Puddle etching method of thin film by using spin-processor

#1. Field of the Invention

#The present invention relates to a wet etching method of semiconductor processing, and more particularly, to a method for wet etching of thin film by forming a puddle of etching solution on the wafer in a spin processor

#2. Description of Relative Prior Art

#FIG. 1 is a cross section view of a spin processor of a prior art with the heating lamps raised up so that the injection pipe can go to the front side of the wafer.

#FIG. 2 is a cross section view of a spin processor of a prior art after the injection pipe leaving the wafer and the heating lamps lower down.

#FIG. 3 is a flow chart of puddle etching.

#Preferred embodiment of the present invention will now be explained with reference to the accompanying drawings. The preferred embodiment of the present invention made use of etching silicon dioxide as an example by using a spin processor of UFO-200 made by Grand plastic Technology Corporation to perform the puddle etching.

#Refer to FIG. 1 which is a cross section view of a spin processor of a prior art with the heating lamps 7 raised up so that the injection pipe can go to the front side of the wafer, but do not limited on this type, any spin rinse or spin etch processor can be used equivalently. In FIG. 1, a base 1 is a fixed base for supporting the hole processor, an etching chamber 2 is a cylinder or square vacuum chamber, a wafer chuck 4 can be a vacuum chuck or a electric chuck for holding a wafer 5, the wafer chuck can be drove to spin by a motor 3, the spin speed can be adjusted from 0-3000 rpm. An etching solution injection pipe 10 is above wafer 5 for supplying D.I. water or etching solution when wafer 5 is spinning, a back-side-rinse (BSR) pipe (not shown) supply from the backside. Pipe 10 may move to one side so that the heating lamp housing 6 can lower down as shown in FIG. 2, so that temperature can be adjusted during etching and the etching solution may not fly away. Heating lamps 7 in the heating lamp housing 6 heats the wafer rapidly to a controlled temperature. The light shines through a quartz window 8 on the wafer 5. A fan 9 make the thermal-air flow, Out-side the heating lamp housing 6 clean air or nitrogen is fed through for cooling the etching chamber and prevent the etching vapor to be etched. The air exhaust from an exhausted-pipe-line 12 to a waste gas treatment device (not shown), and the used etching solution is flown to a waste-water treatment device (not shown).

#The first embodiment of the present invention made use of etching silicon dioxide as an example. As the flow chart in FIG. 3, which explain the process of puddle etching. In step 301, load a wafer into a spin processor and spin with speed of 800-1200 rpm. In step 302, inject D.I, water and spin at a speed of 800-1200 rpm to pre-wet the wafer. In step 303, inject etching solution from the front side injection pipe 10 and back side rinse (BSR) with an injection rate of 600 cc/min and spin with 800-1200 rpm to remove the thin film on the surface and the photo-resist on the back-side of the wafer for 10-20 min., the speed may not be too low such that the photo-resist can carry out the particles on the wafer. In step 304, keep the wafer spin at a speed of 800-1200 rpm, stop supply etching solution to spin off the etching solution on the wafer for 1 sec. In step 305, the speed is slow down to 0-50 rpm, form puddle of etching solution by injected etching solution, the flow rate is 0.6-5 L/min for 3 sec., the quantity of etching solution is depend on the size of the wafer, larger wafer need more solution, the spin speed of the wafer is kept in 0-50 rpm to keep the solution stay on the wafer, too fast may loose part of the solution, but without spin may result non-uniformity; In step 306, which is the key point of the present invention, stop injection of etching solution, keep the wafer spin with 0-50 rpm, the better is 15 rpm, this speed depend on the kind of thin film and the viscosity of the etching solution, to keep the solution not fry away from the wafer, but may not stop spinning, and should be spin slowly to keep the solution stay on the wafer uniformly to perform puddle etching, the etching time is depend on the thickness of the thin film. Then in step 307, speed up to 800-1200 rpm, inject D.I. water from the front side and BSR to rinse the wafer for 20-25 sec. In step 308, stop supplying D.I. water on both the front side and BSR, pre-spin with 600-1000 rpm for 1 sec. to spin off the D.I. water. In step 309, inject IPA, the speed is slow down to 40-100 rpm for 1.5 sec. by using Marangoni effect to make the wafer more clean, multiple of little water ball can be seen on the wafer and can be spin off by centrifugal force, In step 310, speed up to 1000-2000 rpm for 2 sec. to pre-dry the wafer. Finally, in step 311, speed up to 3000 rpm or more for 20 sec, to dry the wafer completely. The wafer then is moved out of the processor and the etching step is completed.