WO1999046421A1

WO1999046421A1 - Ion assisted electron beam deposition of ring laser gyro mirrors

Info

Publication number: WO1999046421A1
Application number: PCT/US1999/004939
Authority: WO
Inventors: Randy J. Ramberg; Anderson; David W. Sisson
Original assignee: Honeywell Inc.
Priority date: 1998-03-13
Filing date: 1999-03-05
Publication date: 1999-09-16
Also published as: AU2986999A

Abstract

Deposition sources deposit material onto mirrors used in ring laser gyros. The mirrors are placed in a rotating apparatus called a planet which rotates above the deposition sources which emit the material upwards. This operation will result in alternating, multiple layers of the differing materials deposited onto the mirror. An ion beam gun is used to increase the efficiency and ideal operability of the mirrors in the ring laser gyro.

Description

ION ASSISTED ELECTRON BEAM DEPOSITION OF RING LASER GYRO MIRRORS BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention relates to the creation of mirrors for ring laser gyros and more particularly to the deposition of materials to create the mirrors.

2. Description of the Prior Art

Mirror characteristics are very important in the operation of ring laser gyros. It is important in ring laser gyros to maintain the intensity of the laser beams in the ring laser gyro. The intensity of the laser beams depends on the characteristics of the mirrors and remains strong if the mirrors are highly reflective. By utilizing highly reflective mirrors, the ring laser gyro can operate more efficiently by saving excessive power that may be required in keeping the laser beams strong. Mirror characteristics are largely governed by the orientation of the substrate with the respect to material vapors being deposited on the substrate as well as the density of the mirror film on the substrate. If the orientation of the deposited material on the mirrors is correctly aligned and the density of the mirror film is highly packed, the light beams will reflect with all their intensity and will not be weakened. As mentioned before, this would reduce the power necessary to operate the gyro. To fabricate ring laser gyro mirrors, known deposition techniques are used to deposit material onto substrates in a coating chamber. Deposition sources exist in a coating chamber. High energy electrons are emitted from a source and strike target material. The target material is then evaporated onto mirror substrates that exist above the target material. However, during the deposition, the target material is deposited as columns sparsely spaced apart as seen in Fig. 1. This is not desirable. As mentioned before, it is important that the mirror film on the substrate is highly dense so that optimal mirror characteristics are provided to keep the laser beam intensity in the ring laser gyro.

Sparse deposition of material results in mirrors with loss, scatter and instability in humid and helium/plasma environments. In the ring laser gyro, it is desirable for a light beam to reflect perfectly so that the intensity of the beam is maintained and the beam is reflected at the same angle as its incoming angle or incidence angle. However, in current mirrors, some portion of the beams do not reflect properly and some of the original beam reflects at undesirable angles. This is commonly referred to as scatter.

It is also necessary to create partially reflective mirrors in which a portion of the original beam is to be transmitted through the mirror while the remainder is to be reflected. However, some of the light beam desired to be transmitted through the material on the mirrors is instead absorbed by the material on the mirrors. This phenomena is commonly referred to as loss. Scatter is also considered a part of loss.

Another problem with the column structure currently created by known structures and processes is instability in humid environments. Once the mirror film is exposed to humid environments, the columns structures are likely to absorb the moisture in the environment. This significantly changes the optical characteristics of the mirror film. This creates a very uneven and inconsistent film which results in an index of refraction that changes along the film and general unstable operation of the ring laser gyro. To reduce loss, scatter, and instability in humid and helium/neon plasma environments, it would be beneficial to prevent material from being deposited sparsely. Consequently, the laser beam in the ring laser gyro would remain strong and the ring laser gyro would operate more efficiently by requiring less energy.

SUMMARY OF THE INVENTION

The present invention is an apparatus to prevent undesirable deposition on mirror substrates that are used in ring laser gyros. In coating chambers, multiple deposition sources exist to deposit multiple layers of different materials on a substrate. The substrates are placed in planets which rotate above the deposition sources as material is deposited onto the substrate. The rotation of the planets will allow for a homogenous coating of alternating layers of material to be deposited. An ion producing means is aimed at the substrates and bombards the substrates with ions to produce a highly dense mirror film on the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an enlarged side view of a mirror film created on a substrate. Fig. 2 is a side view of a coating chamber with a deposition barrier. Fig. 3 is a top view of a rectangular deposition barrier in a coating chamber. Fig. 4 is a top view of a curved deposition barrier in a coating chamber. Fig. 5 is a side view of material being deposited onto a substrate with spacers in the coating chamber. Fig. 6 is an enlarged view of a highly dense mirror film created on a substrate.

DETAILED DESCRIPTION OF THE PRESENT INVENTION In an electron beam deposition coating chamber as seen in Fig. 2, planets 4 exist with deposition masks 6. The substrate 8 to be coated is placed in the deposition masks 6. A first and second target source 12a and 12b exist below the planets which emit material to be coated onto the substrate 8. The sources 12 emit different material 13 which is placed on top of the sources 12. The sources 12 hold the material 13 and contains the elements that perform electron beam deposition. As is well known in electron beam deposition, electrons that are very high in energy are shot at the source material 13. Once the electrons hit the source material 13, the source material 13 is evaporated on the substrate 8. An analogy to better understand this form of deposition is placing something of high temperature in water. The water evaporates and steam is emitted upwards. The steam then forms condensation on whatever it touches. The condensation example is a good analogy for how the source material 13 forms on the substrate 8.

Electron beam deposition is one form of deposition that can be used with the present invention. However, many forms of deposition can be used with the present invention such as chemical vapor deposition as well as other forms of deposition. The present invention will be discussed in its use with electron beam deposition as one illustration of an embodiment of the present invention, but is not limited to use with only electron beam deposition.

The purpose for a first and second source 12 is to create a multi-layer coating on the substrate 8. However, many sources can be used depending on how many differing layers are desired for coating the substrate 8. The planets 4 are rotated around the coating chamber 2 to create a homogenous, alternating, multi-layer coating. The sources 12 emit different materials and due to the rotation of the planets 4, homogenous alternating layers of the different materials are 4

deposited on the substrate 8. Once the material hits the substrate 8 it forms a coating on the substrate 8. This coating is known as a mirror film.

A barrier 14 is appropriately placed to prevent high angle deposition. A good height for the barrier 14 should be such that an angle of deposition greater than 40° is prevented. Fig. 3 shows a top view of the electron beam sources 12 and the source material 13 that exists on the sources 12. Between the sources 12 is a rectangular- shaped barrier 14. This rectangular barrier 14 is a simple and effective way to prevent high angle deposition, but different size and shaped barriers 14 can be used as well depending on mirror requirements. Fig. 4 shows a top view of another possible shape that can be used for the barrier

14. The curve shaped barrier 14 prevents undesirable deposition when the planets 4 are at a point in their rotation where high angle deposition could occur. The curve shaped barrier has advantages over the rectangular barrier in that it "cuts off' higher angle deposition. Obviously, the highest angle of deposition that can be prevented is best. However, more time and money is required in producing the curve shaped barrier 14 than the rectangular barrier since the curve shaped barrier needs to be shaped.

Also, to assist in preventing high angle deposition, raising the substrate 8 off the deposition mask 6 prevents almost all of the high angle deposition. Fig. 5 shows the use of a spacer 16, about 6 mm, to lift the substrate 8 from the deposition mask 6 so that high angle deposition is prevented. In the present embodiment, the spacer is approximately 6 mm high, however the dimensions could vary greatly in each application. Also, a kapton washer is used as a spacer 16. A kapton washer would be a preferred embodiment to prevent scratching of the substrate 8, but any type of spacing means could be used as the spacer 16. Arrows represent the material emitted from the sources 12. The material emitted at high angles misses the substrate 8. High angle deposition is prevented, but, as mentioned in the background of the invention, sparse coating still results. This is not beneficial since sparse coating causes loss and scatter in the mirror.

An ion beam gun 20 is placed in the chamber 2 to solve the problem of sparse coating. Ions from the gun 20 are aimed at an area through which the substrates 8 are rotated. The ion gun 20 directly bombards gas ions onto the substrate 8 with high energy ions to push the mirror film down so that it becomes highly dense. Inert gases 5

are used since they do not affect the mirror film. Such inert gases that can be used are Xenon or Argon, but any inert gas can be used. Also, an ion gun is described as the preferred embodiment, but any apparatus that projects ions toward the substrate surface could be used. For example, ion plating could also be used to transmit ions to the substrate surface. As can be seen in Fig. 6, the mirror film is now extremely dense and highly packed which solves the prior problems of loss, scatter, and instability in humid environments.

The invention has been described herein in considerable detail in order to comply with the Patent Statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment details and operating procedures, can be accomplished without departing from the scope of the invention itself.

Claims

6CLAIMS The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. Apparatus to prevent undesirable deposition on a substrate in a deposition chamber comprising: a plurality of different deposition sources which deposit differing material onto the substrate; a plurality of planets that exist above the plurality of different deposition sources with deposition masks that hold the substrate and rotate in the deposition chamber to coat the substrate with alternating layers of material from the different deposition sources; a barrier placed between the different deposition sources to prevent the deposition sources from coating the substrate in an undesirable deposition; and ion emitting apparatus projecting ions at the substrate to create high density substrates.

2. The apparatus of claim 1 wherein the barrier is of a height such that deposition at 40° or more is prevented.

3. The apparatus of claim 1 wherein the barrier has a shape of a rectangle with the barrier resting on the long side of the rectangle.

4. The apparatus of claim 1 wherein the barrier has a curved shape curving slightly around the deposition sources.

5. The apparatus of claim 1 further comprising a spacing apparatus placed in the deposition masks to lift the substrate from the deposition masks so that undesirable deposition is prevented.

6. The apparatus of claim 1 wherein the ion emitting apparatus is an ion beam gun.