Reactive Ion Beam Etching of Surface Relief Gratings for AR- & MR-Devices

Augmented Reality (AR) describes a technology where computer-generated objects and information are displayed in real-life surroundings. The technology is used for several applications in business, like service and surgery assistance, as well as for consumer market applications, like navigation. State of the art augmented reality as well as mixed reality (MR) devices use optical waveguides with diffraction gratings in order to guide light from a display by total internal reflection (TIR) into the view of the human eye.

Figure 1 shows schematic the optical gratings used as light couplers. The smaller input grating diffracts light coming from a display into the waveguide. At the out-coupler grating, light is diffracted in direction of the viewer. 

Different approaches for the design of coupling gratings exist. One type is the so called Surface Relief Grating (SRG). Within this group the gratings are divided into blazed gratings, slanted gratings, binary gratings and analog surface relief gratings.

In order to manufacture those gratings, in the first step photo lithography is used to create a mask or pattern on a glass substrate. In the next step this mask will be used to structure an intermediate metal mask or the glass directly. For this the widely used dry etching technology reactive ion etching (RIE) is not suitable, as here ions are always perpendicularly accelerated to the surface. In contrast to RIE the reactive ion beam etching (RIBE) process offers unique advantages. Due to the ion beam source, that extracts an ion beam in which the substrate can be freely tilted, slant angles as flat as 60 degree (from substrate normal) can be etched .

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Related Products: scia Mill 150 & scia Mill 200 & scia Mill 300

• Full surface etching with superior uniformity
• Reactive gas compatibility in RIBE and CAIBE processing, including fluorine / chlorine gases
• Substrate holder featuring rotation and tilt for arbitrary angles of incidence
• Thermal control of wafers during the process over a wide temperature range
• Ion beam source with high stability, adjustable ion energy and ion current density
• Complete software integration and automated processes via recipe