Plasma etching method using faraday cage

1. A plasma etching method using a Faraday cage, comprising:

providing an etch substrate in a Faraday cage, wherein the etch substrate comprises a metal mask provided on one surface thereof, and wherein an upper surface of the Faraday cage is provided with a mesh portion;

a first patterning step of forming a first pattern area on the etch substrate; and

a second patterning step of forming a second pattern area on the etch substrate after shielding at least a part of the mesh portion with a shutter,

wherein the first pattern area includes a first groove pattern having a depth gradient of 0 to 40 nm per 5 mm, and

the second pattern area includes a second groove pattern having a depth gradient of 50 to 300 nm per 5 mm.

2. The plasma etching method of claim 1 , wherein the shutter shields 20 to 80% of the mesh portion.

3. The plasma etching method of claim 1 , wherein the second patterning step includes aligning the etch substrate such that an area where the depth gradient of the second pattern area starts and an end of the shutter are on a common line.

4. The plasma etching method of claim 1 , wherein the second patterning step includes forming the second pattern area by etching an area of the etch substrate, the area of the etch substrate including at least a part of the first pattern area formed in the first patterning step.

5. The plasma etching method of claim 1 , wherein the etch substrate is provided on a support having an inclined surface, and

the first groove pattern and the second groove pattern are inclined groove patterns.

6. The plasma etching method of claim 1 , wherein the etch substrate maintains a separation distance of at least 7 mm from the mesh portion.

7. The plasma etching method of claim 1 , wherein the etch substrate is a quartz substrate or a silicon wafer.

8. The plasma etching method of claim 1 , wherein the mesh portion has a sheet resistance of 0.5 Ω/sq or more.

9. The plasma etching method of claim 8 , wherein the mesh portion comprises carbon fluoride radicals adsorbed on a metal mesh.

10. The plasma etching method of claim 1 , wherein the plasma etching is carried out by adjusting an output of a plasma etching apparatus to 0.75 kW or more and 4 kW or less.

11. The plasma etching method of claim 1 , wherein the plasma etching comprises supplying a mixed gas containing a reactive gas and oxygen gas to a plasma etching apparatus at a rate of 10 sccm or more and 75 sccm or less.

12. The plasma etching method of claim 11 , wherein a content of the oxygen gas flow amount in the total flow amount of the mixed gas is 1% or more and 20% or less.

13. The plasma etching method of claim 1 , wherein a bottom surface of the Faraday cage includes a metal having a lower ionization tendency than the metal mask.

14. The plasma etching method of claim 1 , wherein a bottom surface of the Faraday cage includes a metal whose standard reduction potential is higher than a standard reduction potential of the metal mask by 1 V or more.

15. The plasma etching method of claim 1 , wherein the metal mask includes at least one of aluminum and chromium and a bottom surface of the Faraday cage includes copper.

16. The plasma etching method of claim 1 , wherein the etch substrate after patterning is suitable for use as a mold substrate for a diffraction grating light guide plate.

17. A mold substrate for a diffraction grating light guide plate, wherein the mold substrate comprises the substrate after patterning using the plasma etching method of claim 1 .