How does NVC oppose the patterned substrate to improve the efficiency of LED light extraction?

Patterned substrate, referred to as PSS (Patterned Sapphire Substrate), commonly known as patterned substrate, that is, a mask for dry etching is grown on a sapphire substrate, and the mask is patterned by a standard photolithography process, and etched by ICP. The etch technique etches sapphire, removes the mask, and then grows GaN material thereon, causing the longitudinal epitaxy of the GaN material to become laterally epitaxial, etched (in sapphire C-face dry etch/wet etch) on a sapphire substrate Designed to produce micro- or nano-scale patterns with micro-structure specific rules, in order to control the output light form of the LED (the concave-convex pattern on the sapphire substrate will produce light scattering or refraction effect to increase the light output rate), while the GaN film grows A lateral epitaxial effect is produced on the patterned sapphire substrate, which reduces the difference between the GaN grown on the sapphire substrate, improves the epitaxial quality, and improves the internal quantum efficiency of the LED and increases the light extraction efficiency. Compared to LEDs that grow on a typical sapphire substrate, PSS can increase brightness by more than 70%.

DONGGEUN KO, JACOBYOON, JANGHO SEO describes how to reduce the defect density and total reflection loss by patterning the wafer, thereby improving the LED light extraction efficiency.

Manufacturers are rapidly adopting nitride-based LEDs as standard light sources for a wider range of products, from general lighting, headlights, traffic lighting to background lighting for consumer electronics such as HDTVs, smartphones, and tablets. Computer and size display. LED performance and cost make LED technology widely available. In fact, low cost and high light efficiency can promote the acceptance of the consumer market. LED chip manufacturers are looking for patterned sapphire substrate production technology to maximize light extraction efficiency and promote the use of LEDs.

Applying patterning to an LED substrate or wafer can improve light output in two ways. This technique can increase the light exit of the active quantum well layer by reducing the epitaxial defect density. Moreover, the patterned sapphire substrate can reduce the light loss due to total reflection by the photon scattering effect.

Researchers have designed patterns of periodically varying structures of different shapes and sizes on the surface of sapphire substrates, including cones, domes, pyramids, and columnar structures. Such a sapphire substrate is referred to as a patterned sapphire substrate.

There are currently two methods in the industry for producing patterned sapphire substrates: dry plasma etching and wet chemical etching, but most of the patterned sapphire substrates are produced using dry plasma etching techniques. The accuracy and uniformity of the example etching, such as dry etching, is easier to control than wet chemical etching. The fabrication of patterned sapphire substrates discussed herein will focus primarily on the use of inductively coupled plasma dry reactive corrosion.

By collaborating with 100-mm and 150-mm patterned sapphire substrates with many of the world's most advanced LED manufacturers, Rubicon has the opportunity to understand the range of effective patterned sapphire substrates. The most critical requirements are pattern size, shape, aspect ratio (eg, aspect ratio of the pattern), wafer uniformity, and wafer-to-wafer uniformity.

Because of the high customization of the epitaxial process in the LED industry, we are unable to obtain an optimal solution for patterned sapphire substrates. The design of the pattern is ever-changing, and there is no convergence in the design of the patterned sapphire substrate in the future. Typical pattern shapes include cones, domes, square pyramids or triangular pyramids. Even academic studies have shown that the smaller the pattern size (100-1000 nm), the better the light efficiency, but the LED industry still dominates the 3-4 μm pattern.

Process parameters affecting key characteristics are dimensional accuracy, uniformity of photoresist mask, selectivity of sapphire etching to photoresist mask, RF power, inductively coupled plasma process pressure, RF coil Design plasma consistency, ratio of trifluoromethane to boron trifluoride, and substrate temperature.

Increase light extraction rate

Low light extraction rates are a big challenge for producing high brightness LEDs. The patterned sapphire substrate allows photons outside the totally reflective vertices to be scattered into the total reflection vertebral (Fig. 1a), thereby improving light extraction efficiency. This effect is equivalent to increasing the critical angle of photon overflow (Figure 1b). The study found that by this means the light extraction efficiency can be increased by up to 30%.

Figure 1: The patterned sapphire substrate scatters photons (a) and effectively expands the escape cone (b), which increases the light extraction rate by 30%.