JPS6242537Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a semiconductor wafer inspection device that determines the quality of a semiconductor wafer, which is important at the initial stage of an LSI manufacturing process.

[Background of the idea]

At the initial stage of manufacturing ICs and LSIs, which require multiple processing steps, it is necessary to determine the quality of wafers, which are the original substrates, online in order to improve the yield of LSI devices.

Generally, it is well known that the swirl defect, which is one of the typical defects of semiconductor wafers, is closely related to the lifetime of minority carriers. Therefore, it is common practice to determine the quality of a wafer based on the value of the minority carrier life. By the way, the standard method for measuring the lifetime of minority carriers is to attach an electrode with ohmic contact to a semiconductor sample, irradiate it with a single pulse of light, and measure the decay time of the output signal related to the photoconductive phenomenon. be. For such a method, Japanese Industrial Standard (JIS) H0604-
There is a lifetime measurement method using the silicon photoconductive decay method described in 1978. However, this method requires the formation of electrodes on the wafer, resulting in a destructive test, so such a test method can only be used for sampling tests. On the other hand, one method for measuring the lifetime of minority carriers in a non-contact manner without forming electrodes is to inject minority carriers with a single pulse of light and detect their attenuation characteristics using microwave absorption. However, this method requires an expensive device called a microwave device, and has the problem that the entire device becomes complicated.

[Purpose of invention]

Therefore, the present invention provides a configuration for improving the yield of the entire semiconductor device production line by determining the quality of the semiconductor wafer, which is the original substrate, at a stage before the start of the process. It is an object of the present invention to provide a semiconductor wafer inspection device suitable for production sites that is simple and inexpensive.

[Summary of the idea]

In order to achieve the above purpose, in this invention,
The semiconductor wafer is irradiated with intermittent light, the generated photovoltage is detected in a non-contact manner, and the detected optical signal is discriminated using a predetermined threshold value to determine whether the semiconductor wafer is good or bad. It is characterized by being configured as a wafer inspection device.

Due to the characteristic structure of the present invention, non-destructive and
In addition, it has become possible to determine the quality of semiconductor wafers online, and as a result, it has become possible to check for defects in semiconductor wafers at an early stage of the manufacturing process, thereby improving the yield of the entire manufacturing line. For the time being, the target semiconductors are P-type Si wafers with oxide films, n-type Si wafers, and substrate wafers (P-type or n-type) with a thin bonding layer on the surface.
Although Si wafer substrates are mainly used, it is natural that it can be applied to other _{semiconductor} materials such as Ge and _GaAs .

Hereinafter, the present invention will be explained in detail using the drawings. First, the principle of the present invention will be described.

That is, the present invention applies the measurement of minority carrier lifetime using the photovoltaic effect. The so-called photovoltage generated by light irradiation is caused by the relatively high electric field inherent in the semiconductor surface or the boundary of the P-n junction or n-n ₊ junction, which causes electron-hole pairs generated by light to arises from separation. As a typical example, we will take the case where an oxide film is attached to a P-type Si wafer, but in a P-n junction, when the thickness of the bonding layer to the substrate is sufficiently smaller than the diffusion distance of the bonding layer, the same phenomenon occurs. can be handled.

In general, the photocurrent density J generated by light irradiation
As is well known, is approximately expressed by the following equation.

J=αL/αL+1Φ ₀ ...(1) Here, α: Absorption coefficient of irradiated light in the semiconductor L: Diffusion distance of minority carriers Φ ₀ : Number of photons absorbed per unit time and unit volume Furthermore, αL ≪Light with a small absorption coefficient of 1 (for example, for Si, a wavelength of 1μ)
If near-infrared light (on the order of m) is used, the photocurrent density J will be given by the following equation.

J=αLΦ ₀ (2) In the above equation, it is well known that the diffusion distance L of the minority carriers is proportional to the square root of the lifetime time of the minority carriers. Therefore, in some way the photocurrent density J
By detecting this, it is possible to measure the minority carrier life time within the substrate wafer, which is the object of the present invention.

On the other hand, when the intensity of light is pulsed in frequency, the diffusion distance L of the minority carriers is expressed by the following equation using the lifetime time τ of the minority carriers and the diffusion constant D.

L=(D〓/1+j2πτ)〓...(3) Now, when the photocurrent is determined, as is well known, it occurs at both ends of the junction, that is, in the case of the present invention, between the front and back of the wafer. The photovoltage V _p is expressed by the following equation.

V _p =KαZ _j (D〓/1+j2πτ)〓……(4
) Here, K is a constant, and Z _j is an impedance inherent in a junction or the like. Here, if the pulse frequency is selected so that <<1/2πτ, the photovoltage V _p becomes as follows.

V _p = KαZ _j √〓 ……(5) That is, the photovoltage V _p is proportional to the square root of the carrier lifetime τ, and the carrier lifetime τ
The crystal state can be evaluated from the correlation between the and the crystal defects.

As already mentioned, since the purpose of the present invention is non-destructive testing, electrodes must not be formed on the wafer. Therefore, it is necessary to non-contactly measure the photovoltage shown in equation (5) above.

Therefore, in the present invention, the photovoltage V _p is detected through electrical capacitance. That is, by arranging a transparent electrode through which light can pass close to the wafer surface directly under the irradiation of light, the photovoltage V _p can be capacitively detected. Note that the photovoltage V _p is detected capacitively because the light is pulsed, and one feature of the present invention is that it uses pulsed light (rather than a single pulse) instead of the conventional DC light. , a continuous pulse with a duty factor of approximately 1/2 is optimal.)
The point is to use the .

[Example of idea]

Next, a specific example of the present invention will be described.

FIG. 1 shows the basic configuration of a semiconductor wafer inspection apparatus according to the present invention. Grounded metal sample stage 1
A semiconductor sample 2 is placed on top of the sample. The sample stage 1 also has a vacuum chuck (not shown) function for fixing the sample 2. A glass plate 3' having a transparent electrode 3 is placed at an interval of several hundred μm from the surface of the sample 2. The light from the light emitting diode 5 (pulse repetition frequency = around 1KHz) driven by the pulse power source 6 is transmitted to the transparent electrode 3 by the lens 4.
The surface of sample 2 is irradiated through the beam. The generated photovoltage V _p is applied to electrode 1, which also serves as a sample stage, and transparent electrode 3.
and is amplified by a synchronous detection amplifier 7 using the output of the pulse power source 6 as a reference signal. Thereafter, the signal processing circuit 8 obtains an output signal of the optical voltage V _p shown in equation (5). In this way, by relatively moving the light irradiation point on the sample (wafer) 2, the lifetime τ of the minority carriers within the plane of the wafer 2, and furthermore, the state of the superiority/inferiority distribution of the crystals can be detected.

FIGS. 2a to 2d show an embodiment of a detection section for the photovoltage V _p in a production line. Sample 2 is flowing in the direction of the black arrow as shown in FIGS. 2b and 2d. Figure a shows an example in which a light emitting diode (LED) 5, a lens 4, and the surface of the sample 2 are irradiated. At this time, the transparent electrode 3 is kept at a constant distance from the sample stage 1 by the spacer 3''.
An embodiment is shown in which the light from the LED 5 is guided to near the surface of the sample 2 through an optical fiber 4', and a transparent electrode 3 is attached to the tip of the fiber 4' for extracting the photovoltage _Vp .

FIGS. 3a and 3b show an example of measuring _{the photovoltage V p when} the sample wafer 2 shown in FIG. The horizontal axis in Figure b corresponds to the position AB on the sample 2 in Figure A, which is irradiated with light, and the vertical axis represents the photovoltage _Vp . If sample 2 has a crystal defect such as a swirl, the lifetime τ of the minority carriers in that part becomes small, and as a result, the photovoltage V _p also appears small, and S ₁
As shown by and S ₂ , a concavity appears in the distribution of the photovoltage V _p , and the presence of a defect is determined.

Furthermore, if it is applied to the line after the wafer 2 has been rotated 90 degrees, the wafer 2 can also be inspected in the cross direction (CD direction) shown in a in the same figure, which naturally improves the reliability of the inspection. .

For example, the change in the photovoltage V _p shown in FIG. 3b is
By processing the wafer 2 in the signal processing circuit 8, recognizing the maximum value and minimum value, and setting a specific threshold value thereto, it is possible to determine whether the wafer 2 is a good product or a defective product. If this discrimination signal is applied to the flow path control unit (not shown) of the wafer 2, the wafer 2
automatic sorting becomes possible.

Although we have only mentioned LED5 as a light source, semiconductor lasers, other lasers,
Alternatively, it goes without saying that a general light source such as a Canon lamp with a suitable light filter can be used.

Furthermore, if a microcomputer is applied to the signal processing section 8, it goes without saying that replacing the discrimination threshold value will be simplified and the operability will be improved.

[Effect of idea]

As described above, according to the present invention, semiconductor wafer substrates on a production line can be inspected online using a simple and inexpensive device. Therefore, it is possible to check at the initial stage of the production line, which is extremely effective in improving yield and has great industrial effects.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the basic configuration of a semiconductor wafer inspection apparatus according to the present invention, Figures 2 a to d are diagrams showing an embodiment of the sensor section in Figure 1, and Figures 3 a and b are diagrams depending on the location of the sample. FIG. 3 is a diagram showing an example of measuring the distribution of photovoltage. 1...Sample stage (also electrode), 2...Sample (wafer), 3...Transparent electrode, 3'...Glass substrate, 3''
... Spacer, 4 ... Lens, 5 ... Light emitting diode (LED), 6 ... Pulse power supply, 7 ... Synchronous detection amplifier, 8 ... Signal processing circuit.

Claims (1)

[Claims for Utility Model Registration] 1. Light irradiation means for irradiating a semiconductor wafer with intermittent light, and light that passes through a transparent electrode provided at a distance from the semiconductor wafer, resulting in light generation within the semiconductor wafer. detection means for extracting a photovoltage due to the photovoltaic effect with respect to the semiconductor wafer through capacitive coupling; and means for detecting the detected signal;
signal processing means for discriminating the detected optical voltage signal according to a predetermined threshold value to determine the quality of the semiconductor wafer; The absorption coefficient is α, the diffusion distance of minority carriers is L,
When the minority carrier life time is τ and the pulse frequency of the irradiation light is αL≪1, and ≪
A semiconductor wafer inspection device characterized by using continuous pulsed light having a wavelength satisfying 1/2πτ. 2. The semiconductor wafer inspection apparatus according to claim 1, wherein the detection means is a synchronous detection amplifier. 3. The semiconductor wafer inspection apparatus according to claim 1, wherein the emitted light is pulsed light having a duty factor of approximately 1/2.