Pretreatment method for photoresist wafer processing
Certain embodiments herein relate to methods and apparatus for processing a partially fabricated semiconductor substrate in a remote plasma environment. The methods may be performed in the context of wafer level packaging (WLP) processes. The methods may include exposing the substrate to a reducing plasma to remove photoresist scum and/or oxidation from an underlying seed layer. In some cases, photoresist scum is removed through a series of plasma treatments involving exposure to an oxygen-containing plasma followed by exposure to a reducing plasma. In some embodiments, an oxygen-containing plasma is further used to strip photoresist from a substrate surface after electroplating. This plasma strip may be followed by a plasma treatment involving exposure to a reducing plasma. The plasma treatments herein may involve exposure to a remote plasma within a plasma treatment module of a multi-tool electroplating apparatus.
1. A method of removing photoresist scum and electroplating metal into photoresist features, the method comprising
(a) receiving a substrate in a multi-tool electroplating apparatus, the multi-tool electroplating apparatus comprising:
(i) a plasma treatment module comprising a plasma treatment chamber and a plasma generation chamber connected to the plasma treatment chamber; and
(ii) an electroplating module comprising an electroplating chamber;
wherein the substrate comprises:
(i) a metal seed layer, and
(ii) a layer of photoresist over and directly in contact with the metal seed layer, wherein the layer of photoresist comprises photoresist features patterned therein, and wherein a bottom of the photoresist features comprise photoresist scum;
(b) generating a first oxidizing plasma from a first oxidizing plasma generation gas in the plasma generation chamber and flowing the first oxidizing plasma from the plasma generation chamber into the plasma treatment chamber to thereby expose the substrate to the first oxidizing plasma and react the photoresist scum with the first oxidizing plasma, to thereby remove at least a portion of the photoresist scum and oxidize a portion of the metal seed layer;
(c) generating a reducing plasma from a reducing plasma generation gas in the plasma generation chamber and flowing the reducing plasma from the plasma generation chamber into the plasma treatment chamber to thereby expose the substrate to the reducing plasma and react the oxidized portion of the metal seed layer with the reducing plasma, to thereby reduce the oxidized portions of the metal seed layer; and
(d) transferring the substrate to the electroplating module and electroplating metal on the metal seed layer in the photoresist features.
2. The method of claim 1 , wherein the reducing plasma generation gas comprises one or more of hydrogen, ammonia, nitrogen, carbon monoxide, diborane, sulfite compounds, hydrocarbons, phosphites, and/or hydrazine.
3. The method of claim 1 , wherein the reducing plasma generation gas comprises hydrogen.
4. The method of claim 1 , further comprising:
(e) after electroplating in (d), transferring the substrate to the plasma treatment chamber, generating a stripping plasma in the plasma generation chamber from a stripping plasma generation gas, flowing the stripping plasma from the plasma generation chamber into the plasma treatment chamber, exposing the substrate to the stripping plasma, and thereby reacting the stripping plasma with the layer of photoresist to strip the layer of photoresist from the substrate.
5. The method of claim 4 , wherein operation (e) forms oxidized portions of the metal seed layer, and further comprising:
(f) after stripping the layer of photoresist in (e), generating a second reducing plasma in the plasma generation chamber from a second reducing plasma generation gas, flowing the second reducing plasma from the plasma generation chamber into the plasma treatment chamber, and exposing the substrate to the second reducing plasma to thereby react the oxidized portions of the metal seed layer with the second reducing plasma to reduce the oxidized portions of the metal seed layer.
6. The method of claim 5 , wherein the second reducing plasma generation gas comprises one or more of hydrogen, ammonia, nitrogen, carbon monoxide, diborane, sulfite compounds, hydrocarbons, phosphites, and/or hydrazine.
7. The method of claim 1 , wherein the photoresist features define the geometry of at least one wafer level packaging structure.