Trench Depth

Some design features of trenches should be noted. Commonly recommended trench dimensional proportions are a width of twice the depth. Under no circumstances should trench depth exceed the width to ensure adequate ventilation. Where heavy wheeled traffic, such as forklift trucks, may occur in a process structure or area with trenches, the trenches can be designed with extra-heavy duty grating that can support heavy equipment. 

Under well controlled conditions, a micrometer letter T in Fig. 50a was produced in a thick PMMA film by 75 nm indentation of the tip into the sample which resulted in a trench depth of 20 nm. 

The introduction of silicon-on-insulator (SOI) technologies in manufacturing as a way of decreasing parasitic leakages and capacitances in MOS devices will alleviate the planarization process because of the reduced trench depth and consecutively reduced initial step height. 

After the pattern is generated and the trench depth is measured by profilometry, Si02 is deposited and subsequently planarized by CMP. After CMP, the surface is again measured by profilometry and the amplitude of the square wave subsequent to polish is compared to die amplitude prior to oxide deposition. Figure 5.26 shows the ratio of the post-polish CMP amplitude, to the predeposition amplitude. A , vs. oxide removed for several trench widths. Note that the plot of log (A/A ) vs. oxide removed is a straight line. Renteln et al. use this fact to define the metric planarization rate, P, which is equal to the slope of the lines in Figure 5.26. 

Square wave patterns with trench depths of 1.0 pm are etched into silicon substrates to determine the planarization rate, P, of two oxide CMP processes. After patterning, 2.0 pm of Si02 is deposited onto the substrates. The wafers are then polished to remove oxide in 0.2 pm increments. The surface amplitude is measured after each polish and the resultant data tabulated in the table below. Plot log(A Aj) vs. oxide removed and determine P for each process and each trench width. Which process is more effective at planarizing ... 

Fig. 15. Effect of the trench depth on the development of deposit nonuniformity for /i = 5 and w = 2. (Figure and caption reprinted from Hume et al. [48] by permission of the publisher, The Electrochemical Society, Inc.).

Figure 3 Trench Depth Reduction vs. Trench Width for equal time polish increments...

First, no planarization is achieved for feature sizes above 4.5 mm. For feature sizes 1.0 mm to 4.5 mm, only partial planarization is possible, and with the exception of the 3, 3.5 and 4 mm structures, its effectiveness increases monotonically with feature size reduction. And finally, for feature sizes 1.0 mm and below, nearly constant planarization efficiency was achieved, as the trench depth was reduced from 0.8 pm to zero. We believe that the irregularity in our experimental data for 3-4 mm feature sizes was caused by an error in the exposure. This caused each of these structures on wafers from this particular lot to be actually composed of two smaller trenches with slight separation, as evidenced from visual inspection of the pre-polished wafers. 

Figure 6 Post-CMP nitride and oxide slopes independent vyith silicon trench depth and oxide deposition thickness. All the wafers were polished to approximately the same trench oxide target.

STl CMP performance depends on several factors such as deposited nitride thickness, trench depth, thickness and type of deposited trench-fill oxide, removal rate consistency fhe physicochemical nature of Ce02 particles. 

Trench Depth (ft) Horiz. Spacing (ft) Cross Braces ... 

The aspect ratio of the microtrenches is defined as the ratio of the trench depth to the trench width. DRIE can easily reach an aspect ratio of 30. With special recipe and high plasma power, the highest aspect ratio can reach as high as 100 [7]. The smallest feature size is dependent of the patterning capability. Using the normal optical lithogra-... 

Fig. 37 AFM height micrographs of a fractal aggregation of sparse, solution-processed TBP b aligned domain formation in more dense TBP c a close view of TBP aggregation within trenches and d a wider-scale view of TBP aggregation wire formation within trenches. The axes dimensions are a 3 ixm, b 2 ixm, c 2.2 ixm, and d 25.2 xm. Samples in (c) and (d) have a trench periodicity of 450 nm and a trench depth of 10 nm (reprinted with permission from [129]. (2007) American Institute of Physics)...

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