JP2012253147A - Resistivity measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To implement resistivity measurement under an appropriate measuring condition, depending upon a measuring object.SOLUTION: The resistivity measurement method, measuring the electric resistance of a sample with a four-probe resistivity measurement device, supplies an application current for each of a plurality of measuring points of the sample and measures a voltage value and, when the measured voltage value is determined to be beyond a predetermined range of a voltage value at the last measurement point, reconfigure a current value of the application current.

Description

  The present invention relates to a resistivity measuring method for measuring the resistivity of a sample by four-probe resistivity measurement.

  Semiconductor wafer resistivity measuring device is based on the resistivity of the wafer, the resistivity of the epitaxially grown film formed on the wafer surface, the sheet resistance of the diffusion layer or the implanted layer when impurities are diffused or implanted from the surface, and the metal produced on the surface. The sheet resistance of the film is measured. The result measured by the resistivity measuring apparatus is fed back to the process conditions of each semiconductor manufacturing apparatus and used as an important index for keeping the quality of the semiconductor device uniform.

  Patent Document 1 discloses a technique regarding a method for determining a current value used for measurement of a sample in a four-probe resistivity measuring apparatus.

JP 2010-38699 A

  However, there are various types of surface materials for semiconductor wafers to be measured by the resistivity measuring apparatus. For example, when the in-plane resistance distribution of the semiconductor wafer is non-uniform and the resistance value suddenly changes, there is a problem that the resistance value is not displayed because it is determined as a voltage range error during measurement.

  The present invention has been made paying attention to the above circumstances, and an object of the present invention is to provide a resistivity measurement method for performing resistivity measurement under appropriate measurement conditions according to a measurement object.

  In order to achieve the above object, one aspect of the present invention is a resistivity measurement method for measuring an electrical resistance of a sample using a four-probe resistivity measuring device, and supplying an applied current for each of a plurality of measurement points in the sample. Then, the voltage value is measured, and when it is determined that the measured voltage value exceeds the predetermined range of the voltage value at the previous measurement point, the current value of the applied current is reset.

  That is, according to the present invention, it is possible to provide a resistivity measurement method capable of measuring resistivity under an appropriate measurement condition depending on a measurement object.

The figure which shows the structural example of the 4 probe resistivity measuring apparatus which concerns on one Embodiment of this invention. Schematic of a resistivity measurement circuit. The figure which shows the example of a measurement at the time of assuming the sample of non-uniform in-plane resistance. The flowchart which shows the electric current determination process which concerns on this embodiment. The flowchart which shows the electric current determination process at the time of a measurement start. The figure which shows the example of a condition setting screen. The flowchart which shows the electric current determination process at the time of electric current reset.

Embodiments according to the present invention will be described below with reference to the drawings.
(Constitution)
FIG. 1 is a diagram illustrating a configuration example of a 4-probe resistivity measuring apparatus according to an embodiment of the present invention. The four-probe resistivity measuring device 10 is connected to each unit to control the entire operation, a stage 15 on which a sample W such as a semiconductor wafer is placed, and a measurement current to the sample to measure the sample W. And a four-probe probe 14 for measuring the voltage of the sample. Further, the 4-probe resistivity measuring device 10 is connected to the control unit 11 to supply a constant current to the 4-probe probe 14 and a constant-current applying circuit 12 connected to the control unit 11 to receive a measurement voltage from the 4-probe probe 14. A voltage measurement circuit 13 to be received, an operation unit 17 that supplies an operation signal to the control unit 11 according to a user operation, and a display unit 16 that displays measurement results and operation information measured by the control unit 11 on a screen. Yes.

  There are various surface materials for the semiconductor wafers to be measured by the four-probe resistivity measuring apparatus 10 having such a configuration. In order to measure the resistivity of these semiconductor wafers, a low resistivity sample of 0.075 Ω · cm or less in the standard of JIS H 0602 “Resistance measurement method of silicon single crystal and silicon wafer by four-probe method” In this case, in order to avoid heat generation, the upper limit of the applied current is set to 100 mA, and in the case of a high resistivity of 2000 Ω · cm or more, it is desirable to use a current that makes the potential difference of the middle probe 10 mV or less. It is recommended. In other words, it is necessary to measure the resistivity under two conditions: firstly, a current that is 10 mV or less, and secondly, the applied current has an upper limit of 100 mA.

  FIG. 2 shows a schematic diagram of a resistivity measuring circuit of the four-probe resistivity measuring device 10. The constant current application circuit 12 includes a current range switching unit 121 that can switch the current range of the constant current applied to the sample W via the four-probe probe 14 to 1 μA, 10 μA, 100 μA, 1 mA, 10 mA, and 100 mA. The voltage measurement circuit 13 includes a voltage range switching unit 131 that can switch the voltage range of the voltage applied to the sample W via the four-probe probe 14 to 2 mV, 20 mV, 200 mV, and 2 V. The 4-probe resistivity measuring apparatus 10 controls the constant current applying circuit 12 and the voltage measuring circuit 13 by the control unit 11, and measures the resistivity using, for example, voltage ranges of Auto3 mV, Auto10 mV, and Auto30 mV. In the case of measurement using Auto 3 mV, Auto 10 mV, or Auto 30 mV, the current determination process of the constant current application circuit 12 is required before starting the measurement.

  In this current determination process, the current value is changed several times and applied in order to determine the optimum current. For example, in the current tracking mode of Auto 10 mV, a current of 1 μA is applied so that the measurement voltage becomes 10 mV, the current is adjusted to reach 10 mV, and an appropriate current value is determined from Ohm's law. Then, the current determined before the measurement is applied and the resistivity is obtained from Ohm's law V = I * R and various correction factors.

  Here, it is assumed that the sample W to be measured has a nonuniform in-plane resistance distribution as shown in FIG. Then, the resistivity is measured at a plurality of measurement points over the surface 1 (assuming 400Ω / sq), the surface 2 (assuming 1000Ω / sq), and the surface 3 (assuming 400Ω / sq).

  When measuring such a sample W, for example, a method of shifting the voltage range during measurement is conceivable. In the voltage range determination process, a measurable area is set in advance in the voltage range of the selected voltage measurement circuit, and the determination criterion is that the measured voltage value is within that range. When the voltage range 20 mV is selected, the underrange region is 1.3 mV or less and the overrange region is 23 mV or more. When the voltage range is 200 mV, the underrange region is 23 mV or less and the overrange region is 230 mV or more. . The applied current is 0.000113A.

  For example, when measuring with the voltage range of 20 mV selected, if the measured value of surface 1 is 0.01 V and the measured value of surface 2 is 0.025 V, it is determined to be overrange and the voltage range is changed to 200 mV. And re-measure. The remeasurement result is 0.025 V, which is within the voltage range, and measurement of surface 2 is possible. The measured value of the surface 3 is 0.01 V, and it is determined that the voltage range is 200 mV, and the voltage range error is determined. In other words, the method of shifting the voltage range during measurement does not cause a voltage range error if the in-plane resistance is uniform, but the in-plane resistance is uneven and the resistance value changes suddenly. Is judged as a voltage range error and the resistance value is not displayed.

  In order to solve this problem, in this embodiment, when the measured voltage value exceeds the predetermined range of the voltage value of the previous measurement point, the voltage is measured by resetting the applied current. To avoid. Hereinafter, details of the current determination processing according to the present embodiment will be described.

FIG. 4 is a flowchart showing a current determination process according to the present embodiment.
[Step S1a: Current Determination Process at Measurement Start]
The control unit 11 determines an initial current value of the applied current of the constant current application circuit 12 at the start of measurement (step S1a). Here, it is assumed that an Auto 10 mV current determination sequence is executed. FIG. 5 is a flowchart showing a current determination process at the start of measurement.

  The control unit 11 selects the voltage range 20 mV in the voltage range switching unit 131 of the voltage measurement circuit 13 (step S1b), and determines the first applied current of the constant current application circuit 12 to 1 μA (step S2b). The applied current is adjusted so as to increase from the minimum current of 1 μA so as not to damage the sample W. The control unit 11 selects a current range in the current range switching unit 121 of the constant current application circuit 12 (step S3b). For an applied current of 1 μA, a current range of 10 μA is selected. Under the above measurement conditions, the control unit 11 supplies an applied current from the constant current applying circuit 12 to the four-probe probe 14, and starts measuring the voltage value of the sample W (step S4b).

  The control unit 11 measures the voltage value received from the four-probe probe 14 by the voltage measurement circuit 13 (step S5b), and when the measurement result cannot be determined as the target voltage value of 10 mV, Ohm's law V = I * R Then, the resistance R is calculated, and the current value I = 0.01 / R of the applied current is calculated so that the target voltage value is 10 mV. The control part 11 repeats the process of step S3b-S5b until it can determine with a measurement result being 10 mV of target voltage values, and determines an electric current value. If it is not possible to determine 10 mV even after performing the predetermined number of measurements in step S5b, the process proceeds to step S9b to determine a voltage range determination error.

  When the current value is determined in step S5b, the control unit 11 supplies the applied current from the constant current application circuit 12 to the four-probe probe 14 with the determined current value, and starts measuring the voltage value of the sample W (step). S6b). The control unit 11 measures the voltage value received from the four-probe probe 14 by the voltage measurement circuit 13 (step S7b), and repeats until the number of times that the measurement result is determined to be 10 mV continues n times. When the measurement result can be determined to be 10 mV a predetermined number of times, the initial current value of the applied current of Auto 10 mV is determined (step S8b). In step S7b, it is determined that the current determination has ended, for example, the number of times the measured voltage has entered the range of 7 mV to 13 mV (70% to 130%) lasts 4 times or more, and finally, 9.8 mV to 10.2 mV. It is assumed that it is in the range of (98% to 102%).

[Step S2a: Measure Voltage Value]
For each measurement point of the sample W, the control unit 11 supplies the application current of the initial current value determined in step S1a from the constant current application circuit 12 to the four-probe probe 14, and the voltage measurement circuit 13 The voltage value is measured (step S2a).

[Step S3a: Current Reset Determination]
The controller 11 determines whether or not the voltage value measured in step S2a is within a predetermined range (± XX%) of the measurement value at the previous measurement point (step S3a). If the measured voltage value is within the predetermined range, the process proceeds to step S4a. If the measured voltage value exceeds the predetermined range, the process proceeds to step S5a, and the current redetermination process during measurement is performed. In the current resetting determination process, the applied current is determined again when the measured voltage value exceeds a certain range of the voltage value of the previous measurement point, and the measurement is continued with the applied current after the determination, or the first If it is possible to select whether to return to the measurement point and perform measurement again, a voltage range error during measurement can be avoided.

  FIG. 6 shows an example of the condition setting screen. Whether to continue the measurement with the current resetting determination criterion and the applied current after the re-determination or to return to the first measurement point and measure it as a measurement parameter is registered in advance so that it can be freely changed. . When “Yes” is selected in “Automatic current change”, it is possible to set “Current redetermination fluctuation range” and “Remeasurement operation”. “Current redetermination fluctuation range” determines the applied current by performing the current determination sequence process again at the measurement point when the fluctuation range of the voltage value of the measurement result exceeds ± XX%. In the “re-measurement operation”, it is set whether to continue the measurement with the newly determined current (continuous measurement) or to return to the first measurement point and continue the measurement (measurement from the first point). The measurement result file outputs the applied current at each measurement point and the measured voltage value.

[Step S4a: Resistivity calculation, measurement value display]
When it is determined that the voltage value measured in step S3a is within the predetermined range of the measurement value at the previous measurement point, the control unit 11 determines from the measurement result based on Ohm's law V = I * R and various correction coefficients. The resistivity R is calculated and the measured value is displayed on the display unit 16 (step S4a).

[Step S5a: Current redetermination process during measurement]
On the other hand, when it is determined that the voltage value measured in step S3a exceeds the predetermined range of the measurement value of the previous measurement point, the control unit 11 performs a sequence of current redetermination processing during measurement. FIG. 7 is a flowchart showing current determination processing at the time of current resetting. Here, “Yes” is selected for “Automatic current change” on the condition setting screen of FIG. 6B, “90%” is set as “current redetermination fluctuation range”, and “continuous measurement” is set as “remeasurement operation”. It is assumed that it is set in advance.

  The control unit 11 selects the voltage range 20 mV in the voltage range switching unit 131 of the voltage measurement circuit 13 (step S1c), estimates the resistance value from the voltage value when it is determined that the current is reset, and determines the first applied current. A current value is determined (step S2c). When the measured voltage value is V1, and the current determination value at the start of measurement is I1, the resistance value R1 can be obtained from R1 = V1 / I1. The current value I of the first applied current can be calculated from I = 0.01 / R1.

  The control unit 11 selects a current range in the current range switching unit 121 of the constant current application circuit 12 (step S3c). Under the above measurement conditions, the control unit 11 supplies an application current from the constant current application circuit 12 to the four-probe probe 14 and starts measuring the voltage value of the sample W (step S4c).

  The control unit 11 measures the voltage value received from the four-probe probe 14 by the voltage measurement circuit 13 (step S5c), and when the measurement result cannot be determined as the target voltage value of 10 mV, Ohm's law V = I * R Then, the resistance R is calculated, and the current value I = 0.01 / R of the applied current is calculated so that the target voltage value is 10 mV. The control part 11 repeats the process of step S3c-S5c until it can determine with a measurement result being 10 mV of target voltage values, and determines an electric current value. Note that if it is not possible to determine 10 mV even after performing the predetermined number of measurements in step S5c, the process proceeds to step S9c to determine a voltage range error.

  When the current value is determined in step S5c, the controller 11 supplies an applied current from the constant current application circuit 12 to the four-probe probe 14 with the determined current value, and starts measuring the voltage value of the sample W (step S5c). S6c). The control unit 11 measures the voltage value received from the four-probe probe 14 by the voltage measurement circuit 13 (step S7c), and repeats until the number of times that the measurement result is determined to be 10 mV continues n times. When the measurement result can be determined to be 10 mV a predetermined number of times, the initial current value of the applied current of Auto 10 mV is determined (step S8c). In step S7c, it is determined that the current determination has ended, for example, the number of times the measured voltage has entered the range of 7 mV to 13 mV (70% to 130%) lasts 4 times or more, and finally 9.8 mV to 10.2 mV. It is assumed that it is in the range of (98% to 102%).

  The current re-determination process during the measurement in step S5a is the first time when it is determined that the resetting is performed, compared to the method in which the minimum current of 1 μA is supplied to the first point shown in the current determination process at the start of measurement in step S1a Since the resistance value is estimated from the voltage determined to be the current resetting of the measurable region of the voltage measurement circuit 13 in terms of the capability of the voltage measurement circuit 13, the estimated resistance value is approximately close to the true value, and measurement starts The current value can be determined earlier than the current determination process.

  FIG. 3B shows an example in which a method for resetting the applied current during measurement is applied. The current redetermination fluctuation range resets the applied current when the measured voltage value changes by 90% or more with respect to the voltage value at the previous measurement point. The applied current at the start of measurement is 0.000113 A, and the voltage range is 20 mV.

  When the measured value of the surface 1 becomes 0.01V and the measured value of the surface 2 becomes 0.025V, the current value is changed by 250% from the voltage value (0.01V) at the previous measurement point, and the current redetermination process is performed. By changing the applied current after resetting to 0.000045 A, the measured value of the surface 2 becomes 0.01 V, and the measurement of the surface 2 becomes possible. Further, when the surface 3 is measured, it becomes 0.004 V, which is 250% different from the voltage value (0.01 V) at the previous measurement point, and the current redetermination process is performed. By changing the applied current after resetting to 0.000113A, the measured value of the surface 3 becomes 0.01 V, and measurement within the surface 3 becomes possible.

  Therefore, according to the present embodiment, measurement of the resistivity of the non-uniform film of the semiconductor wafer, measurement of the resistivity of the mottled pattern film as the wafer diameter increases (450 mm) in the future, It is possible to measure the resistivity formed on the wafer under various conditions at once, and to realize effective use of the wafer and improvement of throughput.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  DESCRIPTION OF SYMBOLS 10 ... 4 probe resistivity measuring apparatus, 11 ... Control part, 12 ... Constant current application circuit, 13 ... Voltage measurement circuit, 14 ... 4 probe probe, 15 ... Stage, 16 ... Display part, 17 ... Operation part, W ... wafer, 121 ... current range switching unit, 131 ... voltage range switching unit.

Claims (1)

A resistivity measuring method for measuring the electrical resistance of a sample with a four-probe resistivity measuring device,
Supply an applied current for each of a plurality of measurement points in the sample to measure a voltage value,
A resistivity measurement method, comprising: resetting a current value of the applied current when it is determined that the measured voltage value exceeds a predetermined range of the voltage value at the previous measurement point.

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