G. Bouton, B. Connolly, D. Courboin, A. Di Giacomo, F. Gasnier, R. Lallement, D. Parker, M. Pindo, J. C. Richoilley, F. Royere, A. Rameau-Savio, M. Tissier
Scattering bars (SB) are sub-resolution lines added to the original database during Resolution Enhancement Techniques
(RET) treatments. Their goal is stabilizing the CD of the adjacent polygons (by suppressing or reducing secondary
diffraction waves). SB increase the process window in the litho process by lowering the first derivative of the CD.
Moreover, the detailed knowledge of SB behavior around the fab working point is a must for future shrinks and for
preparing the next technology nodes.
SB are inserted in the generation of critical levels for STMicroelectronics 90 nm technology embedded memories before
invoking the Model for Optical Proximity Corrections (MBOPC). This allows the software to calculate their contribution
to the intensity in the aerial image and integrate their effects in Edge Proximity Error (EPE) corrections. However the
Rule-Based insertion of these assist features still leaves behind occurrences of conflicting priorities as in the image below. (See manuscript PDF)Detection of Hot Spots in 2D simulations for die treatment validation (done on BRION equipment on each critical level
before mask making) is in most cases correlated with SB singularities, at least for CD non-uniformity, bridging issues
and necking in correspondence with OPC fragmentation effects.
Within the framework of the MaXSSIMM project, we established a joint STMicroelectronics and Toppan Photomasks
team to explore the influence of assist features (CD, distance), convex and concave corner rounding and CD uniformity
by means of specific test patterns. The proposed study concerns the algorithms used to define the mask shop input as
well as the physical mask etching.
A set of test cases, based on elementary test patterns, each one including a list of geometrical variations, has been defined.
As the number of configurations becomes rapidly very large (tens of thousands) we had to apply Design of Experiments
(DOE) algorithms in order to reduce the number of measurements to a reasonable range (a few hundred). The proposed
test cells have been inserted in the scribe lanes of an engineering Gate mask of one of STMicroelectronics' high volume
products. Real Hot Spots, detected in the product chosen as the test vehicle, have also been submitted to the same
variations and inserted in scribe blocks. In parallel with OPC-like scribe layouts, four best-guess treatments were applied, on the same critical mask, to assess transistor performance and yield impact by standard wafer splitting on engineering
lots.
The advanced binary 4×6" reticle for 193nm exposure has been manufactured by Toppan Photomasks in the AMTC
facility in Dresden using the standard production process on the NuFlare5000 e-beam writing platform.
The exploration of the parameter space around the current working point will determine if the current process settings
already represent an optimum or if there is room for significant improvement of the wafer manufacturing process.
KEYWORDS: Etching, Photomasks, Critical dimension metrology, Picture Archiving and Communication System, Photoresist processing, Lithography, Scanning electron microscopy, Standards development, Semiconducting wafers, Process control
In previous study the high impact of development by-products on Critical Dimension (CD) through the microloading effect has been demonstrated for a Novolak resist. In this paper, through further tests involving Chemically Amplified Resist (CAR) and Novolak resist, the microloading effect of development is characterized and tentative mechanism is presented.
Megasonic Immersion Development (MID), a high flow rate development technique similar to the Proximity Gap Suction Development (PGSD), was used and compared with spin spray development and puddle development.
On TOK IP3600, a Novolak resist, we have explored a wide range of process conditions with MID. Developer temperature was varied from 5°C to 40°C with TMAH developer concentration of 1.9% and 2.38% resulting in an isofocal dose range of 90mJ to 190mJ. Exposure Focus Matrix (EFM) with a specific microloading pattern and resist cross sections were performed. The best conditions are quite far from the standard process advised by the resist supplier. Very nice standing wave profile was obtained at high temperature development.
On CAR, JEOL 9000MVII, a 50kV e-beam vector scan tool, and ETEC ALTA 4300, a DUV raster scan tool, were used with different develop process techniques including MID. FujiFilm Arch FEP-171 positive CAR and Sumitomo NEB-22 negative CAR were used on 50kV writing tool. Sumitomo PEK-130 was used on DUV writing tool. FEP-171 and PEK-1300 show microloading effect on high density patterns but not NEB-22.
MID shows also improved reproduction of develop features in the chrome and a 20% improvement of CD uniformity. The results of this study seem to indicate that a closer look in their development process is needed for 90nm and 65nm technologies.
The move towards smaller feature size continuously requires more accurate lithography models. Part of models improvement comes from a better understanding of involved physics and chemistry. State of the art models assume development rate to be dependent on level of de-protection of resist film while development kinetics is not taken into account. Model refinements consist in getting a good model of development rate versus de-protection level. Recent studies have put in evidence the importance and the influence of development kinetics. Based on this, a new development process concept has been developed: the Proximity Gap Suction Development (PGSD). This paper presents a parallel approach to PGSD using megasonic agitation in order to improve development process understanding. Analysis has been performed by focusing on microloading effect characterization, also taking into account Critical Dimension (CD) linearity, CD iso-dense bias. Interpretation and analysis were achieved through use of DOE techniques. Results are then discussed with respect to previous PGSD studies but also to current development models. It is believed that improvement of development process could be also achieved in wafer making through the use of high flow rate development techniques such as PGSD or megasonic development.
As the CD specification on Masks is getting more tighten, the fogging effect by re-scattered incident electron at a high acceleration e-beam system and the loading effect at dry etching step due to pattern density are current critical issues for mask making. These give rise to the variation of mean CD value and the degradation of global CD uniformity. So we have to correct these effects accurately in order to meet the CD specification for design rule 0.15um or below devices. In this paper, we have applied a new positive CA (chemically amplified) resist from Fuji Film Arch co., It was written at 50 kV variable vector scan E-beam system and we tried to classify the CD error by the fogging and loading effect, respectively. Also we have compared with ZEP7000 resist, non-CAR positive type, which is used widely for conventional e-beam mask making to assess the CAR performance, especially in terms of CD error causing by the fogging effect. Through this comparison test, we found that the CD error due to the fogging effect shows somewhat different value according to resist type and writing strategy even though use same exposure dose. In this paper, we have assumed that such results are due to the difference of dose latitude. Dose latitude is different as intrinsic contrast value of each resist and writing strategy such as writing pass, should affect on beam profile (dose profile), it can also change pattern profile of resist and it can finally cause a dose latitude difference. Finally, we have evaluated for CD mean error and uniformity error by fogging and etch loading as open ratio changing, respectively.
This paper describes the optimization of the key parameters (exposure and development) needed to reach CD uniformity below 20 nm necessary for 150 nm generation devices. The three factors (exposure dose, spot size and development time) were investigated by design of experiment (DOE). ZEP 7000 is an e-beam dry-etchable resist which requires higher dose than PBS and EBR-9 HS-31 usual e-beam resists. Therefore the exposure was made on a MEBES 4500 system combined with multipass gray writing strategy. A puddle development was done on a STEAG ASE500 tool. CD measurements have been done after development on LEICA IPRO system using reflective light in order to eliminate the error induced by etching. The DOE results have been interpreted separately on the X and Y axis. The results of the DOE have been verified by measuring the edge resist slope with a scanning electron microscope and by measuring chrome CD uniformity after dry etching and stripping.
Advanced reticule specifications for 150 nm generation devices require large-scale improvements to resolution and critical dimension (CD) control. Resolution can be obtained by the adoption of electron-beam (e-beam) exposure and plasma etching with zero bias processes. However, CD control cannot be achieved without a writing and development strategy optimization. This paper describes the optimization of the key parameters (exposure and development) needed to reach CD uniformity below 20 nm necessary for 150 nm generation devices. The three factors (exposure dose, spot size and development time) were investigated by design of experiment (DOE). ZEP 7000 is an e-beam dry-etchable resist which requires higher dose than PBS and EBR-9 HS-31 usual e-beam resists. Therefore the exposure was made on a MEBES 4500 system combined with multipass gray (MPG) writing strategy. A puddle development was done on a STEAG ASE500 tool. CD measurements have been done after development on LEICA IPRO system using reflective light in order to eliminate the error induced by etching. The DOE results have been interpreted separately on the X and Y axis. The results of the DOE have been verified by measuring the edge resist slope with a scanning electron microscope (SEM) and by measuring chrome CD uniformity after dry etching and stripping.
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