JP2002280432A - Method/equipment for evaluating diffused layer of semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a resistance value to the depthwise direction of a diffused layer concerning a method/equipment for evaluating the diffused layer of a semiconductor substrate for evaluating the resistance value of an isolation diffused layer. SOLUTION: Voltage Vf is applied between a first diffused layer 11 and a third diffused layer 13 among the diffused layers 11 to 13 formed plurally to make current I flow between the layer 11 and the layer 13. Next, voltage Vs is obtained between the layer 11 and the second diffused layer 12, and resistance ρ per unit area to the depthwise direction of the respective layers 11 to 13 is obtained by an expression described hereunder. ρ=(Vf-(1+b/a).Vs)/((-b/a.1/S1+1/S3).I.h) Where, S1 is the area of the first diffused layer, S3 is the third diffused layer, (h) is the depth of the diffused layers, the reference character (a) is a clearance between the first diffused layer and the second diffused layer and the character (b) is a clearance between the second diffused layer and the third diffused layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for evaluating a diffusion layer of a semiconductor substrate, and more particularly to a method and an apparatus for evaluating a diffusion layer of a semiconductor substrate for evaluating a resistance value of an isolation diffusion layer.

[0002]

2. Description of the Related Art In recent years, semiconductor devices have been rapidly increasing in density and miniaturization, and on the other hand, high reliability has been required. Therefore, in manufacturing a semiconductor device, it is important to evaluate the electrical characteristics of a semiconductor substrate (wafer).

As one of the electrical characteristics evaluations for the semiconductor substrate, there is a resistance evaluation of a diffusion layer (for example, an isolation diffusion layer). Since the isolation diffusion layer separates the active elements from each other, it is important to evaluate the resistance of the isolation diffusion layer in evaluating the characteristics of the semiconductor substrate.

Conventionally, a four-probe method has been known as a method for measuring the resistance of a diffusion layer. In this four-probe method, four probes (tips) are brought into contact with a diffusion layer to be measured, and a constant current I is caused to flow through the diffusion layer to be measured using two outer probes. The voltage V between the two inner probes is measured by using the above probe. Assuming that the distance A between the four probes is equal, the specific resistance ρ of the diffusion layer to be measured is obtained as ρ = (2 · π · VA) / I.

[0005]

As described above, what can be measured by the conventional four-probe method is the specific resistance of the entire diffusion layer to be measured. However, in the conventional four-probe method, the direction of the depth of the diffusion layer relative to the substrate (hereinafter referred to as the depth direction) is increased.
Cannot be measured.

That is, conventionally, since the element structure formed on the semiconductor substrate is relatively simple, it is sufficient to evaluate the current flowing through the diffusion layer by evaluating the current flow in the plane direction. However, as the density of devices has increased and the diffusion layer formed on the semiconductor substrate has become more complicated as in recent years, a structure in which a current flows in the depth direction in the diffusion layer has been adopted. Was.

As described above, in the structure in which a current flows in the depth direction in the diffusion layer, it is necessary to measure the resistance value of the diffusion layer in the depth direction in order to reliably perform element evaluation. However, the conventional method for measuring the resistance value of the diffusion layer has a problem that the resistance value in the depth direction of the diffusion layer cannot be measured.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method and an apparatus for evaluating a diffusion layer of a semiconductor substrate, which can measure a resistance value in a depth direction of the diffusion layer. Aim.

[0009]

Means for Solving the Problems In order to solve the above problems, the present invention is characterized by taking the following means.

According to a first aspect of the present invention, there is provided a method for evaluating a diffusion layer of a semiconductor substrate, which evaluates a resistance in a depth direction of the diffusion layer formed on the semiconductor substrate. By applying a voltage Vf between the first diffusion layer and the third diffusion layer, a current I flows between the first diffusion layer and the third diffusion layer, and the first diffusion layer; A voltage Vs between the first diffusion layer and a second diffusion layer formed between the third diffusion layer and the second diffusion layer is measured, and a resistance ρ per unit area in a depth direction of the diffusion layer is measured. Is obtained by the following equation.

Ρ = (Vf− (1 + b / a) · Vs) /
((−b / a · 1 / S1 + 1 / S3) · I · h) where S1 is the area of the first diffusion layer S3 is the area of the third diffusion layer h is the depth of the diffusion layer a is The distance b between the first diffusion layer and the second diffusion layer is the distance between the second diffusion layer and the third diffusion layer.

According to a second aspect of the present invention, there is provided an apparatus for evaluating a diffusion layer of a semiconductor substrate, which evaluates a resistance in a depth direction of the diffusion layer formed on the semiconductor substrate. , The voltage V between the first diffusion layer and the third diffusion layer.
f, applying a current I between the first diffusion layer and the third diffusion layer, the first diffusion layer, the first diffusion layer, and the third diffusion layer. Voltage measuring means for measuring a voltage Vs between the diffusion layer and a second diffusion layer, and calculating means for obtaining a resistance ρ per unit area in the depth direction of the diffusion layer by the following equation: And characterized in that:

Ρ = (Vf− (1 + b / a) · Vs) /
((−b / a · 1 / S1 + 1 / S3) · I · h) where S1 is the area of the first diffusion layer S3 is the area of the third diffusion layer h is the depth of the diffusion layer a The distance b between the first diffusion layer and the second diffusion layer is the distance between the second diffusion layer and the third diffusion layer.

According to the first and second aspects of the present invention, it is possible to easily evaluate a resistance value in a depth direction of a diffusion layer formed on a semiconductor substrate, thereby improving the reliability of a semiconductor device. Can be contributed to.

[0015]

Next, embodiments of the present invention will be described with reference to the drawings.

FIGS. 1 to 3 show a method for evaluating a diffusion layer of a semiconductor substrate according to an embodiment of the present invention (hereinafter referred to as an evaluation method).
FIG. 3 is a diagram for explaining a diffusion layer evaluation device 20 (hereinafter, referred to as an evaluation device). FIG. 1 is a plan view showing an example of a semiconductor substrate 10 to be evaluated, FIG. 2 is a diagram showing a cross section of the semiconductor substrate 10 together with the configuration of an evaluation device 20, and FIG. FIG. 5 is an equivalent circuit diagram of each diffusion layer.

As shown in FIGS. 1 and 2, a semiconductor substrate 10 to be evaluated in this embodiment includes a plurality of diffusion layers 1.
1 to 13 are formed. Specifically, each diffusion layer 11
Reference numerals 13 to 13 denote a semiconductor substrate 10 made of a p-type silicon semiconductor.
The n ⁺ -type layer for example, by epitaxial growth, the n ⁺
It is formed by diffusing a p-type impurity into the mold layer. The first to third diffusion layers 11 to 13 function as isolation.

The area of each of the diffusion layers 11 to 13 in plan view is S1 for the first diffusion layer 11, S2 for the second diffusion layer 12, and S3 for the third diffusion layer 13.
It is. The distance between the first diffusion layer 11 and the second diffusion layer 12 is a, and the distance between the second diffusion layer 12 and the third diffusion layer 13 is b. The depth of the diffusion layer is h
It is. The depth of the diffusion layer is equal to the thickness of the epitaxial growth layer, and the depth of the diffusion layers 11 to 13 is the same, since the nuclear diffusion layer is formed on the above-described epitaxial growth layer.

Next, the configuration of the evaluation device 20 will be described with reference to FIG. The evaluation device 20 includes the semiconductor substrate 1
0 in the depth direction of each of the diffusion layers 11 to 13 (in the figure,
The resistance value (in the direction of arrow Z) is evaluated. The evaluation device 20 includes a power supply circuit 21, a current measurement circuit 22, a voltage measurement circuit 23, an input device 24, a calculation device 25, and three probes 26 to 28.

The power supply circuit 21 is provided between the first probe 26 and the third probe 28, that is, the first diffusion layer 11 and the third
A constant voltage Vf is applied to the diffusion layer 13 of FIG. Therefore, the voltage Vf is applied between the first diffusion layer 11 and the third diffusion layer 13. In addition, the current measurement circuit 22
Between the second probe 26 and the third probe 28, that is, the first
Current I flowing between the first diffusion layer 11 and the third diffusion layer 13
Is measured.

The voltage measuring circuit 23 measures a voltage between the first probe 26 and the second probe 27, that is, a voltage Vs between the first diffusion layer 11 and the second diffusion layer 12. I do. The input device 24 is, for example, a keyboard,
Areas S1 to S3 of diffusion layers 11 to 13 and diffusion layers 11
13 are used for inputting the separation distances a and b.

The arithmetic unit 25 includes a voltage Vf between the first diffusion layer 11 and the third diffusion layer 13 sent from the power supply circuit 21 and a first diffusion layer sent from the current measurement circuit 22. The current I flowing between the first diffusion layer 11 and the third diffusion layer 13 and the first diffusion layer 11 and the second
Vs between the diffusion layers 12, the areas S1 to S3 of the diffusion layers 11 to 13 input from the input device 24, the separation distances a and b between the diffusion layers 11 to 13, Based on the depth h, a resistance ρ per unit area in the depth direction of the diffusion layer is calculated.

More specifically, the values of the voltage Vf, the current I, the voltage Vs, the areas S1 to S3, the depth h, and the separation distances a and b are substituted into the following equations to obtain the per unit area of the diffusion layer. Is calculated. ρ = (Vf− (1 + b / a) · Vs) / ((− b / a · 1 / S1 + 1 / S3) · I · h) Here, the arithmetic unit 25 calculates the resistance ρ per unit area of the diffusion layer. A method for obtaining the above expression used for the calculation will be described.

FIG. 3 shows an equivalent circuit of the semiconductor substrate 10 on which the diffusion layers 11 to 13 are formed. In the figure, R1 is the resistance value of the first diffusion layer 11 in the depth direction, and R1 = ρ · h / S1. R2 is the resistance value of the second diffusion layer 12 in the depth direction, and R2 = ρ · h / S
2.

R3 is the resistance value of the third diffusion layer 13 in the depth direction, and R3 = ρ · h / S3. Further, the resistance value r is a resistance value in the plane direction (X direction in FIG. 2) of the first diffusion layer 11 and the second diffusion layer 12.

First, the second diffusion layer 12 and the third diffusion layer 1
The resistance r1 in the surface direction of No. 3 is obtained. As mentioned above, the first
The plane resistance of the first diffusion layer 11 and the second diffusion layer 12 is r, the distance between the first diffusion layer 11 and the second diffusion layer 12 is a, and the second diffusion layer 12 and the third diffusion layer 12 are Since the separation distance of the diffusion layer 13 is b, r1 = (b / a) · r.

Subsequently, the following equation is obtained when an equation relating to the voltage Vf and the voltage Vs is obtained. Vf = {R1 + r + (b / a) · r + R3} · I = {ρ · h · (1 / S1 + 1 / S3) + (1 + b / a) · r} · I Vs = (R1 + r) · I = (Ρ · h / S1 + r) · I Next, when − × (1 + b / a) is obtained, the following equation is obtained. Vf− (1 + b / a) · Vs = I · ((− b / a) · ρ · h · 1 / S1 + ρ · h · 1 / S3) = I · ρ · h (− (b / a) · 1 / S1 + 1 / S3) By combining the expressions with ρ, the following expression can be obtained. ρ = (Vf− (1 + b / a) · Vs) / ((− b / a · 1 / S1 + 1 / S3) · I · h)... As is clear from the equation, the first diffusion layer 11 and the 2
The distance a between the second diffusion layer 12 and the third diffusion layer 12
In the case where the separation distance b from the first diffusion layer 13 is equal (a = b) and the area S1 of the first diffusion layer 11 is equal to the area of the third diffusion layer 13 (S1 = S3), the present invention is applied. It should be noted that the evaluation method cannot be applied.

The above equation is stored in the arithmetic unit 25, and as described above, the power supply circuit 21 and the current measurement circuit 2
2. The values of the voltage Vf, the current I, the voltage Vs, the areas S1 to S3, the depth h, and the separation distances a and b are input from the voltage measurement circuit 23 and the input device 24, so that the per unit area of the diffusion layer is obtained. Is calculated.

Accordingly, the area S of each of the diffusion layers 11 to 13 is simply determined.
1 to S3, the depth h and the separation distances a and b, and the diffusion layers 11 to 13 formed on the semiconductor substrate 10.
The resistance ρ per unit area in the depth direction of the diffusion layers 11 to 13 can be obtained by a simple process of simply bringing the first to third probes 26 to 28 into contact.

As a result, the diffusion layers 11 to 13 formed on the semiconductor substrate 10 become complicated due to the increase in the density of the device, and a structure in which a current flows in the diffusion layers 11 to 13 in the depth direction is adopted. Even if these diffusion layers 11 to 13
It is possible to easily evaluate the resistance value in the depth direction of the semiconductor device, which can contribute to the improvement of the reliability of the semiconductor device.

In the above-described embodiment, an example in which the evaluation device 20 is used to determine the resistance ρ per unit area in the depth direction of the isolation diffusion layers 11 to 13 has been described. Diffusion layer 11-
The present invention is not limited to the evaluation of No. 13, but can be applied to other element structures.

More specifically, the saturation voltage (ON resistance) of the bipolar transistor 40 as shown in FIG.
It is also applicable as a method for evaluating the deep N ⁺ type diffusion layer 41 for reducing the density. In the figure, 42 is an emitter diffusion layer, 43 is a base diffusion layer, 44 is a buried diffusion layer, 45
Is isolation.

In this application example, when forming the bipolar transistor 40 shown in FIG. 4 on a wafer, the first transistor shown in FIG.
The evaluation element 30 having the third to third deep N ⁺ type diffusion layers 31 to 33 is formed in advance. The evaluation element 30 includes a first deep N ⁺ -type diffusion layer 31, a second deep N ⁺ -type diffusion layer 32, and a third deep N ⁺ -type diffusion layer 33.
Each of the deep N ⁺ -type diffusion layers 31 to 33 is formed of an N ⁺ buried layer 34.
Are electrically connected.

The resistance value of each of the diffusion layers 31 to 33 in the depth direction (resistance value per unit area in the depth direction)
Can be evaluated by the same evaluation method as in the above-described embodiment. Thus, the present invention can be applied to the evaluation of the resistance value in the depth direction (resistance value per unit area in the depth direction) of the diffusion layers 31 to 33 constituting the active element. .

In the above embodiment, the diffusion layers 11 to 1
The resistance value per unit area in the depth direction of No. 3 was evaluated. On the other hand, it is conceivable to evaluate the resistance value ρ per unit volume in the depth direction of the diffusion layers 11 to 13.

However, the area S of the diffusion layers 11 to 13
Although 1 to S3 can be easily obtained by measuring the surface of the semiconductor substrate 10, it is not easy to obtain the volume of the diffusion layers 11 to 13. Therefore, in this embodiment, the resistance value ρ per unit volume in the depth direction was evaluated using the areas S1 to S3 of the diffusion layers 11 to 13.

However, when the volume of the diffusion layers 11 to 13 can be obtained, the depth direction can be calculated by an arithmetic expression that is substantially the same as the above-described equation for solving the resistance value ρ per unit area in the depth direction. It is also possible to determine the resistance value per unit volume with respect to.

In the above embodiment, the semiconductor substrate 1
Although an example in which three diffusion layers 11 to 13 are formed in 0 is shown, in a configuration in which four or more diffusion layers are formed, arbitrarily three diffusion layers out of four or more diffusion layers are used. The resistance value ρ per unit area in the depth direction can be obtained by selecting and performing the same evaluation as in the above embodiment.

Further, according to the present invention, the resistance ρ per unit area in the depth direction of the diffusion layer is determined. However, since the resistance value of the diffusion layer in the depth direction can be obtained by multiplying the resistance ρ per unit area in the depth direction by the area of the diffusion layer, the resistance ρ per unit area in the depth direction of the diffusion layer is Obtaining the value is substantially equivalent to obtaining the resistance value in the depth direction of the diffusion layer.

[0040]

As described above, according to the present invention, it is possible to easily evaluate a resistance value in a depth direction of a diffusion layer formed on a semiconductor substrate, which contributes to improvement in reliability of a semiconductor device. it can.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of a semiconductor substrate to be measured by a diffusion layer evaluation method and a diffusion layer evaluation apparatus according to one embodiment of the present invention.

FIG. 2 is a configuration diagram of a diffusion layer evaluation apparatus according to one embodiment of the present invention.

FIG. 3 is an equivalent circuit of a semiconductor substrate to be measured.

FIG. 4 is a diagram for explaining an application example of the present invention (part 1).

FIG. 5 is a diagram for explaining an application example of the present invention (part 2).

[Explanation of symbols]

Reference Signs List 10 semiconductor substrate 11 first diffusion layer 12 second diffusion layer 13 third diffusion layer 20 evaluation device 21 power supply circuit 22 current measurement circuit 23 voltage measurement circuit 24 input device 25 arithmetic device 26 to 28 probe 30 bipolar transistor 31 1 deep N ⁺ type diffusion layer 32 second deep N ⁺ type diffusion layer 33 third deep N ⁺ type diffusion layer 34 buried diffusion layer 35 isolation diffusion layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Ogawa 1601 Sakai, Atsugi-shi, Kanagawa Prefecture Inside Atsugi Works, Ltd. (72) Inventor Takaaki Kuragano 1601, Sakai, Atsugi-shi, Kanagawa Prefecture F-term in Atsugi Works, Ltd. Reference) 4M106 AA01 AA10 BA01 CA10

Claims (2)

[Claims] 1. A method for evaluating a resistance of a diffusion layer formed on a semiconductor substrate in a depth direction, the method comprising: evaluating a first diffusion layer and a second diffusion layer among a plurality of diffusion layers formed on the semiconductor substrate. Applying a voltage Vf between the first diffusion layer and the third diffusion layer to cause a current I to flow between the first diffusion layer and the third diffusion layer; And a second diffusion layer formed between the second diffusion layer and the third diffusion layer.
s, and the resistance ρ per unit area in the depth direction of the diffusion layer
Is determined by the following equation: ρ = (Vf− (1 + b / a) · Vs) / ((−− b / a ·
1 / S1 + 1 / S3) · I · h) where S1 is the area of the first diffusion layer S3 is the area of the third diffusion layer h is the depth of the diffusion layer a is the depth of the first diffusion layer The distance b between the second diffusion layer and the second diffusion layer is the distance between the second diffusion layer and the third diffusion layer. 2. An apparatus for evaluating a diffusion layer of a semiconductor substrate, which evaluates a resistance in a depth direction of the diffusion layer formed on the semiconductor substrate, wherein a first diffusion layer and a second diffusion layer of the plurality of diffusion layers are formed. A current generating means for causing a current I to flow between the first diffusion layer and the third diffusion layer by applying a voltage Vf between the first diffusion layer and the third diffusion layer; A voltage V between a first diffusion layer and a second diffusion layer formed between the third diffusion layer and the third diffusion layer.
voltage measuring means for measuring s; resistance ρ per unit area in the depth direction of the diffusion layer
And a calculating means for calculating the following formula by the following formula: ρ = (Vf− (1 + b / a) · Vs) / ((− b / a ·
1 / S1 + 1 / S3) · I · h) where S1 is the area of the first diffusion layer S3 is the area of the third diffusion layer h is the depth of the diffusion layer a is the depth of the first diffusion layer The separation distance b between the second diffusion layer and the second diffusion layer is the separation distance between the second diffusion layer and the third diffusion layer.