JPS5829623B2 - Method for measuring semiconductor wafer characteristics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims at irradiating a semiconductor wafer with a light beam or an electron beam, and detecting conductivity based on the difference in the spatial distribution of excess carriers in the semiconductor wafer excited under different excitation conditions by the irradiation of the light beam or electron beam. Relating to a method for measuring the characteristics of a semiconductor wafer, in which the surface recombination rate on one side of the semiconductor wafer, the surface recombination rate on the other side, and the bulk lifetime can be measured separately by utilizing the difference in rate change. It is something.

Conventionally, there has been almost no method to separately measure the surface recombination rate on one side of a semiconductor wafer, the surface recombination rate on the other side, and the bulk lifetime without performing any shape processing or surface treatment on the semiconductor wafer. However,
Recently, a method using a phase difference method using sinusoidal modulated light has been reported.

In this method, a semiconductor wafer is irradiated with sinusoidally amplitude-modulated light as an excess carrier excitation source to generate excess carriers, and the resulting change in conductivity is detected as a response wave.
The modulation frequency dependent characteristics of the phase difference between the excitation wave and the response wave are measured, and by curve fitting the characteristic curve and the theoretical curve, the surface recombination speed on one side of the semiconductor wafer and the surface recombination rate on the other side are determined. This is a method of determining velocity and bulk lifetime separately.

However, this method takes into account a large number of combinations of a total of three parameters, two surface recombination rates and one bulk lifetime, and the curve between the theoretical curve and the characteristic curve measured over a wide modulation frequency range. Fitting has drawbacks such as the need to determine these three values simultaneously and a complicated calculation process.

Additionally, this method has a drawback unique to curve fitting in that the parameters cannot be determined unless the frequency characteristics of the phase difference are measured over a wide frequency range of 10 to 106 hertz.

The present invention does not require complicated calculation processes or extensive actual measurement data as in the above-mentioned method, only changes at least two types of excess carrier excitation conditions, and does not require shape processing or surface treatment of the semiconductor wafer. Semiconductor wafer
・11 in the state of the original wafer regardless of its shape or size
The present invention provides a method for measuring semiconductor wedge characteristics that allows the surface recombination rate and bulk lifetime of one surface and the other surface to be measured separately.

More specifically, the present invention involves sequentially irradiating one side and the other side of a semiconductor wafer with light beams of the same or different wavelengths or electron beams having the same or different electron energies, or is sequentially irradiated with light beams of different wavelengths or electron beams with different electron energies, and at least two different spatial distributions are generated due to differences in carrier excitation conditions of excess carriers instantaneously excited by the irradiation of the light beam or electron beam. By detecting the temporal change in conductivity of the semiconductor wafer based on these different spatial distributions, we can separate the surface recombination rate on one side of the semiconductor wafer, the surface recombination rate on the other side, and the bulk lifetime. The present invention relates to a method for measuring semiconductor wafer characteristics.

The purpose of the method of the present invention is to quickly and accurately measure the surface recombination rate and bulk lifetime of each side of a semiconductor wafer, and to quickly evaluate its crystallinity and surface condition from these values. .

Semiconductor wafers used for fabricating devices on their surfaces include wafers with a mirror finish on the device fabrication side and a rough finish on the other side, wafers with an oxide film on only one side, or wafers with one side irradiated with laser, etc. As can be seen in the example of wafers whose defects have been controlled by damage or mechanical damage, the surface condition of one side of a semiconductor wafer is different from the other side, so it is natural that resurfacing each side is necessary. The binding rates are also different.

The method of the present invention quickly and accurately separates and measures the surface recombination rate and bulk lifetime of each surface in order to quickly and accurately evaluate the crystallinity and surface condition of the surface of the semiconductor wafer. be.

Hereinafter, the method for measuring semiconductor wafer characteristics according to the present invention will be explained in detail with reference to the drawings.

Figure 1 is an explanatory diagram showing a state in which both sides of a semiconductor wafer are sequentially irradiated with a light beam having the same wavelength or an electron beam having the same electron energy, and Figure 2 is an explanatory diagram showing a state in which both sides of a semiconductor wafer are sequentially irradiated with a light beam or an electron beam having the same wavelength. A model diagram of the time change in conductivity when irradiated and σa(0) from it.

An explanatory diagram showing how to obtain σa1(0) and h. FIG. 3 is a model diagram of the time change in conductivity when a light beam or an electron beam is irradiated to the surface 1B side in FIG. 1, and σb(o) from it.

An explanatory diagram showing how to obtain σb1(0) and h; FIG. 4 is an explanatory diagram showing a state in which two types of light beams or electron beams with different wavelengths or electron energies are sequentially irradiated onto the same side of a semiconductor wafer; FIG. 5 is an explanatory diagram showing a state in which two types of light beams or electron beams are sequentially irradiated onto both sides of a semiconductor wafer.

In the drawing, 1 is a semiconductor wafer, 1A is a semiconductor wafer...
One side of 1, 1B is a semiconductor wafer...the other side of 1,
2 represents a light beam having the same wavelength or an electron beam having the same electron energy, 2a and 2b represent a light beam having a different wavelength or an electron beam having different electron energy, and W
is the thickness of the semiconductor wafer.

The method of the present invention involves sequentially irradiating one side of the semiconductor wafer 1 and the other side 1B with light beams of the same or different wavelengths or electron beams having the same or different electron energies, or Either side 1A or 1 of
This is based on the effect that different spatial distributions of excited excess carriers are generated by sequentially irradiating B with light beams of different wavelengths or electron beams with different electron energies.

That is, in the method of the present invention, as described above, the semiconductor wafer 1 is irradiated with a light beam or an electron beam to produce at least two different spatial distributions of excess carriers instantaneously excited due to differences in carrier excitation conditions. By detecting the time change in conductivity of the semiconductor wafer 1 based on the distribution, the surface recombination rate on one side 1A of the semiconductor wafer 1, the surface recombination rate on the other side 1B, and the bulk lifetime can be separated. This is the way to find out.

As described above, the method of the present invention is basically a method for measuring the characteristics of the semiconductor wafer 1 by generating at least two different spatial distributions of excited excess carriers, and therefore, the method of the present invention can take various forms as follows. .

First, a detailed description will be given of a specific method in which both surfaces 1A and 1B of the semiconductor wafer 1 are sequentially irradiated with light beams having the same wavelength, while also explaining the principle of the method of the present invention.

As shown in FIG. 1, when both sides of a semiconductor wafer 1 are sequentially irradiated with light beams 2 having the same wavelength, the semiconductor wafer 1 is
The surface recombination speed of one surface IA (hereinafter referred to as surface 1A) of 1 is So, the surface recombination speed of the other surface IB (hereinafter referred to as surface 1B) is SW, and the bulk lifetime is τb1 Wafer thickness Impulse light with an absorption coefficient α was irradiated onto the single person side of the semiconductor wafer where W is W so that 1=0 and the spatial distribution of excited excess carriers is as follows: When the conductivity change of the semiconductor wafer 1 is σ(t), the formula for the continuity of U carriers is determined using the series coefficient determination method under the boundary conditions regulated by So and Sw and the initial conditions of formula (1). By solving, the following equation (2) is obtained.

The conductivity change σ(1) decreases over time after light irradiation because excess carriers are reduced by surface recombination and volume recombination, as an example of which is shown in FIG.

After a sufficient amount of time has elapsed, σ(1) resolves only at i=1 in equation (2), becomes a straight line that coincides with σ1 (t) (dashed line in Figure 2), and the straight line reaches 1=0. If the extrapolated value is σal(0) and σ(1) at t-0 is σa(0), then the ratio σa(0) is the integral of g(z) in equation (1) from O to Wt. Therefore, it can be expressed as equation (7).

Next, when the light beam of equation (1) is irradiated onto the surface 1B side, the distribution of excited excess carriers is different from when it is irradiated onto the surface 1A side, so the surface recombination rate on the surface 1A and the surface recombination rate on the surface 1B are different. Due to the difference in binding rate, the conductivity change σ differs from that shown in Figure 2*.
(1) is obtained as shown in Figure 3.

Therefore, the equation (8) corresponding to equation (7) is obtained by replacing So and Sw on the right side of equation (7).

Obtain the values on the left side of equations (7) and (8) by measurement, as shown in Figures 2 and 3, and solve both equations numerically or graphically by combining them. BaSoW
/D and SwW/D are determined simultaneously, and if the thickness W and the diffusion constant of the semiconductor wafer 1 are known or measured by another method, the surface recombination rate So of the surface 1A and the surface 1
The surface recombination rate Sw of B can be determined at the same time.

Further, after a sufficient period of time has elapsed, logσ(1) becomes a straight line, and its slope h is expressed by the relationship between bulk lifetime τb and equation (9).

Therefore, the slope h is determined as shown in FIG. 2 or 3, and using the already determined So and Sw, a
By determining l, τb can be determined using equation (9).

In reality, the signal of the conductivity change σ(1) can be measured using the conventional non-contact method or the contact method using conductivity attenuation wide, so the signal is σa1(0)/σ
a(0), σb1(0)/σb(O), and h can be easily obtained.

※※ '5 O In this analysis, the case where an impulse beam is irradiated is explained as an example of the initial condition, but it is also possible to irradiate the child i with a pulsed beam or a pulse having a short pulse width.

Next, the surface recombination speed So of one surface of semiconductor 1, the surface recombination speed Sw of surface 1B, and the bulk lifetime τb are separated by using the difference in the spatial distribution of excited excess carriers due to the difference in the absorption coefficient of irradiation light. You can also ask for it.

In this case, since the absorption coefficient α of the light beam with respect to the semiconductor wafer 1 differs depending on the wavelength λ of the light, using this fact, as shown in FIG. Sequential irradiation, that is, a light beam 2a (wavelength λa) with a short pulse width and an absorption coefficient αa is irradiated, and then a light beam 2a (wavelength λa) with an absorption coefficient αb is irradiated on the same surface.
b (wavelength λb), a conductivity change σ(1) similar to that shown in the examples of Figures 2 and 3 is observed, and the equations (7) and (8) shown above are The corresponding equations are as shown in equation (io) and equation (11) below, respectively.

Therefore, σal(0)/σa(0) on the left side.

σb1(O)/σb(0) is determined by measurement, and the formula (1o
) and the equation υ, the surface recombination speed So of the surface 1A and the surface recombination speed Sw of the surface 1B can be determined.

Furthermore, the bulk lifetime τb is the log after a sufficient period of time has elapsed.
σa(t)V can be determined using equation (9) using the slope h of the straight line portion of logσb(t).

As shown in FIG.
Also, by irradiating surface 1B, the surface recombination rate of one surface can be calculated in the same way as above using two equations: equation (10) and equation (11) with So and Sw replaced. So
, the surface recombination rate Sw and the bulk lifetime τb of the surface 1B can be determined.

Furthermore, when the semiconductor wafer 1 is irradiated with electron beams having different electron energies, different spatial distributions of excess carriers can be excited depending on the difference in electron energy. Pulsed electron beams are sequentially irradiated onto the surface 1 side or surface 1B side of semiconductor wae 1 as shown in Figure 4, or the surface 1 side and surface 1 of semiconductor wae 1 are sequentially irradiated as shown in Figure 5.
The surface recombination speed So of the surface 1A, the surface recombination speed Sw of the surface 1B, and the bulk lifetime τb are determined by sequentially irradiating the B side and detecting the time change in conductivity in the same way as when the above-mentioned light beam is irradiated. can be found.

In this way, when an electron beam is used as an excitation source, instead of formula (1) as an initial condition, the already known formula representing the spatial distribution of excess carriers due to electron beam excitation is used.As detailed above, the present invention The method for measuring the characteristics of semiconductor wafers is to sequentially irradiate one side of the semiconductor wafer 1 and the other side 1B with light beams of the same or different wavelengths or electron beams with the same or different electron energies. or either surface 1A or 1B of semiconductor wafer 1
Excess carriers are excited by sequentially irradiating the semiconductor wafer with light beams with different wavelengths or electron beams with different electron energies, and by utilizing the difference in conductivity over time due to at least two different carrier excitation conditions, the semiconductor wafer is...1 It measures the surface recombination rate of one surface, the surface recombination speed of surface 1B, and the bulk lifetime of a semiconductor wafer.
Even if the surface recombination speed of surface 1 is different from the surface recombination speed of surface 1B, shape processing or surface treatment of semiconductor wafer 1 will be applied, and the shape and size of the shredded semiconductor wafer 1 will be different. It has the excellent advantage that the surface recombination rate of surface 1A, the surface recombination speed of surface 1B, and the bulk lifetime can be determined separately and accurately regardless of the conductivity time. If we use previously proposed non-contact measurement methods to detect changes,
It also has the excellent advantage of being able to quickly detect these physical constants non-contact, non-destructively, and measure the surface recombination rate and bulk lifetime of each surface. Since it is possible to quickly and accurately measure the properties of semiconductor wafers, it is possible to quickly and accurately evaluate the crystallinity and surface condition of semiconductor wafers based on these values, which has great industrial value.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing a state in which both sides of a semiconductor wafer are sequentially irradiated with a light beam having the same wavelength or an electron beam having the same electron energy, and Fig. 2 is an explanatory diagram showing a state where a light beam or an electron beam is irradiated on the side 1A of Fig. 1. Model diagram of conductivity change over time and σa(0) from it. An explanatory diagram showing how to obtain σal (OL h. Figure 3 is a model diagram of the time change in conductivity when a light beam or an electron beam is irradiated to the surface 1B side in Figure 1, and from this, σb (0). σ1) 1(0), an explanatory diagram showing how to obtain h, FIG. 4 is an explanatory diagram showing a state in which two types of light beams or electron beams with different wavelengths or electron energies are sequentially irradiated on the same side of a semiconductor wafer, FIG. 5 is an explanatory diagram showing a state in which two types of light beams or electron beams are sequentially irradiated onto both surfaces of a semiconductor wafer. 1... Semiconductor wafer..., 1A... One side of the semiconductor wafer, 1B... The other side of the semiconductor wafer, 2... Same A light beam with a wavelength or an electron beam with the same electron energy, 2a, 2b
...Light rays with different wavelengths or electron beams with different electron energies, W... Thickness of semiconductor wafer.

Claims (1)

[Claims] 1. One side 1A and the other side 1 of semiconductor wafer 1.
B is sequentially irradiated with light beams with the same or different wavelengths or electron beams with the same or different electron energies, or either surface 1A or 1B of the semiconductor wafer 1 is irradiated with light beams with different wavelengths or with different electron energies. sequentially irradiating with an electron beam having the above-mentioned electron beam, producing at least two different spatial distributions due to differences in carrier excitation conditions of excess carriers instantaneously excited by the irradiation of the beam or the electron beam,
By detecting the time change in conductivity of semiconductor wafer 1 based on this different spatial distribution,
A method for measuring the characteristics of a semiconductor wafer, characterized in that the surface recombination rate on one side 1A, the surface recombination rate on the other side 1B, and the bulk lifetime are measured separately. 2 One side 1A and the other side 1B of semiconductor wafer 1
2. The method for measuring semiconductor wafer characteristics according to claim 1, wherein different spatial distributions of excess carriers are generated by sequentially irradiating light beams of the same wavelength with short pulse widths. 3 One side 1A and the other side 1 of semiconductor wafer 1
A method for measuring characteristics of a semiconductor wafer according to claim 1, wherein B is sequentially irradiated with an electron beam having a short pulse width and the same electron energy to generate different spatial distributions of excess carriers. 4. Claim 1, wherein at least two types of light beams having short pulse widths and different wavelengths are sequentially irradiated on either surface 1A or 1B of semiconductor wafer 1 to generate different spatial distributions of excess carriers. A method for measuring characteristics of a semiconductor wafer described in . 5 One side 1A and the other side 1 of semiconductor wafer 1
A method for measuring characteristics of a semiconductor wafer according to claim 1, wherein B is sequentially irradiated with at least two types of light beams having short pulse widths and different wavelengths to generate different spatial distributions of excess carriers. 6 At least two pulses having a short pulse width and different electron energies on either surface 1A or 1B of the semiconductor wafer 1.
2. The method for measuring semiconductor wafer characteristics according to claim 1, wherein different types of electron beams are sequentially irradiated to generate different spatial distributions of excess carriers. 7 One person on one side of semiconductor wafer 1 and 1 person on the other side
A method for measuring characteristics of a semiconductor wafer according to claim 1, wherein B is sequentially irradiated with at least two types of electron beams having short pulse widths and different electron energies to generate different spatial distributions of excess carriers. .