Differential contrast plating for advanced packaging applications
A method of electroplating a metal into features, having substantially different depths, of a partially fabricated electronic device on a substrate is provided. The method includes adsorbing accelerator into the bottom of recessed features; partially filling the features by a bottom up fill mechanism in an electroplating solution; diffusing leveler into shallow features to decrease the plating rate in shallow features as compared to deep features; and electroplating more metal into the features such that the height of metal in deep features is similar to the height of metal in shallow features.
1 . A method of electroplating a metal into features of a substrate comprising a partially fabricated electronic device with features in a layer of photoresist over a metal seed layer, wherein the sidewalls of the features in the layer of photoresist are non-conductive, the method comprising:
(a) exposing a surface of a substrate to a pre-acceleration solution comprising an accelerator compound;
(b) immersing at least the surface of the substrate in an electroplating solution comprising ions of the metal, a suppressor, and a leveler of a type that reduces a plating rate of more exposed regions of the substrate surface relative to more recessed regions of the substrate surface;
(c) while the surface of the substrate is immersed in the electroplating solution, electroplating the metal into the features to partially fill the features; and
(d) removing the substrate from the electroplating solution, wherein the features in the layer of photoresist have different depths, different loadings, different shapes, and/or different critical dimensions when viewed top down toward the substrate, and combinations thereof, wherein metal pillars are formed during (c) having top surfaces that deviate from coplanarity by less than bottom surfaces of the features prior to the electroplating in (c).
2 . The method of claim 1 , wherein the surface of the substrate in (a) becomes saturated with accelerator compound.
3 . The method of claim 1 , wherein the leveler reduces the plating rate of more exposed regions of the substrate surface relative to more recessed regions of the substrate surface by polarizing deposition at the more exposed regions of the substrate surface relative to more recessed regions of the substrate surface or by reducing the depolarization effect of the accelerator compound at the more exposed regions of the substrate surface relative to more recessed regions of the substrate surface.
4 . The method of claim 1 , wherein the leveler is characterized by producing an electrochemical response in the following test:
(i) contacting a test solution having an known concentration of the leveler with a metal surface of a test electrode substantially saturated with the an accelerator compound;
(ii) measuring the electrochemical response while plating the test electrode in the test solution having the known concentration of the leveler; and
(iii) determining that the electrochemical response has at least a threshold magnitude.
5 . The method of claim 4 , wherein the test solution has a known concentration of leveler between about 0.1 and about 50 ppm.
6 . The method of claim 4 , wherein the test solution has a known concentration of leveler between about 1 and about 25 ppm.
7 . The method of claim 4 , wherein the test electrode is a rotating disk electrode.
8 . The method of claim 1 , wherein the metal is copper.
9 . The method of claim 1 , wherein the pre-acceleration solution comprises 0.05 to 10 g/L accelerator compound in deionized water or weak acid.
10 . The method of claim 1 , wherein the accelerator compound is a mercapto sulphonic acid compound or a dimercapto sulphonic acid compound.
11 . The method of claim 1 , wherein the accelerator compound is selected from the group consisting of mercaptopropane sulfonic acid, dimercaptopropane sulfonic acid, mercaptoethane sulfonic acid, dimercaptoethane sulfonic acid, and bis-(3-sulfopropyl)-disulfide.
12 . The method of claim 1 , wherein the electroplating solution comprises no accelerator or accelerator at a concentration of less than about 1 ppm.
13 . The method of claim 1 , wherein the leveler in the electroplating solution is selected from the group consisting of polyethylenimines, polyamidoamines, dialkylamines, trialkylamines, arylalkylamines, triazoles, imidazoles, tetrazoles, benzimidazoles, benzotriazoles, piperidine, morpholine, piperazine, pyridine, oxazole, benzoxazole, pyrimidine, quonoline, isoquinoline, and epihalohydrins.
14 . The method of claim 1 , wherein the suppressor in the electroplating solution is selected from the group consisting of polyethylene glycols, polyethylene oxides, polypropylene glycols, and polypropylene oxides.
15 . The method of claim 1 , wherein exposing the surface of a substrate to the pre-acceleration solution comprising an accelerator compound is performed in a first chamber and wherein electroplating the metal into the features to partially fill the features is performed in a second chamber.
16 . The method of claim 15 , wherein the first chamber is operated at sub-atmospheric pressure while exposing the surface of a substrate to the pre-acceleration solution comprising an accelerator compound.
17 . The method of claim 1 , wherein pillars are formed during the electroplating (c) having less non-uniformity than the features in the layer of photoresist prior to the electroplating in (c).
18 . The method of claim 1 , further comprising:
stopping electroplating metal in (c) before the features in the layer of photoresist are fully filled;
immersing at least the surface of the substrate in a second electroplating solution comprising ions of the metal, and an additive composition that is different from that in the electroplating solution used in (b) and (c); and
electroplating more of the metal into the features in the layer of photoresist, to further fill the features, while contacting the features with a second electroplating solution.
19 . The method of claim 18 , wherein second electroplating solution comprises a greater concentration of leveler and accelerator than are present in the electroplating solution used in (b) and (c).
20 . The method of claim 1 , further comprising:
stopping electroplating the metal in (c) before the features in the layer of photoresist are fully filled;
again exposing the surface of a substrate to the pre-acceleration solution and allowing the surface of the substrate, as partially electroplating with the metal, to become substantially saturated with the accelerator compound; and
electroplating additional metal in the features in the layer of photoresist using a second electroplating solution.
21 . The method of claim 1 , wherein the electroplating in (c) produces metal pillars that are a component of wafer level packaging.
22 . The method of claim 21 , further comprising forming a contact between the metal pillars and a tin silver composition.
23 . The method of claim 1 , wherein the features in the layer of photoresist on the substrate are holes, and wherein electroplating the metal in operation (c) forms metal pillars in the holes.
24 . The method of claim 23 , wherein the bases of the holes comprise a conductive seed layer.
25 . The method of claim 1 , wherein the features in the layer of photoresist have an average depth of at least about 20 to 70 μm.
26 . The method of claim 1 , wherein the features in the layer of photoresist have an average depth of at least about 5 μm.
27 . The method of claim 1 , wherein the features in the layer of photoresist have an average depth of at most about 270 μm.
28 . The method of claim 1 , wherein the features in the layer of photoresist have an average width of at least about 10 to 100 μm.
29 . The method of claim 1 , wherein the features in the layer of photoresist have a difference in depth between deepest and shallowest features of at least about 5 microns.
30 . The method of claim 1 , wherein the shallowest feature in the layer of photoresist is at least about 5% shorter than the deepest feature in the layer of photoresist.
31 . The method of claim 1 , wherein the shallowest feature in the layer of photoresist is at least about 10% shorter than the deepest feature in the layer of photoresist.
32 . The method of claim 1 , wherein at least some of the features in the layer of photoresist have an aspect ratio of between about 1:2 and 10:1.
33 . The method of claim 1 , wherein during electroplating in (c), the deepest feature has a mass transfer boundary layer in the electroplating solution having a thickness of less than about 50 micrometers.
34 . The method of claim 1 , wherein during electroplating in (c), fluid velocity near the substrate surface is between about 0.1 and 1.0 m/s and the fluid flow is at least partially laminar.
35 . The method of claim 1 , wherein during electroplating in (c), leveler diffuses into shallow features faster than deep features, reducing the electroplating rate in shallow features compared to deep features.
36 . The method of claim 35 , wherein at least one of the deep features is at least 5% deeper than at least one of the shallow features.