WO1994011745B1

WO1994011745B1 - Method and apparatus for measuring film thickness

Info

Publication number: WO1994011745B1
Application number: PCT/US1993/011076
Authority: WO
Filing date: 1993-11-10
Publication date: 1994-07-07

Abstract

An apparatus (20) for measuring film thickness and handling wafers is described. A four-point probe (22) engages the surface of a film (28), and a measuring apparatus outputs a voltage waveform which induces a current in the outer probes of the four-point probe and through the surface of the film. The two inner probes measure a voltage in the film created by the current. A sheet resistance of the film is calculated by taking a least square fit of the measured current and voltage and calculating the slope of the least square line fit. The thickness of the film is calculated by dividing the film resistivity by the calculated sheet resistance. An apparatus for handling wafers in which a wafer pick moves along a horizontal x-axis to unload a wafer from a cassette and position the wafer over a chuck (212). The chuck moves upwardly along a z-axis perpendicular to the surface of the wafer and lifts the wafer off the pick. The pick retracts and the four-point assembly moves along the x-axis to position itself over the wafer and chuck with reference to a calculated wafer center. The chuck then moves upwardly to engage the surface of the wafer with the probe. Wafer characteristics, such as film thickness, are tested at several test points on the circle on the surface of the wafer.

Claims

- 29 -

AMENDED CLAIMS

[received by the International Bureau on 3 June 1994 (03.06.94); original claim 1 , 15 and 23-26 amended; remaining claims unchanged (3 pages)]

1. An apparatus for measuring film thickness comprising: a probe assembly including four probes; means for engaging said probe assembly with a surface of a film; current sensing means; variable voltage source means coupled to said probe assembly by said current sensing means to create a variable current in said film when said probe assembly is engaged with said surface of said film by said means for engaging; voltage sensing means coupled to said probe assembly to sense a voltage between two probes of said probe assembly; and means for determining film thickness from said measured current and said measured voltage.

2. An apparatus for measuring film thickness as recited in claim 1, wherein said means for engaging includes a chuck means for supporting a wafer to be tested in an x-y plane, said chuck means being positioned below said probe assembly.

3. An apparatus for measuring film thickness as recited in claim 2, wherein said means for engaging includes means for selectively moving said chuck means along a z-axis substantially perpendicular to said x-y plane to cause an upper surface of said wafer to engage and disengage said probes of said probe assembly.

4. An apparatus for measuring film thickness as recited in claim 3, wherein said means for engaging includes means for moving at least one of said probe assembly and said chuck means in a plane substantially parallel to said x-y plane.

5. An apparatus for measuring film thickness as recited in claim 1 wherein said current sensing means includes a sense resistor between said voltage source means and one of said probes.

6. An apparatus for measuring film thickness as recited in claim 5 wherein said current sensing means includes voltage sensing means for sensing a voltage across said sense resistor. - 30 -

15. A wafer testing apparatus comprising: a tester means; chuck means for supporting a wafer to be tested in an x-y p]ane, said chuck means being positioned below said tester means and being stationary with respect to translation in said x-y plane; means for selectively moving said chuck means along a z-axis substantially perpendicular to said x-y plane to cause an upper surface of said wafer to engage and disengage said tester means; and means for translating said tester means in a plane substantially parallel to said x-y plane.

16. A wafer testing apparatus as recited in claim 15 further comprising handling means operative to position said wafer on said chuck means.

17. A wafer testing apparatus as recited in claim 16 wherein said handling means includes vacuum pick means.

18. A wafer testing apparatus as recited in claim 16 wherein said handling means includes means for moving said handling means in a plane parallel to a plane of said tester means.

19. A wafer testing apparatus as recited in claim 15 wherein said tester means includes a four-point probe assembly.

20. A wafer testing apparatus as recited in claim 19 wherein said tester means includes current sensing means and voltage source means coupled to said probe assembly by said current sensing means to create a current in said film when said four-point probe assembly is engaged with said surface of said film by said means for selectively moving.

21. A wafer testing apparatus as recited in claim 20 wherein said tester means includes voltage sensing means coupled to said probe assembly to sense a voltage between two probes of said probe assembly.

22. A wafer testing apparatus as recited in claim 21 wherein said tester means includes means for determining film thickness from said sensed current and said sensed voltage. 23. A wafer testing apparatus as recited in claim 15 further comprising chuck rotating means for rotating said chuck means in a plane substantially parallel to said x-y plane.

24. A wafer testing apparatus as recited in claim 15 wherein said means for translating said tester means in a plane substantially parallel to said x-y plane includes means for translating said tester means in an x-direction.

25. A wafer testing apparatus as recited in claim 24 wherein said means for translating said tester means includes a carriage moved along a screw rotated by a stepper motor.

26. A wafer testing apparatus as recited in claim 15 further comprising control means operative to coordinate said means for selectively moving and said means for translating.

27. A wafer testing apparatus as recited in claim 26 further comprising means for finding the center of said surface of said wafer coupled to said control means.

28. A wafer testing apparatus as recited in claim 26 further comprising means for finding an index mark of said wafer coupled to said control means.

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STATEMENT UNDER ARTICLE 19

Claim 1 has been amended to specify that voltage source means is a variable voltage source means which creates a variable current in the film. This variable current allows a plurality of currents to be measured in the film for more accurate results.

Claim 15 has been amended to specify that the chuck means is stationary with respect to translation in the x-y plane. In addition, the means for moving at least one of said tester means and said chuck means has been amended as a means for translating said tester means in a plane substantially parallel to said x-y plane.

Claims 23-26 have been amended to provide consistency with amended claim 15. Claim 23 recites that the wafer testing apparatus further comprises chuck rotating means for rotating said chuck means in a plane substantially parallel to said x-y plane. Claims 24-26 recite the means for translating in place of the former means for moving.