Process for atomic layer deposition
The present invention relates to a process of making a zinc-oxide-based thin film semiconductor, for use in a transistor, comprising thin film deposition onto a substrate comprising providing a plurality of gaseous materials comprising at least first, second, and third gaseous materials, wherein the first gaseous material is a zinc-containing volatile material and the second gaseous material is reactive therewith such that when one of the first or second gaseous materials are on the surface of the substrate the other of the first or second gaseous materials will react to deposit a layer of material on the substrate and wherein the third gaseous material is inert with respect to reacting with the first or second gaseous materials.
1. A process of making an n-type zinc-oxide-based thin film semiconductor, for use in a transistor by depositing a thin film material on a substrate, comprising:
simultaneously directing a series of gas flows along elongated substantially parallel channels, and wherein the series of gas flows comprises, in order, a first reactive gaseous material, an inert purge gas, and a second reactive gaseous material, optionally repeated a plurality of times, wherein the first reactive gaseous material is capable of reacting with a substrate surface treated with the second reactive gaseous material to form the n-type zinc-oxide-based thin film semiconductor, wherein the first reactive gaseous material is a volatile organo-zinc precursor compound comprising both zinc and organic groups;
introducing a volatile acceptor dopant precursor into the first reactive gaseous material, the second reactive gaseous material, the inert purge gas, or an additional gas flow of a supplemental gaseous material;
wherein the process is carried out substantially at or above atmospheric pressure, and wherein the temperature of the substrate during deposition is under 250° C., whereby the volatile acceptor dopant precursor reacts and is incorporated as an acceptor dopant in the n-type zinc-oxide-based thin film semiconductor; and
supplying the one or more of the first and second reactive gaseous materials and the inert purge gas, to the substrate surface by a deposition device having a face, in order to provide a pressure that creates a gas bearing delivery head in the deposition device, thereby maintaining a separation of the substrate surface from the face of the deposition device of 0.3 mm or less.
2. The process of claim 1 wherein the incorporated acceptor dopant provides an increase in on-off ratio of by a factor of at least 10.
3. The process of claim 2 wherein the on-off ratio of the n-type zinc-oxide-based thin film semiconductor without the incorporated acceptor dopant is less than 1.0 ×10 6 .
4. The process of claim 2 wherein the presence of the incorporated acceptor dopant also provides an increase in mobility of at least 50 percent.
5. The process of claim 1 wherein the incorporated acceptor dopant introduces an energy level within the band-gap of the n-type zinc-oxide-based thin film semiconductor that is below the energy level of shallow donors and is able to accept an electron.
6. The process of claim 1 wherein the incorporated acceptor dopant has fewer valence electrons than the atom it replaces, whether a Group (V) element substituting for oxygen or a Group (I) or (IB) element substituting for zinc.
7. The process of claim 1 wherein the presence of the incorporated acceptor dopant provides an increase in resistivity of at least 10 2 .
8. The process of claim 6 wherein the resistivity of the n-type zinc-oxide-based thin film semiconductor without the incorporated acceptor dopant is less than 500 ohm*cm.
9. The process of claim 1 wherein a given area of the substrate is exposed to a gas flow in a channel for less than 100 milliseconds.
10. The process of claim 1 wherein relative movement of the substrate to a deposition device is at a speed at least 0.1 cm/sec.
11. The process of claim 1 wherein the series of gas flows are at least1 cm/sec.
12. The process of claim 1 wherein the temperature of the substrate during deposition is under 200° C.
13. The process of claim 1 wherein the second reactive gaseous material is a non-metallic compound.
14. The process of claim 1 wherein the volatile organo-zinc precursor compound can be vaporized at a temperature under 300° C. at atmospheric pressure.
15. The process of claim 1 wherein the volatile acceptor dopant precursor comprises an element selected from the group consisting of N, P, As, Li, Na, K, Cu, Ag, or mixtures thereof.
16. The process of claim 1 wherein the volatile acceptor dopant precursor comprises a Group V element.
17. The process of claim 1 wherein the volatile acceptor dopant precursor comprises nitrogen.
18. The process of claim 1 wherein the volatile acceptor dopant precursor comprises nitrogen in the form of NO, N 2 O, NO 2 , or ammonia.
19. The process of claim 1 wherein the substrate or a support for the substrate comprises a moving web.
20. The process of claim 1 wherein the process is in unsealed relationship to ambient atmosphere.
21. A process of making an n-type zinc-oxide-based thin film semiconductor, for use in a transistor by depositing a thin film material on a substrate, comprising:
simultaneously directing a series of gas flows along elongated substantially parallel channels, and wherein the series of gas flows comprises, in order, a first reactive gaseous material, an inert purge gas, and a second reactive gaseous material, optionally repeated a plurality of times, wherein the first reactive gaseous material is capable of reacting with a substrate surface treated with the second reactive gaseous material to form the n-type zinc-oxide-based thin film semiconductor, wherein the first reactive gaseous materials is a volatile organo-zinc precursor compound comprising both zinc and organic groups;
introducing a nitrogen-containing volatile acceptor dopant precursor that reacts with the volatile organo-zinc precursor compound into the second reactive gaseous material or into an additional gas flow of a supplemental gaseous material, which additional gas flow is separate from the first reactive gaseous material and separate from the inert purge gas; and
wherein the process is carried out substantially at or above atmospheric pressure, and wherein temperature of the substrate during deposition is under 250° C., whereby the nitrogen-containing volatile acceptor dopant precursor reacts and nitrogen dopant is incorporated as an acceptor dopant in the n-type zinc-oxide-based thin film semiconductor; and
supplying the one or more of the first and second reactive gaseous materials and the inert purge gas, to the substrate surface by a deposition device having a face, in order to provide a pressure that creates a gas to create an air bearing delivery head in the deposition device, thereby maintaining a separation of the substrate surface from the face of the deposition device of 0.3 mm or less.
22. The process of claim 21 wherein presence of the incorporated nitrogen dopant provides an increase in on-off ratio of by a factor of at least 10 and provides an increase in mobility of at least 50 percent.