One of the biggest issues in extreme ultraviolet (EUV) lithography technology is resist material development to
improve optimum exposure dose and reduce line edge roughness (LER)/ line width roughness (LWR) and resolution. In
order to attain these development targets, various kinds of challenges and innovative ideas are addressed by resist
material researchers, for instance, introduction of polymer with lower molecular weight and increase of photo acid
generator (PAG) addition amount have been presented. It is expected that these changes of resist materials will have big
influence on not only general lithography performance but also track performance.
In this paper, the application performance of EUV photoresist material, especially the spread behavior of photoresist
just after resist dispense for a coating process, is evaluated using the model resist, dynamic contact angle measurement of
resist material, dynamic drop base diameter measurement of resist droplet and so on. We have found that resist materials
with small polymer size and high PAG loading have low spread property. From these results, we propose a new
hypothesis that localized distribution of solid components that is formed just after resist dispense remains in a resist film
after pre-baking and impacts resist performance.
Exposure wavelength has been changing dramatically as semiconductor design rules shrink, and for 32nm-node fine processes and beyond, it is predicted that the drop in optical contrast when using 193nm immersion lithography exposure technology will make it difficult to ensure good resolution performance in fine and dense resist patterns. To address this problem, studies have begun on extreme ultraviolet (EUV) lithography technology and double patterning technology that uses 193nm immersion lithography as alternative technologies, but many problems have been reported at the present stage of development.
Against the above background, we investigated various process flows with the aim of reducing production processes and cost in double patterning technology that uses 193nm immersion lithography. We consequently developed an advanced process technique for use after 1st resist pattern formation and established a litho-litho-etch (LLE) process. The application of this technology decreases the number of total processes used in ordinary double patterning technology.
In this paper, we focus on double patterning technology in 193nm immersion lithography and report on the performance of our original advanced process technique and on our evaluation of double patterning technology.
The use of a conventional thermal cross-link materials such as negative resists, anti-reflective
coating (BARC), and planarizing layers does not lead to excellent planarization for multilevel
interconnects, and specially via arrays prior to trench patterning for an advance lithography.
The large thicknesses bias between the blanket areas and interconnect areas, and between the
blanket areas and via arrays are usually observed. This large thickness bias creates problems
during next lithography by narrowing the process latitude.
Recently, chemical mechanical polishing (CMP) technology has been proposed to achieve
global planarization. However, the CMP planarization technique is very sensitive to pattern
density, and chemical etching reaction had high possibility to increase the dielectric constant.
The current CMP technique still requires a new investment in the CMP equipment. In this paper, we reported another novel approach for global planarization using UV
cross-link material (XUVTM) and the dielectric ultra violet exposure unit in coater equipment
(TOKYO ELECTRON LTD CLEAN TRACKTM). This planar technique provides benefits for
reducing the thickness bias observed in the 22-65 nm generation lithography and imprint
processes. Using this technique, a remarkable reduction in via topography with 1.1 μm as a
depth and 0.9-1.0 μm as a diameter has been achieved excellent thickness bias less than 20 nm.
And, the planarization of the film obtained from the XUVTM was very high as compared with
that of the film obtained from thermal cross-link gap fill material as the reference, particularly
under severe coating conditions such as dense patterns.
With 32nm and 22nm feature size node in the near future, Double patterning type processing will be in
mainstream device manufacturing in most cutting edge Fabrication facilities. These type of processes
requires cooperation between the litho cell and the other processing modules. In a collaboration
between ASML and TEL we have developed a integrated solution to image 30nm Contacts. We
describe a novel technique to achieve a geometric shrink from a starting geometry of 65nm down to the
final feature size of 30nm for each of the two contact images Processing 2 images separately could
produce two distinct populations for alignment and critical dimensions. We will show the ability to
image 65nm contacts on a 130nm pitch with acceptable process windows and then apply the novel CD
shrink process to shrink the 65nm contacts to 30nm final dimension. The second level of contacts is
imaged in between the 1st set of contacts allowing us to image a 32nm ½ pitch contact pattern.
We show the ability to Image 2 separate sets of contacts using a split clip layout with a single
distribution for critical output parameters. We address the following process challenges:
1) Overlay capability across the slit and across the field.
2) Critical Dimension capability across the slit and across the Field.
3) Sidewall angle integrity with acceptable process window.
Using the novel CD shrink process TEL has developed and imaging capability of the an ASML 1700i
TWINSCAN, we can achieve a double pattern contact process with acceptable process capability.
Exposure wavelength is being reduced significantly, along with design rule reductions. The sub-100-nm node process is currently underway with 193-nm lithography. The problems that need to be solved for the shift in wavelength from 248-nm to 193-nm lithography are those attributed to resist materials, such as plasma resistance, SEM (scanning electron microscope) shrink, and problems attributed to processes, such as pattern collapse and deposition defects (Fig. 1). Although thin films are preferable to improve resist resolution limits, pattern collapse is more likely to occur in 193-nm and 157-nm processing due to DIW (deionized water) rinse surface tension during the drying step after development. This is because of the increased A/R (aspect ratio) of the resist used to improve etching durability and lower the rigidity of 193-nm resist compared to the 248-nm resist. We had focused on controlling the capillary effect between the resist pattern and the rinse solution to avoid swelling. We evaluated the method with the use of DIW with additives rinse, and named its process “FIRM (Fishing-up by improved rinse materials)”. In this paper, we report the effectiveness of the FIRM treatment for each resist by using a dispenser of track system. We had confirmed the pattern collapse within the wafer, the process margin, CD (critical dimension) variation, CDU (CD uniformity), Defect test and, the effectiveness of the FIRM treatment in the etching process. Results indicated that the FIRM process could be used in mass production. Additionally, we had investigated application of this method to the sub-65-nm node process. We created a 55-nm line (Pitch 200-nm), with A/R = 4.47 by overdosing and performed the FIRM treatment. We were able to confirm that the FIRM treatment improved the results while all patterns had collapsed after a standard development. We believe that the FIRM treatment will be applicable to the 65-nm node.
The device design rule is continuously shrinking toward optical resolution limit where k1 factor is below 0.3. The requirement for 193 nm photoresist below 90 nm node is quite challenging at the manufacturing phase. Using DI water rinse after development gives a significant amount of line collapse when the aspect ratio is over 3. To avoid line collapse, we co-developed special rinse solution for FIRM process with Tokyo Electron Ltd. Utilizing FIRM process, 90 nm dense line collapse was measured by CD SEM using focus-exposure matrices. The line collapse property has been observed using experimental 193 nm positive tone resist by varying monomer ratio of the polymer and process conditions. The surface property of the resist was also studied to investigate the interaction with rinse solution at the de-protected polymer region. However, a high surfactant concentration in the DI water rinse leads the swelling of the resist pattern profile. The resist component is the key to determine adequate surfactant concentration in rinse solution to minimize line collapse and pattern deformation
Reduction of critical dimension in lithography technology is aggressively promoted. At the same time, further resist thickness reduction is being pursued to increase the resolution capabilities of resist. However, thin film has its limitation because of etch requirements etc. As that result, the promotion of reduction results in increasing the aspect ratio, which leads to pattern collapse. It is well known that at drying step in developing process the capillary effect operates the photoresist pattern. If the force of the capillary effect is greater than the aggregation force of the resist pattern, the pattern collapse is generated. And the key parameters of the capillary effect are the space width between patterns, the aspect ratio, the contact angle of the D.I water rinse and the surface tension of rinse solution. Among these parameters the surface tension of rinse solution can be controlled by us. On the other hand, we've already reported that the penetration of TMAH and D.I water into the resist plays an important role on the lithographic latitude. For example, when we use the resist which TMA ion can be easily diffuse into, D.I water and TMA ion which are penetrated in the resist decreases the aggregation force of resist pattern and causes the pattern collapse even by the weak force against resist pattern. These results indicate that the swelling of photoresist by TMA ion and water is very important factor for controlling the pattern collapse. Currently, two methods are mainly tried to reduce the surface tension of rinse solution: SCF (Super Critical Fluid) and addition of additive to D.I water rinse. We used the latter method this time, because this technique has retrofittability and not special tool. And in this evaluation, we found that the degree of suppressing pattern collapse depends on the additive chemistry or formulation. With consideration given to process factors such as above, we investigated what factors contribute to suppressing pattern collapse for each resist platform when using additive-added rinse solutions. This report describes the results of our examinations and discussions of the pattern collapse mechanism.
Along with the trend of reducing the critical dimension in photolithography, exposure wavelength has been shortened from 248nm to 193nm. Resin structures of resist including their chemical characteristics have been altered from PHS to acrylate polymer. On the other hand, 2.38wt% TMAH developer solution is widely used, which was optimized at the time of 436nm resist process. However, since the resist backbone and chemical characteristics of 193nm resist are different from that of 436nm resist. So, TMAH concentration of 2.38wt% is not necessarily the best value for 193nm process and may even worsen the process latitude. Therefore, we have studied improvement of the process latitude such as CD uniformity, pattern defect, and dissolution mechanism of 193nm resist in developer solution, by applying Diluted Developer Solution (DDS) on 193nm resist process.