LIQUID CONTACTS FOR USE IN SEMICONDUCTOR DOPING PROFILE ANALYSIS

• US 3,803,489 A
• Filed: 01/04/1973
• Issued: 04/09/1974
• Est. Priority Date: 01/04/1973
• Status: Expired due to Term

• Current Assignee: Gabriel Lorimer Miller
• Original Assignee: Gabriel Lorimer Miller
• Inventors: Miller, Gabriel Lorimer
• Primary Examiner(s): Smith, Alfred E.
• Assistant Examiner(s): Karlsen, Ernest F.
• Application Number:
  US05/320,977
• Time in Patent Office: 460 Days
• Field of Search: 324/158D,158T,158R 29/574
• US Class Current: 324/754.04
• CPC Class Codes: G01R 1/06783 containing liquids
• CPC Class Codes: G01R 31/2637 for testing other individual devices G01R31/2608 - G01R31/2632, G01R31/27 take precedence

Abstract

In semiconductor doping profile apparatus of the type using current feedback for maintaining a constant modulation parameter, non-destructive analysis is achieved by using a liquid electrode rectifying contact for forming each required diode region. A metal electrode contacts the electrolyte and is surrounded by an annular guard ring, maintained at rf ground, which defines precisely the area of the diode region.

Claims

1. In apparatus for analyzing semiconductor wafers comprising means for forming a diode region on the wafer, means comprising a steady dc voltage source for reverse-biasing the diode region, thereby to form a stable depletion layer, means for adjusting the reverse-bias voltage to adjust the thickness of the depletion layer, and means for directing rf current through the diode region to determine doping densities at various depths in the wafer, the improvement wherein:

the diode region forming means comprises a liquid electrolyte included between a solid electrode and a first surface of the wafer;

said electrolyte being of a material that is substantially noncontaminating and nondestructive with respect to the semiconductor wafer material, whereby wafer analysis may be accomplished without damaging the wafer.

2. The improvement of claim 1 wherein:

the electrolyte comprises water including an impurity which is sufficiently conductive to impart to the water electrolyte a resistivity of approximately 105 ohm-centimeters or less.

3. The improvement of claim 2 wherein:

the electrolyte consists of water containing approximately two percent by volume of a water-soluble conducting polymer.

4. The improvement of claim 1 further comprising:

means for defining the area of the diode region comprising an annular conductive guard ring surrounding the solid electrode and insulated therefrom, and being in contact with the liquid electrolyte.

5. The improVement of claim 4 wherein the reverse-bias means comprises means for maintaining the solid electrode and the guard ring at substantially the same dc voltage;

the rf current-directing means comprises means for directing rf current through the solid electrode; and

further comprising;

means for maintaining the guard ring at rf ground voltage.

6. The improvement of claim 5 wherein:

the electrolyte comprises water including an impurity which is sufficiently conductive to impart to the water electrolyte a resistivity of approximately 105 ohm-centimeters or less.

7. The improvement of claim 5 wherein:

the reverse-biasing means comprises an annular electrode contacting the same wafer surface as the solid electrode and the guard ring, the annular electrode surrounding the guard ring and being biased at a dc voltage with respect to the solid electrode.

8. The improvement of claim 7 further comprising:

means for submerging both the annular electrode and the solid electrode in the electrolyte; and

means for raising the annular electrode, solid electrode and guard ring from the electrolyte so as to contact the wafer, whereby a thin film of the electrolyte constitutes an electrical interconnection between the wafer and both the solid and annular electrodes.

9. The improvement of claim 8 wherein:

the electrolyte comprises water including an impurity which is sufficiently conductive to impart to the water electrolyte a resistivity of approximately 105 ohm-centimeters or less.

10. The improvement of claim 9 wherein:

the electrolyte consists of water containing approximately two percent by volume of a water soluble conducting polymer.

11. In a process for analyzing semiconductor wafers comprising the steps of forming a diode region on the wafer, reverse biasing the diode region thereby to form a depletion layer, adjusting the reverse bias voltage to adjust the thickness of the depletion layer, and directing rf current through the diode region to determine doping densities at various depths in the wafer, the improvement wherein:

the step of forming the diode region comprises the steps of contacting a liquid electrolyte to one exposed surface of the semiconductor wafer and contacting a solid electrode to the electrolyte; and

the step of directing rf current through the diode region comprises the step of directing rf current through the solid electrode, the liquid electrolyte and the wafer, whereby wafer analysis may be accomplished without damaging the wafer.

12. The improvement of claim 11 further comprising the step of:

defining the area of the diode region comprising the step of contacting the liquid electrolyte with an annular conductor which surrounds the solid electrode and is insulated therefrom.

13. The improvement of claim 12 wherein:

the step of reverse biasing the diode region comprises the step of maintaining the solid electrode and the annular conductor at substantially the same dc voltage; and

the step of directing rf current comprises the step of maintaining the annular conductor at a substantially constant rf reference voltage.

14. The improvement of claim 13 wherein:

the step of forming the diode region comprises the step of including on a wafer surface an electrolyte comprising water including an impurity which is sufficiently conductive to impart to the water electrolyte a resistivity of approximately 105 ohm-centimeters or less.

15. The improvement of claim 14 further comprising the steps of:

forming an annular electrode which surrounds both the annular conductor and the solid electrode;

submerging the annular electrode, annular conductor and solid electrode in the electrolyte such that the annular electrode, annular conductor and solid electrode all have a surface lying substantially on a common plane beneath the surface of the electrolyte;

raising the solid electrode, annular conductor, and annular electrode to a location above the Surface of the electrolyte, thereby contacting the wafer with a thin film of the electrolyte which constitutes the electrical interconnection between both the solid and annular electrodes and the wafer.

16. In a process for analyzing a semiconductor wafer comprising the steps of forming a diode region in the wafer, successively applying different values of reverse bias voltage to the bias region, thereby forming successive depletion layers of different depth, applying a substantially constant rf current of frequency f1 to the diode region, detecting the voltage across the diode region at frequency f1, said voltage being indicative of the depletion layer depth, applying a voltage of frequency f2 to the diode region, said frequency f2 being small compared to f1, said f2 voltage resulting in a modulation parameter Delta X2 equal to the variation in depletion layer depth and a modulation parameter Delta E2 equal to the variation of electric field in the depletion layer, maintaining one of the modulation parameters substantially constant with changes of depletion layer depth X, and detecting the modulation of the f1 signal at frequency f2 for different values of bias voltage, thereby to analyze the diode region at different depths, the improvement wherein:

the step of forming the diode region comprises the steps of contacting a liquid electrolyte to one surface of the wafer and contacting a solid electrode to the electrolyte; and

the step of directing rf current through the diode region comprises the step of directing rf current through the solid electrode, the liquid electrolyte and the wafer, whereby the wafer analysis may be accomplished without damaging the wafer.

17. The improvement of claim 16 further comprising the step of:

contacting the liquid electrolyte with an annular guard ring which surrounds the solid electrode and is insulated therefrom;

maintaining the solid electrode and the guard ring at substantially the same dc voltage; and

maintaining the guard ring at rf ground.

18. The improvement of claim 17 wherein:

the liquid electrode comprises water including an impurity which causes it to have a resistivity of approximately 105 ohm-centimeters or less.

19. The improvement of claim 18 further comprising the steps of:

forming an annular electrode which surrounds both the guard ring and the solid electrode;

submerging the annular electrode, annular conductor and solid electrode in the electrolyte such that the annular electrode, annular conductor and solid electrode all have a surface lying substantially on a common plane beneath the surface of the electrolyte;

placing the wafer at a location above the common planar surface of the electrodes; and

raising the solid electrode, annular conductor and annular electrode to contact the wafer, whereby a thin film of the electrolyte constitutes an electrical interconnection between both the solid and annular electrodes and the wafer.