**4.3 Experimental results**

### **4.3.1 Formation of 20 nm x 20 nm pitched dot arrays [16]**

Figure 4. 4 shows the SEM images of 20 nm x 20 nm pitch dot arrays patterns drawn by 30 keV electron beam at a dosage of 16 mC/cm2 using various resist thicknesses of 11.8 to 16.3 nm. In Figs. 4. 4(a) and (b), there are many defects such as the dots combined with neighbor dots. On the other hand, the number of defect decreases with the thickness. At the resist thickness of 13.1 nm, the 20 nm x 20 nm pitch dot array have completely been drawn as shown in Fig. 4. 4(c). Furthermore, using further thin resist film, the dot arrays appear unclearly (Fig. 4. 4(d)) because the SEM contrast becomes poor due to thin thickness. Therefore, the resist thickness of about 13 nm is very suitable for formation of 20 nm x 20 nm very fine pitch dot arrays.

Fig. 4.4. SEM images of 20nm x 20nm fine pitch dot arrays formed by 30keV EB lithography at a dosage of 16 mC/cm2, (a) with a resist thickness of 16.1 nm, (b) 14.7, (c) 13.1 nm and (d) 11.8 nm**.** 

The conventional EB drawing system was used as described in section 3. 1. The drawing was done on a resist layer coating on a piece of Si after we set the sample on the XY table in the system. The EB drawing was done under a probe current of 100 pA at an acceleration voltage of 30 kV. In the other system parameters, the address resolution was 2.5 nm in a

The calixarene resist films on Si substrate with a thickness of 11.8 nm to 16.9 nm, which were controlled by the spin coating at a speed of 3000 rpm to 8000 rpm for 190 s was prepared as shown in Fig. 4. 3. The thicknesses were measured by contact mode atomic force microscope

The resist process is as follows. After coating the resist on the Si substrate, pre-baking was done at the 110 oC for 3 min in air. Then, the EB drawing was done by raster scanning with the CAD data. After the developing and rinsing with a developer of ZEP-RD and isopropanol, respectively, The pattern quality was checked whether complete formation of the

> **2500 3500 4500 5500 6500 7500 8500 Rotation r(rpm)**

Fig. 4.3. Thicknesses of 11.8 nm to 16.9 nm controlled by the spin coating at a speed of 3000

Figure 4. 4 shows the SEM images of 20 nm x 20 nm pitch dot arrays patterns drawn by 30 keV electron beam at a dosage of 16 mC/cm2 using various resist thicknesses of 11.8 to 16.3 nm. In Figs. 4. 4(a) and (b), there are many defects such as the dots combined with neighbor dots. On the other hand, the number of defect decreases with the thickness. At the resist thickness of 13.1 nm, the 20 nm x 20 nm pitch dot array have completely been drawn as shown in Fig. 4. 4(c). Furthermore, using further thin resist film, the dot arrays appear unclearly (Fig. 4. 4(d)) because the SEM contrast becomes poor due to thin thickness. Therefore, the resist thickness of

about 13 nm is very suitable for formation of 20 nm x 20 nm very fine pitch dot arrays.

Fig. 4.4. SEM images of 20nm x 20nm fine pitch dot arrays formed by 30keV EB lithography at a dosage of 16 mC/cm2, (a) with a resist thickness of 16.1 nm, (b) 14.7, (c) 13.1 nm and (d) 11.8 nm**.** 

**4.2 EB drawing and sample preparation** 

drawing field of 25 µm x 25 µm.

drawn dot arrays was done or not.

**10**

**4.3.1 Formation of 20 nm x 20 nm pitched dot arrays [16]** 

**12**

**14**

**Thickness t(nm)**

**16**

**18**

(AFM).

rpm to 8000 rpm

**4.3 Experimental results** 

Fig. 4.5. Variations of average calixarene dot size with thicknesses for various exposure dosages.

Fig. 4.6. SEM images of 20nm x 20nm pitched calixarene resist dot arrays formed by 30keV EB drawing on Si substrate (1.6 Tb/in2) in 9 shots/dot drawing.

From Fig. 4. 4, the variations of average calixarene dot size for various thicknesses and exposure dosages were obtained as shown in Fig. 4. 5. The figure shows that the dot diameter decreases with not only thickness but also exposure dosage. Although the diameter variation with exposure dosage means that proximity effect occurs in the EB writing, the thin resist layer contributes to get small drawing probe. In order to draw the 20 nm x 20 nm pitch dot arrays pattern, we need a dot size of 15 nm at least. From Fig. 4. 5, it is neccessary to choose an exposure dosage of < 16 mC/cm2 and a resist thickness of < 13 nm for the fine pitch arrays formation.

Figure 4. 6 shows the result of the 20 nm x 20 nm pitch dot arrays patterns drawing with a thickness of 11.8-14.7 nm at some exposure dosages. The exposure dosages were 14 mC/cm2, 16 mC/cm2 and 18 mC/cm2. At a dosage of 14 mC/cm2, there are some vacancies as defects. It may be caused by that the dosage is not enough to make the resist molecular link. When using commercial developer, the insufficient exposed resist part was solved so

Electron Beam Lithography for Fine Dot Arrays with Nanometer-Sized Dot and Pitch 17

when a thinner resist film on Si substrate was used in the 30-keV-EB drawing. Nevertheless, a complete 20 nm x 20 nm pitch dot array was successfully achieved using the unique EB drawing condition for EB drawing with a resist thickness of 13.1 nm and an exposure dosage of 16 mC/cm2 as described above. The exposure dosage is dependent on dot pattern data. In the experiment, we used the dot pattern data of 3 x 3 shots/dot. We have also

Fig. 4.8. SEM images of 20x20, 25x25, 30x30 nm2 pitched calixarene resist dot arrays formed

Fig. 4.9. A proper region of 30-keV-EB drawing available for very fine pitch dot arrays in a relationship between exposure dosage and unit cell area (square pitch) in 9 shots/dot

From the above results, we can obtain an available drawing margin with regard to dot packing and exposure dosage for 30-keV EB drawing. The margin indicates that a minimum pitch exists for 30-keV EB drawing of the dot array pattern. In the 30-keV EB drawing and calixarene resist system, the smallest pitch is about 18 x 18 nm2. The dosage margin of about 6% is estimated at the pitch. This means that we need a stable EB-drawing system including the EB source, resist material and its thickness. Figure 4. 10 shows that there is the possibility of forming 18 x 18 nm2 pitch dot arrays using EB drawing. Our results demonstrate that 18 x 18 nm2 pitch dot arrays can be partially drawn. It is clarified that the

indicated the exposure dosage with a unit of C/dot, as shown in Fig. 4. 9.

by 30keV EB drawing on 13.1-nm-thick resist film on Si substrate.

drawing.

that the completed dots could not be formed. At a dosage of 16 mC/cm2, it is enough to makes complete dots. In a case of a dosage of 18 mC/cm2, the dot was combining together with neighbor dots because the dot size becomes larger than that at 16 mC/cm2. Figure 4. 7 shows the variations of the dot size with exposure dosage of the 20 nm x 20 nm dot arrays pattern at a resist thickness of 13.1 nm. The fluctuation of the dot size between minimum and maximum dot sizes are about 3 nm. This is as small as that in previous section. The experimental results demonstrated that 30 keV EB drawing can form 20 nm x 20 nm very fine pitch dot arrays pattern using optimal resist thickness and exposure dosage.

Fig. 4.7. Variation of the resist dot size measured from the 20 nm x 20 nm pitch resist dot arrays formed by EB-drawing with 30 keV incident electron.

#### **4.3.2 Challenge to form 18 nm x 18 nm pitched dot arrays [5, 16]**

#### *(1) Dependences of resist thickness and exposure dosage on 20-nm-pitch EB drawing*

Initially, we studied the effects of resist thickness and exposure dosage on 30-keV EB drawing of the dot arrays with a pitch of 20 nm x 20 nm. Figure 4. 6 indicates that the optimal thickness and exposure dosage were about 13.1 nm and 16 mC/cm2, respectively. On the other hand, we did not obtain good results using a thickness of 11.8 nm, although the thickness was as thin as possible. This may be caused by insufficient contrast of SEM images due to an excessively thin resist and poor focus adjustment. Thus, it is necessary to use a thin resist film to suppress the scattering of the primary electrons in the resist. The tendency that finer dot arrays patterns can be drawn with thinner resists are demonstrated, and agrees with the simulation result. Nevertheless, there exists a critical thickness for fine evaluation of the drawn pattern as described above.

#### *(2) Possibility of forming 18 nm pitch dot arrays pattern*

To anticipate the ultimate pitch of the dot arrays using 30-keV EB drawing, we studied the EB drawing margin by EB drawing of highly packed dot arrays with pitches of 20 x 20, 25 x 25, and 30 x 30 nm2 by ranging the exposure dosages between 14 and 40 mC/cm2. Figure 4. 8 shows the SEM images of the 20 x 20, 25 x 25, and30 x 30 nm2 pitch dot arrays patterns formed using various dosages at a constant resist thickness of 13.1 nm. The experimental results indicate that the optimal condition for drawing becomes narrow as dot packing increases. We successfully formed 20 x 20 nm2 pitch dot arrays at an exposure dosage of 16 mC/cm2. In contrast, the available proper exposure dosages increased to 14-22 and 14-30 mC/cm2 for the pitchs of 25 x 25 and 30 x 30 nm2, respectively. The results show that it is very difficult to form 20 x 20 nm2 pitch dot arrays in the resist film on Si substrates even

that the completed dots could not be formed. At a dosage of 16 mC/cm2, it is enough to makes complete dots. In a case of a dosage of 18 mC/cm2, the dot was combining together with neighbor dots because the dot size becomes larger than that at 16 mC/cm2. Figure 4. 7 shows the variations of the dot size with exposure dosage of the 20 nm x 20 nm dot arrays pattern at a resist thickness of 13.1 nm. The fluctuation of the dot size between minimum and maximum dot sizes are about 3 nm. This is as small as that in previous section. The experimental results demonstrated that 30 keV EB drawing can form 20 nm x 20 nm very

fine pitch dot arrays pattern using optimal resist thickness and exposure dosage.

Fig. 4.7. Variation of the resist dot size measured from the 20 nm x 20 nm pitch resist dot

Initially, we studied the effects of resist thickness and exposure dosage on 30-keV EB drawing of the dot arrays with a pitch of 20 nm x 20 nm. Figure 4. 6 indicates that the optimal thickness and exposure dosage were about 13.1 nm and 16 mC/cm2, respectively. On the other hand, we did not obtain good results using a thickness of 11.8 nm, although the thickness was as thin as possible. This may be caused by insufficient contrast of SEM images due to an excessively thin resist and poor focus adjustment. Thus, it is necessary to use a thin resist film to suppress the scattering of the primary electrons in the resist. The tendency that finer dot arrays patterns can be drawn with thinner resists are demonstrated, and agrees with the simulation result. Nevertheless, there exists a critical thickness for fine

To anticipate the ultimate pitch of the dot arrays using 30-keV EB drawing, we studied the EB drawing margin by EB drawing of highly packed dot arrays with pitches of 20 x 20, 25 x 25, and 30 x 30 nm2 by ranging the exposure dosages between 14 and 40 mC/cm2. Figure 4. 8 shows the SEM images of the 20 x 20, 25 x 25, and30 x 30 nm2 pitch dot arrays patterns formed using various dosages at a constant resist thickness of 13.1 nm. The experimental results indicate that the optimal condition for drawing becomes narrow as dot packing increases. We successfully formed 20 x 20 nm2 pitch dot arrays at an exposure dosage of 16 mC/cm2. In contrast, the available proper exposure dosages increased to 14-22 and 14-30 mC/cm2 for the pitchs of 25 x 25 and 30 x 30 nm2, respectively. The results show that it is very difficult to form 20 x 20 nm2 pitch dot arrays in the resist film on Si substrates even

arrays formed by EB-drawing with 30 keV incident electron.

evaluation of the drawn pattern as described above. *(2) Possibility of forming 18 nm pitch dot arrays pattern* 

**4.3.2 Challenge to form 18 nm x 18 nm pitched dot arrays [5, 16]** 

*(1) Dependences of resist thickness and exposure dosage on 20-nm-pitch EB drawing* 

when a thinner resist film on Si substrate was used in the 30-keV-EB drawing. Nevertheless, a complete 20 nm x 20 nm pitch dot array was successfully achieved using the unique EB drawing condition for EB drawing with a resist thickness of 13.1 nm and an exposure dosage of 16 mC/cm2 as described above. The exposure dosage is dependent on dot pattern data. In the experiment, we used the dot pattern data of 3 x 3 shots/dot. We have also indicated the exposure dosage with a unit of C/dot, as shown in Fig. 4. 9.

Fig. 4.8. SEM images of 20x20, 25x25, 30x30 nm2 pitched calixarene resist dot arrays formed by 30keV EB drawing on 13.1-nm-thick resist film on Si substrate.

Fig. 4.9. A proper region of 30-keV-EB drawing available for very fine pitch dot arrays in a relationship between exposure dosage and unit cell area (square pitch) in 9 shots/dot drawing.

From the above results, we can obtain an available drawing margin with regard to dot packing and exposure dosage for 30-keV EB drawing. The margin indicates that a minimum pitch exists for 30-keV EB drawing of the dot array pattern. In the 30-keV EB drawing and calixarene resist system, the smallest pitch is about 18 x 18 nm2. The dosage margin of about 6% is estimated at the pitch. This means that we need a stable EB-drawing system including the EB source, resist material and its thickness. Figure 4. 10 shows that there is the possibility of forming 18 x 18 nm2 pitch dot arrays using EB drawing. Our results demonstrate that 18 x 18 nm2 pitch dot arrays can be partially drawn. It is clarified that the

Electron Beam Lithography for Fine Dot Arrays with Nanometer-Sized Dot and Pitch 19

function to Eq. (3.1), the 1, 2, C1/C2, and values are about 5 nm, 15 nm, 0.03 and 0.27, respectively. In the Monte Carlo simulation, we obtained EDD in 15-nm-thick resist on Si substrate (Fig. 4. 11(b)). When roughly fitting it to the EID function, they are about 2 nm, 10 nm, 0.02 and 0.5 nm, respectively. Although the resist materials are difficult in the experiments and simulations, the values of 1, 2, C1/C2 in the experiment are almost same as those in the simulation. Comparing between experimental and simulated results, the values of 1 in both cases agree well because the electron probe size of 2 nm and the resist molecular size of 1 nm can be considered in the EB drawing. According small 1 and values, the system is very suitable for very fine dot and very fine pitch dot arrays drawing. Figures 4.12(a)-(d) show SEM images of very fine pitch resist dot arrays on Si substrate with various pitches of 20 x 20 nm2 to 40 x 40 nm2. The exposure dosage was 16 mC/cm2. In these experiments, we succeeded in obtaining the highest-packed dot array pattern with a pitch of 20 x 20 nm2 (Fig. 4. 12(a)), which corresponds to the ultrahigh recording density of about 1.61 Tb/in2 in patterned media. The dot sizes of about 12.5 to 18 nm are changed as shown in Fig. 4. 12(e). The size fluctuation is about 2 nm and almost constant in a range of 0.4 to 1.6 Tb/in2. This shows that the drawings are carried out in no relation with the dot pitch. Figures 4. 13(a) and (b) show SEM images of 25 x 25 nm2 pitched resist dot arrays at side and corner of the drawing area Fig. 4.13 SEM images (a), (b) and histograms (c)-(e) of 25 nm x 25 nm pitch resist dot arrays on Si substrate at a dosage of 16 mC/cm2, (a) at side of the written pattern area, (b) at corner, (c) at center, (d) at

at an exposure dosage of 16 mC/cm2. The dot sizes histograms are shown in Figs. 4. 13(c)- (e). Comparing the distributions at center, side and corner of the drawing area, the histograms and the mean values are almost same. These experimental results demonstrate the proximity effect is extremely small in this system. The system is suitable for formation of very fine pitch dot arrays with very fine dot. From the results, a curvature of corner in the

In addition, using 50 keV EB lithography, we can consider that the 1 and values will be improved small to a twice of those in 30 keV EB lithography. This is because the forward scattering area in 50 keV EB lithography is suppressed to a twice of that in 30 keV EB lithography. Therefore, 50 keV lithography is more suitable for fine dots patterning than 30

Fig. 4.11. Experimental result (a) and Monte Carlo calculation (b) of EID function and roughly fitting to EID function in 30 keV EB drawing and 15 nm thick calixarene resist on Si substrate.

side and (e) at corner.at an exposure dosage of 16 mC/cm2.

drawing pattern could be sharp shape with a radius of 7-8 nm.

keV EB lithography.

30-keV EB drawing has the potential to form 18 x 18 nm2 pitch dot array patterns in thinner resist films on Si substrates by accurately selecting the optimum EB drawing conditions. For the formation of complete dot arrays pattern with 18 x 18 nm2 pitch, stability in the EB system is also required. At least, we have to use stable electron probe current with a deviation within 6% for 2 Tbit/in2 magnetic storage using 30-keV EB drawing.

The exposure dosages were 10-11 mC/cm2, which are smaller than the dosage estimated in 18 x 18 nm2 pitch drawing (Fig. 4.9). The small exposure dosages are caused by using different exposure shot numbers per square pattern as a dot. In Fig. 4. 10, we increased the number of shots/dot from 9 to 16 (4x4) for fast EB drawing. The dosage of 10 mC/cm2 in 16 shots/dot drawing corresponds to about 18 mC/cm2 in 9 shots/dot drawing. The 18 mC/cm2 almost agrees with the estimated dosage in Fig. 4. 9.

Fig. 4.10. SEM images of 18 x 18 nm2 pitched resist dot arrays formed by 30 keV EB drawing on Si substrate (about 2.0 Tb/in2).

#### **4.3.3 Small proximity effect using calixarene resist [17]**

The proximity effect of the EB drawing and thinner calixarene resist system is considered using the EID in the experiment and the EDD in Monte Carlo simulation.

Assuming that the EID function is defined with 2 Gaussian distributions as described in previous section, the 1st and 2nd terms in Eq. (3. 1) represent the energy depositions due to electron forward scattering (FS) and backward scattering (BS), respectively. For the miniaturization of the bit size, very small proximity effect and small 1 and 2 values are crucial. The ratio of the total energies due to FS and BS is very important.

$$\eta = \left[\mathbf{C}\_1 \exp(-\frac{r^2}{\sigma\_1^2}) dr \;/\int \mathbf{C}\_2 \exp(-\frac{r^2}{\sigma\_2^2}) dr = \left(\frac{\mathbf{C}\_2}{\mathbf{C}\_1}\right) \left(\frac{\sigma\_2}{\sigma\_1}\right)^2\tag{4.1}$$

The value has to be less than 1 because the drawing energy due to FS becomes dominant for very fine dot arrays formation. On the other hand, considering EB drwing of square, the drawing energy due to BS at side and corner of the square becomes a half and a quarter of that at center, respectively, based on reciprocity principle [9]. The variation of BS drawing energy on exposure dosage at everywhere of the drawing area is suppressed to be negligible small if the value is less than 1.

In the experiments, the exposure dosages were changed from 10 C/cm2 to 5 C/cm2. We obtained the EID using calixarene as shown in Fig. 4. 11(a) [23]. When we roughly fit the EID

30-keV EB drawing has the potential to form 18 x 18 nm2 pitch dot array patterns in thinner resist films on Si substrates by accurately selecting the optimum EB drawing conditions. For the formation of complete dot arrays pattern with 18 x 18 nm2 pitch, stability in the EB system is also required. At least, we have to use stable electron probe current with a

The exposure dosages were 10-11 mC/cm2, which are smaller than the dosage estimated in 18 x 18 nm2 pitch drawing (Fig. 4.9). The small exposure dosages are caused by using different exposure shot numbers per square pattern as a dot. In Fig. 4. 10, we increased the number of shots/dot from 9 to 16 (4x4) for fast EB drawing. The dosage of 10 mC/cm2 in 16 shots/dot drawing corresponds to about 18 mC/cm2 in 9 shots/dot drawing. The 18

Fig. 4.10. SEM images of 18 x 18 nm2 pitched resist dot arrays formed by 30 keV EB drawing

The proximity effect of the EB drawing and thinner calixarene resist system is considered

Assuming that the EID function is defined with 2 Gaussian distributions as described in previous section, the 1st and 2nd terms in Eq. (3. 1) represent the energy depositions due to electron forward scattering (FS) and backward scattering (BS), respectively. For the miniaturization of the bit size, very small proximity effect and small 1 and 2 values are

2 2 2

1 2 1 1

  2 2

*C*

(4.1)

deviation within 6% for 2 Tbit/in2 magnetic storage using 30-keV EB drawing.

mC/cm2 almost agrees with the estimated dosage in Fig. 4. 9.

**4.3.3 Small proximity effect using calixarene resist [17]** 

using the EID in the experiment and the EDD in Monte Carlo simulation.

crucial. The ratio of the total energies due to FS and BS is very important.

1 2 2 2

exp( ) / exp( ) *r rC <sup>C</sup> dr C dr*

The value has to be less than 1 because the drawing energy due to FS becomes dominant for very fine dot arrays formation. On the other hand, considering EB drwing of square, the drawing energy due to BS at side and corner of the square becomes a half and a quarter of that at center, respectively, based on reciprocity principle [9]. The variation of BS drawing energy on exposure dosage at everywhere of the drawing area is suppressed to be negligible

In the experiments, the exposure dosages were changed from 10 C/cm2 to 5 C/cm2. We obtained the EID using calixarene as shown in Fig. 4. 11(a) [23]. When we roughly fit the EID

on Si substrate (about 2.0 Tb/in2).

small if the value is less than 1.

function to Eq. (3.1), the 1, 2, C1/C2, and values are about 5 nm, 15 nm, 0.03 and 0.27, respectively. In the Monte Carlo simulation, we obtained EDD in 15-nm-thick resist on Si substrate (Fig. 4. 11(b)). When roughly fitting it to the EID function, they are about 2 nm, 10 nm, 0.02 and 0.5 nm, respectively. Although the resist materials are difficult in the experiments and simulations, the values of 1, 2, C1/C2 in the experiment are almost same as those in the simulation. Comparing between experimental and simulated results, the values of 1 in both cases agree well because the electron probe size of 2 nm and the resist molecular size of 1 nm can be considered in the EB drawing. According small 1 and values, the system is very suitable for very fine dot and very fine pitch dot arrays drawing. Figures 4.12(a)-(d) show SEM images of very fine pitch resist dot arrays on Si substrate with various pitches of 20 x 20 nm2 to 40 x 40 nm2. The exposure dosage was 16 mC/cm2. In these experiments, we succeeded in obtaining the highest-packed dot array pattern with a pitch of 20 x 20 nm2 (Fig. 4. 12(a)), which corresponds to the ultrahigh recording density of about 1.61 Tb/in2 in patterned media. The dot sizes of about 12.5 to 18 nm are changed as shown in Fig. 4. 12(e). The size fluctuation is about 2 nm and almost constant in a range of 0.4 to 1.6 Tb/in2. This shows that the drawings are carried out in no relation with the dot pitch. Figures 4. 13(a) and (b) show SEM images of 25 x 25 nm2 pitched resist dot arrays at side and corner of the drawing area Fig. 4.13 SEM images (a), (b) and histograms (c)-(e) of 25 nm x 25 nm pitch resist dot arrays on Si substrate at a dosage of 16 mC/cm2, (a) at side of the written pattern area, (b) at corner, (c) at center, (d) at side and (e) at corner.at an exposure dosage of 16 mC/cm2.

at an exposure dosage of 16 mC/cm2. The dot sizes histograms are shown in Figs. 4. 13(c)- (e). Comparing the distributions at center, side and corner of the drawing area, the histograms and the mean values are almost same. These experimental results demonstrate the proximity effect is extremely small in this system. The system is suitable for formation of very fine pitch dot arrays with very fine dot. From the results, a curvature of corner in the drawing pattern could be sharp shape with a radius of 7-8 nm.

In addition, using 50 keV EB lithography, we can consider that the 1 and values will be improved small to a twice of those in 30 keV EB lithography. This is because the forward scattering area in 50 keV EB lithography is suppressed to a twice of that in 30 keV EB lithography. Therefore, 50 keV lithography is more suitable for fine dots patterning than 30 keV EB lithography.

Fig. 4.11. Experimental result (a) and Monte Carlo calculation (b) of EID function and roughly fitting to EID function in 30 keV EB drawing and 15 nm thick calixarene resist on Si substrate.

Electron Beam Lithography for Fine Dot Arrays with Nanometer-Sized Dot and Pitch 21

The possibility of forming very fine pits or dots with a pitch of less than 25 nm was researched using reactive ion etching (RIE) and nano-imprinting with EB drawn pattern as a mask for the future process. We were able to fabricate ultrahighly packed dot arrays with a dot diameter of less than 15 nm and a dot pitch of 25 nm x 25 nm in negative calixarene resist using EB drawing. We also formed nan-Si dot arrays patterns by CF4 RIE. Furthermore, pit arrays were formed in polymer film through nano-imprinting by the photo-polymer method using a Si dot arrays pattern as the master mold. We demonstrated that the EB-drawn dot arrays resist pattern is very suitable for the fabrication of Si dot arrays and pit arrays with a pitch of 25 nm x 25 nm in this polymer. The Si dot and pit diameters

RIE O2 ashing EB drawing

We tried to apply the EB drawing to dry etching process. We checked if the pattern is available for reactive ion etching (RIE) process, and we carried out CF4-RIE using the resist patterns. We performed to do RIE of the Si substrate with the resist dot arrays pattern after post baking of the resist pattern, and to remove the remained resist by O2 ashing. The process flow is shown in Fig. 5. 1. The experiments conditions are represented in Table 5. 1.

Table 5.1. RIE and ashing conditions for Si dot formation and resist removal, respectively. As the experimental results, we obtained very fine Si dot arrays with a pitch of 30 nm x 25 nm to 25 nm x 25 nm (Fig. 5. 2). The minimum diameter of the Si dot is < 10 nm, and the height is about 20 nm. Figure 5. 3 shows histograms of the EB drawn resist dot and the RIE Si dot sizes in a pitch of 25 nm x 25 nm. According RIE and ashing, the resist dot size is

Fig. 5.1. Process flow for Si nano-dot arrays by RI etching and ashing.

**5. Application of EB drawing to formation of nano-Si-dot and nano-polymerpit arrays with a pitch of 25 nm x 25 nm using EB drawing, reactive ion** 

**etching (RIE) and nano-imprinting [23, 25]** 

were less than 10 nm.

calixarene

**5.1 Dry etching (RIE and ashing)** 

The EB writing with thin calixarene resist promises to open the way toward ultrahighdensity recording at >1 Tb/in2 and quantum devices.

Fig. 4.12. SEM images (a)-(d) and the dot size variation (e) of very fine pitch resist dot arrays at center of the drawing area on Si substrate at a dosage of 16 mC/cm2 with a pitch of (a) 20 nm x 20nm, (b) 25 nm x 25 nm, (c) 30 nm x 30 nm and (d) 40 nm x 40 nm.

Fig. 4.13. SEM images (a), (b) and histograms (c)-(e) of 25 nm x 25 nm pitch resist dot arrays on Si substrate at a dosage of 16 mC/cm2, (a) at side of the written pattern area, (b) at corner, (c) at center, (d) at side and (e) at corner.
