Cleaning and liquid contact with solids – Processes – Including application of electrical radiant or wave energy...
Reexamination Certificate
1998-07-23
2001-04-17
Meeks, Timothy (Department: 1762)
Cleaning and liquid contact with solids
Processes
Including application of electrical radiant or wave energy...
C134S018000, C134S022110, C134S022140, C427S248100, C427S255280
Reexamination Certificate
active
06216708
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a direct liquid injection system which provides for on-line cleaning, and more particularly to a system and process for the controlled deposition of metal oxide layers using chemical vapor deposition techniques.
Semiconductor devices such as dynamic random access memories (DRAMs) have undergone substantial decreases in size and increases in charge storage density over the past several years, and it is expected that these trends will continue into the future. In order to increase capacity while decreasing size, DRAM designs have become increasingly complex. One problem has been the design of capacitors in the DRAM which will hold the necessary electrical charge representing stored data.
Oxides of silicon have conventionally been used as the dielectric materials in such DRAM capacitors. Silicon oxides, however, have relatively low dielectric constants and limited charge storage densities. Accordingly, there has been an effort in the art to identify materials having higher dielectric constants which are suitable for use in DRAM designs. Interest in ferroelectric materials such as barium strontium titanates (Ba
1−x
Sr
x
TiO
3
, known as BSTs) and lead zirconate titanates (Pb(Zr
x
Ti
1−x
)O
3
, known as PZTs) has grown because such materials have relatively higher dielectric constants than silicon oxides, are structurally stable, and can be prepared using known techniques.
Of the many chemical and physical deposition techniques used in the art to form thin film layers of such ferroelectric materials, metal organic chemical vapor deposition (MOCVD) using direct liquid injection appears to hold the most promise. For example, Desu et al, U.S. Pat. Nos. 5,431,958 and 5,527,567 teach MOCVD techniques, including direct liquid injection ('567 patent), to provided layered ferroelectric films for the manufacture of capacitors. Si et al, U.S. Pat. No. 5,629,229, also teach the manufacture of DRAMs using MOCVD techniques.
In MOCVD, the metalorganic precursors which are used are dissolved in liquid solvents which are then pumped in precise proportions to a vaporizer. The vaporized precursors are then sent to a CVD chamber where they are deposited on a substrate. The composition and properties of the deposited films of the ferroelectric materials are highly dependent on the ability of the direct liquid injection system to supply the correct proportions of precursors to the vaporizer and thence to the CVD chamber. Other variables in the system will also affect the composition and properties of the deposited films and include the condition of the vaporizer, the temperature of the vaporizing surfaces in the vaporizer, the concentrations of the metalorganic precursors in the solvent, and local temperature variations on the substrate surface in the reactor. The local temperature variations as well as accumulation of precursor compounds on the surfaces of the vaporizer both affect vaporization efficiency and can cause fluctuations in the composition and properties of the films which are deposited.
Such accumulations of precursor compounds and oxidative reaction products of the precursor compounds have the tendency to build-up over time and clog both the outlet to the vaporizer as well as the direct liquid injection mechanism. This leads not only to undesirable variations in the ratios of the precursor compounds which are deposited, but also to possible clogging and shutdown of the deposition process. To address these problems, Gardiner et al, U.S. Pat. No. 5,362,328, teach the use of a cleaning subsystem in a chemical vapor deposition process in which a solvent is supplied to the vaporizer to solubilize any deposited compounds and flush them away. However, the Gardiner et al cleaning subsystem requires that the CVD process be periodically shut down during the cleaning cycle. Accordingly, the need still exists in this art for a direct liquid injection system which provides for on-line cleaning without the need for shutting down the CVD process.
SUMMARY OF THE INVENTION
The present invention meets that need by providing a direct liquid injection system which has on-line cleaning of the vaporizers without the need for shutting down the CVD process, and thus eliminating down time. The present invention also provides alternative sources of cleaning fluid which may be selected to remove metalorganic precursor and oxidation product residues which are deposited in the vaporizers.
In accordance with one aspect of the present invention, a process for the on-line cleaning of a direct liquid injection system is provided and includes the steps of providing at least one metalorganic precursor to a first vaporizer to produce a vapor containing the at least one precursor; transporting the vapor to a deposition chamber; periodically interrupting the supply of the at least one metalorganic precursor to the first vaporizer; providing the at least one metalorganic precursor to a second vaporizer to produce a vapor containing the at least one precursor; transporting the vapor to the deposition chamber; and during at least a portion of the time when the supply of the metalorganic precursor is interrupted to the first vaporizer, providing a cleaning fluid to the first vaporizer, which fluid is effective to at least partially remove deposits of the metalorganic precursor and oxidation products. Preferably, the cleaning fluid is effective to remove substantially all of the deposits and residue of the at least one metalorganic precursor and any oxidation products which may have formed.
The process may be either carried out as a batch process, or more preferably, as a continuous process. Thus, when the supply of metalorganic precursor is interrupted to the first vaporizer for cleaning, the supply to the second vaporizer is initiated so that there is a continuous flow of vaporized precursor being supplied to the deposition chamber. That supply of metalorganic precursor is maintained to the second vaporizer until a buildup of deposits or residue is detected. Then the procedure is reversed by resuming the supply of the at least one metalorganic precursor to the first vaporizer and interrupting the supply of the at least one metalorganic precursor to the second vaporizer. During at least a portion of the time when the supply of the metalorganic precursor is interrupted to the second vaporizer, a cleaning fluid is provided to the second vaporizer, which fluid is effective to at least partially remove deposits of the metalorganic precursor and oxidation products, and preferably, is effective to substantially completely remove deposits and residues of the metalorganic precursor and any oxidation products which may have formed.
In a preferred form, the at least one metalorganic precursor is dissolved in a liquid solvent carrier which is supplied to the vaporizers. The cleaning fluid may comprise a liquid solvent for the at least one metalorganic precursor. The cleaning fluid may be recovered and recycled after it has been passed through the vaporizer. Alternatively, the cleaning fluid may comprise a gas plasma which is an etchant for the deposits of metalorganic precursor and oxidation products. The gas plasma may be formed in a conventional manner, such as, for example, using microwave energy to form the plasma. The gas plasma is formed from an etchant gas which is preferably selected from the group consisting of NF
3
, CIF
3
, and HF. The plasma is formed at a temperature and at a pressure which permits it to be sufficiently long-lived to effect its cleaning function in the vaporizers.
Additionally, the vaporizer may be cleaned by sequentially supplying different cleaning fluids to it. Thus, the vaporizer may be cleaned by first using a gas plasma which is then followed by a solvent-containing fluid. Alternatively, the vaporizer may be cleaned by first using a solvent-containing cleaning fluid which is followed by a gas plasma treatment.
The step of monitoring the build up of deposits in the first vaporizer and interrupting the supply of the metalorganic precurs
Chen Bret
Killworth, Gottman Hagan & Schaeff, L.L.P.
Meeks Timothy
Micro)n Technology, Inc.
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