JPH11186350A - Recombination life time measuring method for minority carriers of semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology, which is capable of quantitatively evaluating the recombination lifetime of the minority carriers of a semiconductor. SOLUTION: This method measures the recombination lifetime of the minority carriers in a semiconductor. The voltage in a region of inverted voltage is applied on the semiconductor, and excess minority carriers are generated in the semiconductor. Thereafter, in a state in which the carriers are held constant with the first voltage in this inverted voltage region, the time change of the electrical capacitance of the semiconductor is measured. Based on the time change of the electrical capacitance, the recombination lifetime of the minority carriers in the semiconductor is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for measuring the lifetime of a minority carrier of a semiconductor.

[0002]

2. Description of the Related Art Since impurities or lattice defects in a semiconductor substrate (hereinafter, also simply referred to as "substrate") have a great effect on the characteristics of a semiconductor device, the evaluation of impurities and lattice defects in the substrate requires the manufacture of the semiconductor device. It is one of the important test items in the process. In order to evaluate impurities and lattice defects in a semiconductor substrate, the lifetime of a minority carrier correlated with the density of impurities and lattice defects has been conventionally measured.

[0003] The lifetime measurement method for minority carriers includes a generation lifetime measurement method that captures the generation process of a deficient minority carrier, and a recombination lifetime measurement method that captures the recombination process of an excess minority carrier. There is. Both measurement methods capture the lifetime of the minority carrier when shifting from the non-equilibrium state to the thermal equilibrium state.

As a method for measuring the recombination lifetime by capturing the recombination process of excess minority carriers, μ-PCD (Phot
oconductive decay method, SPV (Surface Photo Volta)
ge) method.

[0005]

In the measurement by the μ-PCD method, first, a semiconductor substrate is irradiated with light to form a non-equilibrium state in which an excess minority carrier exists. Thereafter, when the light irradiation is stopped, the excess minority carriers disappear by recombination. The presence of this excess minority carrier affects the specific resistance of the semiconductor substrate. Therefore, by measuring the time change of the reflectance of the microwave with respect to the semiconductor substrate, the time change of the specific resistance, that is, the time change of the excess minority carrier (recombination process) can be grasped. As described above, in the μ-PCD method, the disappearance of excess minority carriers injected by irradiating a semiconductor substrate with light is obtained from the microwave reflectance.

However, the measurement results obtained by the μ-PCD method include not only all effects in the depth (thickness) direction of the semiconductor substrate but also effects on the back surface of the semiconductor substrate. . In other words, the measurement result obtained by this method includes, in addition to the recombination lifetime of the excess minority carrier to be measured, diffusion into the semiconductor substrate and effects such as recombination on the front and back surfaces of the substrate. . In addition, since information obtained from microwave reflectivity is limited to the penetration depth of the microwave (skin depth), it is difficult to quantitatively evaluate the recombination lifetime of minority carriers using this method. There was a problem.

On the other hand, in the measurement by the SPV method, first, an electric charge for forming an inversion layer inside a semiconductor substrate is added to an electrode provided on a surface of an insulating layer of a semiconductor wafer. This charge forms an inversion layer and a depletion layer inside the semiconductor substrate. Next, by applying intermittent light, excess minority carriers are generated in the inversion layer. The generated excess minority carriers recombine at the same time, but some are left behind. The width of the depletion layer is reduced with respect to the remaining excess minority carriers, thereby satisfying the charge neutrality condition. As the depletion layer width changes, the surface potential of the semiconductor substrate changes. Therefore, by measuring the amount of change, the recombination process of excess minority carriers can be grasped. As described above, the SPV method evaluates the recombination lifetime from the change in the surface potential depending on the recombination amount of excess minority carriers when light is irradiated.

However, the SPV method has a problem that it is difficult to separately evaluate the recombination lifetime and the surface recombination speed, and it is difficult to quantitatively evaluate the recombination lifetime.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the prior art, and has as its object to provide a technique capable of quantitatively evaluating the recombination lifetime of minority carriers of a semiconductor. I do.

[0010]

In order to solve at least a part of the above-mentioned problems, a first recombination lifetime measuring method according to the present invention comprises: Measuring the change over time in the capacitance of the semiconductor while maintaining a constant voltage at a first voltage in the inversion voltage region after generating an excess minority carrier inside the semiconductor by applying a voltage of And (b) obtaining a recombination lifetime of minority carriers in the semiconductor based on a time change of the electric capacity.

The capacitance of a semiconductor is quantitatively related to the amount of excess minority carriers. Therefore, by measuring the time change of the electric capacity of the semiconductor in the process of recombination of the excess minority carriers, the recombination lifetime of the minority carriers in the semiconductor can be quantitatively obtained. Note that the semiconductor here includes a semiconductor substrate and a semiconductor wafer having an insulating layer on a surface of the semiconductor substrate.

In the first recombination lifetime measuring method, it is preferable that the step (a) includes a step of irradiating the semiconductor with light to generate the excess minority carriers.

In this case, since a large number of excess minority carriers can be generated in a short time, the recombination lifetime can be measured quickly and easily.

[0014] In the first recombination lifetime measuring method, the step (a) includes the step of:
By changing the voltage from the first voltage to the first voltage,
Preferably, the method includes a step of generating the excess minority carriers, and the first voltage is a voltage closer to a depletion voltage region than the second voltage.

[0015] In this case, the measurement can be further facilitated because a larger number of minority carriers can be generated at the first voltage than the excess minority carriers at the second voltage.

In the first recombination lifetime measuring method, a CV characteristic is measured while changing a DC component of a voltage from the depletion voltage region to the inversion voltage region, and the CV characteristic is measured based on the CV characteristic. It is preferable that a turn-on voltage, which is a voltage at a boundary between an inversion voltage region and the depletion voltage region, is measured, and the first voltage is determined based on the turn-on voltage.

This makes it possible to know the turn-on voltage at which excess minority carriers are generated more.
Can be more appropriately determined and measured.

The second recombination lifetime measuring method according to the present invention further comprises the steps of: (a) applying a charge of a first polarity to the upper surface of the insulating layer of the semiconductor wafer to cause the inside of the semiconductor substrate to be inverted Forming a layer, and (b) irradiating the semiconductor wafer with light to generate excess minority carriers inside the semiconductor substrate, and then contactlessly contact the surface of the insulating layer above the insulating layer. Measuring a potential change over time; and (c) determining a recombination lifetime of minority carriers in the semiconductor substrate based on the time variation of the surface potential.

The surface potential of the insulating layer formed on the surface of the semiconductor substrate is quantitatively related to the amount of excess minority carriers in the substrate. Therefore, by measuring the change over time of the surface potential of the insulating layer of the semiconductor wafer in the process of recombining the excess minority carriers, the recombination lifetime of the minority carriers in the semiconductor substrate can be determined quantitatively.

In the second recombination lifetime measuring method, the step (b) is performed by adding a second charge different from the first polarity to such an extent that the inversion layer does not disappear. It is preferable to include a step of generating minority carriers.

In this way, by adding charges having different polarities, more excess minority carriers can be generated, and the measurement becomes easier.

[0022]

DETAILED DESCRIPTION OF THE INVENTION Basic idea of measurement method:
Hereinafter, in this specification, an n-type semiconductor substrate will be described as an example of a semiconductor substrate. FIG. 1 is a conceptual diagram showing a basic configuration used in a minority carrier lifetime measurement method according to the present invention. In FIG. 1A, a semiconductor wafer 10
Reference numeral 0 denotes an insulating layer 102 formed on the upper surface of a semiconductor substrate 101, and an electrode 200
Are formed, and a so-called MIS structure (metal-insula) is formed.
tor-semiconductor). Also, an electrode 210 that is in ohmic contact is formed on the back surface of the semiconductor substrate 101. As the insulating layer 102, an insulator such as a silicon oxide film or an air gap can be used.
A voltage V is applied between the electrodes 200 and 210, and an electric capacity (hereinafter referred to as “capacity”) between the electrodes is measured by the impedance meter 13.

FIG. 1B shows an equivalent circuit of the structure shown in FIG. This equivalent circuit has a capacitance Cd of a depletion layer formed on the semiconductor substrate 101 and a capacitance Cox of the insulating layer 102.
It is represented by a series connection with Here, Cox is always constant. Therefore, when voltage V is applied, Cd and Cox
The value of Cd can be determined by measuring the combined capacitance C with Here, the combined capacitance C is represented by Expression (1).

[0024]

(Equation 1)

FIG. 2 is a conceptual diagram showing a configuration of a measuring apparatus for measuring the combined capacitance C while realizing the configuration shown in FIG. The configuration and operation of this measuring device are described in detail in Japanese Patent Application Laid-Open No. 4-132236 disclosed by the present applicant. This measuring device includes a fixed base 1, a piezoelectric actuator 2 installed below the fixed base 1, and a gantry 3 installed further below the piezoelectric actuator 2. A prism 4 is provided on the bottom of the gantry 3. A light emitting element 5 such as a GaAlAs laser is fixed on one slope of the gantry 3, and a light receiving element 6 is fixed on the other slope.

The bottom surface 4a of the prism 4 is
00 is placed in parallel with the surface (parallel plane (xy plane)) of the sample stage 7 on which the sample 00 is mounted. The bottom surface 4a of the prism 4
, A ring-shaped measurement electrode 201 is formed.
Below the prism 4, the semiconductor wafer 100 is held on a metal sample stage 7 via a gap G, and the surface 100 a of the semiconductor wafer 100 is
It is set to be almost parallel with. In this measuring apparatus, as described in detail in Japanese Patent Application Laid-Open No. 4-132236, the values of the gap G and dair are measured by utilizing the tunnel effect of laser light totally reflected by the bottom surface 4a of the prism 4. doing. In the measurement apparatus shown in FIG. 2, the electrode 200 shown in FIG.
1, the insulating layer 102 has a gap G and the semiconductor wafer 1
The electrode 210 corresponds to the sample stage 7 made of metal on the insulating layer 00.

The piezoelectric actuator 2 has a position control device 1
1 is connected, and moves the gantry 3 in the z direction according to the voltage given from the position control device 11. Light receiving element 6
Is connected to the light quantity measuring device 12, and the measuring electrode 201 and the metal sample table 7 are connected to the impedance meter 13, respectively. The impedance meter 13 is a device that measures a combined capacitance C between the measurement electrode 201 and the sample table 7. The position control device 11, the light quantity measuring device 12, and the impedance meter 13 are connected to a host controller 14, which controls the entire measuring device and processes the obtained data. As the host controller 14, for example, a personal computer is used.

FIG. 3 is a graph showing a change in capacitance when the applied voltage is swept with respect to the MIS structure of FIG. FIG. 3A shows a temporal change of the DC component V of the applied voltage. In practice, a voltage in which a high-frequency signal is superimposed on this DC component is swept in a stepwise manner. In the figure, the voltage Va, V _T, will be described later Vinv. FIG. 3 (B)
Shows a capacitance-voltage (CV) characteristic when a voltage is swept as shown in FIG. 3A for an n-type semiconductor substrate. In FIG. 3B, the accumulation region (accumulation voltage region)
, Depletion region (depletion voltage region), strong depletion region (strong depletion voltage region), and inversion region (inversion voltage region)
Is shown. When the lifetime of the minority carrier (hole) of the n-type semiconductor is longer than the sweep speed of the voltage, that is, when the generation and recombination process of the minority carrier cannot follow the sweep speed of the voltage, FIG. ),
Hysteresis appears. Note that the shape of the hysteresis curve changes depending on the voltage sweep speed (dV / dt). The area surrounded by the hysteresis curve decreases as the sweep speed decreases. Therefore, the generation of minority carriers
When the recombination process follows the voltage sweep speed, no hysteresis appears and no strong depletion region exists. At this time, in the inversion region, the combined capacitance C is always equal to the inversion capacitance Cinv. The inverting capacitance Cinv will be described later.

In FIG. 3A, the applied voltage is changed to an arrow d1.
When changing from Va to Vinv as shown in FIG.
Is changed from Cox to C as shown by arrow D1.
Change to a value smaller than inv. In the accumulation region, since no depletion layer exists inside the semiconductor substrate 101 (FIG. 1), the combined capacitance C is equal to the capacitance Cox of the insulating layer 102. In the depletion region, a depletion layer is formed inside the semiconductor substrate 101. Since the width increases with the voltage sweep, the capacitance Cd of the depletion layer gradually decreases, and as a result, the combined capacitance C decreases. At the boundary between the depletion region and the inversion region, the combined capacitance C becomes the inversion capacitance Cinv. At this time, a depletion layer is formed inside the substrate 101, and an inversion layer is formed near the substrate surface. The voltage V _T at the boundary between the depletion region and the inversion region is called the turn-on voltage.

When the combined capacitance C indicates the inversion capacitance Cinv,
That is, when in a thermal equilibrium state in the inversion region, it is given by the following equation (2).

[0031]

(Equation 2)

Here, V is the applied voltage in the inversion region, Qf
Is the amount of charge of the minority carrier to be in a thermal equilibrium state at the applied voltage V, q is the elementary charge, and Nd is
Is the depletion layer width in the thermal equilibrium state (when the combined capacitance C indicates the inversion capacitance Cinv), ε ₀ is the vacuum dielectric constant, and ε _S is the relative dielectric constant of the semiconductor substrate 101. The first term on the right side of equation (2) is the voltage Vox applied to the insulating layer 102.
(FIG. 1). The second term indicates the voltage Ψs (FIG. 1) applied to the semiconductor substrate 101, which is derived from Poisson equation.

In the strong depletion region, the combined capacitance C is smaller than the capacitance Cinv in a state of thermal equilibrium. This indicates that the width of the depletion layer is larger than the value Winv in the thermal equilibrium state. In the heavily depleted region, the generation process of minority carriers in the semiconductor substrate 101 does not follow the voltage sweep, so that the minority carriers are in a non-equilibrium state. The voltage distribution formula at this time is given by the following formula (3) instead of the formula (2).

[0034]

(Equation 3)

Here, ΔQ indicates the amount of charge of the deficient minority carrier, and ΔW indicates an increased depletion layer width to compensate for ΔQ.

Next, in FIG. 3A, when the applied voltage is changed from Vinv to Va as shown by an arrow d2,
The combined capacitance C shown in (B) is Cin as shown by arrow D2.
Changes from a value smaller than v to Cox. In the inversion region, the combined capacitance C is larger than the value Cinv in the thermal equilibrium state. This indicates that the width of the depletion layer is smaller than the value Winv in the thermal equilibrium state.
In the inversion region, since the process of recombination of minority carriers in the semiconductor substrate 101 does not follow the voltage sweep, the non-equilibrium state in which minority carriers are excessive is provided. The voltage distribution equation at this time is given by the following equation (4) instead of the above equation (2).

[0037]

(Equation 4)

Here, ΔQ indicates the amount of excess minority carrier charge, and ΔW indicates the depletion layer width reduced to compensate for ΔQ.

The recombination lifetime can be obtained by utilizing the process of recombining excess minority carriers generated in the inversion region in this manner. That is, by keeping the sweep voltage constant in the inversion region, excess minority carriers are recombined, and a transition from a non-equilibrium state to a thermal equilibrium state is made. In the thermal equilibrium state, the combined capacitance C becomes Cinv. By measuring and analyzing the change over time of the combined capacitance C, the recombination lifetime can be obtained. As this analysis method, an analysis method based on the cell bust method, which is a method for analyzing the generation lifetime, can be applied. The Zerubst method is described in detail in Zelbust's reference (M. Zerbst, Z. Angew, Phys. Vol. 22, p. 30, 1996).

B. First Embodiment FIG. 4 is a graph showing a method for measuring a recombination lifetime in the first embodiment. FIG. 4A shows the time change of the applied voltage V and the timing of light irradiation in this embodiment. After changing the voltage from the voltage Va in the accumulation region to the voltage Vinv in the inversion region, the voltage is kept constant at Vinv. When the voltage is kept constant at Vinv, light is applied to generate excessive minority carriers. The wavelength of this light is
It is preferable that the wavelength has energy equal to or larger than the energy gap of the semiconductor substrate 101. Then, the voltage V
Is stepwise changed to the measurement voltage Vm in the inversion region and is kept constant. In the first embodiment, Vinv corresponds to the second voltage in the present invention, and Vm corresponds to the first voltage in the present invention.

FIG. 4B shows CV characteristics when voltage sweep and light irradiation are performed as shown in FIG. 4A. By maintaining the voltage at Vinv and irradiating light, minority carriers are generated and the shortage state of minority carriers is eliminated, and by irradiating light, minority carriers shift to an excess non-equilibrium state. I do. Here, by stopping the light irradiation and changing the voltage stepwise to a voltage Vm closer to the depletion region in the inversion region, an excess minority carrier is generated and the combined capacitance C becomes Cm. Vinv
The change of the voltage from Vm to Vm generates more excess minority carriers because the amount of minority carriers in thermal equilibrium at Vm is smaller than at Vinv.

By keeping the voltage Vm constant, the excess minority carriers recombine and shift from the non-equilibrium state to the thermal equilibrium state. At this time, the change of the combined capacitance C with time (C
The recombination lifetime can be determined by measuring and analyzing the −t characteristic).

The measurement voltage Vm in the first embodiment, a voltage of the inverted region, is preferably between the voltage Vinv and the turn-on voltage V _T of the time of light irradiation. That is, it is preferable to satisfy the following conditions.

[0044]

(Equation 5)

[0045] formula (5), since Vm even when equal to Vinv, the excess minority carriers are present, Although it is possible to measure C-t characteristics of recombination processes, Vm is a value close to V _T Is preferred. This is because if there are a large number of excessive minority carriers, the amount of change in the combined capacitance C becomes large, and the Ct measurement in the recombination process becomes easier. In addition,
If Vm is greater than V _T, since the diffusion of minority carriers into the semiconductor substrate inside can not be ignored, the measurement of the lifetime due to recombination process becomes difficult.

The value of the inversion capacitance Cinv can be determined in advance from dimensions and physical properties of the semiconductor substrate and the insulating layer. Therefore, as shown in FIG.
In the case where the swept Vinv from, it is possible to know the turn-on voltage V _T from the C-V characteristics of FIG. 4 (B). Thus, the measurement voltage Vm in the recombination process can be easily determined during one voltage sweep, and appropriate measurement can be performed.

FIG. 5 is a graph showing the measurement results of the Ct characteristics in the process of recombination of excess minority carriers. In addition, as the semiconductor substrate 101, n-type Si, surface index (10
0), a substrate having a specific resistance of 10 Ω · cm was used. Further, a SiO ₂ film was formed as an insulating layer on the surface of the substrate 101, and an Al electrode was formed thereon. For the voltage V, the sweep speed is 1 V / sec, Va is +5 V, Vinv is -5 V, and Vm is-
2V. In FIG. 4A, by keeping the applied voltage constant at Vm, the combined capacitance C changes from Cm to Cinv. The recombination lifetime can be obtained by analyzing using the Ct characteristic of FIG.

The transient characteristics due to the recombination of minority carriers are as follows:
The following two expressions (6) and (7) are used to represent the expression (8).

[0049]

(Equation 6)

[0050]

(Equation 7)

[0051]

(Equation 8)

Here, Q, W and C are measured values of the charge amount of the minority carrier, the depletion layer width, and the combined capacitance at time t. On the other hand, the time change of the minority carrier is equal to the sum of the time change of the minority carrier due to the surface recombination on the surface of the semiconductor substrate 101 and the change of the minority carrier due to the recombination inside the substrate 101. Therefore, the time change of the minority carrier can be expressed by Expression (9).

[0053]

(Equation 9)

Here, ni is the intrinsic carrier density, S is the surface recombination speed, and τ is the recombination lifetime. Also,
Winv is the thermal equilibrium state in the inversion region, that is, the depletion layer width when the combined capacitance C becomes Cinv. From Expressions (8) and (9), Expression (10) holds.

[0055]

(Equation 10)

In equation (10), only the combined capacitance C depends on the time t, and the other parameters are constants.
Therefore, it can be seen from equation (10) that the slope of the time change of the square of (Cox / C) and the value of (1-Cinv / C) have a linear relationship.

FIG. 6 is a graph showing the Ct characteristic of FIG. 5 in a Zerubst plot. This Zerubst plot corresponds to equation (10). Therefore, the recombination lifetime τ can be obtained from the slope of the straight line, and the surface recombination speed S can be obtained from the intercept. As a result, it becomes possible to evaluate the recombination lifetime in which τ and S are separated.

According to the measuring method of the present embodiment, reasonable results were obtained with a recombination lifetime τ of minority carriers of 26.4 μsec and a surface recombination velocity S of 9.5 × 10 ⁻³ cm / s.

C. Second Embodiment FIG. 7 is a graph showing a method of measuring a recombination lifetime in a second embodiment. FIG. 7A shows a time change of the applied voltage V in this embodiment. After changing the voltage from the voltage Va in the accumulation region to Vinv, the voltage is kept constant at the voltage Vinv in the inversion region. Thereafter, the applied voltage is changed stepwise to the measured voltage Vm in the inversion region, and the voltage is kept constant. In the second embodiment, no light irradiation is performed.

FIG. 7B shows the CV characteristics when the applied voltage is swept as shown in FIG. By keeping the voltage constant at Vinv, a minority carrier deficient is generated, and the state shifts from the non-equilibrium state to the thermal equilibrium state. Thereafter, by setting the voltage to Vm in the inversion region in a step-like manner, excessive minority carriers are generated. By keeping Vm constant, excess minority carriers recombine and transition to a thermal equilibrium state. The recombination lifetime can be obtained by measuring and analyzing the time change (Ct characteristic) of the combined capacitance C at this time.

The measurement voltage Vm of the second embodiment is a voltage in the inversion region, and preferably satisfies the following conditions.

[0062]

[Equation 11]

Equation (11) differs from equation (5) of the first embodiment in that no excess minority carriers are generated by light irradiation, so that the recombination lifetime cannot be measured when Vm is equal to Vinv.

[0064] Further, Vm satisfies the condition of formula (11), close to V _T is preferred. In this case, measurement of the recombination process becomes easy because a large number of excess minority carriers are generated.

D. Third Embodiment FIG. 8 is a graph showing a method for measuring a recombination lifetime in the third embodiment. FIG. 8A shows the time change of the applied voltage V and the timing of light irradiation in this embodiment. After applying a voltage at a constant voltage Va in the accumulation region, at time t3
Then, the voltage is changed stepwise to the voltage Vinv in the inversion region and kept constant. At this time, light is irradiated to generate excessive minority carriers. At time t4, the light irradiation is stopped, and the applied voltage is changed stepwise to the measured voltage Vm in the inversion region and kept constant.

FIG. 8B shows Ct characteristics when voltage sweep and light irradiation are performed as shown in FIG. 8A. Until time t3, the applied voltage is held at Va in the accumulation region, and thus the combined capacitance C is constant at Cox. At time t4, by changing the applied voltage to the voltage Vinv in the accumulation region, the inside of the semiconductor substrate 101 becomes a non-equilibrium state in which minority carriers are insufficient. At this time, the combined capacitance C has a value smaller than Cinv. After that, light irradiation generates excessive minority carriers. In FIG. 8B, at time t4, the combined capacitance C is larger than Cinv, and it can be seen that excessive carriers are generated. At time t4, the light irradiation is stopped, and the applied voltage is changed to the measurement voltage Vm in the inversion region, so that an extra minority carrier is generated. After this,
By keeping the measurement voltage Vm constant, excess minority carriers are recombined, and a transition from a non-equilibrium state to a thermal equilibrium state is made.

It is preferable that the measured voltage Vm of the third embodiment satisfies the condition of equation (5). However, since in this case can not know the V _T value than C-V characteristics, the determination of the measured voltage Vm value is more difficult than in the first embodiment. That is, a step such as a preliminary test for knowing the _VT value is required. However, even if the measurement voltage Vm is the same voltage as Vinv, recombination lifetime can be measured because excessive minority carriers are generated.

The recombination lifetime can be obtained by analyzing the excess minority carriers generated as described above using the Ct characteristics after time t4.

E. Fourth Embodiment FIG. 9 is a graph showing a method for measuring the recombination lifetime in the fourth embodiment. FIG. 9A shows a time change of the applied voltage V in this embodiment. After a voltage is applied at a constant voltage Va in the accumulation region, at time t5, the voltage is stepwise changed from Va to a voltage Vinv in the inversion region and is kept constant. Thereafter, at time t6, the applied voltage is changed stepwise to the measurement voltage Vm in the inversion region and kept constant. The fourth
In the embodiment, no light irradiation is performed.

FIG. 9B shows Ct characteristics when voltage sweep is performed as shown in FIG. 9A. Until time t5, the applied voltage is held at Va in the accumulation region, so that the combined capacitance C is constant at Cox. At time t5, by changing the applied voltage to the voltage Vinv in the accumulation region, the inside of the semiconductor substrate 101 enters a non-equilibrium state in which minority carriers are insufficient. At this time, the combined capacitance C has a value smaller than Cinv. By maintaining the voltage as it is, minority carriers are generated, and the state shifts from the non-equilibrium state to the thermal equilibrium state. In FIG. 9B, at time t6, the combined capacitance C becomes Ci.
nv, which indicates that it is in a thermal equilibrium state. Time t
In step 6, by changing the applied voltage to the measured voltage Vm in the inversion region, excess minority carriers are generated. By maintaining the voltage, the excess minority carriers recombine and transition from the non-equilibrium state to the thermal equilibrium state.

It is preferable that the measured voltage Vm of the fourth embodiment satisfies the condition of the equation (11). However, since in this case can not know the V _T value than C-V characteristics, the determination of the measured voltage Vm value is more difficult than the case of the second embodiment. That is, a step such as a preliminary test for knowing the _VT value is required.

The recombination lifetime can be obtained by analyzing the excess minority carriers generated as described above using the Ct characteristics after time t6.

F. Fifth Embodiment FIG. 10 is an explanatory diagram showing a method of measuring a recombination lifetime using a Kelvin probe. In this embodiment, the insulating layer 122 is provided on the upper surface of the semiconductor substrate 121, and the electrode 220 is provided on the rear surface. In the first to fourth embodiments, the recombination lifetime was determined from the Ct characteristic while the applied voltage V was constant.
In the method of measuring a recombination lifetime using a Kelvin probe, a charge is added to the insulating layer 122 and the potential of the upper surface of the insulating layer 122 is measured with a constant amount of charge to obtain a recombination lifetime.

FIG. 10A shows a state where a negative charge is added to the insulating layer 122. The negative charge is added from the discharge needle 300 by corona discharge. When a negative charge is added, a depletion layer is formed in the semiconductor substrate 121, and the semiconductor substrate 121 is in a non-equilibrium state in which minority carriers are insufficient. As time passes, minority carriers are generated, and finally, a thermal equilibrium state is reached. Note that FIG.
The state shown in (a) corresponds to the voltage V in the inversion region in FIG.
This corresponds to a state where inv is applied. In FIG. 10B, light is irradiated to generate excessive minority carriers in the semiconductor substrate 121. At this time, the semiconductor substrate 121 is in a non-equilibrium state in which an excess minority carrier exists. FIG.
At 0 (c), positive charges are added by corona discharge to reduce the amount of negative charges on the insulating layer 122. FIG.
The state indicated by 0 (c) corresponds to the state where the voltage Vm in the inversion region is applied in FIG. In FIG. 10D, a change in potential on the upper surface of the insulating layer 122 due to a process of recombining excess minority carriers is measured in a non-contact manner using the probe 400. In this measurement, the amount of charge induced in the probe 400 by the negative charge on the insulating layer 122 is AC-coupled to a coupling capacitor (not shown) while vibrating the probe 400 up and down, so that it is proportional to the potential on the upper surface of the insulating layer 122. It is obtained as an alternating signal. The Kelvin probe device is well known and is described in Z. Physin, 115, 296 (1940).
(Gysae) and S. Wagener, which are published in detail in (Year).

FIG. 11 is an explanatory diagram schematically showing the inside of the semiconductor substrate in the state of FIG. By the processing of FIGS. 10A to 10C, the inside of the semiconductor substrate 121 is
A depletion layer and an inversion layer are formed, and excess minority carriers are generated in the inversion layer.

The neutral condition of the electric charge via the insulating layer 122 in FIG. 11 is expressed by Expression (12), and the potential V on the upper surface of the insulating layer 122 is expressed by Expression (13).

[0077]

(Equation 12)

[0078]

(Equation 13)

Here, Qm in the equation (12) is the insulating layer 122
This is the amount of negative charge above. The first term on the right side is the amount of charge in the depletion layer, q is the elementary charge, Nd is the donor density of the semiconductor substrate 121, and W is the width of the depletion layer. Further, Q in the second term is the charge amount of the minority carrier in the inversion layer. Note that the absolute value of the left side is based on the fact that the right side is positive and the left side is negative.

In the equation (13), Vox is a voltage applied to the insulating layer 122, and Δs is a voltage applied to the semiconductor substrate 121.

Here, when equation (12) is differentiated with respect to time t, equation (14) holds because Qm is constant.

[0082]

[Equation 14]

Also, differentiating equation (13) with time t gives:
Since Vox is constant, equation (15) holds.

[0084]

(Equation 15)

Further, Ψs is expressed by equation (16) from the Poisson equation.

[0086]

(Equation 16)

In the equation (16), ε ₀ indicates a vacuum dielectric constant, and ε _S indicates a relative dielectric constant of the semiconductor substrate 121.

Using equations (15) and (16), equation (1)
It can be seen that the time change of the excess minority carriers in 4) is represented by the time change of the potential on the upper surface of the insulating layer 122 as shown in the equation (17).

[0089]

[Equation 17]

Further, Expression (18) is established from Expression (17) and Expression (9) showing the time change of the minority carrier.

[0091]

(Equation 18)

By using the equation (18), it is possible to evaluate the recombination lifetime in which τ and S are separated, similarly to the equation (10) showing the time change of the capacitance in the first to fourth embodiments. .

As described above, by using the measurement method of the present invention, it is possible to measure the capacitance and potential depending on the recombination lifetime τ and the surface recombination velocity S of minority carriers. Therefore, the recombination lifetime τ and the surface recombination velocity S can be separated by applying the analysis method based on the Zerubst method, and the recombination lifetime τ of minority carriers can be quantitatively evaluated.

The present invention is not limited to the above Examples and Embodiments, but can be implemented in various modes without departing from the gist of the invention.
For example, the following modifications are possible.

(1) In the first and second embodiments, as shown in FIGS. 4A and 7A, the applied voltage V
Is stepwise changed from the voltage Va in the accumulation region to the voltage Vinv in the inversion region, but is not limited to this as long as the turn-on voltage can be determined. For example, the voltage may be swept linearly.

(2) In the first and second embodiments, as shown in FIGS. 4A and 7A, the applied voltage V
And although the voltage Va of the storage area to a voltage Vinv of the inversion region are varied at a constant sweep rate, in order to accurately measure the turn-on voltage V _T, also to reduce the sweep rate only near Good. In this case, a more appropriate first voltage Vm can be determined.

(3) In the first and second embodiments, as shown in FIGS. 4A and 7A, the applied voltage V
And although the voltage Va of the storage area to a voltage Vinv of the inversion region are varied at a constant sweep rate, in order to accurately measure the turn-on voltage V _T, it may be measured by near. This allows the first voltage Vm to be determined more quickly.

(4) In the fifth embodiment, in order to generate more excess minority carriers, FIG.
Although the charge amount on the insulating layer 122 is reduced as shown in FIG. 10C, the step shown in FIG. 10C may be omitted.
Even in this case, excess minority carriers can be generated by light irradiation.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a basic configuration used in a minority carrier lifetime measuring method according to the present invention.

FIG. 2 is a conceptual diagram showing a configuration of a measuring device that measures a combined capacitance C while realizing the configuration shown in FIG.

FIG. 3 is a graph showing a change in capacitance when an applied voltage is swept with respect to the MIS structure of FIG.

FIG. 4 is a graph showing a method for measuring a recombination lifetime in the first embodiment.

FIG. 5: Ct in the process of recombination of excess minority carriers
5 is a graph showing measurement results of characteristics.

FIG. 6 is a graph showing the Ct characteristic of FIG. 5 in a Zerubst plot.

FIG. 7 is a graph showing a method for measuring a recombination lifetime in the second embodiment.

FIG. 8 is a graph showing a method for measuring a recombination lifetime in the third embodiment.

FIG. 9 is a graph showing a method for measuring a recombination lifetime in the fourth embodiment.

FIG. 10 is an explanatory diagram showing a method for measuring a recombination lifetime using a Kelvin probe.

FIG. 11 is an explanatory view schematically showing the inside of the semiconductor substrate in the state of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fixed stand 2 ... Piezoelectric actuator 3 ... Stand 4 ... Prism 4a ... Bottom surface 5 ... Light emitting element 6 ... Light receiving element 7 ... Sample table 11 ... Position control device 12 ... Light quantity measuring device 13 ... Impedance meter 14 ... Host controller 100 ... Semiconductor Wafer 100a Surface 101 Semiconductor substrate 102 Insulating layer 121 Semiconductor substrate 122 Insulating layer 200, 210 Electrode 201 Measurement electrode 220 Electrode 300 Discharge needle 400 Probe G Gap Accumulation region Depletion region Strong depletion region… Inversion region

Claims (6)

[Claims] 1. A method for measuring the recombination lifetime of minority carriers in a semiconductor, comprising: (a) applying a voltage in an inversion voltage region to the semiconductor to generate an excess minority carrier inside the semiconductor; And a step of measuring a time change of the capacitance of the semiconductor while maintaining the voltage constant at a first voltage in the inversion voltage region; and (b) measuring a time change of the capacitance in the semiconductor based on the time change of the capacitance. Determining a recombination lifetime of minority carriers. A method for measuring a recombination lifetime of minority carriers. 2. The recombination lifetime measurement method according to claim 1, wherein the step (a) includes a step of irradiating the semiconductor with light to generate the excess minority carriers. Characterized recombination lifetime measurement method. 3. The recombination lifetime measuring method according to claim 1, wherein in the step (a), the second voltage in the inversion voltage region is changed to the first voltage. Thereby generating the excess minority carriers, wherein the first voltage is closer to the depletion voltage region than the second voltage. 4. The recombination lifetime measuring method according to claim 3, further comprising: measuring a CV characteristic while changing a DC component of a voltage from the depletion voltage region to the inversion voltage region; Measuring a turn-on voltage, which is a voltage at a boundary between the inversion voltage region and the depletion voltage region, from the -V characteristic, and determining the first voltage based on the turn-on voltage. Measuring method. 5. A method for measuring a recombination lifetime of a minority carrier in a semiconductor wafer having an insulating layer on a surface of a semiconductor substrate, the method comprising: (a) providing a first polarity on a top surface of the insulating layer of the semiconductor wafer; Forming an inversion layer inside the semiconductor substrate by adding a charge;
(B) irradiating the semiconductor wafer with light,
A step of measuring a time change of a surface potential of the insulating layer in a non-contact manner above the insulating layer after generating an excessive minority carrier inside the semiconductor substrate; and (c) measuring a time change of the surface potential. Determining the recombination lifetime of minority carriers in the semiconductor substrate. 6. The recombination lifetime measuring method according to claim 5, wherein in the step (b), a second charge different from the first polarity is added to such an extent that the inversion layer does not disappear. A method for generating the excess minority carriers by the method.