TW201821813A - Resistivity measuring method - Google Patents

Abstract

The present invention provides a resistivity measuring method comprising: a mercury electrode forming step of forming a mercury electrode by bringing mercury into contact with a semiconductor single crystalline wafer; a forward bias voltage application step of applying a forward bias voltage to the mercury electrode; a C-V measuring step of applying a reverse bias voltage to the mercury electrode, and measuring a varying capacitance of the semiconductor single crystalline wafer; and a resistivity computing step of computing a resistivity on the basis of a relationship between the reverse bias voltage and the capacitance. In this way, a resistivity measuring method using a C-V technique is provided by which the resistivity of a semiconductor single crystalline wafer can be more reliably measured.

Description

Resistivity measurement method

The present invention relates to a resistivity measurement method, and more specifically, to a resistivity measurement method according to the C-V method.

Conventionally, a C-V (capacitance-voltage) method using mercury as an electrode to measure resistivity is widely known. In the CV method using mercury as an electrode, a Schottky barrier is formed by contacting a mercury electrode with a surface of a semiconductor single crystal wafer such as a silicon epitaxial layer, and a reverse bias voltage is continuously changed from, for example, 1V and simultaneously applied to Mercury electrodes expand the empty layer inside the semiconductor single crystal wafer to change its capacity.

Then, the dopant concentration in the desired depth is calculated from the relationship between the reverse bias and the capacity. In addition, a conversion formula such as ASTM STANDARDS F723 is used to convert the dopant concentration into resistivity. Hereinafter, conversion of the dopant concentration into the resistivity using the ASTM STANDARDS F723 conversion type is abbreviated as ASTM conversion.

When a mercury single electrode is used to repeatedly measure the electrical characteristics of a semiconductor single crystal wafer, in order to obtain electrical characteristics with improved reproducibility, a mercury stack or a mercury conduit is grounded to remove static electricity generated during the movement of mercury. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2015-99833

[Problems to be Solved by the Invention] For example, in the resistivity measurement method of the CV method using mercury as an electrode, in order to manage the resistivity measurement device at ordinary times or to measure the resistivity for product reassurance, it is only required for semiconductor The continuous measurement of the same position on the main surface of a single crystal wafer is repeated several times, and the resistivity tends to gradually decrease or gradually increase.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a resistivity measurement method based on the C-V method, which can more accurately measure the resistivity of a semiconductor single crystal wafer. [Technical means to solve problems]

In order to achieve the above object, the present invention provides a method for measuring resistivity, including: a mercury electrode forming step, which is a method in which mercury is brought into contact with a semiconductor single crystal wafer to become a mercury electrode; a forward bias applying step is applied to the mercury electrode to apply forward Bias voltage; CV measurement step is to apply a reverse bias voltage to the mercury electrode and measure the capacity of the semiconductor single crystal wafer that changes accordingly; and resistivity calculation step is to calculate the resistance from the relationship between the reverse bias voltage and the capacity rate. In addition, the so-called forward bias in the present invention means that a voltage is applied between a semiconductor single crystal wafer forming a Schottky barrier and a mercury electrode in a direction in which a current flows.

As a result, the electric charge accumulated between the mercury electrode and the semiconductor single crystal wafer is eliminated and eliminated due to the reverse electric charge supplied by the forward bias, so that the resistivity can be measured more accurately and accurately, and can be implemented. Resistivity measurement with good reproducibility.

At this time, the applied amount of the forward bias is preferably set to be larger as the resistivity of the semiconductor single crystal wafer is lower.

The lower the resistivity, the higher the impurity concentration, and the easier it is to accumulate charge between the semiconductor single crystal wafer and the mercury electrode. Therefore, as long as the amount of forward bias is adjusted, the reproducibility can be improved. Resistivity measurement.

According to the resistivity measurement method of the present invention, since the tendency to gradually reduce or increase the resistivity that is apparent when a semiconductor single crystal wafer is measured by a plurality of consecutive CVs is reduced, the semiconductor single crystal wafer can be measured more reliably. Resistivity.

Hereinafter, embodiments of the present invention will be described based on the drawings. FIG. 1 is a schematic diagram showing an example of the resistivity measurement method of the present invention, and represents the present invention in accordance with a mercury electrode formation step (step a), a forward bias application step (step b), and a CV measurement step (step c). And the resistivity calculation step (step d).

FIG. 2 is a schematic diagram of a mercury probe 10 showing an example of a C-V method measurement device used in the resistivity measurement method of the present invention. On the main surface of an epitaxial silicon wafer formed as a semiconductor single crystal wafer 1 by forming a silicon epitaxial layer on a single crystal silicon substrate, for example, mercury 31 and 32 stored in the storage containers 12 and 13 are guided upward from below. They were brought into contact with each other at the same time, and became mercury electrodes 33 and 34. The CV measurement was performed to obtain the resistivity. As a semiconductor single crystal wafer 1 other than silicon, it can be applied to resistivity measurement of compound semiconductor single crystal wafers such as GaP, GaN, and SiC.

In the mercury probe 10 shown in FIG. 2, the semiconductor single crystal wafer 1 is supported on the work table 11 with the main surface to be measured downward, and is carried above the mercury electrodes 33 and 34. When the CV measurement is performed to obtain the resistivity, the mercury 31 and 32 stored in the storage containers 12 and 13 rise through the inside of the conduits 15 and 16 and contact the main surface of the semiconductor single crystal wafer 1 to form a Schottky barrier. Mercury electrodes 33,34. The mercury electrode 33 is grounded 61 with a reverse bias voltage V applied to the mercury electrode 34.

When the mercury 31, 32 used as an electrode is contaminated by particles attached to the main surface of the semiconductor single crystal wafer 1 whenever it contacts the semiconductor single crystal wafer 1, the resistance of the mercury 31, 32 will gradually increase, and It adversely affects the measurement of electrical characteristics. In order to prevent this, the mercury 31, 32 that has been in contact with the semiconductor single crystal wafer 1 is temporarily returned to the storage containers 12, 13, and the mercury 31, 32 is bubbled, stirred and purified as a whole, and then the mercury 31, 32 is supplied to the electrodes. use.

When this foaming and stirring is performed, the mercury 31 and 32 rub against the inner walls of the storage containers 12 and 13 to generate static electricity. When the storage containers 12 and 13 are made of polycarbonate, for example, they are charged to a minus (negative) pole. In contrast, mercury 31, 32 will be charged to the + (positive) pole.

In addition, when the mercury 31, 32 rises through the inside of the ducts 15, 16, the mercury 31, 32 rubs against the inner walls of the ducts 15, 16 to generate static electricity. If the catheters 15 and 16 are made of Teflon (registered trademark), they will be charged into minus (negative) poles. In contrast, mercury 31, 32 will be charged to the + (positive) pole.

Therefore, the storage containers 12 and 13 are connected to the ground wires 52 and 54 through the conductive rubber pads 41 and 42 covering the storage containers 12 and 13. The ducts 15 and 16 are connected to the ground wires 51 and 53 through conductive rubber gaskets 43 and 44 covering the ducts 15 and 16. The conductive rubber gaskets 41, 42, 43, and 44 have a low resistivity of about 0.008 Ω ･ cm due to the combination of conductive materials such as carbon fiber or silver, so they can be easily absorbed in the storage containers 12, 13, or the duct 15. The static electricity generated by, 16 causes it to escape to the ground lines 51, 52, 53 and 54 of the ground 62, 63.

The CV characteristic measurement system 100 for measuring resistivity shown in FIG. 3 includes: a mercury probe 130 (the mercury probe 10 in FIG. 2), which is used as an electrode to allow mercury 31 and 32 to contact the semiconductor single crystal wafer 1; The LCR measuring instrument 140 provides high-frequency waves through measurement leads 161 and 162 connected to the mercury probe 130, and after applying a forward bias, a reverse bias is applied to the semiconductor single crystal wafer 1 to form an empty layer. While measuring the capacity of the empty layer; an analysis software installed on a PC (personal computer) 150 connected to the LCR meter 140 via a GPIB (General Purpose Interface Bus) transmission line 163, based on the reverse bias and the empty layer Capacity to calculate resistivity.

When measuring the resistivity of the semiconductor single crystal wafer 1, the LCR meter 140 is used to continuously change the reverse bias voltage V and simultaneously apply the reverse bias voltage V to form a Schottky barrier with the semiconductor single crystal wafer 1 carried in the mercury probe 130. The mercury electrode 34 on the inside of the semiconductor single crystal wafer 1 expands the empty layer to change the capacity C, and the capacity C is measured by the LCR meter 140. Then, using the analysis software installed on the PC 150, the resistivity was calculated based on the relationship between the reverse bias voltage V and the capacity C of the empty layer.

As long as a mercury probe 10 similar to that in FIG. 2 is used, and according to a conventional method, the resistivity of a P-type silicon epitaxial layer formed on a single crystal silicon substrate as a semiconductor single crystal wafer 1 is repeatedly measured (at the same position). The CV measurement is repeated to obtain the resistivity), as shown in FIG. 4, the resistivity tends to gradually decrease. Furthermore, as long as the resistivity of the N-type epitaxial layer is repeatedly measured, as shown in FIG. 5, the resistivity tends to gradually increase. It is conceivable that this is because whenever the resistivity measurement is repeated, that is, whenever the reverse bias voltage V is applied, the charge between the mercury electrode 34 of the mercury probe 10 and the semiconductor single crystal wafer 1 gradually accumulates.

Therefore, in the present invention, the charge accumulated between the mercury electrode 34 and the semiconductor single crystal wafer 1 when the reverse bias V is applied is removed by applying a forward bias. The timing of applying the forward bias may be before or after the reverse bias V is applied. When the mercury electrode is brought into contact with the semiconductor single crystal wafer and the CV measurement is repeated at the same position, the timing of applying the forward bias is set to the application of the reverse bias V, which means that the timing of applying the forward bias is set to Before the reverse bias V is applied once. For this reason, the reverse bias voltage V is applied and the C-V measurement step is performed, and the electric charge accumulated between the mercury electrode and the wafer at one time can be removed by the subsequent forward bias application step. In addition, since the next C-V measurement is performed, it is possible to prevent the resistivity from gradually increasing and decreasing due to charge accumulation as in the conventional method.

In FIG. 6, when the resistivity of the P-type silicon epitaxial layer is repeatedly measured, the resistivity variation when the forward bias voltage is not applied (known method) and when the present invention is applied (the present invention) is exemplified. In the example of FIG. 6, the reverse bias voltage V is increased from + 1V to + 15V at 1V intervals after the absolute value of the forward bias voltage is increased from -1V to -18V at 1V intervals. At the same time, the resistivity was measured by applying it at the same time. In contrast to the case where the resistivity gradually decreases when no forward bias is applied, as long as the forward bias is applied, the resistivity can be maintained almost constant. However, it is not necessary to gradually increase the absolute value of the forward bias voltage to the desired voltage. For example, a certain voltage may be applied as the forward voltage.

The amount of forward bias applied is preferably set to be larger as the resistivity of the semiconductor single crystal wafer 1 is lower. As an example, the relationship between the resistivity and forward bias of the P-type silicon epitaxial layer is shown in FIG. 7 (a), and the resistivity and forward bias of the N-type silicon epitaxial layer is shown in FIG. 7 (b). Relationship. However, whether the applied amount of forward bias is smaller than the value obtained according to the relationship of Fig. 7 (a) and Fig. 7 (b), or it is a certain value regardless of the resistivity, it can be the same. The tendency of the resistivity to gradually increase (or decrease) during repeated CV measurement of the position is suppressed.

More specifically, if the semiconductor single crystal wafer 1 is a P-type, a negative (-) voltage is applied, and if it is an N-type, a positive (+) voltage is applied as a forward bias to the semiconductor single crystal wafer 1. 1 A mercury electrode 34 that forms a Schottky barrier by contacting it with mercury 32 [Fig. 8 (1)]

In this way, the charge remaining between the mercury electrode 34 and the semiconductor single crystal wafer 1 will be eliminated and eliminated due to the opposite charge supplied by the forward voltage, so that the semiconductor single crystal wafer 1 can be stored in the semiconductor single crystal wafer 1. The thickness of the formed empty layer 35 returned to a normal level [Fig. 8 (2)]. In this state, as long as a reverse bias is applied to the mercury electrode 34, an empty layer 35 with a normal horizontal thickness will be formed [Fig. 8 (3)]. Therefore, the resistivity when the CV measurement is repeated at the same position is N. Both the tendency to rise in the pattern and the decline in the P-type are improved.

Since the semiconductor single crystal wafer 1 has a lower resistivity, the impurity concentration increases, and a mercury electrode 34 in contact with the semiconductor single crystal wafer 1 also tends to leave a lot of electric charge. Therefore, the lower the resistivity of the semiconductor single crystal wafer 1, the larger the amount of forward bias applied is preferably set.

As described above, in the present invention, first, using a device as shown in FIGS. 2 and 3, contact a mercury with a semiconductor wafer to form a mercury electrode (a mercury electrode forming step) (step a). In addition, after the step of applying a forward bias to the semiconductor single crystal wafer 1 (step b), the LCR measuring instrument 140 is used to continuously change the reverse bias V and simultaneously apply it to the mercury electrode 34. While the empty layer is enlarged inside the circle 1 to change the capacity C, the CV measurement step is performed by the LCR meter 140 (step c). When repeating the measurement at the same position, a forward bias application step (step b) may be performed after the C-V measurement step (step c). At this time, as described above, the forward bias applying step (step b) is performed after the CV measuring step (step c), which means that the forward bias applying step is performed before the next CV measuring step (step c) at the same position. (Step b).

Next, using the analysis software installed on the PC 150, a resistivity calculation step (step d) of calculating the resistivity based on the relationship between the reverse bias voltage V and the capacity C of the empty layer is performed. At this time, as long as the relationship between the reverse bias voltage V and the capacity C is plotted, a CV characteristic can be obtained. In addition, as long as the reverse bias voltage and capacity are substituted into the following equations (1) and (2), the depth W in the semiconductor single crystal wafer 1 and the dopant concentration N (W in the depth W) can be calculated. ), So that the distribution of the dopant concentration in the depth direction can be obtained. [Mathematical formula 1] W = Aε ₀ ε _Si / C [Mathematical formula 2] N (W) = 2 / (qε ₀ ε _Si A ² ) × {d (C ^-2 ) / dV} ^-1 where A is The electrode area, ε ₀ is the vacuum permittivity, ε _Si is the relative permittivity of Si, and q is the charge of the electron.

In addition, in the distribution of the dopant concentration in the depth direction, as long as the measurement depth is specified, the dopant concentration in the depth can be obtained. Furthermore, by converting the obtained dopant concentration according to a conversion formula such as ASTM STANDARDS F723, the dopant concentration can be converted into resistivity. According to the present invention as described above, it is possible to suppress the phenomenon that the resistivity gradually increases and decreases due to the accumulation of charge between the semiconductor wafer and the mercury electrode in the conventional method, especially when the CV measurement is repeated, and it is more reliable and highly reproducible. Calculate resistivity with high accuracy and accuracy.

In addition, whether the mercury electrode formation, CV measurement, and resistivity calculation are performed again at the same location, or the mercury electrode formation is continued and the mercury electrode is continuously maintained and the CV is repeated at the same location. In the case of measurement, the electric charge is gradually accumulated, so the present invention is effective in any case. The case of duplication will be described more specifically. For example, (step a) to (d) of FIG. 1 may be repeated at the same position. That is, the mercury can be contacted with the main surface of the wafer to form a Schottky barrier, and forward bias application, reverse bias application, and resistivity calculation can be performed in order, and then the mercury can be separated from the main surface of the wafer. And for the next measurement, the mercury is brought into contact with the main surface of the wafer again at the same position and the above process is repeated [see arrow (1) in FIG. 1]. In addition, after performing (step a), the steps (b), (c), and (d) can be repeated directly at the same position. That is, in a state where the Schottky barrier is formed, forward bias application, reverse bias application, and resistivity calculation can be repeated [see arrow (2) in FIG. 1]. In addition, it can also be performed (step a), and then repeat (step b) and (step c) directly at the same position, and then perform (step d). That is, after the Schottky barrier is formed, the forward bias application and the reverse bias application can be repeated directly, and finally the resistivity calculation can be performed together [see arrow (3) in FIG. 1]. Either way, it is possible to suppress the gradual increase and decrease of the resistivity caused by the accumulation of electric charge and measure it. [Example]

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Example 1] The resistivity measurement method of the present invention was implemented. Specifically, (step a) to (step d) shown in FIG. 1 are repeated. Using the mercury probe 10 shown in FIG. 2 and repeating the CV measurement of the P-type silicon epitaxial layer 1 having a resistivity of about 0.9 Ωcm 5 times, the absolute value is increased and applied at intervals of 1V from -1V to -18V After the forward bias, the reverse bias V was increased from + 1V to + 15V at 1V intervals and applied, and the resistivity was measured. As a result, the CV value (coefficient of variation) obtained by dividing the average value of the measured values by the standard deviation σ was 0.03%.

[Comparative Example 1] The P-type silicon epitaxial layer 1 having a resistivity of about 0.9 Ωcm used in Example 1 was measured, and the CV measurement was repeated 5 times without applying a forward bias as in a conventional method to obtain the resistivity. . As a result, the CV value was 0.15%. [Industrial possibilities]

Since the resistivity measurement method according to the present invention can remove the charge accumulated between the mercury electrode and the semiconductor single crystal wafer when the reverse bias voltage V is applied by applying a forward bias voltage, the semiconductor during repeated measurement can be removed. The thickness of the empty layer formed in the single crystal wafer is maintained at a normal level, and the tendency of the resistivity to decrease or increase gradually can be suppressed. As a result, the accuracy of repeated measurement of resistivity can be improved.

In addition, the present invention is not limited by the above embodiments. The above-mentioned embodiment is an example. Anyone having a technical idea that is substantially the same as that described in the patent application scope of the present invention and produces the same effect is included in the technical scope of the present invention.

1‧‧‧Semiconductor single crystal wafer

1‧‧‧P-type silicon epitaxial layer

10‧‧‧ Mercury Probe

11‧‧‧Workbench

12‧‧‧Storage Container

13‧‧‧Storage Container

15‧‧‧ catheter

16‧‧‧ Catheter

31‧‧‧ Mercury

32‧‧‧ Mercury

33‧‧‧ Mercury electrode

34‧‧‧ Mercury electrode

35‧‧‧ empty layer

41‧‧‧Conductive rubber gasket

42‧‧‧Conductive rubber gasket

43‧‧‧Conductive rubber gasket

44‧‧‧Conductive rubber gasket

51‧‧‧ ground wire

52‧‧‧ ground wire

53‧‧‧ ground wire

54‧‧‧ ground wire

61‧‧‧ land

62‧‧‧ land

63‧‧‧ land

100‧‧‧C-V characteristic measurement system

130‧‧‧ Mercury Probe

140‧‧‧LCR measuring instrument

150‧‧‧PC (personal computer)

161‧‧‧Measurement Lead

162‧‧‧Measurement Lead

163‧‧‧GPIB transmission line

FIG. 1 is a schematic diagram showing an example of the resistivity measurement method of the present invention. FIG. 2 is a schematic diagram of a mercury probe showing an example of a C-V method measurement device used in the resistivity measurement method of the present invention. Fig. 3 is a C-V characteristic measurement system used in the resistivity measurement method of the present invention. FIG. 4 is a tendency that appears when a C-V measurement is repeated according to a conventional method to obtain the resistivity of a P-type silicon epitaxial layer. FIG. 5 shows the tendency that occurs when the C-V measurement is repeated to obtain the resistivity of an N-type silicon epitaxial layer according to a conventional method. FIG. 6 is an example of resistivity variation when the C-V measurement is repeated to obtain the resistivity of the P-type silicon epitaxial layer when the forward bias is not applied and when the forward bias is applied. FIG. 7 (a) is an example of the relationship between the resistivity of the P-type silicon epitaxial layer and the forward bias. (B) An example of the relationship between resistivity and forward bias of an N-type epitaxial layer. FIG. 8 is a schematic explanatory diagram when a forward bias is applied to a semiconductor single crystal wafer, where (1) is a state where a forward bias is applied to a semiconductor single crystal wafer with a remaining charge; (2) is a state where a forward bias is applied After the bias is applied, the thickness of the empty layer returns to a normal level; (3) The state where the empty layer with a normal horizontal thickness is formed.

Claims (2)

A resistivity measuring method includes: a mercury electrode forming step of contacting a semiconductor single crystal wafer with mercury to become a mercury electrode; a forward bias applying step of applying a forward bias to the mercury electrode; a CV measuring step of A reverse bias is applied to the mercury electrode and the capacity of the semiconductor single crystal wafer that is changed is measured; and a resistivity calculation step is to calculate the resistivity from the relationship between the reverse bias and the capacity. The resistivity measurement method according to claim 1, wherein the applied amount of the forward bias is set to be larger as the resistivity of the semiconductor single crystal wafer is lower.