Next-generation lithography based on EUV continues to move forward to high-volume manufacturing. Given the
technical challenges and the throughput concerns a hybrid approach with 193 nm immersion lithography is expected, at
least in the initial state. Due to the increasing complexity at smaller nodes a multitude of different masks, both DUV
(193 nm) and EUV (13.5 nm) reticles, will then be required in the lithography process-flow. The individual registration
of each mask and the resulting overlay error are of crucial importance in order to ensure proper functionality of the chips.
While registration and overlay metrology on DUV masks has been the standard for decades, this has yet to be
demonstrated on EUV masks. Past generations of mask registration tools were not necessarily limited in their tool
stability, but in their resolution capabilities. The scope of this work is an image placement investigation of high-end
EUV masks together with a registration and resolution performance qualification. For this we employ a new generation
registration metrology system embedded in a production environment for full-spec EUV masks. This paper presents
excellent registration performance not only on standard overlay markers but also on more sophisticated e-beam
The most important factor in extreme ultra violet (EUV) mask process is thickness variations which
caused by resist dark loss, absorber etching and capping layer durability of cleaning chemical at each
layer. For example if multilayer (M/L) is damaged due to 2.5nm capping layer loss after cleaning, it means it is impossible to get sufficient reflectance to make proper EUV mask.
Process control of line width and etch depth on the photomask production is more important as the industry moves
toward 50nm node and beyond. In this paper, we report the ellipsometer-based scatterometry based metrology system
that provides line width and resist thickness measurements on sub 50 nm node test masks for a mask process monitoring.
Measurements were made with spectroscopic rotating compensator ellipsometer system. For analysis we made up
modeling libraries with a 200 nm half pitch and checked and applied them to ADI and ACI measurements of binary and
phase shift mask (PSM). We characterized the CD uniformity, linearity, thickness uniformity. Results show that linearity
measured from fixed-pitch, varying line/space ratio targets show good correlation to top-down CD-SEM with R2 of more
than 0.99. Resist thickness results show that depth bias is about 2nm between AFM and OCD in ADI step. The data
show that optical CD measurements provide a nondestructive way to monitor mask processes with relatively little time
loss from measurement step.
The crystal growth and haze formation on the reticle continue to be significant problems for the semiconductor industry. Recently, a pattern size has gradually reduced to enhance the integration of semiconductor device. As minimum linewidth has shrunk, the exposure wavelength has also progressively shrunk. The exposure wavelengths have been reduced progressively from g-line (436 nm), i-line (365 nm), KrF (248 nm), to ArF (193 nm). However, expose wavelength shrink caused some serious problems. One of the problems to be solved is growing defect in the reticle during the process. This growing defect on the reticle is called the haze. The haze is formed on both sides of the reticle, on the quartz side of the mask and on the chrome side of the mask. In this investigation, we varied the local haze defect size and the characteristics of the haze defect. And we get the critical dimension and the exposure latitude variation as the haze transmission changes and the haze phase shifts.
Each generation of semiconductor device technology drives many new and interesting resolution enhancement technologies (RET). As minimum feature size of semiconductor devices have shrunk, the exposure wavelength has also progressively shrunk. The 193 nm lithography for low-k<sub>1</sub> process has increased the appearance of progressive defects on masks often known as haze or crystal growth. Crystal growth on a mask surface has become an increasing issue as the industry has adopted a 193 nm wavelength in order to increase lithographic resolution and print ever decreasing device line width. Haze is known to be a growing defect on photomask as a result of increased wafer lithography exposure and photochemical reactions induced by combination of chemical residuals on the mask surface. We build experimental system to create and detect the haze growth. A photomask is enclosed in a glove box where the atmosphere and exposure conditions are controlled and monitored throughout the exposure processing. A test photomask is exposed to accumulate the dose of laser radiation. And then spectroscopic ellipsometry and metallographic microscope techniques are used to check the surface conditions of the masks before and after the laser exposure. We found that spectroscopic ellipsometry measurement values of Δ and Ψ were changed. The results of the spectroscopic ellipsometry analysis show the change of the haze thickness on mask surface. Thickness and roughness of the mask surface is increased with the exposure. This means that haze grows on the mask surface by the exposure. Masks become useless due to transmission loss or defect generation, which is directly related to the formation of the haze. The haze causes the increase of mask thickness, transmission drop and affects the formation of pattern. So, we investigated the linewidth variation and the process window as a function of haze size effect with Solid-E of Sigma-C.
Recently, a pattern size gradually has reduced to enhance the integration of semiconductor device. As minimum linewidths have shrunk, the exposure wavelength has also progressively shrunk. The exposure wavelengths have been reduced progressively from 436 nm to 365 nm to 248 nm to 193 nm. Expose wavelength shrink caused some serious problems. One of the problems to be solved is growing defect in the reticle during the process. Reticle growing defect is called a haze. Haze is formed around the pellicle, on the quartz side of the mask and on the chrome side of the mask. In this investigation, mask haze is intentionally formed on the backside of mask by 193 nm laser irradiation. And the thickness is measured by the spectroscopic ellipsometry. This paper describes the relationship between transmittance and the haze formation, photochemical reactions and the haze effect on the process latitude. In addition, throughput is decreased due to haze formation.
Extreme Ultraviolet Lithography (EUVL) is one of the patterning technologies proposed for the next generation lithography (NGL) which makes pattern less than 50 nm critical dimension (CD). And EUVL uses a very short exposure wavelength of 13.4 nm. So it has many characteristic in common with optical lithography, but EUVL are different from the conventional mask applied to the projection optical lithography. Specially, industry experts generally agree that the biggest challenges and risks for the next generation of lithography systems involve the mask. In EUVL, a mask is produced by applying multilayers of molybdenum and silicon to a flat substrate. The circuit pattern is produced by applying a final EUV-absorbing metal layer and then etching away the metal to form the image of the circuit. Also, the light shining with 6 degrees oblique to mask can not get target CD easily because the shadow effect is influenced on pattern. Therefore we must understand this kind of effect before doing real process. We tried to change the structure of the mask in order to decrease this effect and to have enough process latitude for the 32 nm node. EUV mask is affected by the thickness and kind of absorber and buffer material. First, we changed the absorber material such as Cr, TaN and Ge etc. without changing the buffer material. Second, we changed the thickness of the absorber materials. We tried to minimize the shadow effect by adjusting the side wall angle of the absorber layer parallel to the oblique incidence. Additionally we considered different shapes and depth of the etched multilayer binary mask and the refilled multilayer binary mask such as the inclined side wall of the etched multilayer. In this paper, we will describe the optimized EUV mask structure for 32 nm node by studying not only the aerial image, but also the resist profile. Solid-EUV simulator of Sigma-C is used to calculate the aerial image, resist pattern profile, and the process latitude with the optimized process parameters.
Haze formation on reticle continues to be a significant problem for the semiconductor industry. Haze can be formed on the outside pellicle and on the quartz back side of the reticle. Major component of the haze is known to be aluminum sulfate that comes from the reticle cleaning process. The reticle materials, the exposure wavelength, roughness of photomask and this haze will affect the resolution and process latitude. So the haze on the mask surface becomes more important. We need to know the usable lifetime of the reticle in terms of haze and need to know how to increase the
lifetime by removing the haze, if possible. This paper introduces the haze measurement method by using the spectroscopic ellipsometry. The quantity of the haze including the roughness of the reticle can be accurately measured by the spectroscopic ellipsometry. The spectroscopic data shows the increase of the delta value with the energy dose given to the reticle. We confirm that this signal increase is directly the result of the haze increase with dose.