M. Komuro

Imprinting characteristics by photo-induced solidification of liquid polymer

Imprinting lithography is the most promising technology in terms of mass-production and low-cost of equipment, but thermal cycle above the glass transition temperature (more than 100/spl deg/C) will worsen positional accuracy in stitching and overlay of patterns. In this paper, we describe the imprinting process using liquid polymer, which is solidified with Ultra-violet (UV) light exposure.

Measurement of adhesive force between mold and photo-curable resin in imprint technology

Imprint lithography using photocurable resin is the most promising technique compared with other imprint lithography techniques, because it can complete a pattern transfer at room temperature. Thus, it would be able to implement practical mass-production lithography. In a previous report, however, a part of the solidified polymer was ripped away, because of strong adhesive force between the mold and solidified polymer. In order to improve this phenomenon, release coating of quartz mold and development of a photocurable resin are necessary. In this paper, we describe a measurement method of adhesive force between mold and resin using a tensile tester and, furthermore, durability of release coating material.

Bi-layer resist method for room-temperature nanoimprint lithography

In this paper, we describe a bi-layer resist method for RT-NIL using HSQ (top-layer)/AZ photoresist (bottom-layer)structures.

Room Temperature Nanoimprint Technology Using Hydrogen Silsequioxane (HSQ)

Room-temperature nanoimprint lithography (RT-NIL) technology has been developed to overcome critical dimensions and pattern placement error due to thermal expansion in the conventional nanoimprint lithography (NIL) process. We propose RT-NIL using hydrogen silsequioxane (HSQ) instead of PMMA used in conventional NIL, and demonstrate HSQ replicated patterns with 90 nm hole diameter and 50 nm linewidth realized by room-temperature replications. We performed step-and-repeat replications using HSQ on a 1.5 in. wafer and evaluated the uniformity of the imprinted HSQ patterns.

Improvement of imprinted pattern uniformity using sapphire mold

Imprint lithography is an attractive technology for LSIs era below 40-nm critical dimension from the viewpoints of high-throughput and low-cost equipment. In order to avoid a pattern placement error due to thermal expansion in the conventional thermal imprint process, we have previously attempted to replicate a mold pattern onto a liquid polymer, which was solidified using ultra-violet (UV) light irradiation at room temperature. The imprint technology based on photo-induced solidification has several advantages such as elimination of heat-up and cool-down time and possibility of step and repeat process. However part of the solidified polymer film was remained on the quartz mold surface. In order to improve this problem, in this article we propose to use a sapphire plate as a mold.

Evaluation of Line Edge Roughness in Nanoimprint Lithography Using Photocurable Polymer

To evaluate the ultimate accuracy in nanoimprint replication using photocurable resin, we studied the line edge roughness (LER) of replicated patterns using a mold pattern on a Si (110) substrate produced by anisotropic wet etching. The root mean square (RMS) for the replicated pattern LER was between 0.64 nm and 0.9 nm. This was slightly larger than that for the mold pattern. The RMS for the mold pattern was between 0.48 nm and 0.62 nm. The replicated pattern RMS shows no systematic change when the ultraviolet light exposure dose is increased from 10 mJ/cm2 to 3 J/cm2. Based on the dependence of the RMS for both of the line edge and Ti coated resin surface, we concluded that the increment of the RMS in the replicated pattern is due to the Ti coating which was carried out for scanning electron microscope observation of the replicated pattern.

Fabrication of low line edge roughness mold for photo-nanoimprint

In this paper, we fabricate low LER pattern on Spin On Glass (SOG) by simple nanoimprint process using a Si master mold obtained by anisotropic wet etching.

Photo-nanoimprint lithography combined with thermal treatment to improve resist pattern line-edge roughness

We prepared a standard resist pattern to evaluate critical-dimension atomic-force microscopy (CD-AFM) by photo-nanoimprint lithography using a trilayer resist system. Standard patterns require low line-edge roughness (LER), which is an important factor in the accuracy of high-precision CD-AFM. However, LER can easily be increased during the dry etching necessary in the trilayer resist process. The LER of final standard patterns was 2.5 nm (1 sigma), which was made using a mould of which the LER is 2.2 nm. We thermally treated the standard resist patterns to reduce the LER; the LER improved from 2.5 to 1.2 nm with the thermal treatment.

Pattern defects of nanoimprint in atmospheric conditions

A nanoimprint technology is a promising candidate to fabricate sub-50 nm patterns with high-throughput and low cost. Especially, the nanoimprint using photo solidification is suitable for precise patterning because of suppression of pattern placement errors due to thermal expansion and/or strain of mold and wafer generated by high pressure between them. However, when nanoimprint is carried out in air with rather low pressure, a small volume of air remained in concave mold pattern gives rise to pattern defects (called as bubble defects) in the replicated patterns. In this paper, we investigate characteristics of generation of bubble defects in atmospheric conditions nanoimprint.

Reproducibility of photo-nanoimprint

Nanoimprint lithography is very attractive because of proven potentials for high resolution lithographic techniques [I 1. Sub-1 0-nm-wide pattems can be fabricated by both thennalnanoimprint and photo-nanoimprint. For p hoto-nanoimprint, study on line edge roughness (LER) of patterns fabricated with a mold having ultimately smooth patterns reveals that degradation of LER attributed to the photo-nanoimprint is less than 0.1 nm [Z]. Thus, the reproducibility of photcmanoimprint is believed to be extremely high, however, no quantitative evaluation has been reported. In this paper, we discuss precise evaluation of reproducibility of photenanoimpirnt by comparing two patterns on different imprinted dies using an atomic force microscope (AFM). Photo-nanoimprint was canid out using the step-and-repeat photenanoimprinter [3] and a SOG mold having ultimately low LERs. Photo-curable polymer PAK-01 (Toyogosei) was spun on a Si wafer and 25 dies were photo-nanoimprined, where the imprint pressure was 0.5 MPa and the UV exposure dose was 1 J/cm2. Pattems on 7th die (N0.7 die) and those on 12th die (No.12 die) were alternately measured 5 times each with an AFM as schematically shown in Fig. 1. The AFM scanning area was 3 pm and the image resolution was 600 x 600 pixels. In the measurement, we mechanically moved the samples several times so as to locate the patterns in the 3 pm scanning field. AFM image distortions caused by non-linear piezo scanning were compensated by a calibration program accompanied with the AFM. Line edges were determined by a homemade edge detection program with sub-pixel resolution and the line widths along a 300 nm length were averaged. Figure 2 shows 10 AFM images of photo-nanoimprinted pattems with a pitch of 400 nm on No.7 die and No.12 corresponding to the same mold portion. The images were obtained in the alphabetical order. Line numbers and target area for averaging are shown in the image A. When we compare AFM images precisely, there are mainly two problems. One is distortion still remaining even after calibration and another is difficuity in preserving identity of the AFM cantilever apex. The former problem implies that we cannot accurately measure lengths at different locations of AFM scanning area such as patterns shown in Fig.2. However, using the pattern pitch as a control enables precise measurement wherever pattems are located. We measured not only the pattern width but also the two pitches for a line between two neighboring lines as shown in Fig. 3. The averaged ratio of the width to the pitch hardly includes non-linearii when the distortion is smooth and small. To solve the difficulty in preserving the identity of the AFM cantilever apex, we measured the samples alternately and mean values of averaged widths were obtained. Table 1 shows mean values for 5 images each of No.7 and No.12 dies. The differences between values of No.7 and those of No.12 are -0.12 nm, +0.32 nm and -0.23 nm for line 3, 4 and 5, respectively. The standard deviation of absolute values of difference in mean values is 0.23 nm. This standard deviation proves the extremely high reproducibility of photo-nanoimprint. (This work was partty supported by NEDO.)