Microwave plasma reactors

• US 8,316,797 B2
• Filed: 06/16/2009
• Issued: 11/27/2012
• Est. Priority Date: 06/16/2008
• Status: Active Grant

• Current Assignee: Fraunhofer USA Inc. (Fraunhofer-Institut für Nachrichtentechnik HHI), The Board of Trustees of Michigan State University (Michigan State University)
• Original Assignee: Board of Trustees of Michigan State University Fraunhofer USA
• Inventors: Asmussen, Jes, Grotjohn, Timothy, Reinhard, Donnie K., Schuelke, Thomas, Yaran, M. Kagan, Hemawan, Kadek W., Becker, Michael, King, David, Gu, Yajun, Lu, Jing
• Primary Examiner(s): Dhingra, Rakesh
• Application Number:
  US12/456,388
• Publication Number:
  US 20100034984A1
• Time in Patent Office: 1,260 Days
• Field of Search: 118/723.MW, 118/723.ME, 118/723.MR, 156/345.41, 156/345.35, 156/345.36
• US Class Current: 118/723.MW
• CPC Class Codes: C23C 16/274 using microwave discharges
• CPC Class Codes: C23C 16/279 control of diamond crystallography
• CPC Class Codes: C23C 16/511 using microwave discharges
• CPC Class Codes: C30B 25/105 by irradiation or electric discharge
• CPC Class Codes: C30B 25/16 Controlling or regulating controlling or regulating in general G05
• CPC Class Codes: C30B 29/04 Diamond
• CPC Class Codes: C30B 35/00 Apparatus not otherwise provided for, specially adapted for the growth, production or after-treatment of single crystals or of a homogeneous polycrystalline material with defined structure
• CPC Class Codes: H01J 37/32256 Tuning means
• CPC Class Codes: H05H 1/46 using applied electromagnetic fields, e.g. high frequency or microwave energy H05H1/26 takes precedence

Abstract

New and improved microwave plasma assisted reactors, for example chemical vapor deposition (MPCVD) reactors, are disclosed. The disclosed microwave plasma assisted reactors operate at pressures ranging from about 10 Torr to about 760 Torr. The disclosed microwave plasma assisted reactors include a movable lower sliding short and/or a reduced diameter conductive stage in a coaxial cavity of a plasma chamber. For a particular application, the lower sliding short position and/or the conductive stage diameter can be variably selected such that, relative to conventional reactors, the reactors can be tuned to operate over larger substrate areas, operate at higher pressures, and discharge absorbed power densities with increased diamond synthesis rates (carats per hour) and increased deposition uniformity.

Claims

1. A microwave plasma assisted reactor comprising:

(a) a first microwave chamber having a reference plane at a reference axial location Z₀, the first microwave chamber comprising an electromagnetic wave source and extending in an axial direction z>

Z₀;

(b) a plasma chamber having an outer wall, the plasma chamber extending into the first microwave chamber such that at least a portion of the plasma chamber is located at z>

Z₀ and at least a portion of the plasma chamber is located at z<

Z₀;

(c) a conductive stage for supporting a substrate holder and having a reference surface extending into the plasma chamber and defining a second microwave chamber in the plasma chamber (i) at z<

Z₀ and (ii) between the plasma chamber outer wall and the conductive stage;

(d) a conducting short adjustably disposed in the second microwave chamber below Z₀ and in electrical contact with the plasma chamber outer wall and the conductive stage, the axial distance between the conducting short and Z₀ being L2, and the axial distance between the conducting short and the reference surface of the conductive stage being L1;

wherein L2 and L1 are capable of adjustment in the reactor by moving the conducting short, such that different microwave modes are produced in the first microwave chamber and in the second microwave chamber during operation of the reactor.

2. The microwave plasma assisted reactor of claim 1, wherein during operation of the reactor, evanescent microwave fields are produced in the vicinity of Z₀, the evanescent microwave fields being distinct from the microwave modes in the first microwave chamber and in the second microwave chamber.

3. The microwave plasma assisted reactor of claim 1, wherein the conductive stage is movable such that both L1 and L2 are capable of independent adjustment during operation of the reactor by moving one or both of the conducting short and the conductive stage.

4. The microwave plasma assisted reactor of claim 1, wherein the conducting short is slidable in an axial direction.

5. The microwave plasma assisted reactor of claim 4, wherein the conductive stage is movable and slidable in the axial direction.

6. The microwave plasma assisted reactor of claim 1, wherein the first microwave chamber, the plasma chamber, and the conductive stage have cylindrical cross sections with radii of R1, R2, and R3, respectively.

7. The microwave plasma assisted reactor of claim 6, wherein R3/R2 is about 0.5 or less.

8. The microwave plasma assisted reactor of claim 1, wherein the reactor is capable of producing a plasma having a power density ranging from about 160 W/cm³ to about 600 W/cm³ in the plasma chamber when the electromagnetic wave source provides an excitation frequency of about 2.45 GHz and an operating pressure in the plasma chamber ranges from about 180 Torr to about 260 Torr.

9. The microwave plasma assisted reactor of claim 1, wherein:

(a) the electromagnetic wave source generates waves with an excitation frequency f;

(b) at least one of Ll and L2 is about one-half of a free space wavelength λ

₀, where the free space wavelength λ

₀, is given by the ratio c/f of the speed of light c relative to the excitation frequency f;

(c) the conductive stage is a coaxial conductive stage defining a coaxial microwave chamber as the second microwave chamber; and

(d) the conducting short is in electrical contact with a metal portion of the plasma chamber outer wall and the coaxial conductive stage.

10. A microwave plasma assisted reactor comprising:

(a) a cylindrical chamber defining an interior cylindrical microwave chamber of radius R1 and having (i) a central axis, (ii) a lower boundary at a reference axial location Z₀, and (iii) a upper boundary at an axial location Z_u>

Z₀; and

(b) a base defining an interior base cavity of radius R2 and having (i) an upper boundary adjacent the cylindrical chamber at Z₀ and (ii) a lower portion extending axially downwardly in a direction z<

Z₀;

(c) an upper conducting short in electrical contact with the cylindrical chamber and disposed in an upper portion of the cylindrical chamber at an axial distance L_s above Z₀, the upper conducting short having a central opening and defining the upper boundary of the cylindrical chamber;

(d) an excitation probe extending through the central opening of the upper conducting short and into the upper portion of the cylindrical microwave chamber by an axial distance L_p relative to the upper boundary of the cylindrical chamber;

(e) a coaxial stage for supporting a substrate holder and having a radius R3 and an upper surface extending at least into the base cavity and optionally into a bottom portion of the cylindrical microwave chamber, the coaxial stage defining a coaxial microwave chamber between R3 and R2 in the base cavity, wherein the coaxial stage is conductive;

(f) a lower conducting short adjustably disposed in the coaxial microwave chamber below Z₀ and in electrical contact with the base and the coaxial stage, the axial distance between the lower conducting short and Z₀ being L2 and the axial distance between the lower conducting short and the upper surface of the coaxial stage being L1;

(g) a quartz bell jar mounted on the base and defining a plasma chamber in the bottom portion of the cylindrical microwave chamber and the coaxial microwave chamber;

(h) a feed gas inlet in fluid connection with the plasma chamber; and

,

(i) an effluent gas outlet in fluid connection with the plasma chamber;

wherein

L2 and L1 are capable of adjustment in the reactor by moving the lower conducting short.

11. The microwave plasma assisted reactor of claim 10, wherein the coaxial stage is movable such that both L1 and L2 are capable of independent adjustment during operation of the reactor by moving one or both of the lower conducting short and the coaxial stage.

12. The microwave plasma assisted reactor of claim 10, wherein the lower conducting short has an annular disk shape and is slidable in an axial direction.

13. The microwave plasma assisted reactor of claim 12, wherein the coaxial stage is movable and slidable in the axial direction.

14. The microwave plasma assisted reactor of claim 10, further comprising:

(j) one or more shim inserts axially interposed between the base and the lower conducting short;

wherein the lower conducting short has a disk shape and is adjustably located in an axial direction based on the number and size of shim inserts interposed between the base and the lower conducting short.

15. The microwave plasma assisted reactor of claim 14, wherein both L1 and L2 are capable of independent adjustment in the reactor by independently selecting the number of shim inserts and the axial height of the coaxial stage.

16. The microwave plasma assisted reactor of claim 10, wherein at least one of the upper conducting short and the excitation probe is movable and capable of adjustment during operation of the reactor.

17. The microwave plasma assisted reactor of claim 16, wherein the upper conducting short and the excitation probe are slidable and capable of independent adjustment during operation of the reactor.

18. The microwave plasma assisted reactor of claim 10, wherein R3/R2 is about 0.5 or less.

19. The microwave plasma assisted reactor of claim 10, wherein the excitation probe generates waves with an excitation frequency of about 2.45 GHz.

20. The microwave plasma assisted reactor of claim 19, wherein:

R1 ranges from about 6 cm to about 16 cm;

R2 ranges from about 5 cm to about 12 cm;

R3 ranges from about 0.5 cm to about 7 cm;

Ls ranges from about 15 cm to about 25 cm;

Lp ranges from about 2 cm to about 5 cm; and

,

L1 and L2 independently range from about 4 cm to about 8 cm.

21. The microwave plasma assisted reactor of claim 20, wherein:

R1 is about 8.9 cm;

R2 is about 7.0 cm; and

,

R3 is selected from about 0.95 cm, about 1.9 cm, and about 4.1 cm.

22. A reactor kit comprising the microwave plasma assisted reactor of claim 10 and at least one of:

(a) a plurality of cylindrical chambers, each defining an interior cylindrical microwave chamber of a different radius R1;

(b) a plurality of bases, each defining an interior base cavity of a different radius R2; and

,

(c) a plurality of coaxial stages, each having a different radius R3;

wherein the reactor can be assembled with any combination of the cylindrical chambers, the bases, and the coaxial stages such that at least one of R1, R2, and R3 can be varied in a selected reactor assembly.

23. The microwave plasma assisted reactor of claim 10, wherein:

(a) the excitation probe generates electromagnetic waves with an excitation frequency f;

(b) at least one of Ll and L2 is about one-half of a free space wavelength λ

₀, where the free space wavelength λ

₀, is given by the ratio c/f of the speed of light c relative to the excitation frequency f; and

(c) the lower conducting short is in electrical contact with a metal portion of the base and the coaxial conductive stage.