JPS6223126A - Dose determining method - Google Patents

Abstract

PURPOSE:To rapidly and accurately determine the dose from the change in the reflected luminous energy by a method wherein the luminous energy in the reflected beam is determined against the constant luminous energy for an incident beam. CONSTITUTION:Measurements are performed before and after the implantation of ions by determining the energy present in a reflected beam 16. An incident beam 15 projected by a projector 13 positioned obliquely over a semiconductor wafer 10 lands on the specimen and the reflected beam 16 is determined by the receptor 14. The incident beam 15 travels through a photoresist film 12 and then is reflected by a metal film 11 to travel for the second time through the photoresist film 12 into a reflected beam 16. The color of the photoresist film 12 is different after ion implantation, which causes the luminous energy present in the reflected beam 16 to change accordingly. The change in the luminous energy roughly represents the dose of the ions implanted into the specimen.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for measuring the dose of an ion-implanted semiconductor wafer.

[Conventional technology]

Conventionally, as a method for measuring the dose of ions implanted into a semiconductor wafer, the dose was determined by measuring sheet resistance before and after implanting ions into the semiconductor wafer.

However, since this method performs thermal annealing after ion implantation and then performs measurements, the sheet resistance changes depending on the annealing conditions, making it impossible to measure with sufficient reproducibility.

Furthermore, since annealing takes a long time, it is not useful to know the dose immediately after ion implantation and to control ion implantation based on the status of this dose.

Therefore, as a method for eliminating the above-mentioned drawbacks, a method has been proposed in which ions are implanted into a sample in which a photoresist film is formed on the surface of a wafer-shaped substrate made of a transparent material (generally glass). This method utilizes the fact that the degree of discoloration of the ion-implanted photoresist film varies depending on the dose, and the transmittance also changes accordingly. As shown in FIG. 2, for the sample, a photoresist film 2 is formed on a transparent substrate 1, an incident light beam 3 is irradiated from the top surface, and the amount of transmitted beam 4 is measured. The light intensity of the incident light beam 3 is constant, and the change in the light intensity of the transmitted beam 4 before and after ion implantation is used as a measure of the dose amount.

The above method allows measurements without the need for thermal annealing.

Although the time is significantly reduced, it has the following disadvantages.

1. Substrates made of transparent materials such as glass are mechanically weak. This is because the sample must have the same thickness as the semiconductor wafer, and is made as thin as several 100 μm.

2. Since a substrate made of a transparent material is generally an electrical insulator, charge is accumulated on the substrate surface (including photoresist) during ion implantation and has a potential, which affects the ion beam implantation conditions. Therefore, if the ion beam current is large, a large error will occur.

An object of the present invention is to provide a new method for measuring a dose amount, which fully takes advantage of the color change method of photoresist G and also improves the drawbacks of the method using a transparent substrate.

[Means for solving problems]

In the measurement method of the present invention, ions are implanted into a wafer-shaped sample having a metallic surface that totally reflects light and a photoresist film is formed on the surface. The amount of light reflected by the reflected beam is measured, and the dose amount is determined from the change in the amount of reflected light.

[Effect]

When an incident beam is applied to a sample, the light beam passes through the photoresist film, is reflected from the metal surface of the sample, and passes through the photoresist film again to exit the sample. When passing through the photoresist film twice, the light intensity of the reflected beam after ion implantation is reduced due to discoloration of the photoresist film. Therefore, while the light intensity of the incident beam is kept constant, the ion implantation dose can be determined from the difference in the light intensity of the reflected beam before and after ion implantation.

The resistance method can be used to directly obtain numerical data. The method of the present invention can also numerically determine the dose by calibrating the values of the resistance method carefully performed under sufficient annealing conditions.

〔Example〕

An embodiment of the present invention will be described with reference to the drawings. In FIG. 1, a metal film 11 is deposited to a sufficient thickness on the surface of a semiconductor wafer 10 as a sample. Then, photoresist is further applied, and the photoresist film 12
Set up a cell.

For measurement, before and after ion implantation, an incident beam 15 is applied to the sample from a projector 13 placed obliquely above as shown in the figure.
This is done by measuring the reflected beam 16 with the light receiver 14.

The incident beam 15 enters the photoresist film 12, is reflected by the metal illumination, and is transmitted through the photoresist film 12 again to form a reflected beam 16. Since the photoresist film 11 changes color due to ion implantation, the light intensity of the reflected beam 16 differs before and after the ion implantation. This amount of variation is used as a guideline for the dose of ion implantation.

As a sample, a wafer-shaped metal substrate whose surface is made into a mirror surface, and a photoresist film coated and attached on the mirror surface can be similarly used.

〔Effect of the invention〕

As described above, the present invention can measure the dose more quickly and reliably than the resistance measurement method. Furthermore, in the measurement method using a light-transmitting sample, since the sample is insulating, charge due to ion implantation accumulates, and the resulting potential changes the ion implantation situation, but the sample of the present invention has a metal film. ,
Since there is no potential change due to charge accumulation, highly reliable measurements are possible. Also, semiconductor wafers.

Alternatively, since a metal substrate is used, the mechanical strength of the sample is high, and it is less likely to break due to handling during measurement.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows a conventional example. 10... Semiconductor wafer, 11... Metal film, 12.
...Photoresist film, 13... Emitter, 14... Light receiver, 15, 16... Light beam.

Claims (1)

[Claims] Ions are implanted into a wafer-shaped sample that has a metallic surface that totally reflects light and a photoresist film is formed on the surface, and the amount of reflected beam is measured before and after implantation relative to a constant amount of incident beam. A method for measuring an ion implantation dose, characterized in that the dose is determined from a change in the amount of reflected light.