Kozo Ogino

Proximity effect correction using pattern shape modification and area density map for electron-beam projection lithography

A novel proximity effect correction algorithm using pattern shape modification and the area density map method for electron-beam projection lithography is proposed. This algorithm enables fast, accurate and self-consistent calculation of modified pattern sizes. The correctable minimum feature sizes for shape modification were investigated from two viewpoints, mask fabrication restriction and dose margin. The correctable minimum sizes are mostly determined by the dose margin requirement in the case of isolated and dense repeated patterns, implying that the tool resolution determines correctable minimum sizes. A special technique is required for isolated space patterns where the backscattering energy cannot be reduced by simple sizing. We have implemented an algorithm in which pattern densities at middle parts of large patterns are reduced by using a lines and spaces (L/S) pattern or mesh patterns for that case. Successful correction results down to 60 nm from the simulation and 100 nm from the experiment have been obtained.

Correction for local flare effects approximated with double Gaussian profile in ArF lithography

A method has been developed for correcting line width variations due to midrange flare with a scattering range of over a few tens of micrometers (which we call local flare). It is shown that the conventional single Gaussian point spread function (PSF) is not sufficient and that a double Gaussian point spread function is needed to explain the line width variation caused by local flare. The remaining errors after correction are discussed under the assumptions that the mask correction is linear with respect to local flare intensity and is independent of pattern layout considering the order of the local flare correction (LFC) and optical proximity correction (OPC). This simple sizing method can reduce the critical dimension (CD) variation regardless of whether LFC is done before or after OPC. The LFC performance was evaluated using actual 90-nm-node LSI data. A much faster correction time than that of OPC was achieved by introducing the area density map method. The CD variation due to local flare was reduced from 22 to 5 nm.

Proximity effect correction using pattern shape modification and area density map

A proximity effect correction program in which forward scattering is corrected by shape modification and backscattering is corrected by dose modulation is developed. The amount of the shape modification is determined in such a manner that the full width at half maximum of the forward scattering profile is equal to the designed size. The half maximum of the forward scattering profile is equalized by the dose modulation after the amount of the backscattering is evaluated by the area density map method. This algorithm automates pattern biasing to improve the resolution and assures the resulting pattern size is as designed. The following features are included to improve the conventional methods: The area density map is smoothed iteratively to include higher order effect. Smaller meshes are used for better discretization accuracy. Auxiliary shots are generated to refine correction units where the spatial profile of the deposited energy is steep. The corrected results of 60 nm lines are also presented.

Process variation-aware three-dimensional proximity effect correction for electron beam direct writing at 45nm node and beyond

The simplified electron energy flux (SEEF)model by which the backscattered energy distribution in the multilayered structure is calculated has been applied to the analysis of critical dimension (CD) variations caused by the thickness variations in copper interconnect. The SEEF model defines the reflection, downward transmission, and upward transmission of electron energy fluxes in each layer. Parameters of the SEEF model are expressed as functions of the depth from the substrate surface and are modified by the approximation in regard to the thickness variation. Using this approach, the process window for the dose and thickness variation has been analyzed quantitatively and the necessity of improving the process window has been confirmed especially at 45nm node and beyond. Moreover, a variation-aware proximity effect correction method, in which CD variations caused by process variations are reduced and dose margins for various patterns with the same linewidth are equalized, is proposed. The correction meth...

Three-Dimensional Proximity Effect Correction for Multilayer Structures in Electron Beam Lithography

Proximity effects in multiwiring layers including heavy-metal materials such as tungsten (W) plug are crucial. In this paper, a novel three-dimensional proximity effect correction method which is based on the simplified electron energy flux (SEEF) model combined with the extended area density map method to multilayer structure is proposed. In this SEEF model, electron energy fluxes transmitted and reflected at each layer are discussed and their maps are reconstructed repeatedly by distributing and gathering electron energy fluxes at each layer. The resultant final map of electron energy flux at the surface layer under the resist contributes as the backscattering energy deposited in the resist. Our new correction method has been confirmed by the experiments to powerfully correct the proximity effects in a 3-layer structure. The screening effect due to the W plug array is first observed and can also be corrected by the proposed method.

3D proximity effect correction based on the simplified electron energy flux model in electron-beam lithography

We have confirmed the adequacy of simplified electron energy flux (SEEF) model which can be used in proximity effect correction (PEC) in electron beam lithography. The SEEF model enables calculation of the backscattering energy in a multiwiring structure by obtaining a transmission and reflection energy flux map. We prepared a substrate which contained three pairs of W-plug layers and inter-metal dielectric (IMD) layers, and obtained parameters for correction. The extracted transmittance and reflectance were 1 and 0 for the dielectrics, and 0 and 1.7 for the W plugs. The backscattering energies calculated by using these parameters corresponded with experimental data under the various conditions. We also extracted the scattering range of incident and reflected electrons in dielectrics. We found that the ranges of the reflected electrons were greater than those of the incident electrons because of a wider spread of angle. PEC based on the SEEF model enabled high CD accuracy even at the end of the W-plug are...

Applying photolithography-friendly design to e-beam direct writing in 65-nm node and beyond

It is commonly known that maskless lithography is the most effective technology to reduce costs and shorten the time need for recent photo-mask making techniques. In mass production, however, lithography using photo-masks is used because that method has high productivity. Therefore a solution is to use maskless lithography to make prototypes and use optical lithography for volume production. On the other hand, using an exposure technology that is different from that used for mass production causes different physical phenomena to occur in the lithography process, and different images are formed. These differences have an effect on the characteristics of the semiconductor device being made. An issue arises because the chip characteristics are different for the sample chip and the final chip of the same product. This issue also requires other processes to be changed besides switching to the lithography process. In our previous paper, we reported on new developments in an electron-beam exposure data-generating system for making printed images of a different exposure source correspond to each other in lithographic printing systems, which are electron beam lithography and photolithography. In this paper, we discuss whether the feasibility of this methodology has been demonstrated for use in a production environment. Patterns which are generated with our method are complicated. To apply the method to a production environment we needed a breakthrough, and we overcame some difficult issues.

Study of device mass production capability of the character projection based electron beam direct writing process technology toward 14 nm node and beyond

Techniques to appropriately control the key factors for a character projection (CP) based electron beam direct writing (EBDW) technology for mass production are shown and discussed. In order to achieve accurate CD control, the CP technique using the master CP is adopted. Another CP technique, the Packed CP, is used to obtain suitable shot count. For the alignment on the some critical layers which have the normally an even surface, the alignment methodology differ from photolithography is required. The process that etches the SiO2 material in the shallow trench isolation is added and then the alignment marks can be detected using electron beam even at the gate layer, which is normally on an even surface. The proximity effect correction using the simplified electron energy flux model and the hybrid exposure are used to obtain enough process margins. As a result, the sufficient CD accuracy, overlay accuracy, and yield are obtained on the 65 nm node device. The condition in our system is checked using self-diagnosis on a regular basis, and scheduled maintenances have been properly performed. Due to the proper system control, more than 10,000 production wafers have been successfully exposed so far without any major system downtime. It is shown that those techniques can be adapted to the 32 nm node production with slight modifications. For the 14 nm node and beyond, however, the drastic increment of the shot count becomes more of a concern. The Multi column cell (MCC) exposure method, the key concept of which is the parallelization of the electron beam columns with a CP, can overcome this concern. It is expected that by using the MCC exposure system, those techniques will be applicable to the rapid establishment for the 14 nm node technology.

Model-based OPC/DRC considering local flare effects

Local flare is caused by scattered light from lens surfaces, and it causes the printed line width to vary or degrades printing accuracy. Consequently, local flare must be taken into account when manufacturing IC devices that use lithography generations of less than 90 nm. In particular, an OPC (Optical Proximity Correction) tool with the ability to compensate local flare effects is required to maintain a high degree of printing accuracy. For model-based OPC to work properly, the predicted line width or shape given by a simulator should show good agreement with experimental results. Local flare intensity is calculated from the optical intensity in the absence of local flare, in order to take diffraction effects into account. An aerial image considering local flare effects is given simply by the sum of optical intensity and local flare intensity. To account for local flare effects in a practical manner, the local flare intensity is converted into a variation in the threshold for OPC/DRC (Design Rules Checking) that predicts the desired shape. This paper describes the impact of local flare, the simulation model including local flare effects, and its results. The simulation results show good agreement with the experimental results, indicating that effective OPC/DRC using this method is possible.

High-speed proximity effect correction system for electron-beam projection lithography by cluster processing

We have proposed the techniques of the pattern shape modification method and the pattern density reduction method as a proximity effect correction (PEC) for electron-beam projection lithography.