Coating apparatus – Gas or vapor deposition – Crucible or evaporator structure
Reexamination Certificate
2000-06-14
2003-06-03
Dang, Thi (Department: 1763)
Coating apparatus
Gas or vapor deposition
Crucible or evaporator structure
C392S399000, C122S040000
Reexamination Certificate
active
06572707
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to apparatus for processing of a semiconductor wafer, and more particularly to a system to vaporizing sensitive liquid precursors.
BACKGROUND OF THE INVENTION
Conventional chemical vapor deposition (CVD) processes use vapor precursors for the deposition of thin films on an IC substrate. To broaden the processes, more and more liquid and solid precursors have been used, especially in the area of metal-organic chemical vapor deposition (MOCVD). To perform this task, a liquid precursor is typically turned to vapor, and the vapor is then decomposed on the substrate. A solid precursor must often be dissolved into a solvent to form a liquid precursor. Then, the liquid precursor needs to be converted into vapor phase before introduction into the deposition zone.
Basic components of a liquid precursor vaporization system is the liquid delivery system and the vaporizer. The liquid delivery system carries the liquid precursor from the liquid container to the vaporizer. The vaporizer converts the liquid precursor into vapor form before deliver on the substrate. A carrier gas is normally used in the vaporizer to carry the precursor vapor to the substrate. In some applications, a gas precursor could take place of the carrier gas, performing the carrying function together with the precursor function.
FIG. 1
shows a prior art vaporizer. The vaporizer includes a vaporization chamber
12
with a heater means
10
to bring the vaporization chamber to a vaporization temperature. The liquid precursor enters the vaporization chamber at liquid input
18
. A valve
40
is optional, used for shut off the liquid flow. The liquid input sometimes extends into the vaporization chamber
20
to increase the vaporization efficiency. Another input
16
is for carrier gas with an optional valve
41
for shut off. The carrier gas carries the vaporized liquid to the output
14
. The carrier gas function is essential in providing the vaporized precursor to the output. Without the carrier gas, the vaporized liquid flow is small, leading to the condensation of the liquid precursor inside the vaporization chamber.
FIG. 2
shows a prior art liquid delivery system. The liquid is stored in the container
40
, and is pushed out to the metering device
30
. The liquid continues to travel in the line
18
to the vaporizer
12
through valve
40
. The tip of the liquid line
20
is inside the vaporizer
12
. Carrier gas flows from the line
16
to the vaporizer
12
though valve
41
. Heater
10
heats the vaporizer to a vaporization temperature. The major disadvantage of this delivery system is the reliability of the liquid delivery line. A small line is desirable for small flow, but too easily clogged. Also the proximity of the heat source, in the case of heat-sensitive precursor, could cause precursor degradation.
A related problem is in the delivery of the precursor to the vaporization chamber. To control the flow of liquid precursor, the liquid delivery input port to the vaporization chamber is made small. Large input ports, or small ports under high pressure, introduce too much precursor so that the vaporization process is inefficient. However, small ports used at relatively low pressures have a tendency to fill with decomposing precursor, and eventually clog. This is due to the unstable nature of most precursors and the proximity of heat source used to vaporize the precursor. The system must be shut down, and the decomposed and partially decomposed material removed from the input port, before the vaporization process can continue.
Other problem concerns the distribution pattern of liquid precursor to the vaporization chamber. Small ports at low pressure will form large droplet into the vaporization surface. It is well known to use piezoelectric atomizer to break the liquid precursor into finer droplets at the input section of a vaporization chamber. However, there is still a tendency for the liquid precursor port to clog due to relatively narrow opening and the proximity of heat. Pressure type atomizers are also well known, to break a liquid into droplets by pushing the liquid through an opening, creating a spray. To compensate for the high pressure of the liquid, the spray opening is very small. In this manner an efficient amount of precursor is delivered. Despite the high pressure, the very small opening has a tendency to clog in the heated vaporization chamber environment.
To increase the efficiency of the heat transfer to the liquid precursor, some conventional vaporizers use large extended surfaces, or a plurality of surfaces. While these surfaces do provide heat to vaporize liquid reagents, they are not necessarily efficient, as the heating surfaces extend in only two dimensions. The surface area can be increased by roughing the surface or minimizing the through passages through the plate. Simply increasing the surface area, however, does not necessarily increase the rate of flow of vaporized precursor. A trade-off is generally made between heated surface area and high flow rates of vaporized precursor. That is, conventional heated surface areas may block vapor flow, preventing a high flow rate. High pressure on the input side of the vaporizer creates a high pressure differential from the input to the output. Large inlet pressures may also cause condensation of the vapor. Eventually, condensed liquid blocks the vaporizer output. Alternately, the heated surface area can be reduced to increase the vapor flow conductance. However, when too little heated surface is provided, insufficient liquid precursor is vaporized, and the liquid precursor will collect in the vaporizer and eventually block the output. The above-described trade-off can also be considered an issue of deposition rates vs. efficient use of precursor.
Asaba et al. (U.S. Pat. No. 5,547,708) uses a series of flat plates with perforations as the vaporizing heating element, together with a piezoelectric device to atomize the liquid. Tsubouchi et al. (U.S. Pat. No. 5,421,895) discloses a heated plate and piezoelectric atomizer. A low pressure differential is created, but the heated surface area is small. Ewing (U.S. Pat. No. 5,553,188) discloses a plurality of thin flat heated disks to provide a large heated surface area, but liquid must move along the plates through capillary action. Precursor on heated plates for an extended period of time often solidifies to clog the system. Alternately, the system must be kept running at high liquid flow rates, which is costly and inefficient.
Kirlin et al. (U.S. Pat. Nos. 5,204,314, 5,536,323) disclose a vaporizer having a vaporization matrix to vaporize a liquid precursor. This so-called matrix is typically a flat mesh, grid, or screen. In some aspects of the invention the screen is a cylinder wrapped around an area substantially devoid of any structure. The two-dimensional matrix has relatively small pores to increase the heated surface area. Therefore, the vaporizer works best at low flow rates, for example, 0.2 milliliters (ml) per minute for low-volatility liquids. A porous vaporization element adjacent the vaporization chamber walls to accept a liquid reagent is also disclosed, in order to heat the liquid to vaporization temperature.
One major problem with the prior art vaporizers is low conductance. For sensitive precursors such as MOCVD precursors, the low conductance or small passage of precursor will lead to decomposition and then clogging. With small pores like the vaporizer disclosed by Kirlin et al., even at low flow rate, the system is still clogged after a certain period of time. Another major problem is the low heat conduction to the heated surfaces. When the liquid converts to vapor, it requires an extra amount of energy, called latent heat, for the liquid-gas phase transformation. Therefore efficient heat transfer is essential to avoid cold spot, leading to the condensation and eventually decomposition and clogging.
With small pores like the vaporizer disclosed by Kirlin et al., the heat conduction is poor.
A relate solution for avoi
Dang Thi
Simplus Systems Corporation
LandOfFree
Vaporizer for sensitive precursors does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Vaporizer for sensitive precursors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Vaporizer for sensitive precursors will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3133198