences of including triphenylsulfonium hydroxide (TPS-OH) and 2-nitrobenzyl N-cyclohexylcarbamate (NBC) as a photodecomposable base (PDB) and photobase generator (PBG) were investigated, respectively. It was found that using 5 wt% loadings of TPS-OH or NBC in HSQ in conjunction with a post-exposure bake process enhanced the sensitivity of large features exposed at 25 keV accelerating voltage by approximately 50 and 40 %, respectively. Similarly, the electron beam doses required to print single pixel wide lines exposed at an accelerating voltage of 25 keV were enhanced by 70 and 50%, for 5 wt% loaded TPS-OH or NBC films, respectively. It was also found that the basicity and nucleophilic strength of the sensitizer affects the rate of the undesired hydrolysis reaction of HSQ which occurs in solution. For the sensitizers used in this study, the sterically hindered TPS-OH is a poor nucleophile which stabilized the solution against condensation and formation of a siloxane network, while the moderately nucleophillic NBC slightly decreased the stability of the solution. Also, it was found that thermal baking alone could be utilized to enhance the sensitivity of HSQ, but a drastic loss in contrast was observed. The combination of either TPS-OH or NBC and a post-exposure bake produced superior results, as compared to thermal baking alone, in terms of increasing the sensitivity of HSQ while maintaining good contrast.
A novel chemically amplified resist (CAR) was synthesized incorporating a photoacid generating (PAG) moiety, etch resistant nanoparticle, and various acrylated monomers. The addition of acrylated monomers was found to promote good film formation and to improve film adhesion. Directly tethering the nanoparticle into the polymer increases the etch performance of the resist and helps avoid any potential issues with phase separation of components in the resist film. The PAG in these materials is also directly incorporated into the resist backbone. It has been shown that these materials display enhanced sensitivity and contrast using LVEBL. This paper will discuss the material characteristics and lithographic performance of these materials using 2 keV, 10 KeV, and 20 KeV electron beam (EB) exposure. For example, these materials have demonstrated an extremely high sensitivity of only 0.6 μC/cm2 at 2 KeV. Contrast and sensitivity data along with preliminary imaging results will be presented for these materials. Initial imaging results at 20 keV are promising. Achieving similar resolution at low keV also appears to be possible with this material. The trade-off between sensitivity and resolution will also be presented for different electron beam accelerating potentials. Etch resistance and selectivity of this material will also be studied and compared to PHOST and novolac based resists. It will be demonstrated that such materials show great promise for advanced resist applications in a variety of next generation lithography (NGL) applications including electron beam lithography.
A hybrid bilayer imaging approach has been developed which uses a thin radiation sensitive, single component, metal-organic precursor film in conjunction with a thicker organic planarizing etch barrier. Upon electron beam irradiation, the metal-organic precursors are converted to a metal-oxide etch mask and the pattern can be transferred through the organic etch barrier layer using an oxygen reactive ion etch. These novel precursors can also be converted to the metal-oxide using deep ultraviolet optical irradiation or thermal baking. Therefore, a combination of blanket conversion steps followed by the patterning process can be utilized in order to reduce imaging doses. In this work, results of characterizing a titanium(n-butoxide)2(2-ethylhexanoate)2 precursor are presented due to its combined properties of hydrolytic stability and moderate sensitivity. It was found that using a blanket thermal bake step of 1, 2, and 3 minutes at 150°C prior to electron beam exposure increased the sensitivity of the materials to 200, 90, and 72 µC/cm2 respectively. However, the contrast of the material decreased from 4.40 to 2.17 as a consequence of pre-exposure thermal baking. The etching characteristics of the metal-organic precursor were also studied in ashing and silicon dioxide etching plasmas. It was found that the etch rate in the different plasmas depends strongly on the extent of conversion of the metal-organic film. Films with higher extents of conversion to the metal-oxide provide higher etch resistance in general. The patterning capability with these metal-organic precursors is demonstrated on top of both silicon substrates and hard baked novolac films.
A Monte Carlo study has been performed in order to understand the differences in exposure behavior between organic and inorganic electron beam resists. Typically inorganic resists constitute high atomic number species (Z>10) and are of higher density as compared to traditional organic resists such as acrylates. In this work, the consequences of tethering a high atomic number species such as a silicon or titanium atom onto a PMMA molecule on the electron beam energy deposition in the material have been investigated. The addition of these atoms increases the density of the hypothetical film and therefore the number of elastic and inelastic collisions suffered by an incident electron. The larger electron shell density associated with these high atomic number species more effectively shields the nucleus resulting in a larger average elastic scattering angle but the average inelastic scattering angle remains unaffected. The average radial and depth distance traveled by an incident electron decreases with increasing atomic number of the species tethered to the PMMA molecule. The radial and energy distribution of incident electrons in PMMA, HSQ, and a Titanium based metal-organic precursor film have also been compared. At low accelerating potentials, the broadening of the point source electron beam becomes larger with the increasing atomic number of the atoms in the resist material. However, at high accelerating potentials where the average depth distance traveled into the film increases, the point source electron beam broadening is essentially the same for both organic and inorganic films for thin films. Eventually, at large film thicknesses, the radial spread of incident electrons becomes broader in the inorganic films as a consequence of higher density and larger scattering atoms. Also, as a consequence of a larger number of collisions, the absorbed energy density in inorganic films increases, indicating that these materials will more efficiently capture electron beam energy as compared to traditional organic materials.
A novel negative-tone bilayer scheme has been developed using organometallic imaging materials in conjunction with organic planarizing layers. Precursor films containing the radiation sensitive organometallics are spin coated and converted to a metal oxide through electron beam exposure to form an etch mask for pattern transfer. After exposure, the unexposed regions are washed away using an appropriate developer solution and the etch mask pattern is transferred through the organic planarizing layer by an oxygen reactive ion etch (RIE). In this work, a multicomponent organometallic precursor Ba(Sr,Ti) [Ba(2-ethylhexanote), Sr(2-ethylhexanote), Ti(IV)(diisopropoxide) (bisacetylacetonate)] is evaluated as a possible imaging material for bilayer lithography applications. The sensitivity of the 1:1:2 (molar ratio of metals) Ba(Sr,Ti) precursor was found to be 56.5 (mu) C/cm2 with a contrast of 16.1 at 10keV accelerating potential. In order to enhance the sensitivity, partial conversion of the precursor to the metal oxide prior to electron beam exposure through thermal baking was investigated. It was found that a 30 second thermal bake at 150 degree(s)C enhanced the sensivity to 23.3 (mu) C/cm2 but decreased the contrast to 4.2. Also, blanket etch studies on exposed samples found that the remaining organic ligands in the precursor are further converted to the metal oxide upon exposure to the O2 plasma causing shrinkage of the etch mask. After shrinkage, the precursor offers excellent etch selectivity as compared to hard baked novolac. This bilayer process is demonstrated by printing 200 nm line and space patterns using electron beam patterning.
A novel class of photosensitive organometallic precursor materials is used to pattern thin film mixed-metal oxide structures. In this work a photosensitive organometallic precursor is coated onto a silicon substrate and exposed to ultraviolet light through a mask to form patterned oxide structures. This is a negative-tone process in which the unexposed areas can be washed away using a developer solvent. In this work, lithographic contrast curves were measured to characterize the sensitivity and contrast of thin films composed of a mixture of the organometallic precursors for the oxides barium, strontium and titanium. Experiments directed at finding methods to increase the photo-speed of these materials were also conducted. It was found that partial pre-exposure conversion of these films using thermal baking could be used to enhance the sensitivity of these materials. A pre-exposure bake performed at 150 degrees C for 15 seconds was found to decrease the required exposure dose by a factor of two. Dielectric properties were measured for photochemically converted oxide films via electrical measurements on parallel plate capacitor devices. X-ray photoelectron spectroscopy (XPS) was used to quantify the relative amounts of carbon present in the finished films, and it was determined that thermally processes films had higher levels of carbon contamination.