JPS5816747B2 - ion implanter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion implantation apparatus, and more particularly to an ion implantation apparatus capable of implanting ions to a uniform depth over a wide range of a large-area target.

Recently, ion implantation has been widely used in the semiconductor industry.

As an ion implanter, since the diameter of the ion beam derived from the ion source is about several mmφ at most, it is necessary to use a semiconductor urchin/
Due to the need to uniformly irradiate the S plane, the following method has conventionally been used.

(1) A method in which the ion beam is electrostatically deflected and scanned in the X and Y directions to uniformly describe the ion beam on the surface of the semiconductor wafer, (2) A method in which the ion beam is not unevenly scanned and the semiconductor wafer is instead scanned in the X and Y directions. (3) A method in which the ion beam is scanned only in either the X direction or the Y direction, and a semiconductor sea urchin is moved in the other direction.

Among these, the method (2) is based on the premise of temporal stability of the ion beam, and when the accuracy of the implantation amount is a problem, the method (1) or (3) is usually used.

However, although the method (1) and (3) improves the uniformity of the ion implantation amount compared to the method (2), the size of the semiconductor wafer that guarantees uniformity is about 30 mmφ. is the limit.

If the semiconductor wafer becomes larger than this, the depth of the impurity doped layer due to ion implantation will become shallower at the periphery, and when many chips are cut from the wafer, the characteristics will be significantly different between the center and the periphery. This may cause problems such as misalignment.

In particular, when ion implantation is performed through a thin oxide film, the amount of impurity doped into the substrate in the periphery of the sea urchin is significantly reduced.

This is because when a deflected and scanned ion beam is incident on the wafer peripheral area, the ion beam is tilted significantly from the perpendicular direction with respect to the wafer surface, and as a result, the range of the ions within the wafer becomes shallow.

This invention was made in view of the above-mentioned points, and it is possible to perform ion implantation at a uniform depth over a wide range when performing ion implantation into a large area target, such as a semiconductor sea urchin, by deflecting and scanning an ion beam. The present invention provides an ion implantation device with the following features.

That is, in the present invention, when the ion beam is deflected and scanned, a means is provided to control the relative acceleration energy to the target according to the deflection angle, and the ion implantation is performed by making the ion beam incident on the target from an oblique direction. It is characterized in that it compensates for the decrease in the vertical depth of the layer.

Hereinafter, the present invention will be described in detail with reference to the drawings.

The figure shows a schematic configuration of an embodiment in the case of front-stage and rear-stage acceleration, in which 1 is a semiconductor sea urchin, 2 is a deflection electrode group, and 3
is a deflection voltage generator which applies a heavy pressure close to a sawtooth wave to the electrode group 2, and implants ions into the surface of the semiconductor wafer 1 by deflecting and scanning the ion beam 4 in the homogeneous and vertical directions.

As in a normal ion implantation device, the semiconductor tool 1 is held at an angle of several degrees with respect to the direction of the ion beam when not deflecting and scanning, in order to avoid the single crystal channeling phenomenon.

Therefore, the center O of the deflection scan and the center α of the semiconductor sea urchin...1
The straight line connecting them is not perpendicular to the semiconductor urchin...1, and the perpendicular line intersects with point A.

Assuming that point B is irradiated with the refractory ion beam 4, the angle formed by straight lines OA and OB is assumed to be θ.

In this invention, in such a state, the relative acceleration energy of the ion beam 4 with respect to the semiconductor sea urchin 1 is controlled to be E/cos θ.

In particular, E is the relative acceleration energy with respect to the semiconductor sea urchin .1 when the ion beam 4 is irradiated onto the point A.

This acceleration energy is controlled by the rear acceleration voltage generator 5 while keeping the front acceleration voltage before entering the deflection electrode group 2 constant.

That is, a signal corresponding to the angle θ is obtained from the deflection voltage generator 3 and sent to the subsequent acceleration voltage generator 5.
is the potential of the semiconductor sea urchin...1 according to the angle θ (cos #
-E).

With such a configuration, even if the semiconductor urchin 1 has a large area and is coated with a thin oxide film on its surface, and ions are implanted through this oxide film, the semiconductor urchin 1 can be easily implanted. It is possible to form an impurity doped layer with a uniform depth from the center to the periphery.

The reason why this configuration enables ion implantation with good uniformity is considered as follows.

With the same acceleration energy, the ion beam is transferred to the semiconductor sea urchin...
In the case of irradiation perpendicular to , and the case of irradiation at an angle θ from the perpendicular direction, the range of ions measured from the surface in the semiconductor wafer is reduced by a factor of cos θ in the latter case.

Therefore, if this range is about the same as the thickness of the oxide film on the surface of a semiconductor wafer, the amount of impurities doped into the semiconductor wafer will be extremely small.

As in the example, the relative acceleration energy of the ion beam is set to 1 when the ion beam is perpendicular to the semiconductor urchin, and multiplied by 1/cos θ when the ion beam is tilted at an angle θ, thereby achieving uniform ion implantation. The reason why this property is obtained is that when considering a certain range of acceleration energy, the range of the ion beam in the incident direction is approximately proportional to the acceleration energy.

Therefore, the reduction in the range of ions around the semiconductor sea urchin into the sea urchin by a factor of COSθ is 1/c of the acceleration energy.
This is compensated by the increase in osθ, and the range in the depth direction is kept constant over the entire wafer.

The effects of this invention will be clarified through experiments.

P-type Si with a diameter of 100mm and a resistivity of 20Ω-CrfL
Using a wafer, attach a gate oxide film of about 1,000 layers to it, hold Ueno at a position 1 m away from the deflection electrode group and perpendicular to the straight line OO' in the figure, and heat boron ions at 30K.
A polycrystalline silicon gate, source, and drain were formed by irradiating 6×10 11 /crti with V to fabricate an n-channel MO8+− transistor.

The ion beam was subjected to rask scanning under a constant acceleration voltage.

As a result, the threshold voltage of the transistor was +167V at the center of the sea urchin, and +1.60V near the edges.

As a result of holding a similar sea urchin at an angle of 7° with respect to the straight line OO' and performing similar ion implantation to create an n-channel MOS transistor, the threshold voltage was ++ at the center of the wafer.
1.66V, +1.5 near the farthest edge from the center of the scan
It was 0V.

Next, if a similar n-channel MOS transistor is fabricated on a similar wafer using the apparatus of the embodiment shown in the figure, (1
) When the wafer is held perpendicular to the straight line OO',
The threshold value is sea urchin... +1.66 to +1 over the entire surface.
(2) When the sea urchin .

In the embodiment, the relative acceleration energy of the ion beam 4 with respect to the semiconductor sea urchin 1 is kept constant at the front stage, and the acceleration voltage generator 5 is used at the rear stage to accelerate the relative acceleration energy of the ion beam 4 to the semiconductor sea urchin 1.
- By controlling the potential of 1, the overall potential is changed according to the angle θ.

However, it goes without saying that the pre-stage acceleration voltage may be controlled so that the relative acceleration energy becomes 1/cos θ.

However, in this case, the thickness of the deflection voltage required to irradiate the ion beam to a certain position on the sea urchin is different from that in the embodiment.

[Brief explanation of drawings]

The figure shows a main part configuration of an example of an ion implantation apparatus according to the present invention. 1... Semiconductor sea urchin... (target), 2...
... Deflection electrode group, 3... Deflection voltage generator,
4... Ion beam, 5... Post-acceleration voltage generator.

Claims (1)

[Claims] 1. In a device that implants ions into a predetermined range of a target surface by deflection-scanning an ion beam, the relative acceleration energy with respect to the target when the ion beam is deflected by θ from the perpendicular to the target surface from the center point of scanning is , comprising means for controlling relative acceleration energy of the ion beam to the target so that the ion beam is 1/r:osθ with respect to that when the ion beam is on the perpendicular line, and the ion implantation to be implanted into the target; An ion implantation device characterized by uniform depth.