As minimum feature size of device shrink down below 100 nm, the process margin for the mask fabrication reduced dramatically. Mask makers are enlisting equipment and material suppliers in their efforts to achieve wide process margin from existing processes. One of the most promising methods is thinning Cr thickness as low as possible. However, briging the thin Cr blank into mass production line could cuase some problem for advance photomask fabrication using 50 kV electron beam writing tools. In this paper, we verified the feasibility of Cr film ranged from 400 Å to 1000 Å. The results categorized into two sections. At first, we verified the writing property change with thinning Cr thickness and then investigated the etching characteristics. As a result, we found that Cr thickness don't affect writing properties regardless of Cr thickness. However, the thinner Cr blank represented superior etching characteristics to a conventional one. It showed low etching bias and loading effects. From these results, we concluded the thinner Cr blank could not only make the process wider but also improve the mask quality.
The cleaning of embedded-attenuated phase shift masks (EAPSMs) is one of the most important enabling capabilities in the production of high-quality masks. Particles are commonly generated during Cr and MoSiON etching using inductively coupled plasma (ICP) tools. The cleaning process of EAPSMs requires not only the removal of particles on the phase shifting layer (MoSiON) and glass, but also the ability to leave the phase and transmission properties intact.
Megasonic cleaning is a technique commonly used for removing particles on the surfaces of photomasks. However, megasonic processes employing SC-1 chemistry (specifically ammonium hydroxide) cannot be applied to a MoSiON PSM. Chemical erosion of the alkali-soluble phase shifting layer will drive phase and transmission performance outside of customer specifications. Therefore, EAPSM cleaning must balance simultaneously the complete removal of particles with the prevention physical damage. For these reasons, the cleaning process requires a high degree of control.
In this paper, a new cleaning method was applied to MoSiON-based masks utilizing megasonic cleaning because it had a little change on phase and transmission. Traditional SC-1 chemistry was not used at all. Results obtained through this method showed a little change on phase and transmission. The particles on glass also can be sufficiently removed using megasonic process with the dilute SC-1 chemistry. The cleaning technique for the fabrication of EAPSMs with no variation in phase and transmission after the cleaning process will be presented.
The selectivity and etched profile of MoSiON in high-density CF4/O2/He inductively coupled plasma (ICP) have been studied. The etched profiles of MoSiON along with the quartz surface morphologies were investigated as a function of etching parameters by scanning electron microscopy (SEM). We varied pressure from 5 mtorr to 20 mtorr and CF4 flow rate from 15 sccm to 40 sccm. A smooth quartz surface and a vertical MoSiON slope were observed under 10 sccm CF4, 15 sccm of O2 flow rate, -240 V of DC bias and 5 mtorr pressure. And the other conditions showed rough quartz surface and bad MoSiON slope. Only at the appropriate CF4/O2 Flow rate, high vapor pressure compounds inhibits nonuniform quartz etching.
There is considerable interest in phase shift masks as a route to extending the resolution, contrast, and depth of focus of lithographic tools beyond what is achievable with the normal chrome mask technology. A problem that has so far hindered the introduction of phase shift masks has been the difficulty of phase and transmittance control when a phase shift mask is applied to practical use. Also, to apply phase shift layer (MoSiON), it remains that effects several critical mask parameters including sidewall slope, surface roughness, and critical dimension. For these reasons, this process requires a high degree of control of the etch process of shift layer. So in this paper, we described a technique for the fabrication of phase shift masks by etch rate of a MoSiON layer. Etching experiments of MoSiON were performed using different fluorinated gas mixtures. Four of them, CF4/O2/He, SF6/O2/He, CHF3/O2/He and Cl2/CF4/O2/He were chosen for high etch rate, sidewall slope, and surface morphology. Each added gases had a unique property on the etch rate, anisotropy, surface roughness and sidewall morphology. Result indicates that vertical slope and smooth surface are obtained using the Cl2/ CF4/O2/He and SF6/O2/He mixture. With increasing O2 flow rate to the SF6/O2/He Plasma and added Cl2 gas to the CF4/O2/He Plasma, the MoSiON etching profile becomes anisotropic without undercutting and trench profile. It is probably due to both increasing etch rate and sidewall passivation of Cl2 ion flux. When Cl2 gas was added to the CF4/O2/He Plasma, the small addition of chlorine was enough to protect the exposed sidewall of the undercutting, therefore, higher flow rate of chlorine had to be added to protect the sidewall of the undercutting by forming a sidewall passivation layer. These results show that both increasing O2 flow rate to the SF6/O2/He Plasma and the addition of Cl2 to the CF4/O2/He plasma are necessary in order to achieve a vertical profile and a smooth surface morphology.
Many studies have reported that the alternating phase shift mask (Alt. PSM) improves resolution and depth of focus (DOF). The purpose of this study is to investigate the influence of process latitude and optimize undercut and pre etch depth of both single trench and dual trench process employing the Solid-CMTM simulation tool for 248 nm DUV lithography system. To compensate for the imbalance intensity, we adopted the amount of undercut in the phase shifter regions of both single trench and dual trench. The results suggest that process is improved with optimized undercut for 130 nm line & space (L/S). For the single trench, we can see that with undercut of about 800 Angstrom the max intensities are equal. In the case of dual trench, the margins for image balance of 800 Angstrom and 1600 Angstrom undercuts was obtained up to 800 Angstrom, 1200 Angstrom of pre etch depth, respectively. Finally, it was found that the effect of undercut was improving the process latitude and the balance intensity of both single trench and dual trench.
It is reported that Alternating Phase Shifting Mask (Alt. PSM) enhances the resolution and depth of focus and reduces the mask error enhancement factor efficiently. In spite of above-mentioned advantages, Alt. PSM is rarely used for some problems. One of the problems is the image imbalance between the transmittance of the shift and the nonshift area on Alt. PSM. To minimize the image imbalance, various manufacturing processes are introduced for both single and dual trench structures. In this paper, the image balance was simulated with AIMS and the Solid-CM program. The pattern profile, CD, depth and a phase uniformity of Alt. PSM were investigated experimentally. We carried out 3 types of processes (a) single trench (wet etch process), (b) single trench (dry etch process with undercuts), (c) dual trench (dry etch process with undercuts). The type (a) showed 12 nm of CD uniformity, 1.56 degrees of phase shift uniformity and 63 Angstrom of the shift depth. And its transmittance of the shift region was 99.85 percent. For the type (b), its CD uniformity, phase shift uniformity, depth uniformity and the transmittance of the shift region were 15 nm, 11.56 degrees, 208 Angstrom and 99.76 percent, respectively. And the experiments of the type (c) are now under way.
The attenuated phase-shifting mask (Att. PSM) is one of the most useful technologies for sub-micron lithography.1) However, it is difficult to control the parameters such as phase or transmittance when a phase-shifting mask is applied to practical use. Also, to apply phase shift layer (MoSiON), it remains that affects several critical mask parameters including critical dimension (CD), sidewall slope and surface damage. So, in this paper, the effects of added Cl2 gas, DC bias voltage on the etch characteristics were studied using an inductively coupled CF4-based plasma. The plasma characteristics and etch properties of inductively coupled CF4O2He and Cl2CF4O2He Plasmas were investigated on the etch properties of MoSiON. Each added gas had a unique property on the etch rate, anisotropy, surface roughness and sidewall morphology. As the results of experiment, the most vertical profile and smooth surface were obtained using the 10 sccm Cl2, -200V dc bias. By increasing the dc bias voltage, the undercut on MoSiON layer is not occurred. When plentiful Cl2 gas was added to the CF4O2He plasma, surface roughness was decreased but the edge of Cr slope was damaged at 15 sccm Cl2. It is suggested from the results of this experiment that the pattern profile and surface roughness on MoSiON layer can be controlled by both quantity of Cl2 gas and dc self-bias voltage.