Pattern Density Variation Research Articles

Correlation between pattern density and linewidth variation in silicon photonics waveguides.

We describe the correlation between the measured width of silicon waveguides fabricated with 193 nm lithography and the local pattern density of the mask layout. In the fabrication process, pattern density can affect the composition of the plasma in a dry etching process or the abrasion rate in a planarization step. Using an optical test circuit to extract waveguide width and thickness, we sampled 5841 sites over a fabricated wafer. Using this detailed sampling, we could establish the correlation between the linewidth and average pattern density around the test circuit, as a function of the radius of influence. We find that the intra-die systematic width variation correlates most with the pattern density within a radius of 200 µm, with a correlation coefficient of 0.57. No correlation between pattern density and the intra-die systematic thickness variation is observed. These findings can be used to predict photonic circuit yield or to optimize the circuit layout to minimize the effect of local pattern density.

Optimization of in vitro and ex vitro regeneration and micromorphological studies in Basella alba L.

The optimum concentrations of the plant hormones for in vitro regeneration and subsequent effect of auxins on rooting (in vitro and ex vitro) of shoots of Basella alba L. have been investigated in present study. Nodal shoot segments were used as explants to initiate the cultures. The bud breaking from explants was observed within 1week of incubation on agar gelled Murashige and Skoog's (MS) medium. Multiple axillary shoots (7.30±0.56 shoots per explant) were induced on MS medium supplemented with 2.0mg/L 6-benzylaminopurine (BAP). The shoots were multiplied (maximum 17.10±0.44 shoots per explant) on the same medium fortified with 0.5mg/L each of BAP and Kin (Kinetin) +0.1mg/L IAA. These shoots were excised and rooted in vitro (10.73±0.92 roots per shoot) on half-strength MS medium augmented with 2.0mg/L indole-3 butyric acid (IBA). Hundred percentage success rates have been achieved by ex vitro rooting of the in vitro regenerated shoots with IBA at 300mg/L. The in vitro and ex vitro rooted shoots were acclimatized in greenhouse and subsequently transferred to the natural field conditions where 100% survival rate was reported. The ex vitro rooting method was found more advantageous than in vitro rooting in terms of time, energy and survival percentage of B. alba. A comparative foliar micromorphological study of B. alba was conducted to understand the micromorphological changes in plants while shifting from in vitro to the in vivo conditions in terms of variations in stomatal index, venation pattern and vein density, and the arrangement of crystals. The study could help in understanding the response of in vitro raised plants towards in vivo environment.

Influence of discrete drop locations on film thickness uniformity in UV- nanoimprint lithography

Multi-nozzle inkjetting is the material deposition approach for a variant of UV-nanoimprint lithography called Jet-and-Flash Imprint Lithography (J-FIL). J-FIL has several advantages with respect to addressing pattern density variations in the template as well as achieving low material waste when compared with spin-coating. In this work, the influence of discrete drop placement in J-FIL on residual layer thickness uniformity has been investigated with the help of a novel nonlinear lubrication theory model, which takes into account the compliant nature of the template in the presence of a moving contact line. This work is directed at thin residual layers (sub-20nm), where a correlation exists between minimum drop resolution, inkjet nozzle pitch and residual layer thickness uniformity. Numerical simulations reveal that the non-uniformity resulting from discrete drop placement can exceed desired process tolerances when low film thicknesses are desired with relatively larger drop volumes. The results have been verified experimentally to reveal the same trend. This work can be useful in determining the correlation of inkjet drop resolution with inkjet nozzle pitch to meet process tolerances in the J-FIL process.

In vitro regeneration frequency, micro-morphological studies and ex vitro rooting of Hemidesmus indicus (L.) R. Br.: a multi-potent endangered climber

Hemidesmus indicus is an endangered medicinal plant of Peninsular India. A rapid micropropagation method using nodal segments of a 4 year old plant has been achieved in the present study. The nodal explants (2.0–3.0 cm long) were harvested from actively growing shoots of conventionally raised plants and cultured on Murashige and Skoog (MS) medium supplemented with 2.0 mg l−1 6-benzylaminopurine (BAP). Hundred percent explants responded with 5.2 ± 0.25 cm long multiple shoots (9.0 ± 0.53) from the nodal meristems. The shoots were further multiplied enormously (272 ± 4.12 shoots per explant) by repeated subculture of mother explants and freshly induced shoot clumps on MS medium with the reduced concentrations of BAP (1.0 mg l−1), kinetin (Kin; 0.5 mg l−1) and indole-3 acetic acid (IAA; 0.1 mg l−1) within 4 weeks. Highest root induction (62.0 ± 0.54 roots per shoot) was observed on 1/4th strength MS medium supplemented with 3.0 mg l−1 indole-3 butyric acid (IBA). About 96 % shoots were rooted (45.0 ± 0.48 roots per shoot) by ex vitro methods when the cut ends of the shoots pulse treated with IBA (400 mg l−1) for 5 min. The in vitro as well as ex vitro rooted plantlets were acclimatized successfully in the greenhouse. Ex vitro rooted plantlets exhibited higher percentage (98 %) of survival as compared to the in vitro rooted plantlets (91 %) in the field conditions. There were not any observable differences between in vitro propagated and field transplanted plantlets. A comparative foliar micro-morphological study of H. indicus was conducted to understand the micro-morphological changes in the plants while shifting from in vitro to the in vivo conditions in terms of variations in stomata, venation pattern and vein density, and trichomes. The aforementioned protocol could be successfully used for the large-scale multiplication and conservation of germplasm of this endangered plant species.

Advanced lithography and electroplating approach to form high-aspect ratio copper pillars

Advanced packaging technologies continue to enable the semiconductor industry to meet the needs for ever thinner, smaller and faster components required in mobile devices and other high performance applications. In the early days of advanced packaging, C4 solder bumps were the alternative to wire bonding. Although lead-free solder remains one of the preferred methods for assembly, tall copper structures (copper pillars) are becoming the standard interconnect solution for many applications. A process of lithography and subsequent electroplating are the mainstream process for today's copper pillar formation on wafer level for high-end flip chip devices. The latest trends in advanced packaging require another technology development when it comes to copper pillars. Modern integration schemes such as 2.5D interposer as well as 3D stacking have pushed the limits of standard lithography and copper electroplating capabilities. Specifically, the need for fine-pitch high aspect ratio copper pillars represents a challenge. In addition, the trend towards rectangular panel-based packaging as seen with glass interposers or panel fan-out (P-FO) devices demands a challenging scale-up of lithography and electroplating equipment and processing capabilities. This work specifically focuses on the formation of high-aspect ratio copper pillars in excess of 100μm by means of stepper-based lithography followed by electroplating. A unique test vehicle has been created to evaluate the process latitude for lithography for different resist materials as well as the specific electroplating challenges associated with these tall and narrow structures. The paper investigates the influence of key parameters such as CD uniformity, pattern density variations and resist profile on the critically important pillar height uniformity across the wafer or panel. In addition, the resist profile behavior at the substrate interface is being examined as it influences undercut behavior during wet etch of the plating seed layer. A number of wet and dry-film resist materials and appropriate lithography processes (spin coat or laminate, expose, develop) followed by copper plating based on varying chemistries and process parameters are being explored. The paper also summarizes the current requirements for the above mentioned lithography and plating processes as seen in the industry today.

Chemical Mechanical Planarization: Advanced Material and Consumable Challenges

The unprecedented and continuing increase in the computational power and functionality of microelectronic devices, extending beyond more-than-Moore, are driven by the ever shrinking dimensions of logic and memory circuits, now numbering over a billion and half, all packed into an area of ∼15 cm2. As the costs of these devices drop, they have become ubiquitous across the world, from high performance computing to smart phones to driverless cars to children’s toys. The most common substrate for these devices continues to be Si and the process sequence used to fabricate these devices is frequently divided into front-end-of-the-line (FEOL) and back-end-of-the-line (BEOL) processes, each with its own peculiar technological and manufacturing yield challenges. Once all the active circuit elements are fabricated in the Si substrate using FEOL processes, they need to be interconnected and also connected to an external power source to become functional. While new materials continue to be incorporated at various levels into the processing sequence, copper remains the metal of choice for the interconnect wiring which is created using BEOL processes. The Cu wiring itself is electrically insulated by a low-k dielectric and protected by a diffusion barrier layer that can also act as an adhesion promoter and, depending on its electrical conductivity, enable direct electroplating of Cu. The characteristics of the low-k dielectric and the barrier layer have an immense influence on the manufacturing process sequence as well as the performance and long term reliability of the devices. Significant advances continue to be made in identifying newer sets of materials to fill these roles, especially for the narrower Cu lines where the space for the liner is limited, along with the associated processing steps. While advances in lithographic techniques facilitated the feature size reduction that has already reached 14 nm in high volume commercial production and seemingly headed lower, the same advances in lithography also demand ever more stringent surface planarity requirements, both locally across the chip and more globally across the entire wafer. Chemical mechanical planarization (CMP) is the only technique that has so far been capable of achieving these demanding requirements at the large volume manufacturing level in spite of it being a counter intuitive process that is prone to non-uniform material removal, defects and contamination caused by pad debris, by the billions of abrasive particles contacting the wafer surface and by the host of reactive and nonreactive chemicals used in the planarization process. Mitigating such yield-diminishing factors is one of the major challenges driving the advances in CMP technology and led to improvements in the polisher components like wafer carrier, slurry delivery system, retainer ring, backing film, etc., as well as all the other consumables including polishing pads, conditioners, and polishing slurries. Given the heterogeneity and pattern density and feature size variations of the films being planarized on the wafer surface, process

Direct Patterning of TiO2 Using Step-and-Flash Imprint Lithography

Although step-and-flash imprint lithography, or S-FIL, has brought about tremendous advancement in wafer-scale fabrication of sub-100 nm features of photopolymerizable organic and organo-silicon-based resists, it has not been successful in direct patterning of inorganic materials such as oxides because of the difficulties associated with resist formulation and its dispensing. In this paper, we demonstrate the proof-of-concept S-FIL of titanium dioxide (TiO(2)) carried by an acrylate-based formulation containing an allyl-functionalized titanium complex. The prepolymer formulation contains 48 wt % metal precursor, but it exhibits low enough viscosity (∼5 mPa·s) to be dispensed by an automatic dispensing system, adheres and spreads well on the substrate, is insensitive to pattern density variations, and rapidly polymerizes when exposed to broadband UV radiation to give a yield close to 95%. Five fields, each measuring 1 cm × 1 cm, consisting of 100 nm gratings were successively imprinted. Heat-treatment of the patterned structures at 450 °C resulted in the loss of organics and their subsequent shrinkage without the loss of integrity or aspect ratio and converted them to TiO(2) anatase nanostructures as small as 30 nm wide. With this approach, wafer-scale direct patterning of functional oxides on a sub-100 nm scale using S-FIL can become a distinct possibility.

A Study of 65nm Silicon Etch

During the process development and mass production of 65nm technology node, the role of silicon etch is essential to meet more stringent device requirements. The control of shallow trench isolation (STI) depth uniformity and poly gate profile necessitate the combination of more advanced silicon etch methodology, in-situ measurement and integration scheme. This paper presents a study of the difficulties and corresponding solutions in 65nm silicon etch from the point view of process development and mass production. In development phase, the STI trench profile and the depth uniformity of STI depth can be well controlled by etch recipe tuning. In mass production phase, we focused on the impact of different products on the inter-field variation of STI depth. Results show a good correlation of depth to pattern density variation. Such relationship has been utilized in feed-forward mode to fulfill the tightening and robust process control. Besides, we also address the influence of oxide amount variation in STI fabrication and STI step height difference on poly gate profile and pits defect.

Pattern Density Effect in 65nm Logic BEOL Al-Pad Etch

As semiconductor device is being scaled down to 65nm node and below, the control of pattern density effect in back end of line (BEOL) etch becomes more crucial to ensure the on-target production delivery. Pattern density difference normally stems from the specific design of various products. This paper addresses the challenges and solutions to reduce the influence of pattern density variation in 65nm BEOL logic Al-pad etch processes. Challenges include the impact of pattern density on A) corrosion window with different Al-pad photo transmission rates (TR); B) within-wafer profile loading between Al-line (dense feature) and Al-pad (iso feature). Polymer mode has been proven as one of potential mechanisms for these issues. The corresponding feasible solutions focus on A) the adjustment of polymer gas ratio for any product based on its actual pattern density. B) the optimized combo of chemicals and bias power to reduce the within-wafer dense and iso loading.

Residual layer uniformity using complementary patterns to compensate for pattern density variation in UV nanoimprint lithography

How to form a thin and uniform residual layer, which is difficult to be created for a feature with nonuniform pattern densities, is of critical importance in nanoimprint lithography since residual layer removal by a reactive ion etching process will result in poor pattern transfer fidelity for nonuniform residual layers. A capacity-equalized mold using complementary cavity patterns to balance the imprinted volume of the feature with pattern density variation was verified to be a good method against pattern density variation for producing a uniform residual layer. To obtain an insight into the validity of the capacity-equalized mold, the effects of the introduced complementary patterns for capacity equalization on the residual layer, at locations that were not only at a distance away from the introduced complementary patterns but also the ones that were very close to the introduced complementary patterns, were carefully studied. It was found that a capacity-equalized mold with even very coarse complementary patterns as large as 10 times the minimum width of original patterns could result in a good uniform residual layer. It showed that the residual layer thickness was mainly determined by the volume of the capacity of the pattern trench with varied depths per unit area, but not by the size of the complementary patterns. Furthermore, the local nonuniformity induced by the complementary patterns themselves was also studied. The authors found that this local nonuniformity had little influence on producing a uniform residual layer that contributed to the low viscosity of the UV-curable resin. The authors also found that the nonuniformity of the residual layer was produced even by using a capacity-equalized mold due to the presence of air bubbles.

Homogeneity of Residual Layer thickness in UV Nanoimprint Lithography

In nanoimprint lithography, control of residual layer thickness is a very important issue. Pattern density variation is inconvenient for nanoimprint lithography but UV nanoimprint is considered more adaptive to pattern density variation thanks to the higher fluidity of UV-curable resin. Despite this consideration, methods to overcome pattern density problems have been developed and adopted in UV nanoimprint lithography. These methods work well; however, it is still remains there a question of whether residual layer thickness uniformity is improved without such methods. In this study, UV nanoimprint is carried out using a conformable contact mechanism, and the impact of pattern density variation and pressing time of nanoimprint on the residual layer profile is investigated for an initially thin UV-curable resin. After recess filling, UV-curable resin moves very locally so as to make the residual layer smoothly change, but does not move sufficiently for the residual layer to be modified across the entire imprint field. For a longer pressing time, the residual layer thickness is decreased only at the edges. A small amount of the UV-curable resin was expelled from the mold, but most was retained between the mold and wafer, and the UV-curable resin moved inward. For realization of a thin and uniform residual layer, the residual layer must be thin throughout the imprint field from the beginning of the pressing process; otherwise the resulting residual layer that is thick only at peripheral regions must be thinned by a long pressing time.

Minimizing Device Variation Caused by RTA Temperature Variation Across the Shot Field

Spike Rapid Thermal Annealing (RTA) is commonly used method for source and drain dopant activation in 65nm CMOS technology. It is found that the Idsat variation is very sensitive to RTA temperature. To better control the Idsat uniformity across the shot, a systematic study on STI and poly pattern density distribution across the shot field and their effects on the RTA temperature was carried out. It was demonstrated that the STI and poly pattern density variation across the field will result in more than 10ºC RTA temperature variation. To minimize the effect, an optimization of RTA ramp rate and peak temperature was studied. Source/drain (S/D) extension and S/D implant optimization has also been done for the reduction of PMOS device Idsat temperature sensitivity

Investigating the Planarization Behavior of High Selective Slurry with Initial Step Height and Pattern Density

The purpose of this study is to investigate the planarization behavior of high selective ceria slurry in terms of topography and pattern density variation. Planarization experiments have been performed using ceria slurry with various initial step heights and surrounding pattern density on active trench and shallow trench isolation. The threshold step height was measured in various layouts which showed different pattern density ranges, and the pattern density effect on the threshold step height has been discussed. The planarization capability of high selective slurry and the removal rate of the high density plasma oxide are strongly dependent on the whole chip topography rather than on the micropattern density.

Nanoimprint with thin and uniform residual layer for various pattern densities

Pattern density variation is uncomfortable for nanoimprint lithography which uses a moldable material supplied as a thin film, because the variation of pattern density causes variations of residual layer thickness reflecting on the local pattern density. To solve the problem, a new type of mold “capacity-equalized mold”, which has constant averaged depth regardless of pattern density, was fabricated and the structure of the mold was inspected. UV nanoimprint was then carried out using the mold and thickness and uniformity of the residual layer were investigated. An average thickness of 33.2 nm with a standard deviation of 3.4 nm was obtained for the mold pattern layout with a pattern density of from 0.25 to 0.75. It was found that a standard deviation of 1.2 nm was achieved for pattern density variation of from 0.33 to 0.67 by excluding artifacts.

Transport Phenomena in the Production and Use of Expanded Polystyrene Patterns in Lost Foam Casting

Experiments were carried out to study the effect of process and design variables on defect formation in the lost foam casting process. Emphasis was placed on the production of expanded polystyrene foam patterns and the use of these patterns to create desired castings. Spatial pattern density variation caused by varying the fill and canister pressure for molds with varying distance between injector and opposing wall was measured. The heat transfer coefficient and gas pressure in the gap between the metal front and the foam pattern were also measured. The study found a close correlation between the production of a uniform pattern and the production of a defect-free casting.

Dependence of Oxide Pattern Density Variation on Motor Current Endpoint Detection during Shallow Trench Isolation Chemical Mechanical Planarization

In this study, we evaluate the limitations associated with variable shallow trench isolation (STI) oxide pattern densities for accurate motor current endpoint detection during chemical mechanical planarization (CMP). Results indicate that repeatable motor current endpoint detection can be achieved for STI wafers with oxide pattern density variations of up to 17.4%. Furthermore, results show that a dependence exists between the STI oxide pattern density variation and motor current endpoint success during polishing. According to the findings of this study, a suitable motor current endpoint detection system could yield successful termination points for STI polishing, as well as reduce the need for polishing reworks.

Simulation on Planarization Process of Patterned Si Wafer : Improvements in accuracy of simulation model(M^4 processes and micro-manufacturing for science)

Many models have been proposed for simulation of planarization process of patterned Si wafer. In the previous report, an analytical model has been established to incorporate variations in pattern density, step height of an oxide layout, the tool stiffness and in feed scheme. In this paper, we aimed to further improving the accuracy of the simulation via introducing an actual oxide layout. Instead of a rectangular layout, a triangular layout with multi-step height was used for the simulation model to clarify the effect of pattern profile.

The impact of CMP and underlying back-end topographical features on losses in deposited dielectric waveguides

The bending losses in rectangular dielectric waveguides deposited on a chemical mechanical polished (CMP) surface above the metal interconnect/interlayer dielectric stack of a processed Si wafer are modeled and estimated. CMP efficiently removes local topography and microroughness, but leaves long-range surface profile undulations due to variations in the metal pattern density. These surface undulations are then transferred to the waveguides deposited on this surface. A beam propagation method (BPM) waveguide simulation program and an equation for bending loss developed by Marcuse have been used to examine the bending losses seen by waveguides deposited on such a surface. In order to simplify the simulation of the bending losses of the waveguides, the undulations are modeled as a series of arcs, which is shown to be a good approximation. It was determined that under typical conditions, the bending losses may be ignored as they are less than 0.1 dB/cm, which is below the range of typical propagation losses for a straight guide.

Effects of Macroscopic Pattern Density and O2 Addition on Chamber Stability during Silicon Nitride Layer Etching in UNITY II-IEM Plasma Source

Effects of the wafer level pattern density on chamber particle generation during silicon nitride (Si3N4) layer etching have been studied in the medium density plasma source, UNITY II-IEM. It was found that the macroscopic pattern density of the etched layer strongly affects the etching environment and subsequently affects the chamber stability. The abrupt change in the macroscopic pattern density of the etched layer, especially when the pattern density is lowered, can sometimes results in the hazardous chamber particle generation. Experiments were performed in order to cope with the chamber particle generation induced by the macroscopic pattern density variation. Controlling the F/C ratio within the plasma by varying the amount of feeding O2 gas was proven to be an efficient way to prevent the occurrence of the chamber particles. Based on our experimental results, the mechanism for the chamber particle generation and that for the reduction will be discussed.

Pattern density and deposition profile effects on oxide chemical-mechanical polishing and chip-level modeling

Test masks for characterizing pattern-dependent variation of the remained thickness after chemical-mechanical polishing (CMP) were designed by taking the experimentally obtained interaction distance into consideration. Polishing behaviors were characterized by taking into consideration layout pattern density and pitch variations using these masks. Deposition profile effects were also compared between plasma-enhanced tetra ethyl ortho silicate (PETEOS) and high-density plasma (HDP) oxide. Both the measured post-CMP thickness and the expected oxide pattern density after the consideration of deposition profile effects showed a good correlation with respect to the pitch variation for a constant layout pattern density. Also, the relationship between remained thickness and true layout pattern density was deduced. Chip-level CMP modeling was investigated to obtain the post-CMP thickness distributions across a die from its design layout and a few oxide film and CMP parameters. The experimental CMP results agreed well with the modeling results. The effective dummy filling results were shown to achieve a smaller pattern density variation, which resulted in better post-CMP thickness uniformity. Whether the resulting oxide thickness could be predicted for any location on a die for an arbitrary layout, if the effective pattern density distributions are calculated, was discussed.