Joo-Yoo Hong

Photoresist Adhesion Effect of Resist Reflow Process

Making a sub-100 nm contact hole pattern is one of the difficult issues in the semiconductor process. Compared with another fabrication process, the resist reflow process is a good method of obtaining a very high resolution contact hole. However, it is not easy to predict the actual reflow result by simulation because very complex physics and chemistry are involved in the resist reflow process. We must know accurate physical and chemical constant values and many fabrication variables for better prediction. We made a resist reflow simulation tool to predict approximate resist reflow as functions of pitch, temperature, time, and array, among others. We were able to observe the simulated top view, side view, and changed hole size. We used the Navier–Stokes equation for resist reflow. We varied the reflow time, temperature, surface tension, and three-dimensional volume effect of our old model. However, photoresist adhesion is another very important factor that was not included in the old model. Thus, the adhesion effect was added on the Navier–Stokes equation, and such a case showed distinct differences in the reflowed resist profile and contact hole width from the case of the no adhesion effect.

Critical Dimension Control for 32 nm Node Random Contact Hole Array Using Resist Reflow Process

A 50 nm contact hole (CH) random array fabricated by resist reflow process (RRP) was studied to produce 32 nm node devices. RRP is widely used for mass production of semiconductor devices, but RRP has some restrictions because the reflow strongly depends on the array, pitch, and shape of CH. Thus, we must have full knowledge on pattern dependency after RRP, and we need to have an optimum optical proximity corrected mask including RRP to compensate the pattern dependency in random array. To fabricate optimum optical proximity- and RRP-corrected mask, we must have a better understanding of how much resist flows and CH locations after RRP. A simulation is carried out to correctly predict the RRP result by including RRP parameters such as viscosity, adhesion force, surface tension, and location of CH. As a result, we obtained uniform 50 nm CH patterns even for the random and differently shaped CH arrays by optical proximity-corrected RRP.

Reduction of line width and edge roughness by resist reflow process for extreme ultra-violet lithography

Extreme ultra-violet lithography (EUVL) has been prepared for next generation lithography for several years. We could get sub-22 nm line and space (L/S) pattern using EUVL, but there are still some problems such as roughness, sensitivity, and resolution. According to 2007 ITRS roadmap, line edge roughness (LER) has to be below 1.9 nm to get a 22 nm node, but it is too difficult to control line width roughness (LWR) because line width is determined by not only the post exposure bake (PEB) time, temperature and acid diffusion length, but also the component and size of the resist. A new method is suggested to reduce the roughness. The surface roughness can be smoothed by applying the resist reflow process (RRP) for the developed resist. We made resist profile which has surface roughness by applying exposure, PEB and development process for line and space pattern. The surface roughness is calculated by changing parameters such as the protected ratio of resin. The PEB time is also varied. We compared difference between 1:1 L/S and 1:3 L/S pattern for 22 nm. Developed resist baked above the glass transition temperature will flow and the surface will be smoothed. As a result, LER and LWR will be much smaller after RRP. The result shows that the decreasing ratio of LER due to RRP is larger when initial LER is large. We believe that current ~ 5 nm LWR can be smoothed to ~ 1 nm by using RRP after develop.

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.

Analysis of Microdosimetric Quantities of Mixed Radiation Fields in the Reactor Building at the Wolsong Nuclear Power Plant

A commercially available tissue equivalent proportional counter (TEPC), model FW-AD1, was used as microdosimetric detector to measure the dose equivalent rates at several workplaces in the reactor building of a pressurized heavy water reactor, the Wolsong Nuclear Power Plant unit 3 in Korea. The microdosimetric quantities including the lineal-energy distributions and the dose-mean lineal energy were determined by unfolding the measured data, and then the mean quality factors and the dose equivalent rates were evaluated. The mean quality factors at places where neutron dose rates were significant were in the range of 2.2 to 7.1, while those values were near unity at the places where gamma-ray dose rates dominated. The lineal energy spectra of the reference radiation fields at the Korea Atomic Energy Research Institute (KAERI) were also measured for comparisons. Particularly in the vicinity of the primary heat transport pump, the dose-mean lineal energy and the mean quality factor appeared similar to those values of the D20 moderated 252Cf reference field. The tool and the analysis method can be applied to characterization of other mixed radiation fields.

22nm 1:1 line and space patterning by using double patterning and resist reflow process

According to ITRS road map, it will be achieved 22 nm half pitch until 2016. However, it is hard to make although EUV, high index immersion. We have positive strategy for 22 nm half pitch with immersion and double patterning and RRP. We can make 22 nm half-pitch with hard mask by using RRP that can shrink trench pattern and double patterning that can get over resolution limitation. Immersion technology can make 44 nm half pitch in NA 1.35. When the developed resist profile can be reflow, so line is increased and space is decreased. It can be 22 nm trench pattern with 66 nm width by using RRP. Hence, we can obtain 66 nm line and 22nm space pattern by etching. And then, we can obtain 22 nm half pitch after doing double patterning. We tried to evaluate this strategy by commercial and home-made simulator.

Critical dimension control for 32 nm random contact hole array with resist reflow process

50 nm random contact hole array by resist reflow process (RRP) was studied to make 32 nm node device. Patterning of smaller contact hole array is harder than patterning the line and space. RRP has a lot of advantages, but RRP strongly depends on pattern array, pitch, and shape. Thus, we must have full knowledge for pattern dependency after RRP, and then we need to have optimum optical proximity corrected mask including RRP to compensate the pattern dependency in random array. To make optimum optical proximity and RRP corrected mask, we must have better understanding that how much resist flows and where the contact hole locations are after RRP. A simulation is made to correctly predict RRP result by including the RRP parameters such as viscosity, adhesion force, surface tension and location of the contact hole. As a result, we made uniform 50 nm contact hole patterns even for the random contact hole array and for different shaped contact hole array by optical proximity corrected RRP.

Photoresist adhesion effect of resist reflow process

Making a sub-100 nm contact hole pattern is one of the difficult issues in semiconductor process. Compared with another fabrication process, resist reflow process is a good method to obtain very high resolution contact hole. However it is not easy to predict the actual reflow result by simulation because very complex physics and/or chemistry are involved in resist reflow process. We must know accurate physical and chemical constant values and many fabrication variables for better prediction. We made resist reflow simulation tool to predict approximate resist reflow as functions of pitch, temperature, time, array, and so on. We were able to see the simulated top view, side view and the changed hole size. We used Navier-Stokes equation for resist reflow. We had varied the reflow time, temperature, surface tension, and 3-dimensional volume effect for old model. However the photoresist adhesion is another very important factor that was not included in the old model. So the adhesion effect was added on Navier-Stokes equation and found that there was a distinctive difference in reflowed resist profile and the contact hole width compared to the case of no adhesion effect.

Reflow modeling for elongated contact hole shape

Resist reflow is a simple and cost effective technique by which the resist is baked above the glass transition temperature (Tg) after the typical contact hole pattern has been exposed, baked and developed. Resist reflow method can obtain very high resolution without the loss of process margin than any other resolution enhancement techniques that can make the same linewidth. But it is difficult to predict the results of the thermal flow and the process optimization. If the results of reflow process can be exactly predicted, we can save great time and cost. In order to optimize the layout design and process parameters, we develop the resist flow model which can predict the resist reflow tendency as a function of the contact hole size, initial shape and reflow temperature for the normal and elongated contact hole. The basic fluid equation is used to express the flow of resist and the variation of viscosity and density as a function of reflow temperature and time are considered. Moreover surface tension and gravity effects are also considered. In order to build a basic algorism, we assume that the fluid is incompressible, irrotational and Newtonian. First, we consider the boundary movement of side wall and we think the basic equations for free surface flow of fluid as 2-dimensional time-dependent Navier-Stokes equations with the mass conservation equation. Surface tension acting on the interface pressure difference and gravity force that enable the resist flow are also included.

Wiggly n-dimensional object embedded in (D+1)-dimensional spacetime

Small-scale structures put on an n-dimensional object embedded in (D+1)-dimensional spacetime modify in general the energy per unit n-volume and tension (or pressure) of the coarse-grained n-dimensional object. We seek fixed points of the renormalization group equations, i.e. equations of states that are independent of the presence of small-scale structures and find that these fixed points exist only for n = 1 case (the string), especially for the Nambu-Goto strings.