JPH06260131A - Method and device for plasma doping - Google Patents

Abstract

PURPOSE:To provide an improved method and device for plasma doping by implanting only the desired ions into a wafer in its depth as desired. CONSTITUTION:A plasma doping device has a microwave power supply 1 to emit a microwave, which is introduced to a reaction chamber where a plasma is generated, and the reaction gas introduced into the reaction chamber is ionized, and the ions are implanted into the surface of a wafer 12 in the reaction chamber. The arrangement includes a reaction chamber 3 as expansion of a part of the reaction chamber and a slit-A 9a to admit passage of the ion flow to be implanted into the surface of the wafer 12, and further in other parts, has a disc-A 9 to shut the ions, a rotary shaft 8 penetrating the center of the disc-A 9 and fixed, a disc-B 10 having the same shape as the disc-A 9 and fixed to the rotary shaft 8 while the mounting position to the rotary shaft 8 is dislocated, a motor 7 to rotate the shaft 8, and a control device 11 which controls the revolving speed of the motor 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in a plasma doping apparatus and a plasma doping method.

In the process of manufacturing a semiconductor device, impurities are introduced more than ten times in order to form a diffusion layer on a wafer. For introducing the impurities, a thermal diffusion method, an ion implantation method,
A method such as a plasma doping method is adopted.

There is a demand for a method capable of accurately controlling the concentration of impurities to be introduced and the distribution of impurities, providing good uniformity within a wafer, and introducing impurities in a short time. Of these methods, the ion implantation method is most often used because of its goodness.

In the future semiconductor device manufacturing technology,
It is required to form a junction shallower than 1,000Å. When forming this shallow junction, the energy of the ion implanter is lowered, but the minimum energy is 10e.
850Å even with boron ion implantation due to KV level
An impurity layer of a certain degree is formed.

For this reason, a plasma doping apparatus capable of forming an extremely shallow junction as compared with an ion implantation apparatus has been developed. The structure of this plasma doping apparatus is simpler than that of the ion implantation apparatus, and the apparatus is inexpensive. Therefore, it is more advantageous than the ion implantation apparatus for the place and purpose of introducing impurities. It is said to be useful in the step of doping a liquid crystal display substrate that requires doping.

In the plasma doping apparatus, all the plasma impurity ions generated by the ion source are doped. That is, when the reaction gas containing the target impurities is ionized, the impurities mixed in the reaction gas and nitrogen, oxygen, etc., which are components in the atmosphere, are ionized and doped without being separated.

Thus, if the wafer is doped with impurities other than the intended impurities, the device characteristics that the leakage current of the device formed on the wafer increases and the resistance does not decrease will occur.

Under the above circumstances, there is a demand for a plasma doping apparatus capable of preventing harmful ions ionized together with a reaction gas from being injected into a wafer.

[0009]

2. Description of the Related Art A conventional plasma doping apparatus will be described in detail with reference to FIG. FIG. 4 is a diagram showing a schematic structure of a conventional plasma doping apparatus.

As shown in the figure, the reaction chamber 23 has a vacuum pump 5
The microwave emitted from the microwave power source 1 is introduced into the reaction chamber 23 by the microwave waveguide 2 to generate plasma, and the reaction gas introduction port provided on the wall surface of the reaction chamber 23. The reaction gas introduced from 23a such as boron fluoride (BF ₃ ) becomes ions such as B ⁺ , F ⁺ , BF ⁺ , BF ₂ ⁺ , and the air becomes ions such as N ⁺ and O ⁺ ,
All these ions are injected into the surface of the wafer 12 placed on the stage 4 which is connected to the DC power source 6 for applying a DC voltage provided in the lower portion of the reaction chamber 23.

[0011]

In the conventional plasma doping apparatus described above, when the reaction gas introduced into the reaction chamber is ionized by plasma, fluorine ions other than boron ions to be injected into the wafer, boron fluoride ions. Also, there is a problem that nitrogen ions and oxygen ions of the mixed air are also generated and injected.

In view of the above situation, the present invention separates the ions to be implanted into the wafer from the ions that should not be implanted into the wafer, and plasma doping makes it possible to implant only desired ions into the wafer. The purpose is to provide a device.

[0013]

In the plasma doping apparatus of the present invention, the microwave generated from the microwave power source is introduced into the reaction chamber by the microwave waveguide to generate plasma, and the plasma is provided on the wall surface of the reaction chamber. In the plasma doping apparatus that ionizes the reaction gas introduced from the reaction gas introduction port and injects the ions into the surface of the wafer placed on the stage provided at the bottom of this reaction chamber, a part of this reaction chamber is The expanded reaction chamber, the slit A for passing the flow of the ions injected into the surface of the wafer, and the disk A for blocking the ions in the other parts, and the disk A
The rotating shaft fixed through the center of the
And a slit B through which the flow of this ion injected into the surface of this wafer passes, and this ion is blocked in the other parts, and this slit A of this disk A and this rotation of this slit B The disc B is fixed to the rotary shaft by shifting the mounting position with respect to the shaft, a motor for rotating the rotary shaft, and a control device for controlling the number of rotations of the motor.

The plasma doping method of the present invention is a plasma doping method which is carried out by using the above-mentioned plasma doping apparatus, and utilizes the difference in mass between the ions to be implanted and the ions which should not be implanted in this semiconductor wafer. A plasma doping method in which only ions to be implanted into this semiconductor wafer are implanted, the opening angles of the slit A and the slit B, the mounting intervals of the disk A and the disk B with respect to the rotation axis, and It is configured such that the angle at which the mounting positions of the slit A and the slit B with respect to the rotation shaft are displaced and the rotation speed of the motor controlled by the control device are changed.

[0015]

That is, according to the present invention, a part of the reaction chamber of the plasma doping apparatus is expanded to laterally expand the conventional reaction chamber, and a disk provided with a slit A through which ions pass in the expanded reaction chamber. A and a disk B provided with a similar slit B are fixed to a rotary shaft by shifting the slit A and the slit B, and the rotary shaft is rotated by a motor whose rotation speed is controlled by a control device. , Only the ions to be injected into the wafer pass through the slit A and the slit B, and the ions which should not be injected are shielded by the portions other than the slit A and the slit B of the disk A and the disk B, and are injected into the wafer. It is possible to prevent this.

That is, as shown in the following equations 1 and 2,
Ions having the energy E have a velocity v corresponding to the energy E and the mass m in a vacuum, so that the ions having the same energy E and different masses m have different velocities v.

[0017]

[Equation 1]

[0018]

[Equation 2]

Therefore, the mass m of the ions is given by
As shown in, it can be calculated from the ratio between the mass number of the ion (molecular weight × 10 ^-3 ) and the avocado draw number (6.03 × 10 ²³ ).

[0020]

[Equation 3]

Of the ions that have passed through the slit A of the upper disk A, those that have passed through the slit B of the lower disk B are limited to ions of a certain constant velocity. In other words, mass analysis of ions can be performed by controlling the number of rotations of the rotating shaft that fixes these disks provided with these slits. That is, it is possible to dope only the ion species to be injected into the wafer by changing the distance between the disks and controlling the rotation speed of the rotating shaft.

Therefore, it becomes possible to carry out mass spectrometry in plasma doping, and it becomes possible to inexpensively form a good quality shallow diffusion layer.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to FIGS. 1 to 3 in the case of plasma-doping arsenic into a wafer.

FIG. 1 is a diagram showing a schematic structure of a plasma doping apparatus according to one embodiment of the present invention, FIG. 2 is a side view showing a main part of one embodiment of the present invention, and FIG. 3 is a sectional view taken along line AA of FIG. It is an arrow view and a BB sectional arrow view.

As shown in FIG. 1, the reaction chamber 3 has a vacuum pump 5
The microwave emitted from the microwave power source 1 is introduced into the reaction chamber 3 by the microwave waveguide 2 to generate plasma, and the reaction gas introduction port provided on the wall surface of the reaction chamber 3 The reaction gas introduced from 3a, such as arsenic gas, becomes arsenic ions, nitrogen in the air contained in the atmosphere becomes nitrogen ions, and these ions are slits A9a of the disk A9 and slits B10a of the disk B10. It is designed to be injected into the surface of a wafer 12 placed on a stage 4 which is connected to a DC power source 6 for applying a voltage of 100 V provided in the lower portion of the reaction chamber 3 through the chamber.

Since the DC voltage applied between the plasma and the wafer 12 is 100 V, the ion energy E is E = 100 × 1.6 × 10 ^-19 = 1.6 × 10 ^-17 Joules.

As shown in FIG. 2, this disk A9 and disk B10
The distance S between and is set to 1 meter, and as shown in FIG. 3, the central angle θ ₀ of the slit A9a and the slit B10a formed in the disk A9 and the disk B10, respectively, is 10 ° (π / 18).
As shown in FIG. 3, the rotary shaft 8 is fixed by being displaced by 17.6 °, and the rotary shaft 8 is rotated in the direction shown by the arrow in FIG.

The mass m ₁ of one arsenic ion is m ₁ = 1.244 × 10 ^-25 kg when calculated by the equation 3. Therefore the speed v ₁ of the arsenic ions, as calculated by the number 2, v ₁
= 1.6 × 10 ⁴ m / s.

The mass m ₂ of one nitrogen ion is m ₂ = 2.322 × 10 ⁻²⁶ kg when calculated by the equation 3. Therefore, the velocity v _{2 of} nitrogen ions is
₂ = 3.7 × 10 ⁴ m / s.

Since the time t ₁ required for arsenic ions to pass through the slit A9a of the disk A9 and then through the slit B10a of the disk B10 is S = 1 m, it can be calculated by the following formula 4.

[0031]

[Equation 4]

T ₁ = 6.25 × 10 ^-5 seconds. Similarly, the time t ₂ required for nitrogen ions is t ₂ = 2.70 × 10 ⁻⁵ seconds.

Therefore, the time difference t between the arsenic ion and the nitrogen ion is t = t ₁ -t ₂ = 3.55 × 10 ^-5 seconds. During this t seconds, the disc B10 has a slit angle of 10 ° (π / 18).
Since it is possible to separate the arsenic ions and nitrogen ions if moving above the circumferential speed of the disc A9 and vm / s, the radius of the disk A9 and rm, ₀ the opening angle of the slit θ shown in FIG. 3
Then, since vt = rθ ₀ and v = 2πrn, the rotation speed n is calculated by Equation 5.

[0034]

[Equation 5]

N = 46,950 / min = 782.5 / sec When the rotary shaft 8 is rotated at such a rotational speed, the arsenic ions passing through the slit A9a of the disk A9 are converted into the disk B10.
To pass through the slit B10a of
Needs to be displaced by an angle θ with respect to the slit A9a. Since this angle θ is vt ₁ = rθ and v = 2πrn, θ = 2πnt ₁ = 2 × π × 782.5 × 6.25 × 10 ^-5 = 0.307 radian = 17.6 ° Therefore, the slit A9a of the disc A9 and the disc B10 are Slit B
The opening angle of 10a is 10 °, slit A9a and slit B10a
Rotation axis 8 with the deviation angle on the side opposite to the rotation direction of 17.6 °
The disk A9 and the disk B10 are fixed to and the rotary shaft 8 is set at 46,950 per minute.
When rotated, only arsenic ions that have passed through the slit A9a can pass through the slit B10a, so that it is possible to separate arsenic ions and nitrogen ions.

[0036]

As is apparent from the above description, according to the present invention, it is possible to perform mass spectrometry, which was not possible with the conventional plasma doping apparatus, and it is possible to improve the characteristics of the diffusion layer formed by plasma doping. Therefore, it is possible to provide a plasma doping apparatus and a plasma doping method which are expected to bring about significant economic advantages and reliability improvement effects.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic structure of a plasma doping apparatus according to an embodiment of the present invention,

FIG. 2 is a side view showing the main part of one embodiment of the present invention,

3 is a sectional view taken along the line AA and a sectional view taken along the line BB of FIG.

FIG. 4 is a diagram showing a schematic structure of a conventional plasma doping apparatus,

[Explanation of symbols]

1 is a microwave power supply, 2 is a microwave waveguide, 3 is a reaction chamber, 3a is a reaction gas inlet, 4 is a stage, 5 is a vacuum pump, 6 is a DC power supply, 7 is a motor, 8 is a rotating shaft, 9 is a disk A, 9a is a slit A, 10 is a disk B, 10a is a slit B, 11 is a controller, 12 is a wafer,

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H01L 21/324 P 8617-4M

Claims (2)

[Claims] 1. A microwave generated by a microwave power source (1) is introduced into a reaction chamber by a microwave waveguide (2) to generate plasma, and a reaction gas introduction port provided on a wall surface of the reaction chamber is used. In the plasma doping apparatus that ionizes the introduced reaction gas and injects the ions into the surface of the wafer (12) placed on the stage (4) provided at the bottom of the reaction chamber, a part of the reaction chamber is An expanded reaction chamber (3), a slit A (9a) for passing the flow of the ions injected into the surface of the wafer (12), and a disk A (9) for blocking the ions in other parts. , A rotary shaft fixed through the center of the disc A (9)
(8) has the same external dimensions as the disk A (9), and the wafer (12)
B for passing the flow of the ions injected to the surface of the
(10a) is provided, and the other portions block the ions,
The slit A (9a) and the slit B of the disc A (9)
A disk B (10) fixed to the rotating shaft (8) by shifting the mounting position of the (10a) with respect to the rotating shaft (8), a motor (7) for rotating the rotating shaft (8), and the motor. A plasma doping apparatus comprising: a control device (11) for controlling the rotation speed of (7). 2. The plasma doping apparatus according to claim 1, wherein the semiconductor wafer (12) is injected by utilizing a difference in mass between ions to be injected into the semiconductor wafer and ions not to be injected into the semiconductor wafer (12). A plasma doping method in which only ions to be implanted are injected, the opening angles of the slit A (9a) and the slit B (10a), and the rotation of the disk A (9) and the disk B (10). The mounting interval with respect to the shaft (8), the angle by which the mounting positions of the slit A (9a) and the slit B (10a) with respect to the rotating shaft (8) are displaced, and the motor controlled by the control device (11). A plasma doping method, characterized in that the rotation speed of (7) and is changed.