The layout of sub-micro protein patterns that we design is illustrated in Figure 3.1 and Table 3.1. 6 set of patterns to be plotted; including line patterns (0.3 and 0.6um), line combing dash line patterns, T shape (1.8um) and dash line patterns (0.6 um). Each of them has 4 different steps with variable pitch.
3 4
Figure 3.1 The design of mask layout.
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3.1.1 Narrow Line patterns
The design rule of narrow line patterns is 0.3 um. Each of them has 4 variations of steps with different pitch and named 1A, 1B, 1C, and 1D (Table 3.1). There are 4 purposes to design these patterns.
1. Test the resolution limitation of μCP method.
2. Compare the pattern accuracy with variable space/line ratio in each step of process.
3. Compare the pattern accuracy and neuron outgrowth between two different line widths (1A~1D groups, 2A~2D groups).
4. Observe the cell/neuron outgrowth with variable space/line ratio of protein patterns.
3.1.2 Line patterns
The design rule of line patterns is 0.6 um. Each of them has 4 variations of steps with different pitch and named 2A, 2B, 2C, and 2D (Table 3.1). There are 3 purposes to design these patterns.
1. Compare the pattern accuracy and neuron outgrowth between two different line widths (1A~1D groups, 2A~2D groups).
2. Compare the pattern accuracy with variable space/line ratio in each step of process.
3. Observe the cell/ neuron outgrowth with variable space/line ratio of protein patterns.
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3.1.3 Small dash line with solid line patterns
The design rule of small dash line with solid line patterns; line is 0.6 um and dash line is 0.6X1.2 um. Each of them has 4 variations of steps variation with the distance between two dash lines and named 3A, 3B, 3C, and 3D (Table 3.1). There are 4 purposes to design these patterns.
1. Compare the pattern accuracy with variable space in each step of process.
2. Observe the cell / neuron outgrowth with variable space of protein patterns.
3. Test the maximum distance of dash line patterns that axonal outgrowth could across.
4. Count the number of dash line patterns that axonal outgrowth could across.
3.1.4 T shape patterns
The design rule of T shape patterns is component of 4 squares (1.8X1.8 um ).Each of them has 4 variations of steps with the distance between two squares and named 4A, 4B, 4C, and 4D (Table 3.1). There are 4 purposes to design these patterns.
1. Compare the pattern accuracy with variable space in each step of process.
2. Compare the pattern accuracy with different shape in each step of process.
3. Observe the cell/neuron outgrowth with different shape of protein patterns.
4. Observe the cell/neuron outgrowth with variable space of T shape protein patterns.
3.1.5 Middle dash line patterns
The design rule of middle dash line patterns is 0.6 X 12 um. Each of them has 4 variations of steps with the distance between two dash lines and named 5A, 5B, 5C, and
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5D (Table 3.1). There are 4 purposes to design these patterns.
1. Compare the pattern accuracy with variable space in each step of process.
2. Observe the cell/ neuron outgrowth with variable space of protein patterns.
3. Test the maximum distance of dash line patterns that axonal outgrowth could across.
4. Observe variable line/width of dash line patterns (3A~3D, 5A~5D, and 6A ~ 6D) that axonal outgrowth could across.
3.1.6 Long dash line patterns
The design rule of middle dash line patterns is 0.6 X 60 um. Each of them has 4 variations of steps with the distance between two dash lines and named 6A, 6B, 6C, and 6D (Table 3.1). There are 4 purposes to design these patterns.
1. Compare the pattern accuracy with variable space in each step of process.
2. Observe the cell/ neuron outgrowth with variable space of protein patterns.
3. Test the maximum distance of dash line patterns that axonal outgrowth could across.
4. Observe variable line/width of dash line patterns (3A~3D, 5A~5D, and 6A ~ 6D) that axonal outgrowth could across.
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3.2 New procedures of Micro contact printing (µCP) method
In figure 3.3, the rectangular frame marked by dashed outline represents the new procedures of Micro contact printing (µCP) method we re-designed. We deposited a TEOS film with 0.3 um thickness above the silicon structure of wafer. After photolithography, we use RIE etching and transfer of the patterns into the TEOS film, then using RIE etching again and the patterns have been successfully transfer into substrate of silicon.
When the pattern size is into sub-micro level, the sticking issue between silicon and PDMS will be getting worse. Buffer layers are indeed needed and used to avoid sticking issue between silicon and PDMS. A suitable material could avoid the crosslinking from these two materials and reduce the issue of pattern sticking .
3.2.1 TEOS film hard mask
In this thesis, we use the DUV lithography to fabricate sub-micro patterns.
Through our related researches, photoresist base is used as the master [4]. But in DUV lithography, the thickness of photoresist is usually less than 1um.That means the aspect ratio will be limited.
Upon this, we re-design the procedure of Micro contact printing (µCP) method and add TEOS as a new film stacking above silicon structure of wafer. The TEOS is an oxide film and will be a hard mask to increase the etching selectivity between DUV photoresist and silicon. The range of aspect ratio will be tested by tuning RIE etching recipes, including the power, gas flow rate and components of gases.
We will use the new procedure of Micro contact printing (µCP) method to fabricate sub-micro protein patterns and compare the pattern accuracy with variable size (0.3, 0.6 um), pitch (1:1~1:4) and different shape in each step. In theory, we can get 5 times Photoresist/Silicon etching selectivity by TEOS hard mask.
3.2.2 Buffer layers
In step 5 of figure 3.2, some samples will be tested to be buffer layer. The types of materials are including organic, inorganic films and surfactants. We will choose the suitable one to avoid sticking issue between silicon and PDMS and gets a silicon base of master.
Buffer layer coating
Figure 3.2 Schematic illustration of the procedure of silicon base of Micro Contact Printing
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