Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
1999-08-06
2001-08-07
Quach, T. N. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S753000, C257S763000, C257S764000
Reexamination Certificate
active
06271592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a barrier layer structure deposited on a semiconductor substrate, wherein the barrier layer structure comprises oxygen to improve the performance of the barrier layer, and to the method used to deposit this barrier layer structure on the substrate.
2. Brief Description of the Background Art
As is well-known in the semiconductor device art, conventional integrated circuit processing steps can cause silicon atoms to diffuse from single-crystal silicon into a metal electrode of pure aluminum to such a depth as to short out a shallow p-n junction in the silicon; this phenomenon is known as junction spiking. Variance occurs during the etching of contacts, and when a contact is over-etched, an increase in spiking is observed. Over-etching provides more area for silicon and aluminum interdiffusion to occur at the bottom of a contact.
To elevate the contact bottom and thus prevent the interdiffusion of adjacent layers of aluminum and silicon and the resultant junction spiking at the bottom of a contact, barrier layers were introduced between the silicon and the overlying aluminum layer prior to aluminum filling and planarization. The most commonly used barrier layer for aluminum contacts is titanium nitride. The titanium nitride may be used alone or in combination with titanium, which may be used to decrease the resistance of the contact. Titanium nitride and titanium layers are typically deposited at the bottom and on the sidewalls of a contact via using physical vapor deposition (PVD). PVD techniques are well-known in the art.
Ion Metal Plasma (IMP) sputter deposition is a recently developed method of PVD which provides uniform barrier layer bottom and sidewall coverage in small contacts. IMP sputter deposition of titanium nitride barrier layers is disclosed in U.S. application Ser. No. 08/511,825 U.S. Pat. No. 5,962,923 of Xu et al., assigned to the assignee of the present invention.
In particular, “IMP” sputtering refers to deposition sputtering, where sputtered target material is passed through an ionization means, such as an inductively coupled RF source, to create a high density, inductively coupled RF plasma between the sputtering cathode (target) and the substrate support electrode. This ensures that a higher portion of the sputtered emission is in the form of ions at the time it reaches the substrate surface. Although not required, the substrate toward which the sputtered ions are moving is typically biased to attract the incoming ions.
IMP sputter-deposited titanium nitride films having low stress and providing high bottom coverage in high aspect ratio features are disclosed in U.S. application Ser. No. 09/003,014, filed Jan. 5, 1998. Although IMP sputter-deposited titanium nitride provides excellent bottom coverage for small contacts, as contact size decreases, increasingly rigorous process conditions (for example, higher process temperatures) are needed, which may cause the titanium nitride layer to fail as a barrier layer. One method of improving the effectiveness of the titanium nitride barrier layer is by oxygen stuffing. The presence of the oxygen atoms in the titanium nitride matrix disrupts channel formation through which mobile silicon atoms at the bottom of the contact can travel.
While oxygen stuffing of sputter-deposited titanium nitride films does prevent the migration of silicon upward from the bottom of the contact, it also introduces additional problems: the oxygen can migrate through the thin titanium nitride barrier layer to the titanium wetting layer on the sidewalls of the contact via, contaminating the titanium wetting layer and forming a layer of titanium oxide which can interfere with the filling of the contact via. Additionally, during filling of the contact, the oxygen can react with the aluminum fill as it flows over the barrier layer surface, resulting in the formation of an undesirable layer of aluminum oxide on the interior surface of the contact via. Aluminum oxide at the bottom of the contact layer increases contact resistivity and aluminum oxide on the sidewalls of the contact via prevents aluminum from flowing easily over the surface of the sidewalls and can cause void formation within the contact.
Therefore, a method of depositing an effective oxygen-containing barrier layer at the bottom of a contact to prevent spiking, while minimizing the oxygen content on the contact via sidewalls to permit complete filling of very small contacts, would be highly advantageous.
SUMMARY OF THE INVENTION
Applicants have discovered that depositing the various film layers of a barrier layer structure in a particular order using a combination of IMP sputter deposition and traditional sputter deposition with specific process conditions produces a barrier layer structure having minimum sidewall oxygen content, which provides excellent barrier properties and allows metal/conductor filling of very small feature sizes while preventing spiking.
It is an object of this invention to provide a barrier layer structure which provides excellent barrier properties in order to prevent junction spiking.
It is an object of this invention to provide a barrier metal wetting layer surface having minimum oxygen content.
It is a further object of this invention to provide a method to achieve complete, void-free metal/semiconductor filling of very small (0.25 micron and smaller) features such as contact vias.
Accordingly, disclosed herein is a barrier layer structure deposited on a substrate. The structure comprises the following layers, deposited from bottom to top:
(a) a first layer of a barrier metal (M), wherein the first layer of barrier metal is deposited by IMP sputter deposition;
(b) a second layer of an oxygen-stuffed barrier metal (MOx), an oxygen-stuffed nitride of a barrier metal (MNOx), or a combination thereof;
(c) a third layer of a nitride of a barrier metal (MN
x
), wherein the third layer of barrier metal nitride is deposited by IMP sputter deposition of the barrier metal in the presence of nitrogen; and
(d) a fourth, wetting layer of a barrier metal, wherein the wetting layer of barrier metal is deposited by traditional sputter deposition or by IMP sputter deposition.
The barrier metal is preferably selected from the group consisting of titanium, tantalum, and tungsten, and is most preferably titanium.
Power to an RF coil used for IMP sputter deposition of the first layer of barrier metal preferably ranges from about 500 W to about 3500 W. The second layer of oxygen-stuffed barrier metal and/or oxygen-stuffed barrier metal nitride is preferably deposited by traditional sputter deposition (i.e., diode sputtering where the power to the target provides the power to support the plasma used to sputter the target, and no specialized energy source, such as an internal inductively coupled coil (for purposes of additional ion generation) or external microwave energy source, need be provided to support the standard source of plasma generation), and DC target power used during deposition of the second layer preferably ranges from about 100 W to about 4000 W. Power to an RF coil used for IMP sputter deposition of the third layer of barrier metal nitride preferably ranges from about 500 W to about 3500 W. The fourth, wetting layer of barrier metal is preferably deposited by traditional (i.e., diode) sputter deposition, and DC target power used during deposition of the fourth layer preferably ranges from about 500 W to about 7500 W.
The barrier layer structure preferably further comprises an additional layer of barrier metal deposited between the second layer of oxygen-stuffed barrier metal and the third layer of barrier metal nitride. The additional layer of barrier metal is preferably deposited by traditional sputter deposition, and DC target power used during deposition of the additional layer of barrier metal preferably ranges from about 500 W to about 7500 W.
The substrate at the bottom of a feature such as a contact via preferably comprises silicon, and the first layer of barrier me
Cha Chris
Dorleans Fernand
Fu Jianming
Kim Edwin
Kohara Gene Y.
Applied Materials Inc.
Bean Kathi
Church, Esq. Shirley L.
Quach T. N.
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