Susceptorless reactor for growing epitaxial layers on wafers...

Details Susceptorless reactor for growing epitaxial layers on wafers... Susceptorless reactor for growing epitaxial layers on wafers...

2002-10-10

2004-02-03

Hiteshew, Felisa (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Apparatus

C117S089000, C117S093000, C117S098000, C117S900000, C118S715000, C118S7230VE, C118S7230MP

Reexamination Certificate

active

06685774

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to making semiconductor components and more particularly relates to devices for growing epitaxial layers on substrates, such as wafers.
BACKGROUND OF THE INVENTION
Various industries employ processes to form thin layers on solid substrates. The substrates having deposited thin layers are widely used in microprocessors, electro-optical devices, communication devices and others. The processes for the deposition of the thin layers on solid substrates are especially important for the semiconductor industry. In the manufacturing of semiconductors, the coated solid substrates, such as substantially planar wafers made of silicon and silicon carbide, are used to produce semiconductor devices. After the deposition, the coated wafers are subjected to well-known further processes to form semiconductor devices such as lasers, transistors, light emitting diodes, and a variety of other devices. For example, in the production of the light-emitting diodes, the layers deposited on the wafer form the active elements of the diodes.
The materials deposited on the solid substrates include silicon carbide, gallium arsenide, complex metal oxides (e.g., YBa
2
Cu
3
O
7
) and many others. The thin films of inorganic materials are typically deposited by the processes collectively known as chemical vapor deposition (CVD). It is known that the CVD processes, if properly controlled, produce thin films having organized crystal lattices. Especially important are the deposited thin films having the same crystal lattice structures as the underlying solid substrates. The layers by which such thin films grow are called the epitaxial layers.
In a typical chemical vapor deposition process, the substrate, usually a wafer, is exposed to gases inside a CVD reactor. Reactant chemicals carried by the gases are introduced over the wafer in controlled quantities and at controlled rates while the wafer is heated and usually rotated. The reactant chemicals, commonly referred to as precursors, are introduced into the CVD reactor by placing the reactant chemicals in a device known as a bubbler and then passing a carrier gas through the bubbler. The carrier gas picks up the molecules of the precursors to provide a reactant gas that is then fed into a reaction chamber of the CVD reactor. The precursors typically consist of inorganic components, which later form the epitaxial layers on the surface of the wafer (e.g., Si, Y, Nb, etc.), and organic components. Usually, the organic components are used to allow the volatilization of the precursors in the bubbler. While the inorganic components are stable to the high temperatures inside the CVD reactor, the organic components readily decompose upon heating to a sufficiently high temperature. When the reactant gas reaches the vicinity of a heated wafer, the organic components decompose, depositing the inorganic components on the surface of the wafer in the form of the epitaxial layers.
CVD reactors have various designs, including horizontal reactors in which wafers are mounted at an angle to the inflowing reactant gases; horizontal reactors with planetary rotation in which the reactant gases pass across the wafers; barrel reactors; and vertical reactors in which wafers are rotated at a relatively high speed within the reaction chamber as reactant gases are injected downwardly onto the wafers. The vertical reactors with high-speed rotation are among the most commercially important CVD reactors.
Among the desirable characteristics for any CVD reactor are heating uniformity, low reactor cycle time, good performance characteristics, longevity of the internal parts that are heated and/or rotated inside the reaction chamber, ease of temperature control and high temperature tolerance for component parts. Also important are the cost of the required component parts, ease of maintenance, energy efficiency and minimization of the heating assembly's thermal inertia. For example, if the heated components of a CVD reactor have high thermal inertia, certain reactor operations may be delayed until the heated components reach the desired temperatures. Therefore, lower thermal inertia of the heated components of the reactor increases the productivity since the throughput depends upon the reactor cycle time. Similarly, if the internal parts of the reactor that are rotated during the deposition undergo even a small degree of deformation, the reactor may exhibit excessive vibration during use, resulting in heightened maintenance requirements.
A typical prior art vertical CVD reactor is illustrated in FIG.
1
. As seen from
FIG. 1
, a wafer
10
is placed on a wafer carrier
12
, which is placed on a susceptor
14
. The wafer carrier
12
is usually made from a material that is relatively inexpensive and allows good manufacturing reproducibility. The wafer carrier may have to be replaced after a certain commercially suitable number of reactor cycles. The susceptor
14
is permanently mounted and supported by a rotatable spindle
16
, which enables rotation of the susceptor
14
, the wafer carrier
12
and the wafer
10
. The susceptor
14
, the wafer carrier
12
and the wafer
10
are located in an enclosed reactor chamber
18
. A heating assembly
20
, which may include one or more heating filaments
22
, is arranged below the susceptor
14
, and heated by passing an electric current through electrodes
25
. The heating assembly
20
heats the susceptor
14
, the wafer carrier
12
and, ultimately, the wafer
10
. The rotation of the wafer carrier
12
is intended to enhance the temperature uniformity across the deposition area, as well as the uniformity of the reactant gas introduced over the wafer
10
during the deposition. As the wafer-supporting assembly (spindle/susceptor/wafer carrier) rotates the heated wafer
10
, the reactant gas is introduced into the reaction chamber
18
, depositing a film on the surface of the wafer
10
.
The vertical CVD reactors having both the susceptor and the wafer carrier, similar to the reactor shown in
FIG. 1
, enjoy a widespread and successful use for a variety of CVD applications. For example, the Enterprise and Discovery reactors, made by Emcore Corporation of Somerset, N.J., are some of the most successful CVD reactors in the commercial marketplace. However, as discovered by the inventors of the present invention, the performance of such CVD reactors may be further improved for certain CVD applications.
First, the CVD reactor having both a susceptor and a wafer carrier contains at least two thermal interfaces. Referring to
FIG. 1
, these are the interfaces between the heating assembly
20
and the susceptor
14
, and between the susceptor
14
and the wafer carrier
12
. Research by the inventors of the present invention has shown that a substantial temperature gradient exists at these interfaces. For example, the temperature of the heating assembly
20
is higher than the temperature of the susceptor
14
, which, in turn, is higher than the temperature of the wafer carrier
12
. Consequently, the heating assembly
20
must be heated to a substantially higher temperature than the temperature desired for the wafer
10
during the deposition. The required higher temperatures of the heating assembly lead to higher energy consumption and faster deterioration of the heating assembly's components. In addition, the typical susceptor possesses a significant heat capacity, and thus a large thermal inertia, substantially increasing the time required to heat and cool down the wafer carrier
12
. This results in a longer reactor cycle and consequent reduction in the productivity of the reactor. Also, the inventors have determined that the longer reactor cycle time tends to result in a less precise and less flexible control of the wafer carrier's temperature, increasing the time necessary to stabilize the temperature of the wafer carrier prior to the deposition.
Second, in the CVD reactors similar to the reactor of
FIG. 1
, the susceptor
14
must withstand a large number of reactor cycles since it is

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