Spin-rinse-drying process for electroplated semiconductor...

Details Spin-rinse-drying process for electroplated semiconductor... Spin-rinse-drying process for electroplated semiconductor...

1998-11-30

2001-09-18

Gulakowski, Randy (Department: 1746)

Etching a substrate: processes

Nongaseous phase etching of substrate

Projecting etchant against a moving substrate or controlling...

C438S748000, C438S928000

Reexamination Certificate

active

06290865

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field
The present invention relates to cleaning of unwanted materials deposited on a substrate or other workpiece. Specifically, the invention relates to dissolving deposited metals from the backside and/or edge of a substrate following a deposition.
2. Background
Sub-quarter micron multi-level metallization is one of the key technologies for the next generation of ultra large scale integration (ULSI). The multilevel interconnects that lie at the heart of this technology require planarization of interconnect features formed in high aspect ratio apertures, including contacts, vias, lines and other features. Reliable formation of these interconnect features is very important to the success of ULSI and to the continued effort to increase circuit density and quality on individual substrates and die.
As circuit densities increase, the widths of vias, contacts and other features, as well as the dielectric materials between them, decrease to less than 0.25 &mgr;m, whereas the thickness of the dielectric layers remains substantially constant, with the result that the aspect ratios for the features, i.e., their height divided by width, increases. Many traditional deposition processes have difficulty filling structures where the aspect ratio exceeds 4:1, and particularly where it approaches 10:1. Additionally, as the feature widths decrease, the device current remains constant or increases, which results in an increased current density in the feature.
Aluminum and its alloys have been the traditional metals used to form lines and plugs and other features in semiconductor processing. However, with the increase in circuit densities, copper is becoming a choice metal for filling sub 0.25 &mgr;m, high aspect ratio interconnect features on semiconductor substrates. Copper and its alloys have lower resistivities compared to aluminum and high electromigration resistance. These characteristics are important for supporting the higher current densities experienced at high levels of integration and increased device speed. Copper also has good thermal conductivity and is available in a highly pure state.
Despite the desirability of using copper for semiconductor device fabrication, choices of fabrication methods for depositing copper into very high aspect ratio features, such as a 10:1 aspect ratio, 0.25 &mgr;m wide vias are limited. Precursors for CVD deposition of copper are being developed, and physical vapor deposition into such small features has produced unsatisfactory results because of voids formed in the features. As a result of these process limitations, electroplating, which had previously been used primarily in circuit board fabrication in the electronics industry, is being used to fill features, such as vias, on semiconductor devices. Thus, efforts are being explored to improve the electroplating process to be suitable for substrate manufacturing, especially in high aspect ratio features of substrates.
FIG. 1
is a partial cross section representing a substrate edge with a series of layers deposited thereon. The substrate
2
has a silicon base
4
with an edge profile
6
that typically is beveled with a first bevel
8
on a front side
12
and a second bevel
10
on a backside
14
. The base has doped regions
15
that connect to feature
20
, such as the contact shown, to form a portion of the circuitry of the semiconductor. A dielectric layer
16
is deposited on the base
4
and is etched to form apertures, followed by the deposition of a barrier layer
18
, using Ti, TiN, Ta, TaN, and other known materials. The barrier layer reduces migration and diffusion of adjacent layers and may also provide good adhesion to the silicon oxide and subsequent metal layer. A conductive layer
21
, typically aluminum or copper, is deposited over the barrier layer, such as by electroplating, and fills the apertures to form the interconnects between the layers.
The integrity of the barrier layer in the edge region is sometimes compromised in that typical processes such as physical vapor deposition (PVD) and chemical vapor deposition (CVD) may not uniformly deposit around the edge profile. Thus, the conductive layer material may diffuse into the underlying layers and poison the semiconductor device. Furthermore, some backside deposit
22
may occur on the second surface
14
, further heightening the possibility of unwanted diffusion into the layers. Because copper has a high diffusion capability and can poison the device, this unwanted deposition can adversely affect the performance gains achieved using copper. Therefore, a preferred substrate fabrication process would remove this copper or other unwanted materials from the backside or from other surfaces where it may have been deposited.
FIG. 2
is a partial cross section representing a desired deposition profile on the substrate
2
. The layers are distanced from the edge of the substrate to form an edge exclusion zone
6
a.
In PVD and CVD processing which are typically dry processes, the ability to define the edge exclusion zone is well known, using for instance, clamp rings, shadow rings, and purge gases. However, electroplating is typically a wet process on a substrate facing downward and is more difficult to control, leading to backside and edge deposits on the substrate. If, for instance, the layers had been deposited as in
FIG. 1
, then it would be advantageous to remove the layers from the edge to allow the edge exclusion zone. The edge exclusion zone
6
a
may be from about 1 mm to about 3 mm or more. In processing, there would be less likelihood of the edge deposits being dislocated from the substrate, thereby contaminating subsequent substrates, and less likelihood of unwanted diffusion through the layers.
An advantageous process to reduce or eliminate the unwanted deposition would preferably combine with an existing stage in the electroplating process. Part of the electroplating process involves rinsing the substrate after depositing the material, where the substrate is typically taken to a spin-rinse-dry chamber, represented in
FIG. 3. A
spin-rinse-dry chamber
23
includes a cover
23
a
which helps retain the fluids in the chamber. The chamber also includes a chamber top
23
b,
to which the cover
23
a
attaches, and a chamber bottom
23
c.
In one commercial system, the chamber top and bottom separate with a chamber lift
25
to allow a robot (not shown) to insert a substrate
2
into the chamber onto the pedestal
26
. The pedestal
26
may have a vacuum port
26
a
in each pedestal arm
26
b
that are ultimately connected to a vacuum source
28
, where the pedestal arms hold and center the substrate
2
to the pedestal. The pedestal or portion thereof may raise and lower to contact the substrate delivered by the robot. The pedestal
26
supports the substrate
2
during processing. The pedestal actuator
27
rotates the pedestal to spin the substrate to assist in rinsing and/or drying. The chamber top
23
b
generally includes a plurality of spray nozzles 29. These nozzles spray the rinsing fluid to impact and rinse the substrate surface. Typical rinsing fluids are deionized water, alcohol, or a combination thereof. After rinsing, the pedestal continues to spin the substrate, perhaps at a different speed, to effectively dry the surface.
Therefore, there remains a need for an apparatus and method to remove unwanted backside and edge depositions on a substrate, preferably by integrating the removal process into a spin-rinse-dry chamber.
SUMMARY
The present invention provides a method and apparatus to remove unwanted deposited material from a substrate backside by chemically dissolving the material, while at least partially protecting the substrate front side from the effects of this dissolution and removal process. Preferably, the dissolving process is included with a spin, rinse, and dry process and uses a greater flow of rinsing fluid onto the front side of the substrate compared to the flow of dissolving fluid onto the backside of the substrate to prevent the material from being removed from t

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