JPH11126809A - Method for evaluating semiconductor substrate with p-n junction diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate the density of crystal defects contained in a semiconductor substrate by evaluating the leakage currents from the junctions of p-n junction diodes formed on the semiconductor substrate. SOLUTION: Reverse leak currents from many p-n junction diodes formed on the surface of a semiconductor substrate are measured, and when the measured value of the leakage current from one p-n junction diode exceeds a specific value, the element is discriminated as being a defective element and the density of crystal defects contained in the substrate is deduced by using the element areas and the thicknesses of the depletion layers of the measured diodes. In addition, the density of crystal defects which affect the leak currents and are contained in the substrate can be estimated by evaluating the defects contained in the depletion layers of the p-n junctions with high sensitivity, by increasing the leakage currents from the p-n junctions caused by the defects by forming a well area containing a dopant at a higher concentration in the surface layer of the substrate, deliberately diffusing heavy metal impurities in the substrate, or combining the formation of the well area and diffusion of the impurity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for evaluating crystal defects of a semiconductor substrate used for a semiconductor device. In particular, a method for estimating the density of crystal defects contained in a semiconductor substrate is provided.

[0002]

2. Description of the Related Art A method of forming a pn junction diode on a semiconductor substrate and evaluating a crystal of the semiconductor substrate by a leak current is well known.

When a reverse voltage is applied to a pn junction diode, a leak current flows in the reverse direction. By converting this leak current value into a lifetime, the lifetime of the semiconductor substrate can be obtained (Physic).
s and Technology of Semiic
conductor Devices p172 to p1
92 1967 by John Wiley & S
ons INC A. S. Grove).

Further, by changing the voltage applied in the reverse direction, the width of the depletion layer changes, and the change in the lifetime from the surface to the inside of the semiconductor substrate is known from the change in the amount of leak current with respect to the change in the depletion layer width. (For example, JP-A-4-67646).

As a method for deriving the crystal defect density in a semiconductor substrate, an etching pit observation method by a selective etching method represented by light etching is known.

[0006]

SUMMARY OF THE INVENTION Conventional semiconductor substrate p
In the method for evaluating an n-junction leak current, a crystal defect of a semiconductor substrate can be evaluated as a lifetime value of a surface layer by a leak current. However, the lifetime value obtained by such measurement is only an average evaluation of the crystal defects contained in the depletion layer of the pn junction, which is the source of the leak current, and the crystal defects contained in the semiconductor substrate Density cannot be evaluated.

As a method for deriving the crystal defect density in a semiconductor substrate, it is possible to obtain the defect density by an etching pit observation method by a selective etching method represented by light etching. Since crystal defects do not necessarily increase the leakage current of the pn junction, it is not possible to determine the defect density that affects the pn junction leakage current.

[0008]

The object of the present invention is achieved by the following means. (1) The leakage current in the reverse direction of many pn junction diodes formed on the surface of the semiconductor substrate was measured, and the measured p
An element having an n-junction leakage current value exceeding a specified leakage current is determined to be a defective element, and the defect density is estimated from the measured element area and depletion layer thickness of each pn junction diode according to equation (1). It is characterized by the following.

[0009]

(Equation 2)

In addition, a well region in which the dopant concentration of the surface layer of the substrate is increased, a heavy metal impurity is intentionally diffused into the semiconductor substrate, or a combination of the two is used to form a pn junction leak caused by a defect. By increasing the current, defects contained in the depletion layer of the pn junction can be evaluated with high sensitivity.

(2) A well region in which a concentration of a dopant of the same type as that of the surface of the semiconductor substrate is increased in a surface layer of the semiconductor substrate.

(3) In the pn junction diode formed on the surface of the semiconductor substrate, a heavy metal impurity element is diffused into the semiconductor substrate.

(4) In a pn junction diode formed on the surface of the semiconductor substrate, a heavy metal impurity element is diffused into the semiconductor substrate, and the concentration of a dopant of the same type as the surface of the semiconductor substrate is increased. In which a well region is formed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS When a pn junction diode is formed on the surface of a semiconductor substrate and a leakage current in a direction opposite to that of the pn junction is measured, it is determined that an electrically active crystal defect is contained in a depletion layer of the pn junction. The leakage current increases significantly. By setting an appropriate determination current value in comparison with a leakage current value when no crystal defect is included in the depletion layer of the pn junction,
The presence or absence of a crystal defect in the depletion layer of the evaluated pn junction can be determined.

When no defect exists, the leakage current value is
Since it is proportional to the element area and is about 10 ⁻¹⁰ A / cm ² , the judgment current value is preferably about 10 times that, and is preferably 10 ⁻⁹ A / cm ² . Further, the defect can be evaluated with high sensitivity by reducing the element area to be measured and the leak current value in the defect-free region of the element. By assuming that the probability that a crystal defect is included in the depletion layer of the pn junction is a Poisson distribution as a crystal defect distribution, the following relationship is established.

[0016]

(Equation 3)

By transforming this equation,

[0018]

(Equation 4)

Thus, the defect density can be derived.

The depletion layer thickness can be easily obtained from the capacitance of the element at the time of measurement, and it is known that the capacitance and the depletion layer thickness have the following relational expression.

[0021]

(Equation 5)

The accuracy of this evaluation can be improved based on the area dependence of the evaluation element and the thickness dependence of the depletion layer.

The crystal defects that can be evaluated by the leak current of the pn junction diode are limited to defects in an electrically active state, but can be evaluated with high sensitivity by increasing the electrical activity of the crystal defects. . In order to increase the electrical activity of crystal defects, pn is provided by intentionally providing a well structure in which the dopant concentration of the semiconductor substrate surface layer is increased.
By increasing the electric field strength applied to the depletion layer of the junction, the electrical activity of defects can be increased.

The well concentration is 10 ¹⁶ to 10 ¹⁸ / c
m ³ is preferred. Also, Ti, V, Cr, Mn, Fe,
A heavy metal impurity such as Co, Ni, Cu, W, Mo, Au, Ag, or Pt is diffused and solid-dissolved in the semiconductor substrate and gettered to a crystal defect, whereby a leak current can be increased. The amount of contamination is preferably from 10 ¹⁰ / cm ³ to the solid solubility limit of the diffusion temperature. Further, by combining the treatment for increasing the dopant concentration of the substrate surface layer and the treatment for diffusing and dissolving heavy metal impurities, evaluation with higher sensitivity can be performed. In that case, either treatment may be performed first.

It goes without saying that the same evaluation can be made regardless of whether the substrate is p-type or n-type.

[0026]

【Example】

<< Example 1 >> p-type, 6 inches, substrate resistivity 10 Ωcm
Then, a pn junction diode was formed on the silicon wafer, and the leakage current was measured. The element area is 10 mm ² and the number of evaluation elements is 100. The depletion layer thickness at the time of leak current determination is 5 μm. The judgment value of the leak current amount is 1 × 10
^-9 A / cm ² . The number of defective elements was 40.
From equation (1), the defect density contained in the semiconductor substrate is:
1.0 × 10 ⁴ / cm ³ .

Example 2 A pn junction diode was formed on a 6-inch p-type silicon wafer having a substrate resistivity of 10 Ωcm, and leakage current was measured. Element area is 30m
With m ² , the number of evaluation elements is 100. The depletion layer thickness at the time of leak current determination is 5 μm. The determination value of the amount of leak current was 1 × 10 ⁻⁹ A / cm ² . The number of defective elements is 30
Was individual. From equation (1), the density of defects contained in the semiconductor substrate is 2.4 × 10 ³ / cm ³ .

<< Embodiment 3 >> A silicon wafer having a p-type thickness of 6 inches and a substrate resistivity of 10 Ωcm having a well concentration of 5 × 10
A pn junction diode of ¹⁶ / cm ³ was formed, and the leakage current was measured. The element area is 1 mm ² , and the number of evaluation elements is 100. The thickness of the depletion layer at the time of determining the leak current is 0.5 μm. The judgment value of the leak current amount is 1 × 10
^-9 A / cm ² . The number of defective elements was 40.
From equation (1), the defect density contained in the semiconductor substrate is:
1.0 × 10 ⁶ / cm ³ .

Example 4 A silicon wafer having a p-type thickness of 6 inches and a substrate resistivity of 10 Ωcm was coated with Cu at 10 ¹³ / cm ^3.
Was formed into a pn junction diode, and the leakage current was measured. The element area is 1 mm ² , and the number of evaluation elements is 100. Depletion layer thickness at the time of leak current judgment is 5 μm
It is. The judgment value of the leak current amount is 1 × 10 ⁻⁹ A / cm
^{And 2} . The number of defective elements was 40. From equation (1), the defect density contained in the semiconductor substrate is 1.0 × 10
⁵ pieces / cm ³ .

Example 5 Ni was coated on a silicon wafer having a p-type thickness of 6 inches and a substrate resistivity of 10 Ωcm at 10 ¹³ / cm ^3.
Pn with a solid solution having a well concentration of 5 × 10 ¹⁶ / cm ³
A junction diode was formed, and the leakage current was measured.
The element area is 0.01 mm ² and the number of evaluation elements is 100. The thickness of the depletion layer at the time of determining the leak current is 0.5 μm. The determination value of the amount of leak current was 1 × 10 ⁻³ A / cm ² . The number of defective elements was 40. From equation (1),
The density of defects contained in the semiconductor substrate is 1.0 × 10 ⁸ defects / cm ³ .

[0031]

According to the present invention, it is possible to estimate the density of crystal defects affecting the leakage current contained in the semiconductor substrate, and from the result and the history of the substrate, to reduce the number of defects affecting the pn junction leakage. You can get guidelines for making

Claims (4)

[Claims] A plurality of pns formed on a surface of a semiconductor substrate;
The leakage current in the reverse direction of the junction diode is measured, and the element whose measured pn junction leakage current exceeds a specified leakage current is determined to be a defective element, and each of the measured pn
A method of evaluating a semiconductor substrate using a pn junction diode, comprising estimating a defect density from the element area of the junction diode and the thickness of a depletion layer by the equation (1). (Equation 1) 2. The semiconductor substrate according to claim 1, wherein a well region in which a concentration of a dopant of the same type as that of the surface of the semiconductor substrate is increased is formed in a surface layer of the semiconductor substrate. Evaluation method. 3. A pn formed on a surface of the semiconductor substrate.
2. The method for evaluating a semiconductor substrate using a pn junction diode according to claim 1, wherein a heavy metal impurity element is diffused into the semiconductor substrate in the junction diode. 4. A pn formed on a surface of the semiconductor substrate
2. The junction diode according to claim 1, wherein a heavy metal impurity element is diffused into the semiconductor substrate, and a well region in which the concentration of a dopant of the same type as that of the surface of the semiconductor substrate is increased is formed. A method for evaluating a semiconductor substrate using a pn junction diode.