The following figure shows low-pressure CVD configuration.

The reactor consists of a long, horizontal fused quartz reactor tube which accommodates large number of closely packed silicon wafers.

End caps with vacuum seals are mounted on each end of the reactor tube.

Heating is accomplished using resistive heating elements wrapped around the tube (a “hot-wall” reactor), which heats up the tube and everything inside.

Precursor gases are introduced via a as manifold which has mass flow controllers are associated isolation valves. This enables precise control of gas flow.

Vacuum pumps are needed to reduce and control the pressure, usually in the 0.25 to 2.0 torr range. Deposition temperatures in LPCVD systems range from $300-900^0 C$

In this case, the wafers are stacked upright and the deposition is performed at a reduced pressure.

Advantages:

1. With low pressure faster diffusion is possible which subsequently avoids the problem of less autodoping.
2. Little or no carriers or dilatant gas is needed and gas consumption is much lower.
3. Because of low pressure there are usually fewer gas phase reactions and hence fewer particulates formed that can deposit on the wafers.
4. There is of course a limit to how much the pressure can be lowered. At some point the reactant gas concentration, Cc, or pressure, PG, would have to be lowered to reduce the total gas pressure, which would then decrease the deposition rate.

Disadvantages:

1. Line of sight deposition.
2. Shadowing effect – It is the effect preventing conformal coating of surface feature during deposition i.e. reactant material reaching the surface under certain angle will not uniformly coat vertical walls & bottom of the trench.
3. Poorer step coverage.