High-temperature balance

• US 6,370,955 B1
• Filed: 11/29/1999
• Issued: 04/16/2002
• Est. Priority Date: 06/15/1999
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Tuller, Harry L., Fritze, Holger
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): MILLER, ROSE MARY
• Application Number:
  US09/449,576
• Time in Patent Office: 869 Days
• Field of Search: 735/79, 735/74, 736/02, 310/360, 310/366, 310/311, 204/298.01, 204/298.02, 204/298.03, 427/8, 427/9, 427/10, 427/96, 427/99, 427/100
• US Class Current: 73/579
• CPC Class Codes: C23C 14/546 using crystal oscillators
• CPC Class Codes: G01B 7/066 for measuring thickness of coating apparatus or processes for the manufacture of piezoelectric or electrostrictive resonators for obtaining desired frequency H03H3/04
• CPC Class Codes: G01G 3/13 having piezoelectric or piezoresistive properties
• CPC Class Codes: G01N 2291/0256 Adsorption, desorption, surface mass change, e.g. on biosensors
• CPC Class Codes: G01N 29/036 by measuring frequency or resonance of acoustic waves
• CPC Class Codes: G01N 5/04 by removing a component, e.g. by evaporation, and weighing the remainder

Abstract

A high-temperature balance includes a piezoelectric material, such as langasite, that is stable at high temperatures. The frequency response of the balance is monitored to determine the change in mass of material deposited on the balance in a high-temperature environment. Accordingly, the balance can be used to monitor high-temperature deposition rates or to perform thermogravimetric analysis. The high-temperature balance of this invention can further be operated as a nanobalance to measure monolayer changes in film thickness.

Claims

1. A method of monitoring a change in mass of a thin film on a workpiece comprising:

heating the workpiece to a temperature above about 500°

C.;

providing a piezoelectric balance including a piezoelectric material selected from a group of piezoelectric materials consisting of Ca₃Ga₂Ge₄O₁₄ structure materials and members of the (Al, Ga)N system at approximately the temperature of the heated workpiece;

changing the mass of the thin film on both the piezoelectric balance and the heated workpiece within a deposition chamber including a vapor, the thin film being exposed to the vapor; and

monitoring the frequency response of the piezoelectric balance to monitor the mass of film on the heated workpiece.

2. The method of claim 1, wherein the workpiece and piezoelectric balance are heated to a temperature of about 600°

C. or higher while monitoring the frequency response of the piezoelectric balance.

3. The method of claim 1, wherein the piezoelectric balance includes a piezoelectric material that is stable and retains its piezoelectric properties at temperatures above about 500°

C.

4. The method of claim 1, wherein the piezoelectric balance includes langasite.

5. The method of claim 1, wherein the thin film is deposited simultaneously both on the piezoelectric balance and on the heated workpiece.

6. The method of claim 1, wherein the mass of the thin film is changed by deposition.

7. The method of claim 6, wherein the mass of the thin film is changed by chemical vapor deposition.

8. The method of claim 6, wherein the mass of the thin film is changed by physical vapor deposition.

9. The method of claim 1, wherein the mass of the thin film is changed by vaporization.

10. The method of claim 1, wherein the mass of the thin film is changed by oxidation or reduction.

11. A method of monitoring a change in mass of a thin film on a workpiece comprising:

heating the workpiece;

providing a piezoelectric balance at approximately the temperature of the heated workpiece;

changing the mass of the thin film on both the piezoelectric balance and the heated workpiece;

changing the temperature of the workpiece and the piezoelectric balance; and

monitoring the frequency response of the piezoelectric balance to monitor the mass of film on the heated workpiece.

12. A method of measuring change in mass of a film as a function of temperature comprising:

heating the workpiece;

providing a piezoelectric balance at approximately the temperature of the heated workpiece;

changing the mass of the film on both the piezoelectric balance and the heated workpiece; and

monitoring the frequency response of the piezoelectric balance as a function of temperature.

13. The method of claim 12, wherein the workpiece and piezoelectric balance are heated to a temperature above about 500°

C. while monitoring the frequency response of the piezoelectric balance.

14. The method of claim 13, wherein the workpiece and piezoelectric balance are heated to a temperature of about 600°

C. or higher while monitoring the frequency response of the piezoelectric balance.

15. The method of claim 12, wherein the piezoelectric balance includes a piezoelectric material that is stable and retains its piezoelectric properties at temperatures above about 500°

C.

16. The method of claim 12, wherein the piezoelectric balance includes a piezoelectric material having a Ca₃Ga₂Ge₄O₁₄ structure.

17. The method of claim 12, wherein the piezoelectric balance includes a member of the (Al,Ga)N system.

18. The method of claim 12, wherein the piezoelectric balance includes gallium phosphate.

19. The method of claim 12, wherein the piezoelectric balance includes langasite.

20. The method of claim 13, wherein the thin film is deposited simultaneously both on the piezoelectric balance and on the heated workpiece.

21. The method of claim 13, wherein the mass of the thin film is changed by deposition.

22. The method of claim 21, wherein the mass of the thin film is changed by chemical vapor deposition.

23. The method of claim 21, wherein the mass of the thin film is changed by physical vapor deposition.

24. The method of claim 13, wherein the mass of the thin film is changed by vaporization.

25. The method of claim 13, wherein the mass of the thin film is changed by oxidation or reduction.

26. A method of measuring change in mass of a film as a function of gas composition comprising:

heating the workpiece;

providing a piezoelectric balance at approximately the temperature of the heated workpiece;

changing the mass of the film on both the piezoelectric balance and the heated workpiece; and

monitoring the frequency response of the piezoelectric balance as a function of gas composition to which the film is exposed.

27. A method of monitoring change in mass of a thin film on a heated workpiece comprising:

providing a piezoelectric balance including a piezoelectric material selected from a group of piezoelectric materials consisting of Ca₃Ga₂Ge₄O₁₄ structure materials and members of the (Al, Ga)N system;

changing the mass of the thin film on both the piezoelectric balance and the heated workpiece within a deposition chamber including a vapor, the thin film being exposed to the vapor; and

monitoring the frequency response of the piezoelectric balance to monitor the mass of film on the heated workpiece.

28. The method of claim 27, wherein the piezoelectric balance includes langasite.

29. A method for thermogravimetric analysis of a solid film of a composition comprising:

providing a piezoelectric balance;

depositing the solid film of the composition on the piezoelectric balance;

while exposing the solid film to a gas, scanning the temperature of the piezoelectric balance through a range of temperatures; and

monitoring the frequency response of the piezoelectric balance to monitor the change in mass of the composition as a function of temperature.

30. The method of claim 29, wherein the piezoelectric balance is heated to a temperature above about 500°

C. while monitoring the frequency response of the piezoelectric balance.

31. The method of claim 29, wherein the piezoelectric balance includes langasite.

32. A method for thermogravimetric analysis of a film as a function of gas composition comprising:

providing a piezoelectric balance;

depositing the film on the piezoelectric balance;

changing the composition of gas to which the film is exposed; and

monitoring the frequency response of the piezoelectric balance to monitor the change in the mass of the film as a function of the gas composition.

33. The method of claim 32, wherein the piezoelectric balance is heated to a temperature above about 500°

C. while monitoring the frequency response of the piezoelectric balance.

34. The method of claim 32, wherein the piezoelectric balance includes langasite.

35. An apparatus for depositing a film on a workpiece, comprising:

a vessel defining a deposition chamber;

a source of vapor having access to the deposition chamber, wherein the vapor can be deposited on a workpiece within the deposition chamber;

a heater within the deposition chamber; and

a piezoelectric balance within the deposition chamber and thermal communication with the heater and positioned to be coated with a film comprising deposited vapor, wherein the piezoelectric balance includes a piezoelectric material selected from the group consisting of Ca₃Ga₂Ge₄O₁₄ structure materials, members of the (Al, Ga)N system, and gallium phosphate.

36. The apparatus of claim 35, wherein the piezoelectric balance includes langasite.

37. The apparatus of claim 35, further comprising an impedance analyzer electrically coupled to the piezoelectric balance.

38. An apparatus for performing thermogravimetric analysis, comprising:

a vessel defining a thermogravimetric analysis chamber;

a heater within the chamber; and

a piezoelectric balance within the chamber and in thermal communication with the heater and coated with a composition subject to thermogravimetric analysis, the piezoelectric balance including a piezoelectric material that is stable at high temperatures, the piezoelectric material selected from the group consisting of Ca₃Ga₂Ge₄O₁₄ structure materials, members of the (Al, Ga)N system, and gallium phosphate.

39. The apparatus of claim 38, wherein the piezoelectric balance includes langasite.

40. The apparatus of claim 38, further comprising an impedance analyzer electrically coupled to the piezoelectric balance.