# US 5,349,467 A · Thorium-free coating for germanium IR window

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- Number: US 5,349,467 A
- Document ID: US5349467A
- Status: Granted
- Kind: A
- Application number: 07/966,920
- Filed: 1992-10-27
- Granted: 1994-09-20
- Earliest claimed: 1992-10-27
- Assignees: Texas Instruments Incorporated
- Inventors: Frank C. Sulzbach; Valeria J. Epling
- Web page: https://patentgrep.com/patent/US5349467A

## CPC

- C23C 14/0694: {Halides}
- C23C 14/022: {by means of bombardment with energetic particles or radiation}
- C23C 14/0623: {Sulfides, selenides or tellurides}
- G02B 1/115: Multilayers
- G02B 5/281: {designed for the infrared light}
- C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04)
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

Durable thorium fluoride, low reflectance, high transmittance coatings for germanium (zinc sulfide, zinc selenide, gallium arsenide) exterior window surfaces are replaced using magnesium fluoride, a material previously not considered applicable to the 8 to 12 .mu.m wavelength range. This is enabled by the use of argon ion bombardment of the growing film. This method reduces the intrinsic stress of deposited films and permits growth of magnesium fluoride films of sufficient thickness to be used on the exterior surface of IR windows.

## Claims

### Claim 1

A method of forming a magnesium fluoride coating comprising the steps of:
(a) disposing a substrate in a chamber;
(b) ion beam cleaning the surface of said substrate at ion energies of from about 100 eV to about 2000 eV; and
(c) ion aided depositing a layer of magnesium fluoride on said cleaned substrate while bombarding said substrate with inert gas ions having an energy level of from about 1 eV to about 200 eV,

### Claim 2 (depends on 1)

The method of claim 1 wherein said substrate is polycrystalline germanium,

### Claim 3 (depends on 2)

The method of claim 2 further including the step of forming a first layer of ZnS on said substrate prior to step (c).

### Claim 4 (depends on 2)

The method of claim 2 further including the step of forming a germanium nucleation layer over said cleaned substrate prior to step (c).

### Claim 5 (depends on 4)

The method of claim 4 further including the step of forming a first layer of ZnS on said nucleation layer prior to step (c) .

### Claim 6 (depends on 5)

The method of claim 5 further including the step of forming a layer of germanium on said first layer of ZnS.

### Claim 7 (depends on 6)

The method of claim 6 further including the step of forming a layer of Ta.sub.2 O.sub.5 on said layer of germanium and under said layer of magnesium fluoride.

### Claim 8 (depends on 7)

The method of claim 7 further including the step of forming a second layer of ZnS on said layer of magnesium fluoride.

### Claim 9 (depends on 8)

The method of claim 8 further including the step of forming a second layer of magnesium fluoride on said second layer of ZnS while bombarding said magnesium fluoride with inert gas ions having an energy level of from about 1 eV to about 200 eV.

### Claim 10 (depends on 1)

The method of claim 1 further including the step of forming a first layer of ZnS on said substrate prior to step (c).