JPH05152239A - Simulation method of ion-implantation process in an inclined direction - Google Patents

Abstract

PURPOSE:To obtain an impurity distribution where ion are implanted into a surface of a semiconductor substrate which is positioned at a lower part of an edge part of a lamination film by using a simulation means corresponding to an ionimplantation process in the nearly vertical direction by compensating a film thickness of the lamination film and an edge part inclination angle of the lamination film. CONSTITUTION:First of all, a film pressure (d)of a gate electrode layer 22 as a lamination film is compensated corresponding to an incidence angle thetain an ion-implantation process for obtaining a film pressure dh. Then, an angle of an edge part 26 is compensated corresponding to the incidence angle theta for obtaining an edge part angle of an edge part 26a after compensation, thus enabling a model of the gate electrode layer 22 to be compensated to a model of a pate electrode layer 22a. Therefore, when an ion-implantation simulation from nearly vertical direction is performed, an impurity distribution when ions are implanted from an inclined direction can be simulated relatively accurately, where dh=d.costheta, tanphi=(1/sintheta).costheta.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for simulating an oblique direction ion implantation process, and in particular, using a simple means for simulating a vertical direction ion implantation process,
The present invention relates to a simulation method capable of simulating an ion implantation process that is incident from an oblique direction.

[0002]

2. Description of the Related Art With the increase in the degree of integration of semiconductor memories, the miniaturization of MOS transistors constituting each memory cell of the semiconductor memory is progressing. As the miniaturization of MOS transistors progresses, the generation of hot carriers near the drain, where the electric field strength is highest, becomes a problem. In order to prevent the generation of this hot carrier, a structure such as an LDD structure or a GOLD structure in which the drain part and the gate part overlap is proposed.

In such an overlapping structure, the hot carrier resistance can be improved by weakening the electric field strength at the drain portion. As a method for forming such an overlap structure, a method of implanting ions from an oblique direction of a semiconductor substrate has been developed.

[0004]

On the other hand, in recent years, for the purpose of efficient device design or for studying device physics, devices such as MOS transistors are being simulated while considering process conditions. is there. However, the normally used simulation apparatus does not consider the process of ion implantation from a diagonal direction to the semiconductor substrate,
In many cases, the simulation is possible only when the ions are implanted from the direction of the incident angle of 7 degrees (substantially vertical direction). Therefore, if a simulation of a process of implanting ions from an oblique direction is performed using such a simulation apparatus, the distribution of impurities cannot be accurately grasped, and it is impossible to calculate realistic device characteristics. Is.

It is to be noted that the ion implantation into the semiconductor substrate at a substantially vertical incident angle with a fine inclination of 7 degrees, rather than a completely vertical incident angle, suppresses a channeling effect at the time of ion implantation. In a normal simulation device, the incident angle at the time of ion implantation is fixed at 7 degrees for calculation.

The present invention has been made in view of such a situation, and the distribution of impurity ions in the process of implanting ions from an oblique direction using a simulation apparatus in which the incident angle at the time of ion implantation is fixed in a substantially vertical direction. It is an object of the present invention to provide a simulation method of an oblique direction ion implantation process which can relatively accurately determine the above, and can realistically simulate device characteristics of a MOS transistor or the like.

[0007]

In order to achieve the above object, the simulation method of the present invention reads an incident angle of ion implantation, and according to the incident angle, a model of an oblique ion implantation process is made substantially vertical. Direction, the thickness of the laminated film and the inclination angle of the end of the laminated film are corrected so that the surface of the semiconductor substrate located below the end of the laminated film is ion-implanted. The impurity distribution
It is characterized in that it is obtained by using a simulation means corresponding to an ion implantation process in a substantially vertical direction. When the film thickness of the laminated film before correction is d and the incident angle of ion implantation is θ, the film thickness dh of the laminated film after correction is expressed by the following formula (1), and the corrected edge A simulation is performed by expressing the partial inclination angle Φ by the following mathematical expression (2). dh = d · cos θ (1) tanΦ = (1 / sin θ) · cos θ (2)

[0008]

According to the simulation method of the present invention, when impurity ions are implanted at an oblique incident angle to a simulation substrate in which at least one laminated film is laminated in a predetermined pattern on the surface of a semiconductor substrate, The film thickness of the laminated film and the edge inclination angle of the laminated film are corrected according to the incident angle. For this reason, even if the ion implantation is performed from an oblique direction, when the ion implantation is performed from a substantially vertical direction particularly in the impurity distribution that is ion-implanted into the surface of the semiconductor substrate located below the end portion of the laminated film. It is possible to obtain a simulation model similar to. Therefore, if the simulation of the ion implantation from the substantially vertical direction is performed using the simulation model, it is possible to relatively accurately simulate the impurity distribution when the ion implantation is performed from the oblique direction.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A simulation method of an oblique direction ion implantation process according to an embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic flow chart showing a simulation method of an oblique ion implantation process according to an embodiment of the present invention, and FIGS. 2 to 5 are schematic diagrams showing a correction method of a simulation model simulated by the method of the embodiment. 6 and 7,
FIG. 8 is a schematic cross-sectional view of a main part showing a method for correcting a simulation model according to another embodiment of the present invention, and FIG. 8 is a schematic view of a main part showing a simulation method according to another embodiment of the present invention.

In this embodiment, as shown in FIG. 2, a gate electrode layer 22 as a laminated film is laminated in a predetermined pattern on the surface of a semiconductor substrate 20 made of, for example, silicon via a gate insulating film (not shown). A simulation is performed for the case of ion implantation at an oblique incident angle θ to a given semiconductor device. The oblique incident angle θ is larger than the normal incident angle of 7 degrees. By implanting ions at an oblique incident angle θ, an impurity diffusion layer 26 that overlaps the end of the gate electrode layer 22 can be obtained on the surface of the semiconductor substrate 20, which causes problems due to the miniaturization of MOS transistors. It is possible to improve the resistance to hot carriers.

In an ordinary ion implantation simulation apparatus, as shown in FIG. 3, a direction substantially perpendicular to the semiconductor substrate 20 (actually, in order to suppress the channeling phenomenon,
When the ion implantation is performed from the direction of the incident angle of 7 degrees), the distribution of impurities introduced into the semiconductor substrate 20 is simulated. Moreover, the incident angle θ
Was fixed, and it was not possible to accurately simulate the process in which ion implantation was performed from an oblique direction as shown in FIG.

In the present embodiment, by adopting the simulation method comprising steps 10 to 16 as shown in FIG. 1, a simulation apparatus capable of performing only a normal ion implantation simulation from the vertical direction is used. The simulation of the ion implantation process is performed from the oblique direction as shown in FIG.

As shown in FIG. 1, in the simulation method according to the embodiment of the present invention, when the simulation is started in step 10, the incident angle θ in the ion implantation step is read in step 11. Incident angle θ
2 is represented by an angle with respect to an axis line 24 which is perpendicular to the surface of the semiconductor substrate 20 as a simulation base, as shown in FIG.

Next, in step 12, the film thickness d of the gate electrode layer 22 shown in FIG. 2 is corrected. Assuming that the corrected film thickness is dh as shown in FIG. 4, dh can be expressed by the following mathematical expression (1). dh = d · cos θ (1)

Further, in step 13, the angle of the end portion 26 of the gate electrode layer 22 as shown in FIG. 2 is corrected. Figure 4
As shown in, when the corrected angle of the end portion 26a is Φ, the angle Φ of the end portion 26a can be expressed by the following mathematical expression (2). tanΦ = (1 / sin θ) · cos θ (2)

Based on the above equations (1) and (2), the model of the gate electrode layer 22 as shown in FIG. 1 is corrected to the model of the gate electrode layer 22a as shown in FIG. The correction is made in this way, especially when the ion implantation distribution on the surface of the semiconductor substrate 20 located in the vicinity of the end portion 26 of the gate electrode layer 22 is as shown in FIG. This is to make the simulation model similar to the simulation model at the time of ion implantation from the substantially vertical direction as shown in FIG.

Specifically, the mathematical expression (1) is based on the original film thickness d of the gate electrode layer 22 as a correction term co
It is obtained by multiplying sθ. The correction term cos θ is
This is a correction term for calculating the vertical direction component of the impurity ions incident from the oblique direction at the incident angle θ. Further, the mathematical expression (2) is obtained from the following relationship.

As shown in FIG. 5, a predetermined point C on the surface of the semiconductor substrate 20 is considered, and the impurity concentration at this point C passes through the end portion 26 of the gate electrode layer 22 from the oblique direction A of the incident angle θ to the ion direction. The relational expression is determined so that it is the same in the case of ion implantation and in the case of ion implantation from the substantially vertical direction A ′ through the end portion 26a of the corrected angle Φ.
First, the passage path of ions is changed from the path ABC to the path A ′.
Convert to B'C. However, BC = B'C is satisfied. Therefore, the end portion of the gate electrode layer has a shape that connects OB '. The relationship between the angle Φ ′ of OB ′ and the incident angle θ can be expressed by the following mathematical expression (3) by a simple geometrical arrangement. tanΦ ′ = B′C / OC = B′C / (BC · sin θ) (3)

Further, as will be described later, the implantation energy and the dose amount at the time of ion implantation are multiplied by cos θ in consideration of the vertical component at the time of oblique ion implantation. Instead, B "C = B'C
-Cos θ should be used. Therefore, the end portion 2 of the gate electrode layer that will eventually become the model for simulation is
The relationship between the angle Φ of 6a and the incident angle θ can be obtained as follows.

TanΦ = B ″ C / (BC · sin θ) = cos θ / sin θ Therefore, the above formula (2) is proved. The model of the gate electrode layer is corrected so as to satisfy such formula, By performing a simulation of ion implantation in the vertical direction, at least the impurity distribution at the Si / SiO ₂ interface (point C) existing at the interface between the semiconductor substrate and the gate electrode layer can be accurately calculated.

Returning to FIG. 1, when the description of the method of this embodiment is continued, when step 13 is completed, the process proceeds to step 14, where the ion implantation energy E at oblique ion implantation as shown in FIG. Correct the quantity D and. That is, in order to approximate the oblique direction ion implantation as shown in FIG. 2 to the vertical direction ion implantation as shown in FIG. 4, the implantation energy E and the dose amount D at the time of the diagonal direction ion implantation are used.
Is multiplied by a correction term cos θ indicating a vertical component at the time of oblique direction ion implantation.

Next, in step 15, using the model of the gate electrode layer 22a as shown in FIG. 4, a simulation calculation of the substantially vertical ion implantation of the ion implantation energy E · cos θ and the dose amount D · cos θ is performed, and the semiconductor is calculated. Determine the impurity distribution on the substrate surface. The following three methods have been proposed as basic solution methods for obtaining the impurity distribution. One is a method of giving a static distribution of implanted impurities represented by the LSS theory by an analytical formula. The second is to process the energy and scattering angle lost by the implanted ions in the process of passing through a substrate thin film of a predetermined thickness, using a statistical distribution function, which is a method of numerically solving the Boltzmann transport equation. is there. The third method is a method of performing calculations while individually chasing how the implanted ions interact with the lattice constituent atoms in the silicon substrate, which is called the Monte Carlo method.

The Monte Carlo method, which is the third method, can accurately calculate the amount of ion implantation and can accurately estimate the amount of damage at each position, but since the calculation time becomes enormous, it is a normal process. -It is rarely used in simulation equipment. An analytical method based on the LSS theory, which is the first method, is most often used in a simple process simulation apparatus. LS
In S theory, a probability density function that gives a stationary position distribution of incident particles is defined, an equation that satisfies the probability density function is derived, and then the moment of any order of the distribution is calculated. The first moment of the probability density function thus obtained represents the average projective range Rp. Generally, the nth moment is given by the following equation (4).

[Equation 1]

In the above formula (4), the distribution of the implanted ions using the first and second moments becomes the Gaussian distribution of the following formula (5).

[Equation 2] This Gaussian distribution is the simplest expression expressing the distribution of implanted ions. The actual implantation ion distribution is not such a Gaussian distribution, but distributions having different standard deviations on the left and right of the projection flying degree Rp. As a distribution incorporating the effect of distortion, there is a joint-halh Gaussian distribution having asymmetry on the left and right near the projection range Rp. This can be expressed by the following equations (6) and (7).

[0025]

[Equation 3] This equation includes the third-order effect of the implanted ions, and relatively accurately shows the distribution of the implanted ions.

By performing a simulation calculation in the vertical direction using the corrected model using the above-described mathematical expressions, the simulation of the oblique ion implantation with the incident angle θ, the ion implantation energy E, and the dose D is relatively performed. Can be done accurately. However, the range simulated by ion implantation is the gate electrode layer 2 shown in FIG.
It is preferable that the distance is shorter than the distance L from the corner of 2 to the interface of the surface of the semiconductor substrate 20 along the ion implantation path. In the actual ion implantation, since the semiconductor substrate 20 is rotated and the ion implantation is performed in an oblique direction, if the range is larger than the distance L, the impurity ions implanted in the opposite oblique direction must be considered. Is. When the calculation in step 15 is completed, step 1
At 6, the simulation ends. Note that the effect of channeling is ignored in the calculation of the above-described embodiment.

The present invention is not limited to the above-mentioned embodiments, but can be variously modified within the scope of the present invention. For example, as shown in FIG.
When the gate electrode layer 28 laminated on 0 is composed of the multilayer film 30, the simulation model is corrected to the gate electrode layer 28a as shown in FIG. Assuming that the original film thicknesses of the multilayer films 30 are d1, d2, and d3, the corrected film thicknesses of the multilayer films 30a are d1 · cos, respectively.
θ, d2 · cos θ, d3 · cos θ. Further, the corrected end angle Φ of the gate electrode layer 28a can be expressed by the above-described mathematical expression (2).

Further, in order to perform more accurate calculation and realistically express the impurity distribution deep from the surface of the semiconductor substrate, a simulation of ion implantation is carried out by the above-described method, and then shown in FIG. Such coordinate conversion may be performed. A region in which both x and y are positive is divided into a square lattice,
The impurity concentration N (x, y) at (x, y) is calculated as (x ·
Impurity concentration N ′ (x · cos) at cos θ, y)
θ, y). In the shaded area 40 in FIG. 8, x has the same distribution as the y-direction distribution when it is 0 or less. However, as before, we ignore the effects of channeling.

[0029]

As described above, according to the present invention, impurities for an oblique incident angle are applied to a simulation substrate in which at least one laminated film is laminated in a predetermined pattern on the surface of a semiconductor substrate. When ions are implanted, the film thickness of the laminated film and the edge inclination angle of the laminated film are corrected according to the incident angle. For this reason, even if the ion implantation is performed from an oblique direction, when the ion implantation is performed from a substantially vertical direction particularly in the impurity distribution that is ion-implanted into the surface of the semiconductor substrate located below the end portion of the laminated film. It is possible to obtain a simulation model similar to. Therefore, if the simulation of the ion implantation from the substantially vertical direction is performed using the simulation model, it is possible to relatively accurately simulate the impurity distribution when the ion implantation is performed from the oblique direction. As a result, it is possible to realistically simulate the device characteristics of a MOS transistor or the like manufactured through the oblique ion implantation process using a simple simulation apparatus that supports only vertical direction ion implantation.

[Brief description of drawings]

FIG. 1 is a schematic flowchart showing a simulation method of an oblique ion implantation process according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of an essential part showing a step in a method of correcting a simulation model simulated by the method of the embodiment.

FIG. 3 is a schematic cross-sectional view of an essential part showing a step in a method of correcting a simulation model simulated by the method of the embodiment.

FIG. 4 is a schematic cross-sectional view of an essential part showing a step in the method of correcting the simulation model simulated by the method of the embodiment.

FIG. 5 is a schematic cross-sectional view of an essential part showing a step in the method of correcting the simulation model simulated by the method of the embodiment.

FIG. 6 is a schematic cross-sectional view of an essential part showing a step in a method of correcting a simulation model according to another embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view of an essential part showing a step in the method of correcting the simulation model according to another embodiment of the present invention.

FIG. 8 is a schematic view of a main part showing a simulation method according to another embodiment of the present invention.

[Explanation of symbols]

 20 ... Semiconductor substrate 22, 22a, 28, 28a ... Gate electrode layer 26, 26a ... Edge 30 ... Multilayer film θ ... Incident angle Φ ... Edge angle d, dh ... Film thickness

Claims (2)

[Claims] 1. A simulation substrate in which at least one layered film is laminated on a surface of a semiconductor substrate in a predetermined pattern, and impurity ions are implanted at an incident angle in a diagonal direction that is not substantially vertical. Is a simulation method for obtaining the distribution of impurities introduced into a substrate for use, in which the incident angle of ion implantation is read, and according to the incident angle,
In order that the model of the ion implantation process in the oblique direction can be approximated to the model of the ion implantation process in the substantially vertical direction, the film thickness of the laminated film and the edge inclination angle of the laminated film are corrected and A method of simulating an oblique ion implantation process, characterized in that the distribution of impurities to be ion-implanted into the surface of the semiconductor substrate located at is determined using a simulation means corresponding to the ion implantation process in the substantially vertical direction. 2. When the film thickness of the laminated film before correction is d and the incident angle of ion implantation is θ, the film thickness dh of the laminated film after correction is expressed by the following mathematical expression (1). The method for simulating an oblique ion implantation process according to claim 1, wherein the corrected end inclination angle Φ is represented by the following mathematical expression (2). dh = d · cos θ (1) tanΦ = (1 / sin θ) · cos θ (2)