Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2000-04-06
2002-03-12
Eley, Timothy V. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S054000, C451S063000, C051S307000, C438S692000
Reexamination Certificate
active
06354916
ABSTRACT:
BACKGROUND AND SUMMARY OF INVENTION
Multi-level integrated circuit manufacturing requires many steps for metal and insulator film depositions followed by photoresist patterning and etching or other means of material removal. After photolithography and etching, the resulting wafer or substrate surface is non-planar and contains many features such as vias, lines, or channels. Often these features need to be filled with a specific material such as a metal, and then the wafer topographic surface needs to be planarized again, making it ready for the next level of processing.
Electrodeposition is a widely accepted technique for the deposition of a highly conductive material such as copper (Cu) into the features on the semiconductor wafer surface. Chemical mechanical polishing (CMP) is then employed to planarize the resulting surface.
In
FIG. 1
a
, the large feature
1
and the small feature is are opened in the insulator layer
2
, which is grown on a wafer. To fill these features with Cu, a barrier or adhesive layer
3
is first deposited over the whole wafer surface. Then a conductive Cu seed layer
4
is deposited over the barrier layer
3
. Cu is electrodeposited over the whole surface by (1) making an electrical contact to the barrier layer
3
and/or the Cu seed layer
4
; (2) placing the wafer in a standard Cu plating electrolyte; (3) placing an anode in the electrolyte; and (4) applying a negative voltage to the Cu seed layer with respect to the anode.
FIG. 1
b
shows the wafer after a short period of time which is adequate to deposit a Cu layer
5
with the thickness
5
a
. As shown in
FIG. 1
b
, the Cu layer of nominal thickness
5
a
is adequate to fill in the small feature is since there is Cu film growth even on the conductive vertical walls of this feature. The large feature
1
, however, is still not filled with Cu. To fill the large feature
1
, Cu plating needs to proceed further, eventually yielding the structure depicted in
FIG. 1
c.
As can be seen in
FIG. 1
c
, in this conventional approach, the electrodeposited Cu layer
5
forms a very large metal overburden
6
on the top surface of the insulator
2
and over the small feature
1
s
. The overburden
6
a
over the large feature
1
is very small. The surface of the structure in
FIG. 1
c
is non-planar, and therefore needs to be polished and planarized. The overburden and portions of the barrier layer
3
are customarily removed by CMP, yielding the structure in
FIG. 1
d
, which has electrically isolated Cu-filled features. Removal of the large and non-uniform metal overburden of
FIG. 1
c
from the wafer surface is time consuming and expensive and is a major source of dishing defects
6
b
in large features.
It would be highly desirable if the plating process could yield a Cu film which was planar and had a uniform overburden as depicted in
FIG. 1
e
. CMP of such a substrate would be much faster and more economical and defects would be minimized. If the plating process could yield Cu-filled features with no overburden as depicted in
FIG. 1
f
, then there would not be the need for CMP of the Cu layer. Only the portions of the barrier layer
3
on the top surface of the insulator
2
would have to be removed.
Electrodeposition is commonly performed in specially formulated plating solutions or electrolytes containing ionic species of Cu as well as additives that control the texture, morphology, and the plating behavior of the Cu layer. A proper electrical contact is made to the seed layer on the wafer surface, typically along its circumference, and the wafer surface is dipped in the plating solution. A consumable Cu anode or an inert anode plate is also placed in the electrolyte. Deposition of Cu on the wafer surface can then be initiated when a cathodic potential is applied to the wafer surface with respect to the anode (i.e., when a negative voltage is applied to the wafer surface with respect to the anode plate).
There are many Cu plating solution formulations, some of which are commercially available. One such formulation uses Cu-sulfate (CuSO
4
) as the copper source. James Kelly et al.,
J. Electrochemical Society
, vol.146, p. 2540-45 (1999). A typical Cu-sulfate plating solution contains water; Cu-sulfate; sulfuric acid (H
2
SO
4
); a small amount of chloride ions; and a carrier, such as polyethylene glycols and/or polypropylene glycols. Some other chemicals are then added to this solution in small amounts to achieve certain properties of the Cu deposit. These additives can be classified under general categories such as levelers, brighteners, grain refiners, wetting agents, stress-reducing agents, and the like.
Commonly used levelers and brighteners are generally sulfur-containing compounds, such as derivatives of thiourea. Other levelers and brighteners are sulfonic acid derivatives, such as mercaptobenzene sulfonate. Other brighteners include 2,4-imidazolidine-diol, thiohydantoin, polyethers, polysulfides, and various dyes. There is a large volume of literature on the additives for Cu-plating solutions and their influence on the electroplated deposits. For example, U.S. Pat. No. 4,430,173 discloses an additive composition comprising the sodium salt of &ohgr;-sulfo-n-propyl N,N-diethyldithiocarbamate and crystal violet, which shows excellent stability. U.S. Pat. No. 4,948,474 discloses a brightener additive for a Cu plating solution. U.S. Pat. No. 4,975,159 discloses lists of alkoxylated lactams and sulfur-containing compounds which were found to be effective additives. U.S. Pat. No. 3,328,273 describes Cu plating baths containing organic sulfide compounds.
Although a large volume of literature exists on the subject of additives to Cu plating solutions, many of the additive formulations are kept as trade secrets by plating solution suppliers. Some examples of Cu plating additive solutions provided commercially are: (1) CUBATH M® system, marketed by Enthone-OMI; (2) COPPER GLEAM® system, marketed by LeaRonal; and (3) ULTRAFILL® Addition agent and Suppressor, marketed by Shipley. Commercially available Cu plating solutions with additives typically yield bright and soft Cu deposits that have low stress. Copper layers deposited out of these solutions cannot be polished and planarized with the same solution, simply because the plating solutions are formulated only for plating, not for polishing or planarization.
Copper layers are traditionally polished and planarized by CMP in a machine specifically designed for polishing. In this method, the plated wafer is loaded onto a carrier head. The wafer surface covered with the non-planar Cu deposit (
FIG. 1
c
) is brought into contact with a polishing pad and a polishing slurry. The polishing slurry contains oxidizing chemicals and micron or sub-micron size abrasive particles. When the pad and the wafer surfaces are pressed together and moved with respect to each other, polishing by the abrasive particles is initiated and the metal overburden is removed from the surface. A different CMP slurry is used to remove the barrier layer from the top surface of the insulator. The desired planar surface with electrically isolated Cu-filled features shown in
FIG. 1
d
is eventually obtained.
The chemistry of the polishing slurry and the type of the abrasive particles used in a given CMP process are selected according to the chemical nature of the material to be removed. Therefore, the compositions of the polishing slurries for copper, tungsten, tantalum, tantalum nitride, silicon dioxide, and like materials that are used in integrated circuit (IC) manufacturing may all be different. For example, U.S. Pat. Nos. 4,954,142; 5,084,071; 5,354,490; 5,770,095; 5,773,364; 5,840,629; 5,858,813; 5,897,375; 5,922,091; and 5,954,997, all disclose various CMP slurry compositions for effective polishing of Cu. Slurries typically contain a solvent and a selection of abrasive particles, such as silica or alumina particles, which are suspended in the solvent. Furthermore, complexing agents such as NH
3
and/or oxidizing agents such as NO
3
−
and Fe(CN)
6
3−
are also inc
Basol Bulent
Talieh Homayoun
Uzoh Cyprian
Crowell & Moring LLP
Eley Timothy V.
Nu Tool Inc.
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