Measurement method, semiconductor device manufacturing method, program, and resistivity measuring device

Abstract

The present invention provides a technology that makes it possible to measure resistivity with stable accuracy, even when there is a high-resistance layer on the surface of a target. Provided is a technology comprising: (a) a step for applying a current between a first terminal and a fourth terminal; (b) a step for applying a current between a second terminal and a third terminal; (c) processing for determining whether a target to be measured, the first terminal, the second terminal, the third terminal, and the fourth terminal are in ohmic contact with each other; and (d) a step for measuring the sheet resistance of the target.

Description

Measurement method, method for manufacturing semiconductor device, program and resistivity measuring instrument

[0001] The present disclosure relates to a measurement method, a method for manufacturing a semiconductor device, a program, and a resistivity measuring instrument.

[0002] In order to control the quality of resistivity of wafers such as SiC (silicon carbide) and Si (silicon), resistivity measurement by a contact-type DC probe method is sometimes performed. For example, a measurement technique as disclosed in Patent Document 1 has been proposed.

[0003] Japanese Unexamined Patent Publication No. 2014-029946

[0004] The present disclosure provides a technique that enables measurement of resistivity with stable accuracy even for an object having a high-resistance layer on the surface thereof.

[0005] According to one aspect of the present disclosure, the technique includes: (a) applying a current between a first terminal and a fourth terminal; (b) applying a current between a second terminal and a third terminal; (c) determining whether each of an object to be measured and the first terminal, the second terminal, the third terminal, and the fourth terminal is in an ohmic contact state; and (d) measuring a sheet resistance of the object.

[0006] According to the present disclosure, it is possible to measure resistivity with stable accuracy even for an object having a high-resistance layer on the surface thereof.

[0007] This is a block diagram showing the overall configuration of a resistivity measuring device preferably used in embodiments of this disclosure. This is an external view of the probe vertical drive unit, the four-probe probe, the semiconductor wafer, and the measurement stage preferably used in embodiments of this disclosure. This is a diagram showing the step 1 measurement method using a dual configuration method preferably used in embodiments of this disclosure. Figure 3(a) shows a diagram in which a current is passed between probes P1 and P4 of the four-probe probe by a constant current source, and the voltage between probes P2 and P3 is measured with a voltmeter. Figure 3(b) shows a diagram in which the polarity of the applied current by the constant current source is changed and the measurement is taken, and the average value is calculated. This is a diagram showing the step 2 measurement method using a dual configuration method preferably used in embodiments of this disclosure. This is a flowchart showing the operation during wafer measurement preferably used in embodiments of this disclosure. This is a diagram showing the operation of applying current between the first terminal and the fourth terminal preferably used in embodiments of this disclosure. This is a diagram showing the operation of applying current between the second terminal and the third terminal preferably used in embodiments of this disclosure.

[0008] <An Embodiment of the Present Disclosure> An embodiment of the present disclosure will be described below, mainly with reference to Figures 1-7. Note that the drawings used in the following description are schematic, and the dimensional relationships and ratios of the elements shown in the drawings do not necessarily correspond to those of reality. Furthermore, the dimensional relationships and ratios of the elements do not necessarily correspond between multiple drawings. In this embodiment, a four-probe resistivity measuring device using two pairs of electrodes will be used as an example, but it is also applicable to a two-probe resistivity measuring device using one pair of electrodes.

[0009] Figure 1 shows a resistivity measuring device 1 as a resistivity measuring instrument. As shown in Figure 1, the resistivity measuring device 1 includes a disc-shaped measuring stage (mounting table, table) 11 on which a semiconductor wafer 12 as the object (object to be measured, object to be measured) is placed, a rotation drive unit 13 for rotating the measuring stage 11, a four-prong probe 14 for contacting the upper surface of the object 12 placed on the measuring stage 11 to measure the resistivity of the object 12, and a measurement unit 15 for supplying a measurement current to the object 12 using the four-prong probe 14 to measure multiple measurement items for determining resistivity. The resistivity measuring device also includes a probe vertical drive unit 16 for moving the four-probe probe 14 vertically, a probe horizontal drive unit 17 for moving the probe vertical drive unit 16 and the four-probe probe 14 radially (horizontally) on the measuring stage 11, and an operation unit 18 for inputting control information to specify the position of the measurement point and, if there are multiple four-probe probes 14, to specify one of the multiple four-probe probes 14. The resistivity measuring device further includes a display unit 19 for displaying data such as the position of the measurement point and the resistivity of the measured result, and a control unit 20 configured to drive the rotation drive unit 13, the probe horizontal drive unit 17 and the probe vertical drive unit 16 according to the control information, so that the four-probe probe 14 can be brought into contact with a specified position on the upper surface of the object 12. The control unit 20 includes a computer, which executes a control program to drive the rotation drive unit 13, the probe horizontal drive unit 17 and the probe vertical drive unit 16 according to the control information, so that the four-probe probe 14 can be brought into contact with a specified position on the upper surface of the object 12. The control unit 20 is supplied with a predetermined operating power from the power supply unit 21.

[0010] The surface of the semiconductor wafer, which is the object 12, is subjected to fine processing. For example, an epitaxial growth film, a diffusion layer or implantation layer formed when impurities are diffused or implanted from the surface, or a metal film formed on the surface are formed on the wafer surface. The resistivity measuring device 1 can measure the resistivity of the wafer, the resistivity of the epitaxial growth film formed on the wafer surface, the sheet resistance of the diffusion layer or implantation layer formed when impurities are diffused or implanted from the surface, the sheet resistance of the metal film formed on the surface, and so on.

[0011] The control unit 20 includes an automatic setting means, which is an automatic setting mechanism that automatically sets the descent speed and the amount of indentation into the object 12 until the four-prong probe 14, driven by the probe vertical drive unit 16, contacts the object 12. The configuration of the probe vertical drive unit 16 and the control operation of the control unit 20 with respect to the probe vertical drive unit 16 will be described in detail below.

[0012] Figure 2 is an external view showing the configuration of the probe vertical drive unit 16, the four-probe probe 14, the object 12, and the measurement stage 11 in Figure 1. The probe vertical drive unit 16 includes a probe mounting bracket 16a, a cam receiver 16b, a weight 16c, a vertical drive cam 16d, and a stepping motor 16e.

[0013] The probe mounting bracket 16a is a bracket to which the four-prong probe 14 is attached. The cam receiver 16b is integrated with the probe mounting bracket 16a and receives the vertical driving force of the four-prong probe 14 from the vertical drive cam 16d. The weight 16c is a single weight with sufficient mass to apply a static load vertically to the probe vertical drive unit 16. The vertical drive cam 16d is connected to the shaft of the stepping motor 16e and maintains constant contact with the tip of the cam receiver 16b, thereby supporting the weight of the probe mounting bracket 16a, including the weight of the weight 16c, on the shaft of the stepping motor 16e.

[0014] The vertical drive cam 16d has, for example, an eccentric circular cam shape and moves the cam receiver 16b up and down according to the rotation angle. The stepping motor 16e is axially coupled to the cam receiver 16b, which is supported by the probe mounting bracket 16a, and to the vertical drive cam 16d on a support member independent of the probe mounting bracket 16a, and rotates and stops at any rotation angle position according to control information commanded from the control unit 20.

[0015] With the above configuration, the control unit 20 controls the probe vertical drive unit 16 by providing control information that instructs the amount of indentation to determine the appropriate load to apply to the probe for the type of object 12, and the vertical movement speed of the probe. As a result, the control unit 20 is configured to ensure appropriate contact between the four probes 14 and the object 12, and to measure the resistivity of the object 12 using the measurement unit 15.

[0016] Here, a dual configuration method can be used as the measurement method using four probes 14 arranged in series. The four probes 14 include a first terminal P1 (also called probe P1 or 1-pin P1), a second terminal P2 (also called probe P2 or 2-pin P2), a third terminal P3 (also called probe P3 or 3-pin P3), and a fourth terminal P4 (also called probe P4 or 4-pin P4).

[0017] Figure 3 shows step 1 of the dual configuration method.

[0018] First, as shown in Figure 3(a), a constant current source 33 is used to pass a current I between probe P1 (also called pin 1) and probe P4 (also called pin 4) of the four probes 14, and the voltage Va between probe P2 (also called pin 2) and probe P3 (also called pin 3) is measured with a voltmeter 34. At this time, in order to eliminate errors due to rectification between the four probes P1, P2, P3, and P4 and the semiconductor wafer 12 which is the sample, the polarity of the current I applied by the constant current source 33 is changed and the measurement is taken, and the average value is calculated, as shown in Figure 3(b). Here, the voltage between probe P2 and probe P3 when the current I is passed from probe P1 to probe P4 is defined as "Va+". Also, the voltage between probe P2 and probe P3 when the current I is passed from probe P4 to probe P1 is defined as "Va-". At this time, the smaller the voltage difference between "Va+" and "Va-", the better the contact condition between the probes (P1, P2, P3, P4) and the semiconductor wafer 12 can be determined.

[0019] The resistance value Ra in step 1 can be calculated using the following equation (1): Ra = Va / I = ((| Va + | + | Va - |) / 2) / I ... (1)

[0020] Figure 4 shows step 2 of the dual configuration method. As shown in Figure 4(a), a current I is passed between probes P1 and P3 of the four probes 14 by a constant current source 33, and the voltage Vb between probes P2 and P4 is measured with a voltmeter 34. At this time, in order to eliminate errors due to rectification between the probes and the sample (semiconductor wafer 12), the polarity of the current I applied by the constant current source 33 is changed and the measurement is taken, and the average value is calculated, as shown in Figure 4(b). Here, the voltage between probes P2 and P4 when current I is passed from probe P1 to probe P3 is defined as "Vb+". Also, the voltage between probes P2 and P4 when current I is passed from probe P3 to probe P1 is defined as "Vb-". At this time, the smaller the difference between the voltages "Vb+" and "Vb-", the better the contact condition between the probes (P1, P2, P3, P4) and the semiconductor wafer 12 can be judged to be.

[0021] The resistance value Rb in step 2 can be calculated using the following equation (2): Rb = Vb / I = ((|Vb+|+|Vb-|) / 2) / I ... (2) The probe spacing correction coefficient Ka can be calculated using the following equation (3): Ka = -14.696 + 25.173(Ra / Rb) - 7.872(Ra / Rb)² ... (3) The sheet resistance ρs can be calculated using the following equation (4): ρs = Ka × Ra ... (4) Although the probe spacing of the four probes 14 is adjusted to be equal, slight variations actually occur due to the precision of the bearings, etc. In the dual configuration method, variations in the probe spacing are reflected in the measured voltages Va and Vb, and these are then reflected in the calculated resistance values ​​Ra, Rb, probe spacing correction coefficient Ka, and sheet resistance ρs. This allows for correction of measurement errors caused by variations in the probe spacing.

[0022] In this case, if the object 12 is a SiC wafer, due to its special structure, a high-resistance layer exists on the surface of the SiC wafer, making it difficult to obtain stable ohmic contact, and in some cases, the resistivity cannot be accurately measured using the normal four-probe DC method. Therefore, in this embodiment, before measuring the Va voltage (voltage between pins 2 P2 and 3 P3 when current is passed from pin 1 P1 to pin 4 P4) and Vb voltage (voltage between pins 2 P2 and 4 P4 when current is passed from pin 1 P1 to pin 3 P3) using the normal four-probe DC method (see Figure 3), a high voltage is applied after the probe tips (P1, P2, P3, P4) have made contact with the SiC wafer 12 to confirm that ohmic contact has been achieved, and then the four-probe DC measurement is performed.

[0023] Next, the method for measuring the resistivity of a SiC wafer will be explained according to the flowchart shown in Figure 5. First, to start the measurement, the probe tips (P1, P2, P3, P4) are lowered towards the object 12. Specifically, the four-probe probe 14 attached to the probe vertical drive unit 16 has a weight 16c that sets an appropriate load on the SiC wafer. The control unit 20 lowers the four-probe probe 14 using a vertical drive cam 16d that controls the vertical movement speed, and brings it into contact with the SiC wafer.

[0024] (Procedure 1: Step S1) As shown in Figure 6, Procedure 1 involves connecting a constant current source 33 as an ammeter and a voltmeter 34 between the first terminal P1 and the fourth terminal P4, and applying a small current from the first terminal P1 to the fourth terminal P4. For example, a small current of 0.05 to 30 mA is applied for 5 seconds. Then, under similar conditions, a small current of 0.05 to 30 mA is applied from the fourth terminal P4 to the first terminal P1. The voltage between the first terminal P1 and the fourth terminal P4 while the current is being applied is measured by the voltmeter 34. This Procedure 1 is repeated multiple times, for example, three times.

[0025] Step S1 can be rephrased as (a) a step (procedure) of applying current between the first terminal P1 and the fourth terminal P4. Alternatively, Step S1 can be rephrased as having (a-1) a step (procedure) of passing current from the first terminal P1 to the fourth terminal P4, and (a-2) a step (procedure) of passing current from the fourth terminal P4 to the first terminal P1. Step S1 mitigates the Schottky barrier caused by the contact between the first terminal P1 and the fourth terminal P4 and the object 12.

[0026] (Procedure 2: Step S2) Next, as shown in Figure 7, Procedure 2 involves connecting a constant current source 33 as an ammeter and a voltmeter 34 between the second terminal P2 and the third terminal P3, and applying a small current from the second terminal P2 to the third terminal P3. For example, a small current of 0.05 to 30 mA is applied for 5 seconds. Then, under similar conditions, a small current of 0.05 to 30 mA is applied from the third terminal P3 to the second terminal P2. The voltage between the second terminal P2 and the third terminal P3 while the current is being applied is measured by the voltmeter 34. This Procedure 2 is performed multiple times, for example, three times.

[0027] Step S2 can be rephrased as (b) a step (procedure) of applying current between the second terminal P2 and the third terminal P3. Alternatively, Step S2 can be rephrased as having (b-1) a step (procedure) of passing current from the second terminal P2 to the third terminal P3, and (b-2) a step (procedure) of passing current from the third terminal P3 to the second terminal P2. Step S2 mitigates the Schottky barrier caused by the contact between the second terminal P2 and the third terminal P3 and the object 12.

[0028] (Procedure 3: Step S3) The ohmic state is determined by measuring the voltage value while the four probes (P1, P2, P3, P4) are in contact with the object (SiC wafer). If the measured voltage value is within a predetermined range, that is, within the set threshold range, it is determined to be an ohmic contact state. On the other hand, if the measured voltage value is not within the predetermined range, that is, outside the set threshold range, it is determined to be a non-ohmic contact state. Specifically, if the measured voltage after the completion of Procedure 2 (Step S2) is within the set threshold range, it is determined to be an ohmic contact state, and the process proceeds to the next procedure 4 (Step S4). On the other hand, if the measured voltage at this time is outside the threshold range, an error (for example, an error indicating that sheet resistance measurement is not possible) is issued, and the flow is terminated without measuring the resistivity. The reason for using the measured voltage after the completion of Procedure 2 (Step S2) for determination is that the voltage measured in Procedure 1 (Step S1) may diverge, while the voltage measured in Procedure 2 (Step S2) is more stable and easier to use for determination.

[0029] Step S3 can be rephrased as (c) a step (procedure) to determine whether an ohmic contact state is achieved. In step S3, the voltage between the second terminal P2 and the third terminal P3 after the completion of (b: step S2) is compared with a predetermined range (a set threshold range). The threshold value varies depending on the surface condition of the object 12. For example, if a SiC film is formed on the surface of the object 12, the threshold value will vary due to various factors (process, film thickness). Therefore, currently, the predetermined range is determined based on the voltage value in procedure 2 (step S2) when the same film was measured in the past.

[0030] (Procedure 4: Step S4) As described above, the resistivity of the object is measured using the normal DC four-probe method (see Figures 3 and 4 and their descriptions). Step S4 can be rephrased as (d) the process (procedure) of measuring the sheet resistance.

[0031] The control unit 20 of the resistivity measuring device 1 is configured to execute a program that causes the computer of the control unit 20 of the resistivity measuring device 1 to perform the following steps: (a) a procedure (process) to apply current between the first terminal and the fourth terminal; (b) a procedure (process) to apply current between the second terminal and the third terminal; (c) a procedure (process) to determine whether an ohmic contact state is in place; and (d) a procedure (process) to measure the sheet resistance. The control unit 20 may include a computer-readable recording medium on which the above program is recorded. The control unit 20 is also configured to execute the above program recorded on the computer-readable recording medium.

[0032] After step 4, the resistivity result obtained from the measurement in step 4 is fed back to the process conditions of the semiconductor manufacturing equipment. The process conditions of the semiconductor manufacturing equipment are then modified according to the resistivity result, and a semiconductor device manufacturing method is executed by the semiconductor manufacturing equipment, which includes a step of processing the semiconductor wafer based on the modified new process conditions. In other words, a semiconductor device manufacturing method includes a step of processing the semiconductor wafer by the semiconductor manufacturing equipment based on new process conditions modified according to the resistivity result obtained from the measurement in step 4.

[0033] Here, when a conductor such as metal (probe 14a) is brought into contact with a semiconductor wafer (object 12) which is said to have high resistance, a diode is formed between the conductor and the semiconductor. Diodes have rectifying properties, meaning that current flows easily in the positive bias direction and less easily in the reverse bias direction. When a voltage is applied in the reverse bias direction, a depletion layer is formed at the junction, and it functions to store charge like a capacitor.

[0034] In the flowchart of this embodiment, by utilizing the above-described characteristics, it is expected that in the measurement (step 4) after step 3 (step S3), the accumulated charge will be released, stabilizing the current and obtaining ohmic contact.

[0035] (Modification 1) If the voltage value between probe P2 and probe P3 is not within the predetermined range even after applying current once or multiple times, it is preferable to change the contact position of the probe of the 4-probe 14. In this case, the process from step 1 (step S1) to step 4 (step S4) of the flowchart will be performed again. According to Modification 1, for example, ohmic contact can be reliably obtained even when the in-plane resistance distribution of the SiC wafer is non-uniform, and resistivity measurement can be performed appropriately. The same effects as in the above-described embodiment can be obtained in this modification as well.

[0036] (Modification 2) If the voltage value between probe P2 and probe P3 is not within the predetermined range after applying current once or multiple times, it is preferable to change the current value applied. For example, if ohmic contact is not obtained with one application of current, the current value is increased and current is applied again. By doing so, it becomes possible to reliably obtain ohmic contact for the SiC wafer. In this case as well, the process from step 1 (step S1) to step 4 (step S4) of the flowchart is repeated. The same effects as in the above-described embodiment can be obtained in this modification as well.

[0037] (Modification 3) In Modification 3, the current is set according to the voltage value between probe P2 and probe P3 before applying the high voltage in the above procedure 3 (step S3). For example, if the voltage value before applying the current is large, a larger current is set. In this way, it is possible to quickly obtain ohmic contact with the SiC wafer in fewer attempts. The same effects as in the above embodiment can be obtained in this modification as well.

[0038] As described above, according to this embodiment, one or more of the following effects (1) to (5) can be obtained.

[0039] (1) According to this embodiment, resistivity can be measured even for objects that have a high-resistivity layer on their surface.

[0040] (2) According to the present embodiment, an ohmic contact state can be achieved even for an object having a high resistance layer on the surface thereof such as a SiC wafer, so that resistivity can be measured with high accuracy and high reliability.

[0041] (3) According to the present embodiment, resistivity can be measured by bringing a probe into contact even with an object having a high resistance layer on the surface thereof such as a SiC wafer.

[0042] (4) According to the present embodiment, since the probe can be brought into contact with an object having a high resistance layer on the surface thereof such as a SiC wafer, the resistivity of the surface of the object can be measured with higher resolution than when measuring a SiC wafer in a non-contact manner.

[0043] (5) According to the present embodiment, the surface of an object can be measured with high resolution by bringing a probe into contact therewith. On the other hand, when measuring a SiC wafer in a non-contact manner, an eddy current flowing on the surface of the object is measured, but in this case, the measurement point cannot be obtained with high resolution, resulting in a rough measurement value.

[0044] Hitherto, a resistivity measuring apparatus for a semiconductor wafer that measures the resistivity of a wafer, the resistivity of an epitaxial growth film formed on a wafer surface, the sheet resistance of a diffusion layer or an implanted layer when impurities are diffused or implanted from the surface, and the sheet resistance of a metal film formed on the surface has been specifically described based on the present embodiment. However, it is needless to say that the present invention is not limited to the above embodiments and examples, and various modifications can be made. The above-described aspects and modified examples can be used in appropriate combination.

[0045] Further, although the above embodiment has been described with respect to a power semiconductor wafer having a wide band gap, the present disclosure is not limited thereto.

[0046] P1: a first terminal, P2: a second terminal, P3: a third terminal, P4: a fourth terminal.

Claims

1. A measurement method comprising: (a) applying a current between a first terminal and a fourth terminal; (b) applying a current between a second terminal and a third terminal; (c) determining whether the object to be measured and the first terminal, the second terminal, the third terminal, and the fourth terminal are in an ohmic contact state; and (d) measuring the sheet resistance of the object.

2. The measurement method according to claim 1, further comprising (a-1) a step of passing current from the first terminal to the fourth terminal, and (a-2) a step of passing current from the fourth terminal to the first terminal.

3. The measurement method according to claim 1, further comprising (b-1) a step of passing current from the first terminal to the fourth terminal, and (b-2) a step of passing current from the fourth terminal to the first terminal.

4. The measurement method according to claim 1, wherein (c) the voltage between the second terminal and the third terminal after the completion of (b) is compared with a predetermined range.

5. The measurement method according to claim 4, wherein if the voltage between the second terminal and the third terminal is not within a predetermined range after applying current once or multiple times, the contact position of the probe of the 4 probe is changed.

6. The measurement method according to claim 5, wherein (a)-(d) are performed after changing the contact position.

7. The measurement method according to claim 4, wherein if the voltage between the second terminal and the third terminal is not within a predetermined range after applying current once or multiple times, the current value of the applied current is changed.

8. The measurement method according to claim 5 or claim 7, wherein (a)-(d) is performed after changing the contact position of the probe or the current value.

9. A method for manufacturing a semiconductor device, comprising the steps of: (a) applying a current between a first terminal and a fourth terminal; (b) applying a current between a second terminal and a third terminal; (c) determining whether the wafer and the first terminal, the second terminal, the third terminal, and the fourth terminal are in an ohmic contact state; and (d) measuring a resistance value; and feeding back the results obtained by a measurement method to the process conditions of a semiconductor manufacturing apparatus, modifying them according to the results, and processing the wafer based on the process conditions.

10. A program that causes a resistivity measuring instrument to perform the following steps: (a) a procedure for applying current between the first terminal and the fourth terminal; (b) a procedure for applying current between the second terminal and the third terminal; (c) a procedure for determining whether the object to be measured and the first terminal, the second terminal, the third terminal, and the fourth terminal are in an ohmic contact state; and (d) a procedure for measuring the sheet resistance of the object.

11. A resistivity measuring instrument comprising: a platform on which an object to be measured is placed; a probe including a first terminal, a second terminal, a third terminal, and a fourth terminal on the object; a horizontal drive unit for moving the probe horizontally; a vertical drive unit for moving the probe vertically; and a control unit configured to control the horizontal drive unit and the vertical drive unit to perform: (a) a process of applying current between the first terminal and the fourth terminal; (b) a process of applying current between the second terminal and the third terminal; (c) a process of determining whether the object to be measured and the first terminal, the second terminal, the third terminal, and the fourth terminal are in an ohmic contact state; and (d) a process of measuring the sheet resistance of the object.

12. The resistivity measuring instrument according to claim 11, wherein the object is a SiC wafer.

13. The resistivity measuring instrument according to claim 11, wherein the object is a semiconductor wafer.

14. The resistivity measuring instrument according to claim 13, wherein the surface of the semiconductor wafer is subjected to fine processing.

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