Process and apparatus for forming stoichiometric layer of a metal compound by closed loop voltage controlled reactive sputtering

An improved process for forming a layer of a stoichiometric metal compound on a semiconductor wafer by reactive sputtering a metal target in a chamber in the presence of a reactive gas, wherein the improvements comprise:

• (a) changing the negative potential on said metal target to maintain a stoichiometric supply of sputtered metal atoms available to react with the atoms of said reactive gas at a fixed flow of said gas by changing the power level of a constant power source electrically connected to said target;
• and
• (b) providing a path for the flow of said reactive gas to the zone between said target and said wafer, while restricting the travel of said stoichiometric metal compound from said zone;
• to thereby provide a stoichiometric ratio of said sputtered metal atoms and said reactive gas atoms adjacent said wafer to form said stoichiometric metal compound on said wafer.

An improved apparatus for forming a layer of a stoichiometric metal compound on a semiconductor wafer by reactive sputtering a metal target in a chamber in the presence of a reactive gas, wherein the improvements comprise:

• (a) means for changing the negative potential on said metal target to restore the stoichiometry of the sputtered metal atoms available to react with the atoms of said reactive gas at a fixed flow of said gas to form said stoichiometric metal compound, comprising means for changing the power level of a constant power source electrically connected to said target;
• and
• (b) means for providing a path for the flow of said reactive gas to a zone between said target and said wafer, while restricting the travel of said stoichiometric metal compound from said zone to other portions of said chamber;
• to thereby provide a stoichiometric ratio of said sputtered metal atoms and said reactive gas atoms adjacent said wafer to form said stoichiometric metal compound on said wafer.

Apparatus for reactive sputtering of a layer of a stoichiometric metal compound on a semiconductor wafer formed by reaction between a sputtered metal and a reactive gas, comprising:

• (a) a vacuum chamber having a top wall;
• (b) a metal target mounted adjacent said top wall of said chamber;
• (c) means for retaining a circular semiconductor wafer in said chamber in a position below said target and generally axially aligned therewith;
• (d) a first cylinder having an upper end mounted to said top wall of said chamber and depending downwardly below said target and generally symmetrically surrounding said target;
• (e) a second cylinder generally coaxially surrounding said first cylinder and having an upper end spaced from said said top wall to define a first passageway therebetween and a lower end depending downwardly beyond a lower end of said first cylinder;
• (f) support means in said chamber to support said second cylinder in said chamber in said position coaxially surrounding said first cylinder;
• (g) a third cylinder coaxially positioned within said first cylinder having an inner diameter slightly larger than said semiconductor wafer and having an upper end spaced from said top wall of said chamber to define a second passageway therebetween and a lower end depending down approximately the same distance as said lower end of said second cylinder;
• (h) a circular bottom wall joined to said lower ends of said second and third cylinders to seal off the space therebetween;
• whereby a gas passage will be defined leading from the space in said chamber outside of said second cylinder through said first passageway into the space between said first and second cylinders, then down around said lower end of said first cylinder and to the space between said first and third cylinders and then through said second passageway to permit said reactive gas to emerge adjacent said wafer to react with said sputtered metal to form said coating on said wafer.