We investigated the effects of etch rate on low-k damage induced by dry etching under CF 4 , CF 4 /O 2 , and C 4 F 6 /O 2 /Ar chemistry conditions. The amount of damage increases with decreasing etch rate in all chemistries. This is because the amount of fluorine or oxygen radical diffusion increases with plasma exposure time. These radicals extract CH 3 groups from the low-k film or oxidize the film. To reduce damage to the lowest level possible, it is necessary to suppress the effect of the damage diffusion using etching conditions where the etching speed is higher than the diffusion speed of the damage.
45nm-node multilevel Cu interconnects w i t h porous-ultia-low-k have successfully been integrated. Key features to realize 45nm-node interconnects are as follows: I ) porous ultra-low-k material NCS pano-Clustering Silica [I]) has been applied to both wire-level and via-level dielectrics (what we call hlI-NCS structure), and its sufficient robustness has been demonstmted. 2) 70-nm vias have been formed by high-NA 193nm lithography w i t h fine-tuned model-based OPC and multi-hard-mask dual-damascene process. More than 90% yields of 1M via chains have been obtained. 3) Good TDDB (Time-Dependent DielectricBreakdown) characteristics of 70nm Wire spacing filled w i t h NCS has been achieved. Because it is considered that applied-voltage (Vdd) of a 45nm-node technology will be almost the same as that of the previous technology, the dielectrics have to endure the high electrical field. NCS in Cu wiring has excellent insulating property without any pore sealing materials which cause either keff value or actual wire width to be worse.
This paper describes process technologies for an x-ray mask using Ta as the x-ray absorber and SiC as the x-ray membrane. SiC can be grown heteroepitaxially in a coldwall LPCVD reactor at 1000~ and 3.5 torr using a gas mixture of SiHC13, C3H8, and H2. SiC has a stress of 4 x 109 dyn/cm 2 and a Young's modulus of 4.7 x 10 '2 dyn/cm 2. Pure Ta with Ar ions implanted by 150 keV is more stable and dense than Ta alloys and their nitrides. The film density is about 16 g/cm 3 and the stress change due to annealing of 200~ is below 2 x 108 dyn/cm 2. The yield of stress control is 68% for 2 • l0 s dyn/cm 2. The temperature of the membrane during Ta RIE is controlled by He cooling from the back. It is held between 45 ~ and 100~ at a power density of 0.8 W/cm 2. A mixture of C12 and CC14 (1:1) is used as the etching gas. The gas pressure is from 0.18 to 0.2 torr. The etch rate of Ta is 1.2 ~tm/min and the selectivity of Ta to a resist (AMS-1) is 7. A 0.8 ~m thick Ta pattern of 0.15 ~m lines and spaces is obtained by using a 0.5 ~m thick single-layer resist. Electron beam lithography on a thin membrane requires a high-contrast resist (AMS-1) and a well-controlled correction of the proximity effect because of the high electron backscattering on Ta. Si etchback is done by spray etcher using a mixture of HF and HNO3 (1:3) with a high speed of 8 min per mask. The total fabrication process is designed to minimize mask distortion. The maximum mask distortion due to the absorber stress is 0.11 ~m (3~) including the measurement errors of Nikon 2I. The mask used for the measurement had a circular membrane of 60 mm diam and a 32 • 32 mm field window. The SiC was 2 ~m thick and the Ta was 0.8 ~m thick with a stress of 1.4 x 108 dyn/cm 2.It will be the key factor to establish a well-controlled and zero-defect x-ray mask for a successful application of x-ray lithography to deep submicron devices. The x-ray mask consists of some process technologies. Chemical vapor deposition (CVD), reactive ion etching (RIE), and electron beam delineation are the most common. The requirements for x-ray mask materials and processes are somewhat different from those of electronic devices.The x-ray membrane must have a tensile stress high enough to obtain flat surface and avoid vibration due to pressure difference on the two sides of the membrane. Especially, the mask vibration during the x-ray exposure and alignment process is a severe problem resulting in a loss of overlay accuracy and a loss of critical dimension (CD) control. A high stress above 1 x 109 dyn/cm 2 is preferable for this purpose. A high Young's modulus of membrane is
As a practical curing technique of low-k material for 32-nm BEOL technology node, we demonstrated that electron beam (e-beam) irradiation was effective to improve film properties of nano-clustering silica (NCS). We confirmed that by using optimized e-beam cure condition, NCS was successfully hardened without degradation of dielectric constant and the Young's modulus increased by 1.7 times compared with that of thermally cured NCS. We fabricated two-level Cu wirings layers with NCS cured by optimized e-beam cure technique. The e-beam cure dramatically enhanced the lifetime of time-dependent dielectric breakdown (TDDB) of interlayer dielectrics. We also examined the influence of the charge damage to the MOSFETs under e-beam cured NCS layer and confirmed that there was no e-beam charge damage to the Ion-Ioff characteristics and reliability of MOSFETs with the optimized e-beam cure. IntroductionPropagation speed of signals in the multi-level interconnections of semiconductor devices is determined by the parasitic capacitance and wiring resistance. The low dielectric constant material is used as an interlayer dielectric (ILD) to decrease parasitic capacitance. We used NCS as an ILD that has a dielectric constant (k) of 2.25 (See Table 1 and Fig. 1). The Young's modulus of NCS is higher than that of the other porous low-k materials with almost the same dielectric constant. This is because constituent silica of NCS has nano-size cluster in the film [1,2]. We applied NCS as a homogeneous ILD into intermediate layers of 45-nm node process and excellent integration technology has been established [3].For further improvement of reliability of Cu wirings with NCS ILD for applying 32-nm node, more mechanical strength of NCS, such as high endurance to the mounting stress, and better adhesion between diffusion barrier and NCS, and also between NCS and cap insulation layers, are requested. NCS solution contains pre-composed silica clusters. After spin coating on a wafer, the silica clusters are baked and thermally cured in order to evaporate solvents and form cross-linked structure between clusters [1]. It means that physical properties of the silica clusters in the NCS solution is difficult to change by the baking and thermal curing, and other curing method should be considered. Although broadband ultraviolet (UV) sources have been widely applied for curing low-k materials [4], it has disadvantage of being unable to separate wavelengths suitable for low-k curing. On the other hand, in the case of e-beam, the irradiation energy is tunable by changing an acceleration voltage of e-beam. Therefore we expect that the most suitable irradiation energy can be applied for curing NCS by e-beam.In this paper, we compared several curing method for NCS hardening and found that the mechanical strength of NCS can be improved by the e-beam cure without degradation of low-k dielectric. In addition, we also discuss the reliability of wiring and MOS gate oxide.
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