The design shrinking of semiconductor devices and the pattern complexity generated after OPC (optical proximity
correction) have an impact on the two major cost consuming processes in mask manufacturing, EB (electron beam)
writing and defect assurance. Mask-DFM (design for manufacturing) is a technique with various steps ranging from
the design to the mask manufacturing to produce the mask friendly designs and to reduce the workload in the advanced
mask production. We have previously reported on our system, called MiLE (Mask manufacturing Load Estimation),
which quantifies the mask manufacturing workload by using the results of mask layout analyses. MiLE illustrates the
benefits of mask-DFM efforts as numerical indexes and accelerates the DFM approaches. In this paper, we will show
the accuracy of the workload estimation of the advanced devices by the comparison between the indexes and the process
times in the actual mask manufacturing. The throughput of MiLE calculation of the production masks of a 65nm device
Load of photomask manufacturing for the most advanced semiconductor devices is increasing due to the complexity of
mask layouts caused by highly accurate RET or OPC, tight specification for 2D/3D mask structures, and requirements of
quick deliveries. The mask cost becomes a concern of mask users especially in SoC businesses because the number of
masks required throughout the wafer process is almost the same for each product regardless of the variety in production
volume when a unified platform is applied to the designs. Shares of mask cost within total production cost cannot be
ignored especially in small volume SoC products.
DFM (design for manufacturing) is inevitable in a mask level as well as in a wafer level to solve the cost problem.
"Mask-DFM" is a method to decrease the burden of mask manufacturing and to improve the yield and quality of masks,
not only by modification of mask pattern layouts (design) but also all other things including utilization of designer's
We have developed our Mask-DFM system called "MiLE", that calculates mask-manufacturing workload through
layout analyses combining information of mask configuration, and visualizes the consequence of Mask-DFM efforts.
"MiLE (Mask manufacturIng Load Estimation)" calculates a relative index which represents the mask manufacturing
workload determined by factors of 1) EB writing, 2) defect inspection/repair, 3) materials and processes and 4)
specification. All the factors are computed before tape-outs for mask making in the system by the following methods.
To estimate EB writing time, we applied high-throughput simulator and counted the number of "shot", minimum figure
unit in EB writing, by using post-OPC layout data. Mask layout that caused troubles and extra load in mask
inspection or repair was specified from MRC (mask rule checking) of the same post-OPC data. Additional layout
analysis perceives designer's intents that are described in the layout data and these are reflected in the calculation of the
"MiLE" index. Finally, chip arrangement on a mask is retrieved from so-called electronic mask spec sheets to construct mask layouts.
"MiLE" notifies to designers the index of mask manufacturing workload that is caused by mask layout, while modification and adjustments of design or OPC are iterated to maximize device productivity in early design phases. Therefore, designers can judge and control the mask manufacturability, or mask cost by designs and additional intents
useful for mask making. In the production phases, our system releases useful information for mask manufacturing to a mask shop and decreases the mask manufacturing workload. In this paper, we report the outline and functions of MiLE system and the results of mask manufacturing workload calculation using post-OPC layout data.
Photomask pattern writer requires high-speed data processing that is conducted concurrently with the variable shaped
beam (VSB) writing. As input electron beam (EB) mask data, trapezoid data format is generally used for EB writing
because of the easier handling than polygon data format. Recent years, volume of photomask pattern data is growing
as the increase of pattern density that is caused by additional various subsidiary patterns of optical proximity correction
(OPC). OPC in design rules of 65nm and below is getting approximately 1.5 times more complex than that in the
former generation, which increases the photomask pattern data volume approximately 3 times larger.
VSB writing time is accurately estimated by counting the total number of "shots" which are primitive figures
generated in the data processing of EB writer from the trapezoid patterns in EB mask data. However, no feedback and
layout modification can be taken to LSI designs and OPC, even though problems regarding mask manufacturability such
as explosion of EB writing time is recognized after starting EB writing process.
We developed a simulator that estimates the number of "shots" in VSB EB writing by original shot division method
using design data GDSII instead of EB mask data. This simulator outputs total counts and density map of shots of EB
writing in photomask layout as well as chip layout in a short time using multi-processing. We can use this software as
a core function in our Mask-DFM solutions offering to LSI designers and CAD engineers in order to estimate mask
manufacturability before they finish mask data tape-out, and this work can reduce cost and improve TAT in mask manufacturing.
Application of long wavelength in lithography process has a great benefit for cost of ownerships (COO) of semiconductor manufacturers, however there’s a trade off of reducing process margins due to the low k1 condition, and all the efforts in order to obtain large process windows on wafer connect directly to chip production management. In this paper, the authors used 248 nm wavelength lithography with alternating phase shift mask (alt-PSM) to develop 90 nm line and space patterns in 90 nm half pitch on wafer, and thoroughly investigated printability of defects and defect-repairs on alt-PSM. Sensitivity analysis of photomask defect inspection tools was implemented and it showed that existing inspection tools satisfied requirements for detection of chrome (Cr) and quartz (Qz) defects, which had impacts on wafer. Printability of Cr and Qz defect repairs was evaluated focusing on through-defocus behavior, and conditions of defect repair were optimized to reduce variation of critical dimension (CD) on wafer. The repair conditions were also optimized by estimation of overlaps of process windows of defect-repaired area on that of non-defective references. Process windows were analyzed based on both wafer and aerial image measurements. In the last section of this paper, we discussed managing process windows of defect repairs by controls of biases and Qz heights as parameters on defect-repaired areas and suggested that total topography control around defective area was required in addition to the prospected parameters in order to maximize process margins.
As 90 nm devices enter into the pre-production phase, the quality assurance strategy of photomasks for those devices must be well established with the proper cost and turn-around-time in mind. Such devices will be manufactured with a state-of-the-art photolithography systems equipped with 193nm actinic light sources. Photomasks for these devices are being produced with the most advanced equipment, material and processing technologies and yet, quality assurance still remains an issue for volume production. These issues include defect classification and disposition due to the insufficient resolution of the defect inspection system, uncertainty of the impact the defects have on the printed feature as well as inconsistencies of classical defect specifications as applied in the sub-wavelength era. To overcome these issues, the authors propose a new strategy to assess photomask quality by checking the CD variation on wafer (defect printability) using aerial image simulation. This method of simulation-based mask qualification uses aerial image defect simulation in combination with a high resolution optical review system with shorter review wavelength (248nm) and smaller pixel size (22.5nm)- combining the defect inspection system with a longer inspection wavelength (365nm) and larger pixel size (150nm). This paper discusses a new strategy on mask quality assurance with several experimental results that proves the applicability for enabling 90nm technology nodes. Combining high-resolution optical images captured by DUV measurement tool with Virtual Stepper System has achieved better accuracy for 0.72um contact holes on ArF Att.PSM. However, we need further investigation for precise prediction of CD variation caused by defects on 0.4um line/space patterns on ArF Att.PSM. This paper also discusses future work to make the strategy production-worthy.
The KrF12% tri-tone PSM (phase shift mask) was designed with the programmed defects on the chrome (Cr) and phase shift (PS) layers. From the lithography simulation, the PS defects, generated on the PS layer, were estimated to fluctuate the CD of the contact holes on the wafer more than the defects in the same size on the conventional EAPSM (half-tone PSM). The printability of the PS defects and Cr defects on the contact holes were investigated by the print-test on the wafer. The Cr residues on the PS layer slightly changed the CD of the contact holes on the wafer. The PS defects showed the great influence to the CD variation of the contact holes. The light calibration of the defect inspection was optimized to detect the PS and Cr defects. For the detection of the PS defects in the die-to-die inspection mode, the UV inspection system SLFX7 showed the high performance with the PS/SiO2 calibration, in which the boundary of the PS layer and SiO2 substrate was used as the light calibration point. The SLFX7 also available to detect the Cr defects in the die-to-die mode. For the die-to-database mode to detect the Cr defect, the KLA351, the visible light inspection system, was available by the Cr/PS calibration. The sensitivity of the SLFX7 and KLA351 was adequate for the Cr defects, however, that was not enough to the specification of the PS defects estimated from the print-test. The sensitivity of the SLFX7 showed a slight difference between the tri-tone and binary layout in the specific defect types.
The new repair of the clear defects on the half-tone PSM (EAPSM) was proposed. The Ga (gallium) ions were implanted by the FIB on the area adjacent to the carbon films formed on the clear defects. The Ga ion implanted area on the SiO<sub>2</sub> substrate showed the semi-transparency at the KrF and ArF wavelengths. The lithography simulations of the layouts designed for the defect-repaired area endorsed the concept of the new repair. The Ga ion implantation was optimized to the new repair by using the AIMS and AFM measurements for the transmittance and etched depth of the SiO<sub>2</sub> surface. The authors applied this method to the clear defects programmed on the KrF and ArF EAPSMs. The AIMS analysis showed that the deviation of the CD (critical dimension) of the defect-repaired regions on the wafer was within +/-5% to the non-defective reference at every defocused point. The new repair moderated the specification of the edge placement accuracy of the FIB processing compared to the conventional carbon film deposition.
We are focusing on a high-performance cleaning process with minimum use of chemicals. For the substitution of chemicals, the refined cleaning tools and process have been developed, which use the high-concentration ozonic together with hydrogen water. To optimize a cleaning process, we have evaluated the removal and decomposition efficiency of organic compounds on the mask surface, the optical degradation of Cr and Suicide materials and so on. In conclusion, the substitution of sulfuric acid, ammonia and other chemicals is available for practical cleaning process by combining their functional cleaning steps. Especially in the ArF generation, this cleaning technique was found to be promising for the reduction of optical-damage and chemical residues for mask patterns and as well as high-efficiency particle removal.
In this paper, we focused on the refined cleaning process with minium use of chemicals. We developed a cleaning tools and process using high-concentration ozonic water generated by the high-efficiency ozonizing apparatus (OW00345, Mitsubishi Electric Corp. Industrial Systems), as chemicals substitution. To optimize a cleaning process, we have evaluated the removal and decomposition efficiency of organic compounds on the mask surface, the optical degradation of Cr and Siliside materials and so on.
A new photomask cleaning process using electrolyzed water was suggested in this work. This process using the cathode water with a small amount of ammonium hydroxide showed good efficiencies of removing particles from photomask surfaces. MoSiON surface was not so damaged in the alkaline cathode water compared with in APM. The rinsing process in the anode water eliminated the sulfuric acid residue on the surfaces of quartz substrates. Using electrolyzed water reduced the consumptions of the chemicals, the water and the energy.