JPS62154446A - Charge restraint device for wafer - Google Patents

Abstract

PURPOSE:To restrain the dielectric breakdown of a wafer from occurring, by installing an electron shower and a slit plate. CONSTITUTION:In this device, there is provided with an electron shower consisting of a metallic target, which receives an electron gun and a primary electron to be emitted in a direction orthogonal with an ion beam from this electron gun and with the impact, generates a secondary electron in a beam flowing direction, and in addition a slit plate having a slit almost similar to a beam sectional form is installed in a position proximate to a wafer. At the time of ion implantation, a disc 1 rotates at high speed while reciprocates up and down, and a positive ion beam 5 is irradiated to a wafer 3 part, then an electron is emitted toward the downstream of a beam flow from a target 7 of the electron shower. At this time, the electron not caught by the beam flow advances forward so as to envelope the ion beam 5, but most of electrons are checked of advancement by the slit plate 8, not arriving on the wafer 3. A sudden fall of wafer voltage following an increase in a primary current is not entailed there, and transition to the negative side is not caused as well. Therefore, the proper primary current is selected whereby the wafer voltage comes to be maintainable, insomuch that dielectric breakdown will not happen.

Description

DETAILED DESCRIPTION OF THE INVENTION (Related Industrial Field) The present invention relates to a charge suppression device for a univer in an ion implantation device of a semiconductor manufacturing line.

(Prior art) Conventionally, in an ion implantation device, when positive ions are implanted into a wafer whose surface has been coated or formed with an extremely thin insulating film such as a resist film or oxide film, the positive ions implanted onto the wafer are As a large number of them are deposited on the insulating film, a potential difference occurs, which may lead to dielectric breakdown. This insulation @
This causes breakage and damage to the Sr circuit pattern, resulting in a decrease in the yield of LSI manufacturing. To prevent this, an electron gun is installed perpendicular to the ion beam flow, and the primary electrons emitted from the electron gun in a direction perpendicular to the ion beam are used to generate secondary electrons in the beam flow direction. An electron shower consisting of a metal target is installed to neutralize the positive ions in the ion beam, and the secondary electrons are irradiated onto the wafer surface to neutralize the positive charge generated by the ions implanted into the wafer surface. There are also known methods. When this method is used, the upper wafer voltage appears to drop rapidly (see FIG. 1), but in reality, dielectric breakdown still occurs and the yield of wafers has not been improved.

(Problems to be solved by the invention) The inventor investigated the cause of this dielectric breakdown.

The secondary electrons caused by the electron shower are not sufficiently captured in the ion beam, and move in a ring shape around the beam's periphery, reaching the wafer surface and negatively charging that area, so the average voltage is higher than that of the beam irradiated area. Although the appearance is lower, the important finding is that negatively charged parts and positively charged parts coexist indistinguishably, and this dielectric breakdown occurs because the positive or negative charge generated in each part becomes extremely large. Based on this knowledge, it is an object of the present invention to solve the above-mentioned conventional technology's ':1IAit destruction by extremely simple means.

(Means for solving problems) The wafer antistatic device of this invention has a disk.

A wafer holder provided on the circumference of the disk surface, and a wafer placed on the wafer holder.

In an ion implantation device comprising an ion source for irradiating the wafer with an ion beam, an electron gun is provided in a direction perpendicular to the ion beam flow, and primary electrons are fed from the electron gun in a direction perpendicular to the ion beam. An electron shower consisting of a metal target that generates secondary electrons in the direction of the beam flow by the impact of the wafer is provided, and a slit plate having a slit roughly shaped in the cross-sectional shape of the beam is provided at a position close to the wafer. It is characterized by:

(Embodiment) An embodiment of the present invention will be explained with reference to FIGS. 3 and 4. In the figure, 1 is a disk, and a plurality of wafer stands 2 are attached to the circumference of the disk.

During ion implantation, the wafer 3 on the wafer stand 2 is irradiated with the ion beam 5 from the ion source 4 by rotating at high speed and reciprocating up and down. An electron shower consisting of an electron gun 6 and a target 7 is provided at a position a suitable distance U from the wafer 3. The electron gun 6 generates primary electrons 10 by passing a high current through a filament, and emits the secondary electrons 10 in a direction perpendicular to the beam flow. A target 7 made of, for example, aluminum is provided at a position facing the electron gun 6 with the ion beam 5 in between. Primary electron 10 of target 7
The receiving surface is tilted, and when the negative electrons 10 hit this surface, secondary electrons 11 are generated in the beam flow direction and are partially engulfed in the ion beam 5, neutralizing positive ions on the surface of the wafer 3. I will do it. A slit plate 8 made of aluminum, for example, is provided at a position close to the wafer 3 and perpendicular to the ion beam flow. A slit 9 similar to the beam outline is bored in the center of the slit plate 8. In this embodiment, it is made somewhat larger than the beam outline.

(Function) During ion implantation, the disk 1 rotates at high speed and reciprocates up and down, and the positive ion beam 5 is irradiated onto the wafer 3 portion on the disk 1. Further, electrons are emitted from the target 7 of the electron shower toward the downstream side of the beam flow. On this occasion.

Electrons that are not captured by the beam flow advance so as to surround the ion beam 5, but most of these electrons are prevented from advancing by the thrust plate 8 and do not reach the wafer 3. The relationship between the wafer voltage and the primary current of the electron shower in this embodiment is shown in FIG.

- There is no sudden drop in wafer voltage with increasing primary current, and no negative transition occurs, so a suitable primary ″r
By selecting the rL current, it is possible to maintain the wafer voltage to such an extent that dielectric breakdown does not occur.

In the above embodiment, the size of the slit in the slit plate 8 is set to be wider than the beam outline.

It may be made a little narrower, in which case a part of the beam will hit the slit plate 8, and ? It has the advantage that the neutralization effect of positive ions on the wafer 3 is promoted as a result of the generation of It electrons and their entrainment in the beam flow.

(effect) This invention suppresses dielectric breakdown of the wafer.

As a result, the yield of wafers is significantly improved.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the electron shower current and the wafer voltage at the wafer surface layer when only the electron shower described in 1. FIG. 3 is a schematic diagram showing an embodiment of the present invention; FIG.
The figure is a side view taken along the line -IV of FIG. 3, and FIG. 5 is a graph showing the relationship between the electron shower-secondary current and the wafer voltage at the wafer surface layer in the case of this embodiment. 1 Disk 2 Wafer stand 3 Wafer 4 Ion source 5 Ion beam 6 Electron gun 7 Terkerat 8 Slit plate 9 Slit 10 - Secondary electron 11 Secondary electron Figure 2 Figure 5 Primary dip 9

Claims (1)

[Claims] a disk, a wafer holder provided on the circumference of the disk surface, and a wafer placed on the wafer holder;
An ion implantation apparatus comprising an ion source for irradiating the wafer with an ion beam, an electron gun provided in a direction perpendicular to the ion beam flow, and primary electrons emitted from the electron gun in a direction perpendicular to the ion beam. It is characterized by an electron shower consisting of a metal target that generates secondary electrons in the direction of the beam flow by the impact of the received electrons, and a slit plate having a slit approximately similar to the cross-sectional shape of the beam located near the wafer. Charge suppression device for wafers