With both 193i multiple patterning and EUV technologies, the constraints on the mask manufacturability are becoming increasingly stringent. The necessity for understanding curvilinear shapes implicitly in design (for ILT and EUV) or OPC correction (corner-rounding effects) along with new multi-beam mask writing systems mean the mask manufacturers are at an inflection point: whether the mask shapes are described as curvilinear targets or complex rectilinear targets, the actual mask shapes after exposure are curvilinear and must be accounted for correctly for wafer lithography. We present a GPU-accelerated intrinsically curvilinear mask data preparation system, compatible with both VSB and multi-beam systems, that is capable of full-ship simultaneous shape and dose correction using arbitrary (non-Gaussian) kernels for model shape and dose effects.
Mask writers need to be able to write sub-50nm features accurately. Nano-imprint lithography (NIL) masters need to create sub-20nm line and space (L:S) patterns reliably. Increasingly slower resists are deployed, but mask write times need to remain reasonable. The leading edge EBM-9500 offers 1200A/cm2 current density to shoot variable shaped beam (VSB) to write the masks.
Last year, thermal effect correction (TEC) was introduced by NuFlare in the EBM-95001. It is a GPU-accelerated inline correction for the effect that the temperature of the resist has on CD. For example, a 100nm CD may print at 102nm where that area was at a comparably high temperature at the time of the shot. Since thermal effect is a temporal effect, the simulated temperature of the surface of the mask is dynamically updated for the effect of each shot in order to accurately predict the cumulative effect that is the temperature at the location of the shot at the time of the shot and therefore its impact on CD. The shot dose is changed to reverse the effects of the temperature change.
This paper for the first time reveals an enhancement to this thermal model and a simulator for it. It turns out that the temperature at the time each location receives backscatter from other shots also make a difference to the CD. The effect is secondary, but still measurable for some resists and substrates. Results of a test-chip study will be presented.
The computation required for the backscatter effect is substantial. It has been demonstrated that this calculation can be performed fast enough to be inline with the EBM-9500 with a reasonable-sized computing platform. Run-time results and the computing architecture will be presented.
Over the last two decades, eBeam mask writers have added inline correction features. Particularly when minimum feature sizes on mask went below 100nm a decade ago, the need for more precision within a reasonable write time increased the demand for more corrections. Inline correction is better for turnaround time and throughput, but inline correction is computationally limited because it is unacceptable for computation to limit the machine write time.
Simultaneously, the same need for linearity correction, printability enhancement, and resilience to manufacturing variation has caused much innovation in offline mask data preparation and mask process correction. Typically, the writer performs inline correction for backscatter, fogging, loading, charging and thermal effects, but leaves <10μm effects to offline correction.
With multi-beam writers, the write time is independent of shape count. Any set of input shapes is rasterized to a set of arrays of equal sized pixels that are each independently dosed to write the desired shapes. Multi-beam writers also have a certain minimum write time that is required for writing even a very small number of simple shapes. This gives rise to the possibility of providing linearity correction features, even for the short-range effects as inline correction in the writer. Such inline correction has zero impact on throughput and turnaround time of mask making.
This paper introduces the GPU-accelerated inline linearity correction capability of the NuFlare MBM-1000 for the first time.
For some years it has been known that the presence of a multi-layer stack creates an enhanced back-scatter effect at
the 1μm length scale. Several authors have reported a non-Gaussian behavior – exponential or worse – that is
challenging to both simulate and correct for in a production environment due to the long interaction area of the effect.
With the onset of extreme ultra-violet (EUV) lithography, and the likely use in the new multi-beam mask writers, we
revisit the EUV midrange effect from first principles, identify the impact from the new mask writers, and demonstrate a
production-ready system to characterize and correct for the effect.
For IC design starts below the 20nm technology node, the assist features on photomasks shrink well below 60nm and the printed patterns of those features on masks written by VSB eBeam writers start to show a large deviation from the mask designs. Traditional geometry-based fracturing starts to show large errors for those small features. As a result, other mask data preparation (MDP) methods have become available and adopted, such as rule-based Mask Process Correction (MPC), model-based MPC and eventually model-based MDP.
The new MDP methods may place shot edges slightly differently from target to compensate for mask process effects, so that the final patterns on a mask are much closer to the design (which can be viewed as the ideal mask), especially for those assist features. Such an alteration generally produces better masks that are closer to the intended mask design. Traditional XOR-based MDP verification cannot detect problems caused by eBeam effects. Much like model-based OPC verification which became a necessity for OPC a decade ago, we see the same trend in MDP today.
Simulation-based MDP verification solution requires a GPU-accelerated computational geometry engine with simulation capabilities. To have a meaningful simulation-based mask check, a good mask process model is needed. The TrueModel® system is a field tested physical mask model developed by D2S. The GPU-accelerated D2S Computational Design Platform (CDP) is used to run simulation-based mask check, as well as model-based MDP. In addition to simulation-based checks such as mask EPE or dose margin, geometry-based rules are also available to detect quality issues such as slivers or CD splits. Dose margin related hotspots can also be detected by setting a correct detection threshold.
In this paper, we will demonstrate GPU-acceleration for geometry processing, and give examples of mask check results and performance data. GPU-acceleration is necessary to make simulation-based mask MDP verification acceptable.
Conference Committee Involvement (2)
Optical Microlithography XXX
28 February 2017 | San Jose, California, United States
Optical Microlithography XXIX
23 February 2016 | San Jose, California, United States