a) Field of the Invention
The present invention relates to a method of manufacturing a field emission element, and more particularly to a method of manufacturing a field emission element which emits electrons from a tip of a field emission cathode.
b) Description of the Related Art
A field emission element is an element which emits electrons from a tip of a sharp emitter (field emission cathode) by utilizing electric field concentration. For example, a flat panel display uses a field emission emitter array (FEA) having a number of emitters. Each emitter controls the luminance and the like of a pixel of the display.
FIG. 13 illustrates an etching process of a manufacture method for a field emission element according to conventional techniques. The element shown in FIG. 13 is turned upside down from the state while each layer thereof is formed.
A method of forming each layer of this element will be described. A gate electrode layer 41 is formed on the whole surface of a starting substrate (indicated by a broken line) 40 made of silicon or the like. A resist pattern (not shown) is then formed on the gate electrode layer 41, the resist pattern being formed with a hole having a predetermined shape through photolithography.
By using this resist pattern as a mask, the gate electrode layer 41 and underlying substrate 40 are anisotropically etched to form a gate electrode 41a having a gate hole 48 whose plan (upper surface) shape is circular.
After the resist pattern is removed, a first sacrificial film (insulating film) is deposited and anisotropically etched to leave a partial first sacrificial film (side spacer) 42a indicated by a broken line. Next, a second sacrificial layer (insulating layer) 43 is isotropically deposited on the first sacrificial film 42a and exposed substrate 40. A portion of the second sacrificial film 43 whose diameter is narrowed by the side spacer 42a forms a sharp cusp. Next, a conductive emitter electrode 44 is isotropically deposited over the substrate surface.
A recess of the emitter electrode 44 is filled with a planarizing film 45, e.g., a spin-on-glass film. The planarizing film 45 is then etched back to planarize the back surface (upper surface) of the emitter electrode 44. Next, adhesive 46 made of, for example, Al, is coated on the back surface of the emitter electrode 44, and a support substrate 47 is formed on the adhesive layer 46 to enhance a mechanical strength of the element.
Thereafter, at the etching process shown in FIG. 13, the element is immersed in etching liquid 32 so that the starting substrate 40, the whole of the side spacer 42a, and a portion of the second sacrificial layer 43 are wet-etched isotropically to remove them, leave a second sacrificial layer 43a, and expose a tip of the emitter electrode (field emission cathode) 44.
With the wet etching process shown in FIG. 13, the emitter electrode 44 and gate electrode 41a are exposed. The distance between the emitter electrode 44 and gate electrode 41a is very short and 0.5 to 0.05 .mu.m at the shortest. If particles 33 existing in or generated from the etching liquid 32 enter the gate hole 48, there is a high possibility that some particles 33 make electrical short circuits between the exposed emitter electrode 44 and gate electrode 41a. This phenomenon may also occur during a rinsing process and a drying process.