Gas inlets for wafer processing chamber

Details Gas inlets for wafer processing chamber Gas inlets for wafer processing chamber

1999-06-02

2002-12-31

Sherry, Michael (Department: 2829)

Semiconductor device manufacturing: process

Formation of semiconductive active region on any substrate

C438S492000

Reexamination Certificate

active

06500734

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to semiconductor processing apparatus and, more particularly, to a method and apparatus of supplying two different processing gases to a semiconductor wafer processing chamber.
2. Brief Description of the Prior Art
Present-day equipment for the semiconductor industry is moving toward single substrate processing because processing chambers can be made smaller and processing can be better controlled. Further, modern semiconductor vacuum processing systems have been developed to carry out more than one processing step on a substrate without removing the substrate from a vacuum environment. The use of such vacuum systems results in a reduced number of particulates that contaminate the surface of the wafer during processing, thereby improving the device yield.
A typical example of a modern CVD processing apparatus is shown in FIG.
1
. In this figure, a single substrate reactor
10
is shown to include a top
12
, side walls
14
and a lower portion
16
that, together, define a chamber
18
into which a single substrate, such as a silicon wafer
20
, can be loaded. The wafer
20
is mounted on a susceptor
22
that can be rotated by a drive
23
to provide a time-averaged environment for the wafer
20
that is cylindrically symmetric.
A preheat ring
24
is supported in the chamber
18
and surrounds the susceptor
22
. The wafer
20
and the preheat ring
24
are heated by light from a plurality of high-intensity lamps, schematically indicated as
26
, mounted inside of the reactor
10
. The top
12
and lower portion
16
of the reactor
10
are typically made from clear quartz which is transparent to the light from lamps
26
. Quartz is generally used to make up the top
12
and lower portion
16
because it is transparent to light of both visible and IR frequencies, because it exhibits a relatively high structural strength and because it is chemically stable in the process environment of the chamber.
During the deposition process, processing gas (whether reactant or dopant) is supplied to the interior of the chamber
18
from an exterior source, schematically represented by two tanks
28
. The gas flows from the gas supply
28
along a gas supply line
30
and into the chamber
18
via a gas inlet port
32
. From the port
32
, the gas flows across the preheat ring
24
where it heats up, across the susceptor
22
and wafer
20
in the direction of the arrows
34
, to be evacuated from the chamber
18
through evacuation port
36
. The dominant shape of the flow profile of the gases is laminar from the gas input port
32
and across the preheat ring
24
and the wafer
20
to the exhaust port
36
, even though the rotation of the wafer
20
and thermal gradients caused by the heat from the lamps
26
do affect the flow profile slightly.
The above-described CVD processing chamber can accommodate a number of different processes taking place. Each process differs, depending on the desired end result, and has different considerations associated therewith.
In the polysilicon deposition process, doped or undoped silicon layers are typically deposited onto the wafer using processes such as low-pressure chemical vapor deposition (CVD). In this process, a reactant gas mixture including a source of silicon (such as silane, disilane, dichlorosilane, trichlorosilane or silicon tetrachloride) and, optionally, a dopant gas (such as phosphine, arsine or diborane) is heated and passed over the wafer to deposit a silicon film on its surface. In some instances, a non-reactant carrier gas, such as hydrogen, is also injected into the processing chamber, together with either or both of the reactant or dopant gases. In this process, the crystallographic nature of the deposited silicon depends upon the temperature of deposition. At low reaction temperatures, the deposited silicon is mostly amorphous; when higher deposition temperatures are employed, a mixture of amorphous silicon and polysilicon or polysilicon alone will be deposited.
One problem with the doped polysilicon deposition is that the temperature dependence of dopant incorporation is the opposite of the temperature dependence of the polysilicon deposition rate. This is because adjusting the temperature to obtain thickness uniformity in the polysilicon layer produces a non-uniform dopant incorporation. This is because the dopant gas has, in the past, been incorporated into the processing gas before it is injected into the chamber. There is therefore no control of the dopant gas flow independent of the flow of the silicon species processing gas.
In another process, the nitride deposition process, a stream of reactant gas, which is a mixture of ammonia (NH
3
) and any one of the various silane species, is injected into the chamber. These two gases react at room temperature to produce small crystals. In the arrangement shown in
FIG. 1
, the gas storage
28
is shown to include two tanks, both of which feed into a single supply line
30
. If these tanks contained ammonia and silane respectively and the line
30
were at room temperature, this reaction would occur and particles would form along the entire length of the supply line
30
and within the manifold
32
. These particles are undesirable, as they are a source of contamination in the chamber
18
; and their existence should therefore be eliminated.
In addition, it has been found that some reactant gases pass through the gap between the preheat ring
24
and the susceptor
22
. This causes deposition on the back side of the susceptor
22
and on some of the other components in the lower portion of the chamber
18
. Such deposition is both wasteful and undesirable, as it requires additional cleaning to remove.
Accordingly, a need has arisen for a system of supplying reactant/dopant gases to a semiconductor processing chamber which overcomes these different problems.
SUMMARY OF THE INVENTION
Summary
Briefly, this invention provides for a system for supplying processing fluid to a substrate processing apparatus having walls, the inner surfaces of which define a processing chamber in which a substrate supporting susceptor is located. The system consists of a number of fluid storages, each of which stores a separate processing fluid; at least two fluid conduits along which processing fluid flows from the fluid storages to the processing apparatus; and a fluid inlet which connects the fluid conduits to the processing chamber. The inlet has a separate fluid passage, corresponding to each of the fluid conduits, formed along it. Each fluid passage opens at or near an inner surface of a wall to together define a fluid mixing zone, so that fluid moving along one fluid passage is prevented from mixing with fluid moving along any other passage until reaching the mixing zone.
Typically, at least two of the fluid passages are vertically displaced from one another to, at least partially, define upper and lower fluid flow paths. The fluid inlet may include a mixing cavity formed at or near the inner surface of the wall so that the mixing zone is defined by the boundaries of the mixing cavity. The mixing cavity may be a generally vertical channel disposed between the upper and lower fluid flow paths.
Alternatively, the chamber can be divided into an upper portion and a lower portion by the susceptor and the upper and lower fluid flow paths arranged respectively to open into the upper and lower portions of the chamber. In this arrangement, the chamber typically includes a susceptor-circumscribing preheat ring which defines an annulus between the chamber and the susceptor. The lower fluid flow path may include the annulus. In operation, processing fluid passing into the lower portion of the chamber will pass through the annulus to mix with processing fluid in the upper portion of the chamber.
The details and advantages of the present invention will, no doubt, become apparent to those skilled in the art after having read the following detailed description of the preferred embodiments which are illustrated in the several figures of

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