Kazumasa Yonekura

Investigation of ash damage to ultralow-k inorganic materials

The degradation of porous methyl silsesquioxane (MSQ) films (k=2.2) by plasma irradiation has been investigated using several kinds of gas chemistries, which are used for photoresist strip. The porous MSQ is easily degraded by O2 plasma ash process and the dielectric constant increases largely, even by using the condition that minimizes the damage to nonporous SiOCH films. As the results of several kinds of plasma irradiation, it is clarified that N2 plasma minimizes the degradation of porous MSQ. O2 and H2 plasmas extract methyl (CH3) groups from the porous MSQ films and degrade even the deep part from the film surface. On the other hand, N2 plasma changes the quality of only the film surface and suppresses the degradation of the inside of the film. Furthermore, the small amount of H2 addition to N2 plasma is effective in the increase of the ash rate and the removal of the deposition on the sidewall without the remarkable increase of the dielectric constant. Finally, the optimized N2/H2 ash process minim...

Low-Damage Damascene Patterning Using Porous Inorganic Low-Dielectric-Constant Materials

The degradation of porous low-dielectric-constant (low-k) materials, such as porous methyl silsesquioxane (MSQ) and porous chemical-vapor-deposited SiOCH films, by damascene etch and ash processes has been investigated. The influence of etch damage becomes relatively stronger as ash damage improves. The etch damage to porous low-k dielectric is found particularly at the sidewall of the isolated lines. By investigating the influence of etch conditions on the damage, it is found that O2 and Ar addition causes large sidewall damage. O2-added etch condition, as well as the O2 ash process, produces oxygen radicals, which extract CH3 groups from porous low-k films. On the other hand, Ar plasma does not efficiently extract CH3 groups differently from O2 plasma, but it changes the bonding states of CH3 groups and causes H2O adsorption. This change in film characteristics increases dielectric constant. Finally, we successfully achieved low-damage dual damascene patterning using a porous SiOCH material whose dielectric constant is 2.2.

Prevention of Cu degradation using in situ N2 plasma treatment in a dual-damascene process

The surface state of copper after an etching process using CF4 gas has been analyzed. Copper surface stability against corrosion is evaluated through a storage test performed under high-humidity conditions after the etching process. The storage test reveals that the copper surface suffered from both corrosion and oxidation. The copper degradation is caused by a postreaction between moisture and residual fluorine, wherein the resulting oxygen-containing copper film features a rough surface morphology. We examined in situ plasma treatments with several gases to reduce corrosive reactions. Results indicate that in situ N2 plasma treatment removes fluorine residue from the copper surface, and that this treatment effectively stabilizes the copper surface against corrosive conditions.

UV-hardened high-modulus CVD-ULK material for 45-nm node Cu/low-k interconnects with homogeneous dielectric structures

A UV-hardened high-modulus ULK (ultra low-k) material is proposed for 45-nm-node Cu/low-k interconnects with homogeneous dielectric structures. An elastic modulus as high as 16 GPa was achieved for the ULK material with k=2.65. By combining this material with an advanced dielectric barrier (k=3.7), interconnect test devices with 65-nm-node dimensions were fabricated. The UV-hardened high-modulus ULK material is shown to be effective in improving electrical performance while maintaining sufficient mechanical integrity.

Reduction in Contact Resistance with In Situ O 2 Plasma Treatment

A reduction in contact resistance due to reactive ion etching using an O 2 plasma is reported. This treatment can reduce the contact resistance to the same level as when chemical dry etching is used, which is an isotropic etching process using fluorine-containing gases such as CF 4 . The mechanism of this reduction was investigated using X-ray photoelectron spectroscopy, transmission electron microscopy, and thermal wave modulated reflectance. Removal of a thick modified layer which contains carbon, fluorine, and oxygen reduces the contact resistance. Further, the influence of O 2 plasma treatment time and bias radio frequency power on contact resistance is reported. An increase in contact resistance at high radio frequency power shows that there is reformation of the damaged layer by O 2 plasma treatment, and that it is important to control the removal and reformation of the damaged layer.

Improvement of the wiggling profile of spin-on carbon hard mask by H2 plasma treatment

The H2 plasma treatment for spin-on carbon (SOC) hard mask in the trilayer resist process is expected to serve as a reliable alternative to single layer resist process for 45nm nodes and beyond. The authors have investigated this treatment with a view to suppress the deformation of SOC by oxide etching. The wiggling profile of SOC drastically improves due to the formation of a thicker diamondlike amorphous carbon structure by the H2 plasma treatment with higher-energy hydrogen ions.

Development of high-performance multi-layer resist process with hardening treatment

In the manufacture of devices beyond the 45 nm node, it is important to employ a high-performance multi-layer resist (MLR) process that uses silicon containing ARC (Si-ARC) and spin on carbon (SOC). We examined an additional hardening process of SOC by H2 plasma treatment in order to improve the etching durability of the MLR. The dry etching durability of H2-plasma-hardened SOC film showed a drastic improvement, while the wiggling features of the MLR without H2 treatment observed after SiO2 etching disappeared completely. The hardening mechanism of SOC was analyzed by Fourier transform infrared spectroscopy (FTIR) with gradient shaving preparation (GSP) and Raman spectrometry. The formation of diamond-like amorphous carbon at a depth of approximately 50 nm was observed and was attributed to the improvement in the dry etching durability. In addition, the MLR stack with hardening has good reflectivity characteristics. The simulated reflectivity at the interface between the bottom of the resist and top surface of the MLR stack with hardening below 0.6% was attained over a wide range of Si-ARC thicknesses and hyper NA (~1.3) regions. The measured refractive indices of the hardened SOC film at 193 nm had a high value at the surface; however, they gradually decreased toward the inner region and finally became the same as those of untreated SOC. This might be the origin of the estimated excellent reflectivity characteristics.

Mechanism for difference in etched depth between isolated and dense via holes of SiOCH film

We investigated the mechanism for differences in etched depth between isolated and dense via holes of a damascene structure using a SiOCH film (k=2.8). In Ar∕CHF3∕N2 and Ar∕C4F6∕N2 plasmas, the depth of an isolated (4.8μm pitch) hole was more than 40% varied from a dense (200nm pitch) hole. The difference between dense and isolated holes was found to become larger with increasing air exposure time of the wafer. The amount of H2O in the SiOCH film also increased with increasing air exposure time based on thermal desorption spectroscopy (TDS) analysis. Therefore, we investigated the effects of H2O addition to the plasmas. The investigation revealed that the etched depths of dense holes became similar to those of isolated holes with H2O addition. Based on these results, we concluded that the mechanism for the difference between isolated and dense holes was as follows. When the capping layer on SiOCH is etched, the H2O contained in SiOCH desorbs in etched holes and affects etching reactions. The etching chara...

Influence of electron shading on highly selective SiO2 to Si etching

The dependence of the poly-Si etch rates at the bottoms of SiO2 holes on the patterns of the poly-Si films is investigated using fluorocarbon gas plasma. The etch rate of poly-Si film which is separated from large open areas exposed to plasma is higher than that of film which is connected to large open areas. This tendency is exaggerated as the aspect ratio of the hole increases. From Auger electron spectroscopy of the inside of the hole, a carbon peak is detected on the sidewall just above the poly-Si film which is separated from large open areas. This result indicates that low-energy ions, which are a deposition species, are deflected at the bottom of the hole by the positive charge resulting from the electron shading effect. This causes a decrease in the deposition of fluorocarbon polymer on the poly-Si film, resulting in an increase in poly-Si etch rates.

Double Patterning Using Multilayer Hard Mask Process with Perhydropolysilazane

A new technology called the double patterning (DP) process with ArF immersion lithography is one of the candidate fabrication technologies for 32-nm-node devices. Over the past few years, many studies have been conducted on techniques of the DP process. Among these technologies, the double Si hard mask (HM) process is thought to be the most applicable technology from the viewpoint of high technical applicability to 32-nm-node device fabrication. However, this process has a disadvantage in terms of cost performance compared with other DP technologies since these HMs are formed by the chemical vacuum deposition (CVD) method. In this study, we examined the DP process using a dual spin-on Si-containing layer without using the CVD method to improve process cost and process applicability. Perhydropolysilazane (PSZ) was used as one of the middle layers (MLs). PSZ changes to SiO2 through reaction with water by the catalytic action of amine in the baking step. Using PSZ and Si-BARC as MLs, we succeeded in fabricating a fine pattern by this novel DP technique. In this paper, the issues and countermeasures of the double HM technique using spin-on Si-containing layers will be reported.