Methods and systems for laser machining a substrate
View Patent ↗A formation in a first surface of a substrate is machined by an ultraviolet or visible radiation laser, to a predetermined depth that is less than a full depth of the substrate; and material is removed from a second surface of the substrate opposed to the first surface to the predetermined depth from the first surface to communicate with the formation. Material may be removed by, for example, lapping and polishing, chemical etching, plasma etching or laser ablation. The invention has application in, for example, dicing semiconductor wafers to forming metallised vias in wafers.
1. A method of machining a substrate comprising the steps of:
(a) using a laser emitting visible or ultraviolet radiation to machine a formation in a first surface of the substrate to a predetermined depth from the first surface that is less than a full depth of the substrate; and
(b) subsequently removing material from a second surface of the substrate opposed to the first surface to the predetermined depth from the first surface to communicate with the formation using one of: chemical etching; plasma etching; and laser ablation,
wherein step (a) is performed in a non-ambient controlled gas environment, using at least one of a reactive gas and a passive gas at least one of prior to, during and after laser machining, wherein using the passive gas comprises using a passive gas substantially inert with respect to the substrate substantially to prevent oxidation of the substrate during laser machining thereof, and wherein using the reactive gas comprises using gas reactive with respect to the substrate to reduce roughness of laser-machined surfaces formed in step (a) or to remove debris created in step (a).
2. A method as claimed in claim 1 , wherein step (a) comprises laser machining with a laser emitting radiation of a wavelength of one of substantially 266 nm, 355 nm and 532 nm.
3. A method as claimed in claim 1 , wherein the step of machining the formation comprises machining a channel, and step (b) completes a cut through the substrate at the channel.
4. A method as claimed in claim 3 , wherein step (a) comprises machining a channel with substantially planar opposed side walls between the first surface and the predetermined depth from the first surface and substantially arcuate opposed side walls below the predetermined depth.
5. A method as claimed in claim 3 , wherein step (a) comprises machining a grid of channels, and step (b) completes dicing of the substrate along the grid of channels.
6. A method as claimed in claim 3 , wherein step (b) comprises the application of mechanical pressure to the substrate to break the substrate along the channel.
7. A method as claimed in claim 1 , wherein step (a) of machining the formation comprises machining a via and metallising the via with metal, and step (b) comprises exposing a portion of the metal in the via at the second surface using one of: mechanically removing material, particularly by using one of chemical etching; plasma etching; and laser ablation.
8. A method as claimed in claim 7 , wherein the step of machining a via comprises machining in a path forming a circle or a plurality of concentric circles to form a via centered on a center of the circle or the plurality of concentric circles.
9. A method as claimed in claim 7 , wherein the step of metallising the via includes a prior step of oxidising the via.
10. A method as claimed in claim 1 , wherein the step of using a passive gas comprises using one of argon or helium.
11. A method as claimed in claim 1 , wherein using gas reactive with respect to the substrate comprises using at least one of a chloroflurocarbon-based gas and a halocarbonbased gas.
12. A method as claimed in claim 1 , wherein step (a) comprises a further step of providing a protective layer for the first surface against debris formed in at least one of step (a) and step (b).
13. A method as claimed in claim 12 , comprising providing a spin coated protective layer.
14. A method as claimed in claim 12 , comprising providing a tape as the protective layer.
15. A method as claimed in claim 1 , wherein the substrate is of silicon material.
16. A method as claimed in claim 1 , wherein the substrate is of an optoelectronic material.
17. A method as claimed in claim 1 , wherein the substrate comprises layers of semiconductor and metal material.
18. A method as claimed in claim 1 , wherein step (a) comprises laser machining with a Q-switched laser.