JPH0443408B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to a stepper (projection exposure apparatus).
In particular, the present invention relates to a stepper with an improved autofocus function.

Traditionally, when manufacturing semiconductor devices such as ICs, an exposure method was used in the photo process in which a photomask was placed in close contact with a semiconductor wafer (hereinafter referred to as a wafer), but with the remarkable development of semiconductors, wafers became larger. Also, as optical technology has progressed, reduction exposure methods have come to be used in which the pattern is reduced to 5:1 or 10:1 and transferred directly to the wafer surface rather than a reticle.

In addition, the projection exposure method is used not only for reduction projection but also for 1x exposure, which eliminates the need to create large masks for large wafers and eliminates the negative effects of contact exposure (mask scratches). This is because it has the advantage of being able to eliminate problems such as deterioration in yield and quality due to such occurrence.

On the other hand, new methods of lithography technology that use light, electron beams, and X-rays are being researched and developed, but they are not yet sufficient for mass production, and optical methods are still the mainstream of photoprocessing.

Therefore, the projection exposure method described above is extremely important for semiconductor manufacturing, and the projection exposure apparatus, ie, the stepper, is required to be able to obtain fine patterns with high precision and high yield.

[Prior Art] As the name suggests, a stepper is an exposure device that repeatedly prints (exposes) the same pattern on the wafer surface, so normally the stage on which the wafer is placed is automatically moved one shot at a time. It is equipped with a drive system, automatic alignment function, and automatic focus function, all of which are controlled by a computer control system.

FIG. 3 shows a schematic diagram of the stepper, in which 1 is a wafer, 2 is a stage, 3 is a projection lens, 4 is a reticle, 5 is a condenser lens, 6 is a light source,
A focus sensor 7 and an alignment sensor 8 are provided around the projection lens 3. Further, 9 is a drive system that moves the stage 2, and 10 is a calculation control system that controls the entire system.

In this way, stage movement, focusing, alignment, and exposure are automatically repeated in sequence.
The wafer surface is exposed one shot at a time,
Movement and alignment of the stage are detected and controlled using, for example, a laser interferometer, and focusing is measured and automatically controlled using an air probe or a light beam. In addition, all controls are extremely accurately performed by a computer controller, and alignment processing is performed for each shot with high precision.

Note that one shot here means an exposed area that is irradiated at one time, and although the area is often the same as one chip area, it is not necessarily the same.

[Problems to be solved by the invention] In such steppers, the yield of chips obtained from wafers is never satisfactory, and this is largely due to the autofocus function. .

That is, since the sensor 7 for automatic focusing is provided around the projection lens 3, even if the shot area is completely within the wafer plane, when the most side edge of the wafer is reached, the sensor 7 Part or all of 7 may protrude from the wafer and become undetectable.

FIG. 4 shows diagrams for explaining this. FIG. 4A is a partial plan view of the wafer, and FIG. 4B is a cross-sectional view of A and A'. In the figure, three air probes 17 are connected to the wafer 1 in the shot area a.
However, among the three air probes 17x, 17y, and 17z, the probe 17z protrudes from above the wafer 11 in the shot area b.

Then, the protruding air probe 17
The air pressure appearing at z drops significantly. If the air pressure drops below a certain value, it becomes impossible to measure, and in that case, the exposure of that shot area is stopped and the process moves to the next step, so that the shot area remains unexposed. left alone,
Chips will no longer be created in that area. Therefore, the wafer yield is reduced.

These problems have become more and more significant as chip areas have become wider due to higher integration and density. When making square-sized chips, the chip yield decreases by about 10% due to the number of shots where exposure is stopped.

The present invention proposes a stepper for solving these problems and improving the yield of chips obtained from the wafer surface.

[Means for solving the problem] The purpose is to automatically focus on the shot area to be exposed in a stepper that is equipped with an automatic focusing function and can repeat exposure by moving one shot at a time. When some or all of the multiple focus sensors become unable to measure,
This can be achieved by using a stepper that performs automatic focusing by determining a correction value for the shot area to be exposed from the measurement values of a plurality of focus sensors in adjacent exposed shot areas.

[Operation] In other words, if the focus sensor becomes unable to measure in the shot area scheduled for exposure, since this is the shot at the outermost edge of the wafer, the measurement value of the wafer can be determined from the previously measured values of the nearby exposed shots. The inclination (degree of inclination) is calculated proportionally, and automatic focusing is performed using the corrected value.

In this way, there will be no shot area left unexposed around the wafer, and the chip yield of the wafer can be improved.

[Examples] Hereinafter, examples will be described in detail with reference to the drawings.

FIG. 1 illustrates a top view of a wafer, illustrating a number of shot areas on the surface of wafer 21. FIG. After sequentially exposing shot areas k, 1, and m, the stage was moved to expose shot area n, and measurements were taken using three air probe sensors using the autofocus function. shall be.

Assume that one of the three air probes 17z protrudes from above the wafer 11, and the air pressure drops significantly, making measurement impossible.

In that case, the slope of the wafer surface in that shot area is stored in the calculation control system from the measured values of the exposed shot areas k, 1, and m, and the slope of the shot area n to be exposed is proportionally calculated from that slope. Calculate accurately.

That is, three air probes 17x, 17y, 1
From the measured values measured in each shot region k, 1, m by 7z, the slope degree θk, θ1,
Determine θm and store it in the calculation control system. Second
The figure shows a partial cross-sectional view of the wafer, and its inclinations θk, θ1, and θm are illustrated.

Then, from this degree of inclination, the degree of inclination θn of the shot region n is calculated as follows.

θ1=θk+a ₁ θm=θ1+a ₂ θn=θm+a ₃ θm−θe/θe−θk=a ₂ /a ₁ =r, then θn=θm+r ² a _1From this value, focus the shot area n. , exposure processing. Note that when calculation processing is performed in this manner, next time the stage will not be moved to the adjacent portion, but will be moved in the other direction. This is the same as the conventional method, and the present invention performs focusing using the above calculation only when the air probe (focus sensor) tries to measure and becomes unable to measure.
It is exposed to light.

In this way, there is no need to leave a large unexposed area around the wafer, and the chip yield can be increased.

Further, these calculations are performed within a calculation control system 10 attached to the stepper, and therefore a dedicated memory for storing the slope is provided in the control system.

[Effects of the Invention] As is clear from the description of the embodiments above, the stepper according to the present invention can eliminate unexposed shot areas and significantly improve the chip yield on wafers. can.

Therefore, the stepper according to the present invention greatly contributes to cost reduction of semiconductor devices such as ICs.

[Brief explanation of drawings]

Fig. 1 is a plan view of a wafer for explaining the present invention, Fig. 2 is a sectional view of the wafer at A and A', Fig. 3 is a schematic diagram of a stepper, and Figs. 4 a and b illustrate conventional problems. FIG. 2 is a partial plan view and a cross-sectional view of a wafer for explanation. In the figure, 1, 11, 21 are wafers, 2 is a stage, 3 is a projection lens, 7 is a focus sensor, 8 is an alignment sensor, 9 is a stage drive system, 10 is a calculation control system, 17x, 17y, 17z
is an air probe, a, b, k, 1, m, and n are shot areas, and θk, θ1, θm, and θn are slopes of the shot areas.

Claims (1)

[Claims] 1 In a stepper that is equipped with an automatic focusing function and can repeat exposure by moving one shot at a time, when automatic focusing is performed on the shot area to be exposed, some or all of the multiple focus sensors take measurements. If the exposure becomes impossible, a correction value for the shot area to be exposed is determined from measurement values of a plurality of focus sensors in adjacent exposed shot areas, and automatic focusing is performed. Steppa to do.