Step-and-repeat processing

Not only does multitone eliminate the step-and-repeat process, but it can also provide immediate feedback for equipment adjustments. Watching the entire audio spectrum respond to interactive adjustments with little or no time lag further simplifies audio equipment calibration. 

A step-and-repeat process allows the fabrication of smaller and cheaper stamps and a better control of the placement accuracy [8]. Such a process is easier to implement with a UV system than with a thermal system. 

Flatness issues. At low imprinting force, the imprint quality depends on the flatness of mold and substrate. In the step-and-repeat process, the common 6.3 mm thick quartz mold can be prepared with sufficient flatness. As substrates, double-side polished wafers are preferable to single-side polished ones due to their better flatness and reduced total thickness variation. The wafer chuck flatness also has to be controlled. 

Figure 8. Electron micrographs of a trilevel aluminum lift off process employing a typical polysilane as the 02-RIE barrier. Key left, electron-beam imaged and right, optically imaged Mann step and repeat.

As an example of the latter point, several process and tool innovations have contributed to both the generation of smaller device patterns and the ability to maintain the integrity of those dimensions through the subsequent process steps. Thus, improved exposure tools (e.g., optical step and repeat, E-Beam) and masking materials (resist) allow considerably smaller pattern definitions than was previously possible. Once generated, these patterns can now be maintained with improved pattern etching techniques (reactive ion or plasma etching). 

Sometimes, partial dimensional corrections are required to adjust the distortions of the thin flexible materials. A higher alignment accuracy than -H/-10 microns is required for the finer pitched than 50 microns. The easiest way for the dimensional correction is to reduce the panel sizes. But it reduces the process productivity An alternative method is a step-and-repeat imaging with a small exposure area on a large panel. 

Step 4 Evaluate and repeat process—You will want to check on the success of your program, and Chapter 4 details how your SMS will do that. Of course, you will want to repeat this process on a periodic basis and ensure that your leading indicators are still valid. A very mature SMS will understand that you need to do this when material changes occur in your business but also on a periodic timeline to ensure that unforeseen conditions haven t changed that you did not pick up on. 

In Figure 1.4, some examples of imprinted resist layers, made by our group on an EVG 770 step-and-repeat system, are illustrated. With an optimized initial resist thickness and a known mold design, an excellent contrast between the feature height and the residual layer thickness can be obtained this is a very important point in the case of additional process steps. 

As described in more detail in the review by H. Schift [6], many different tool architectures exist in NIL, depending on the process used or on the targeted application. In UV-NIL, two main types of tools can be identified. The first one is the step-and-repeat tool. The main commercial players are Molecular Imprints [31],... 

Randomly select another solution and repeat process 2 (comparing with the winner solution in step 2) until all solutions have been compared. 

The ARC increases the temperature in discrete steps, waits for the thermal transients to decay, then monitors the temperature of the cell for a fixed time. If the cell temperature is not increasing above a threshold value, typically 0.02 °C/min, the temperature is increased by another step and the process repeated. If the cell temperature is increasing at a rate equal to or above the threshold value, the ARC switches to exothermic mode, during which the ARC temperature closely matches cell temperature, thus maintaining the adiabatic state. The ARC matches the rate of temperature rise of the ceU even at quite high heating rates. 

The reactor now becomes batch, requiring the reaction to be completed before the separation can take place. Figure 4.14 shows the time-event chart for a repeated batch cycle. Note in Fig. 4.14 that there is a small overlap between the process steps. This is to allow for the fact that emptying of one step and filling of the following step occur at the same time. 

Fig. XVIII-14. Schematic illustration of the movement of NO molecules on a Pt(lll) surface. Molecules diffuse around on terraces, get trapped at steps, escape, and repeat the process many times before eventually desorbing. [Reprinted with permission from M. Cardillo, Langmuir, 1, 4 (1985) (Ref. 140). Copyright 1985, American Chemical Society.]...

When we discussed random walk statistics in Chap. 1, we used n to represent the number of steps in the process and then identified this quantity as the number of repeat units in the polymer chain. We continue to reserve n as the symbol for the degree of polymerization, so the number of diffusion steps is represented by V in this section. 

Most commercial adsorbents for gas-phase appHcations are employed in the form of pellets, beads, or other granular shapes, typically about 1.5 to 3.2 mm in diameter. Most commonly, these adsorbents are packed into fixed beds through which the gaseous feed mixtures are passed. Normally, the process is conducted in a cycHc manner. When the capacity of the bed is exhausted, the feed flow is stopped to terminate the loading step of the process, the bed is treated to remove the adsorbed molecules in a separate regeneration step, and the cycle is then repeated. 

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