Methods for optical endpoint detection using an endpoint booster

Abstract

Plasma etching a semiconductor wafer in a vacuum etch chamber includes transmitting an optical signal through an aperture in an endpoint booster that is coupled to a vacuum side of the vacuum etch chamber, analyzing the optical signal to determine an endpoint of the plasma etch process, ending the plasma etch process when the optical signal reaches a first threshold, and cleaning the viewport when the optical signal is below a second threshold. The endpoint booster inhibits process byproducts from accumulating on the viewport during the plasma process, which increases the time between chamber cleanings. The reduction in chamber downtime for cleaning increases production throughput.

What is claimed is: 
     
         1 . A method to etch a semiconductor wafer in a vacuum etch chamber, the method comprising transmitting an optical signal through an aperture in an endpoint booster to a fiber optic cable during a plasma etching process of the semiconductor wafer, the vacuum etch chamber including a viewport window having a vacuum side and an atmospheric side, the fiber optic cable optically coupled to the atmospheric side of the viewport window, the aperture configured to channel the optical signal from the vacuum etch chamber to the fiber optic cable, the endpoint booster having a front side and a back side, the back side of the endpoint booster installed next to the vacuum side of the viewport window within a wall of the vacuum etch chamber and the front side of the endpoint booster exposed to an interior of the vacuum etch chamber, the front side including a removal port configured to receive a removal tool thereby permitting an operator to remove the endpoint booster from within the vacuum etch chamber to clean the viewport window. 
     
     
         2 . The method of  claim 1  further comprising ending the plasma etching process when the optical signal reaches a first threshold. 
     
     
         3 . The method of  claim 2  further comprising removing the endpoint booster from within the vacuum etch chamber using the removal tool to access the viewport window within the vacuum etch chamber. 
     
     
         4 . The method of  claim 2  further comprising cleaning the vacuum etch chamber when the optical signal is below a second threshold due to byproduct deposit on the viewport window. 
     
     
         5 . The method of  claim 1  wherein the endpoint booster increases time between vacuum etch chamber cleanings. 
     
     
         6 . The method of  claim 1  wherein the aperture of the endpoint booster extends from the front side to the back side. 
     
     
         7 . The method of  claim 1  wherein the aperture includes a first diameter and a second diameter. 
     
     
         8 . The method of  claim 7  wherein the endpoint booster further includes a first length and a second length such that the front side of the endpoint booster includes a first opening along the first length corresponding to the first diameter and the back side of the endpoint booster has a second opening along the second length corresponding to the second diameter. 
     
     
         9 . The method of  claim 7  wherein the aperture includes a plurality of clustered holes extending through the endpoint booster from the front side to the back side and forming a plurality of concentric circles about a center point of the endpoint booster, a first concentric circle having the first diameter and a second concentric circle having the second diameter. 
     
     
         10 . The method of  claim 1  wherein the endpoint booster comprises an aluminum cylinder approximately 0.60 inches long with an approximately 1.50 inches outer diameter. 
     
     
         11 . A method to etch a semiconductor wafer in a vacuum etch chamber, the method comprising:
 transmitting an optical signal through an aperture in an endpoint booster to a fiber optic cable during a plasma etching process of the semiconductor wafer, the vacuum etch chamber including a viewport window having a vacuum side and an atmospheric side, the fiber optic cable optically coupled to the atmospheric side of the viewport window, the aperture configured to channel the optical signal from the vacuum etch chamber to the fiber optic cable, a back side of the endpoint booster installed next to the vacuum side of the viewport window within a wall of the vacuum etch chamber and a front side of the endpoint booster exposed to an interior of the vacuum etch chamber;   determining the optical signal is below a threshold; and   removing the endpoint booster from within the vacuum etch chamber using a removal tool, the front side of the endpoint booster including a removal port configured to receive the removal tool thereby permitting an operator to remove the endpoint booster from within the vacuum etch chamber.   
     
     
         12 . The method of  claim 11  further comprising accessing the viewport window after removing the endpoint booster. 
     
     
         13 . The method of  claim 11  wherein determining the optical signal is below a threshold includes determining a signal strength of the optical signal is below the threshold. 
     
     
         14 . The method of  claim 11  further comprising cleaning the vacuum etch chamber when the optical signal is below the threshold due to byproduct deposit on the viewport window. 
     
     
         15 . The method of  claim 14  wherein the endpoint booster increases time between the vacuum etch chamber cleanings. 
     
     
         16 . The method of  claim 11  wherein the aperture of the endpoint booster extends from the front side to the back side. 
     
     
         17 . The method of  claim 11  wherein the aperture includes a first diameter and a second diameter. 
     
     
         18 . The method of  claim 17  wherein the endpoint booster further includes a first length and a second length such that the front side of the endpoint booster includes a first opening along the first length corresponding to the first diameter and the back side of the endpoint booster has a second opening along the second length corresponding to the second diameter. 
     
     
         19 . The method of  claim 17  wherein the aperture includes a plurality of clustered holes extending through the endpoint booster from the front side to the back side and forming a plurality of concentric circles about a center point of the endpoint booster, a first concentric circle having the first diameter and a second concentric circle having the second diameter. 
     
     
         20 . The method of  claim 19  wherein the first diameter is approximately 0.50 inches and the second diameter is approximately 0.25 inches.