Contact Hole Patterns Research Articles

Contact hole shrink process using graphoepitaxial directed self-assembly lithography

A contact hole shrink process using directed self-assembly lithography (DSAL) for sub-30 nm contact hole patterning is reported on. DSAL using graphoepitaxy and poly (styrene-block-methyl methacrylate) (PS-b -PMMA) a block copolymer (BCP) was demonstrated and characteristics of our process are spin-on-carbon prepattern and wet development. Feasibility of DSAL for semiconductor device manufacturing was investigated in terms of DSAL process window. Wet development process was optimized first; then critical dimension (CD) tolerance of prepattern was evaluated from three different aspects, which are DSA hole CD, contact edge roughness (CER), and hole open yield. Within 70+/−5 nm hole prepattern CD, 99.3% hole open yield was obtained and CD tolerance was 10 nm. Matching between polymer size and prepattern size is critical, because thick PS residual layer appears at the hole bottom when the prepattern holes are too small or too large and results in missing holes after pattern transfer. We verified the DSAL process on a 300-mm wafer at target prepattern CD and succeeded in patterning sub-30 nm holes on center, middle, and edge of wafer. Average prepattern CD of 72 nm could be shrunk uniformly to DSA hole pattern of 28.5 nm. By the DSAL process, CD uniformity was greatly improved from 7.6 to 1.4 nm, and CER was also improved from 3.9 to 0.73 nm. Those values represent typical DSAL rectification characteristics and are significant for semiconductor manufacturing. It is clearly demonstrated that the contact hole shrink using DSAL is a promising patterning method for next-generation lithography.

Stochastic Effect on Contact Hole Imaging of Chemically Amplified Extreme Ultraviolet Resists

With the near realization of extreme ultraviolet (EUV) lithography, the critical dimension uniformity and edge roughness of contact holes have attracted much attention. In this study, the stochastic effect on contact hole patterns was investigated using a Monte Carlo method on the basis of the reaction mechanisms of chemically amplified EUV resists. The standard deviation of the number of protected units did not depend on exposure dose or acid generator concentration under the process conditions optimized in terms of the chemical gradient. However, the standard deviation of the number of protected units depended on the effective reaction radius for deprotection.

Chemical Gradient of Contact Hole Latent Image Created in Chemically Amplified Extreme Ultraviolet Resists

A contact hole pattern as well as a line-and-space pattern is a basic element for the fabrication of semiconductor devices. The critical dimension uniformity and edge roughness of contact hole patterns are critical issues for extreme ultraviolet (EUV) lithography. In this study, the quality of the latent images of contact hole patterns was investigated in terms of the chemical gradient using a simulation on the basis of the reaction mechanisms of chemically amplified EUV resists. The latent image formation of contact hole patterns was compared with that of line-and-space patterns. The latent image quality of contact hole patterns was significantly lower than that of line-and-space patterns. To obtain the same latent image quality as line-and-space patterns, the exposure dose should be increased 1.4±0.1 times. Similarly to the line-and-space patterns, the increase of acid generator concentration and effective reaction radius is effective for the enhancement of latent image quality. For the enhancement of latent image quality of contact hole patterns, the enhancement of the effective reaction radius is more effective in a low exposure dose region than a high exposure dose region.

(Invited) Negative Tone Development Process and Resist Materials with ArF Immersion Exposure Process

Negative tone development (NTD) process was proposed as a good candidate to obtain good quality in resist pattern for trench and contact hole (C/H) pattern with ArF immersion resist process. Advantages of NTD compared to positive tone development (PTD) process are discussed in detail. High volume manufacturing capabilities, mainly in the performances of CD uniformity and defectivity, are discussed. The challenges in resist material are addressed, and the material design strategies and new resist materials are introduced.

Improved imaging properties of thin attenuated phase shift masks for extreme ultraviolet lithography

The mask shadowing effect is a unique phenomenon caused by a mirror-based mask structure and an oblique incident angle of light in the extreme ultraviolet lithography process. This results in a horizontal–vertical (H–V) bias, an ellipticity in the contact hole pattern and, eventually, a patterning limit and critical dimension (CD) nonuniformity. Reducing the absorber thickness is the most effective method to minimize the mask shadowing effect, but this can deteriorate the mask image contrast. In this paper, an attenuated phase shift mask (PSM) is proposed as a potential method for extending the patterning limit to below 16 nm. By applying Mo as a phase shift layer, which has a refractive index (n) similar to that of the TaN absorber but with a lower absorption value, thin attenuated PSMs with various reflectivity values were obtained by controlling the Mo thickness. The proposed PSM consists of a 16.5-nm-thick TaN absorber layer and a 24-nm-thick Mo phase shifter on 2-nm-thick Ru-capped Mo/Si multilayers. This attenuated PSM results in 17.98% and 27.52% reductions in the mask error enhancement factor as well as 3.65 and 1.84 nm reductions in the H–V CD bias compared with the conventional binary intensity mask with a 70-nm-thick TaN absorber for the 22 nm line and space 1:1 vertical dense pattern under 0.25 and 0.33 numerical aperture illumination conditions, respectively. Moreover, a 10%–12% improved image contrast was obtained with 11%–17% reflectivity on the absorber stack, which corresponds to a 24–29 nm Mo thickness under 0.25 NA illumination conditions.

Readying Directed Self-Assembly for Patterning in Semi-Conductor Manufacturing

In recent years Directed Self-Assembly (DSA) has come up as a strong candidate technology for advanced lithography. DSA is a complementary technology that is used to enhance established projection lithography. In this paper, an overview is given of activities at imec that are driving towards readying DSA technology for implementation into semi-conductor manufacturing. Flows for line/space and contact hole pattern formation based on chemo- as well as grapho-epitaxy are available and used for understanding process sensitivities, evaluation of defect densities and the demonstration of integration approaches. The state-of-the-art of the various process flows is discussed along with the primary outstanding issues.

Characteristics of thin-film transistors based on silicon nitride passivation by excimer laser direct patterning

This study explored the removal of silicon nitride using KrF laser ablation technology with a high threshold fluence of 990mJ/cm2. This technology was used for contact hole patterning to fabricate SiNx-passivation-based amorphous-silicon thin films in a transistor device. Compared to the photolithography process, laser direct patterning using KrF laser ablation technology can reduce the number of process steps by at least three. Experimental results showed that the mobility and threshold voltages of thin film transistors patterned using the laser process were 0.16cm2/V-sec and 0.2V, respectively. The device performance and the test results of gate voltage stress reliability demonstrated that laser direct patterning is a promising alternative to photolithography in the panel manufacturing of thin-film transistors for liquid crystal displays.

Template Patterning: Flexible Control of Block Copolymer Directed Self‐Assembly using Small, Topographical Templates: Potential Lithography Solution for Integrated Circuit Contact Hole Patterning (Adv. Mater. 23/2012)

The image depicts the flexible control over the directed self-assembly of block copolymers that can be achieved using small topographical templates. On page 3107, H.-S. P. Wong and co-workers explain how differently shaped templates cause the block copolymer to self-assemble to form corresponding nanopatterns, providing a potential solution to contact-hole patterning for integrated circuits beyond the 22 nm technology node.

Flexible Control of Block Copolymer Directed Self‐Assembly using Small, Topographical Templates: Potential Lithography Solution for Integrated Circuit Contact Hole Patterning

Block copolymer directed self-assembly (DSA) using small guiding templates for contact hole patterning in integrated circuits is reported. Flexible and precise DSA control of 25 nm contact holes guided by 66 nm templates for industry-standard 22 nm static random access memory cells is experimentally demonstrated. For 22 nm random logic circuits a DSA-aware design methodology is developed and the contact holes are achieved with a critical dimension of 15 nm and overylay accuracy of 1 nm.

SRAF Optimization for sub-40nm Technology Node Contact Patterning

As 193nm immersion lithography is extended to sub-40nm technology node, how to define a single-pass contact hole patterning process with enough common lithography process window is a very challenging task. Sub-resolution assist features (SRAF) optimization is one crucial step besides illumination optimization and mask bias optimization. This paper presents a comprehensive SRAF optimization flow that achieves a set of SRAF solutions that balances SRAF benefits and mask manufacturing feasibility. As the criterion of patterning performance, the through pitch process window is investigated for different SRAF placement options based on simulated PV-band of a given process variation (focus & dose). Full chip optimization with representative layouts is also studied. Silicon level performance verification is done with final SRAF solution for through pitch pattern and typical layouts. Finally, we conclude the paper by demonstrating the overall benefit of SRAF on CD uniformity, from process capability as well as mask complexity perspectives.

Comparison of EUV Patterning between PTD and NTD for 2Xnm DRAM

The patterning performance of 3Xnm half pitch contact hole for 2Xnm DRAM was achieved from NXE3100, EUV pre-production tool last year. The local CD uniformity of EUV was comparable to that of immersion DPT (Double Patterning Technology), so the EUV patterning performance of 3Xnm half pitch is ready for mass production. But productivity progress of EUV source power is behind the plan and EUV shot noise is still problematic, so EUV resist process need to be improved for sub 3Xnm half pitch contact hole patterning. And also the patterning of sub 20nm half pitch line and space was gathered from NXE3100 but LWR and collapse are critical issues to be improved. Recently we introduced negative tone development (NTD) in immersion lithography for mass production and achieved excellent patterning performance compared to positive tone development (PTD) because negative tone development (NTD) showed better optical contrast on contact hole patterning and swelling-free property of resist film against developer. In this paper, we describe necessity of negative tone development (NTD) on EUV, optimization of mask cell size, upgrade status of resist and resolution limit between positive (PTD) and negative tone development (NTD).

Laser Direct Patterning of Organic Dielectric Passivation Layer for Fabricating Amorphous Silicon Thin-Film Transistors

In this study, a laser direct patterning process application in benzocyclobutene (BCB) organic dielectric passivation-based amorphous silicon (a-Si) thin film transistor (TFT) device fabrication has been carried out using a KrF excimer laser. A BCB organic photoresist material of 2000 nm with a dielectric constant = 2.7 served as the dielectric passivation layer in our device. Compared with conventional processes, laser direct patterning combining BCB organic photoresist dielectric passivation could eliminate at least four process steps. The etching depth of the BCB organic material passivation layer depends on the laser energy density and number of irradiation shots. The hydrogenated a-Si TFT devices are fabricated by replacing the passivation layer and contact hole patterning process. The mobility and threshold voltage reached 0.16 cm2 V-1 s-1 and -3.5 V, respectively. For TFT device performance, laser direct patterning technology is a potential method of replacing photolithography technology in the application of BCB organic dielectric passivation-based TFT manufacture.

Circular apertures for contact hole patterning in 193 nm immersion lithography

Contact hole patterning has always been one of the most challenging issues in lithography. Conventional optical proximity correction (OPC) approach for contact hole patterning involves dimensional biasing, addition of serifs at corners, and insertion of subresolution enhancement features. However, as dimensions reduce, process window enhancement resulted from conventional OPC approach encounters limitations. In this paper, a new approach for contact hole patterning is investigated. Instead of using a square shape as target of a printed feature, a circular shape is proposed. Using the proposed method improvement in aerial image quality is achieved and the average improvement in the depth of focus is around 11%. In addition, the average normalized image logarithmic slope improvement for different pitches is found to be around 15%.

Circle Patterning Technology with Negative Tone Development for ArF Immersion Extension.

Contact hole patterning for half pitch 51nm can be achieved by single exposure for mass production and for half pitch 39nm can be achieved by Litho-Etch-Litho-Etch (LELE). Currently for half pitch 32nm there is no promising solution so far, but ouble patterning and extreme ultraviolet lithography (EUV) are still competing each other for this target. In the current situation of contact hole patterning, single exposure negative tone development (NTD) shows excellent contact hole performance on fidelity, process window and CD uniformity compared to positive tone development (PTD) and finally enables to define half pitch below 50nm. In this paper, we describe necessity for circle patterning on 3-D flash, optimization of exposure condition, upgrade status of resist and device speed of 3-D flash on negative tone development (NTD) process.

Sub 30nm Node Contact Hole Patterning Using Immersion Single Exposure with Negative Tone Development

Contact hole patterning for 22nm node and beyond has become much more challenging. Since extreme ultraviolet lithography (EUV) is not yet ready, double patterning (DP) technology seems to be the most likely solution to achieve minimum half pitch of 40nm and below using immersion ArF lithography. The negative tone development (NTD) technique having excellent image contrast has received considerable attention as a possible alternative because it doesn't have the cost and throughput concerns that double patterning has. In this paper, we describe simulation and lithographic performance comparing single exposure (SE) negative tone development (NTD) technique with single exposure (SE) positive tone development (PTD) technique in terms of resolution through pitch.

Acid diffusion effects between resists in freezing processes used for contact hole patterning

Double patterning following an litho–litho-etch scheme is a possible option to create structure widths below the nominal resolution of optical light with current exposure technology. Interactions between the first and second resist layers may influence the final structure created. In this paper, we perform a model based investigation of the possible consequences of the diffusion of photo-generated acid from the second resist to the first one. As a consequence, less acid is available for the deprotection reaction, and we observe a tendency to an increase of the CD values of the primary structure. We attempt to explain observed footing effects in contact holes by this effect.

Inverse lithography for 45-nm-node contact holes at 1.35 numerical aperture

Inverse lithography technology (ILT) is a procedure that optimizes the mask layout to produce an image at the wafer with the targeted aerial image. For an illumination condition optimized for dense pitches, ILT inserts model-based subresolution assist features (AF) to improve the imaging of isolated features. ILT is ideal for random contact hole patterns, in which the AF are not at intuitive locations. The raw output of ILT consists of very complex smooth shapes that must be simplified for an acceptable mask write time. It is challenging for ILT to quickly converge to the ideal pattern as well as to simplify the pattern to one that can be manufactured quickly. ILT has many parameters that effect process latitude, background suppression, conversion run time, and mask write time. In this work, an optimization procedure is introduced to find the best tradeoff between image quality and run time or write time. A conversion run time reduction of 4.7× is realized with the outcome of this optimization procedure. Simulations of mask write time quantify the ability of ILT to be used for full chip applications. The optimization procedure is also applied to alternate mask technologies to reveal their advantages over commonly used 6% attenuated phase shift masks.

Position Shift Analysis in Resist Reflow Process for Sub-50 nm Contact Hole

Contact hole (CH) patterning, especially for the sub-50 nm node, is one of the most difficult techniques in optical lithography. The resist reflow process (RRP) can be used to obtain smaller CHs. RRP is a simple technique in which the resist, after the development process, is baked above the glass transition temperature. Heating causes resist flow, and smaller CHs can be obtained. However, RRP is an unmanageable method because of the CH offset caused by the pattern position in random array CHs. Thus we tried optical proximity correction to find a uniform critical dimension (CD) for every CH, and we obtained uniform CDs for every CH after RRP. However, we still have a CH position shift problem. Because of the difference in the amount of resist that flows into the hole in a random array during the reflow process, position shift occurs. This position shift causes an overlay error, which may exceed the overlay error budget suggested in the ITRS roadmap. In this work, we try to determine not only uniform CD size of each CH, but also the optimum conditions for correcting CH position shift by homemade simulation. Moreover, we checked the behavior of CH position shift by e-beam lithography. Consequently, we confirmed that CHs shifted in a receding direction from each other, and obtained sub-50 nm CHs in a random array by considering the position shift by simulation and experiment.

Resist Reflow Process for 32 nm Node Arbitrary Pattern

In order to decrease the size of contact holes, which is usually much larger than other patterns, the resist reflow process (RRP) has been widely used. Various types, shapes, and pitches of contact hole arrays are generated by RRP, but the use of RRP was limited to only contact hole patterns. The use of the same RRP method is expanded to 32 nm node arbitrary and complex patterns including dense line and space patterns. There might be simple one-dimensional patterns, but two-dimensional proximity conflict patterns are difficult to generate in general. In particular, the data split with proximity correction requires much attention for double patterning. 32 nm node arbitrary patterns could be generated using RRP without complex data splits when high-index fluid immersion lithography [numerical aperture (NA) 1.55] is used.

Materials and Processes of Negative Tone Development for Double Patterning Process

A new negative tone imaging with application of new developer to conventional ArF immersion resist materials is proposed to form narrow trench and contact hole patterns, which is promising for double patterning process, since it is difficult to obtain sufficient optical image contrast to print narrow trench or contact hole below 60 nm pattern size with positive tone imaging. No swelling property in the developing step realized low LWR number at 32 nm trench patterns. Uniform de-protection ratio through the depth of resist film reduced cuspy resist pattern profile causing micro-bridges at narrow trench pattern, and low frequency LWR number down to 2.4 nm. High resolution potential was demonstrated with 38 nm dense S/L under 1.35 NA immersion exposure. Better CD uniformity and LWR number of trench pattern were obtained by negative tone development (NTD) process with comparison to positive tone development (PTD) process. Excellent defect density of 0.02 counts/cm2 was obtained for 75 nm 1:1 S/L by combination of 0.75 NA dry exposure and NTD process combination. NTD process parameters impacts to defectivity were studied.