JPH0750679B2 - Wafer edge exposure system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a semiconductor substrate typified by a silicon wafer or a dielectric material in a fine pattern forming step in the processing of parts in ICs, LSIs and other electronic elements. , Peripheral exposure of a wafer for removing unnecessary resist in the peripheral portion of the substrate such as metal, insulator, etc. applied to the substrate in a developing process.

[Conventional technology]

In the manufacturing process of ICs, LSIs and the like, when forming a fine pattern, a resist is applied to the surface of a silicon wafer or the like, and then exposed and developed to form a resist pattern. Next, using this resist pattern as a mask, processing such as ion implantation, etching and lift-off is performed.

Usually, the resist is applied by a spin coating method. The spin coating method is a method of rotating a wafer while pouring the resist on the center position of the wafer surface and applying a resist to the surface of the wafer by centrifugal force. However, according to this spin coating method, the resist may protrude from the peripheral portion of the wafer and may go around to the back side of the wafer.

FIG. 3 is a partial cross-sectional view of the wafer showing the resist that has wrapped around to the back side of the wafer. W is the wafer, Wp is the wafer peripheral portion, Ra is the resist in the pattern forming portion, and Rb is the wafer peripheral portion Wp. The resist on the surface, Rc, is the resist that has sneaked from the edge of the wafer W to the back side.

FIG. 4 is a view showing the shape of the circuit pattern exposed on the wafer. One area indicated by K corresponds to one circuit pattern. In most cases, the circuit pattern cannot be correctly drawn on the peripheral portion of the wafer, and the yield is poor even if it can be drawn. Therefore, the resist on the surface of the peripheral portion of the wafer is actually an unnecessary resist.

The presence of the unnecessary resist that wraps around from the edge to the back side of the wafer peripheral portion and the unnecessary resist on the surface of the wafer peripheral portion causes the following problems. That is, the resist-coated wafer is transported by various processing steps and various methods. At this time, the peripheral portion of the wafer is mechanically grasped and held, or the peripheral portion of the wafer is rubbed against the wall of a container such as a wafer cassette. At this time, if unnecessary resist around the wafer is removed and adheres to the pattern forming portion of the wafer, correct pattern formation cannot be performed and the yield is reduced.

It is a serious problem that the unnecessary resist around the wafer becomes "dust" and the yield is lowered, especially in the present situation where the performance and miniaturization of integrated circuits are progressing.

Therefore, as a technique for removing the unnecessary resist on the peripheral portion of the wafer, a technique for spraying a solvent from the back surface of the peripheral portion of the wafer to dissolve and remove the unnecessary resist by a solvent injection method has been put into practical use. But with this method,
The resist Rc on the protruding portion of FIG. 3 can be removed, but the resist Rb on the surface of the peripheral portion of the wafer is not removed. Even if the solvent is sprayed from the surface of the wafer W in order to remove the resist Rb on the peripheral surface of the wafer, not only does the problem of solvent splash occur, but also unnecessary resist Rb on the peripheral surface of the wafer is removed. It is not possible to remove only the unnecessary resist sharply and with good controllability at the boundary with the resist Ra in the pattern forming portion, which is a resist required as a mask layer for etching, ion implantation and the like.

Therefore, recently, in addition to the exposure process for forming a pattern, a wafer peripheral exposure method has been performed in which exposure is separately performed to remove unnecessary resist in the peripheral portion of the wafer in a developing process.
In this wafer edge exposure method, while rotating a wafer coated with a resist, the light guided by a light guide fiber is applied to the wafer edge to circumferentially expose the wafer edge.

[Technical problem to be solved by the invention]

When the resist is applied by the above spin coating method, the film thickness in the peripheral portion of the wafer becomes thicker than that in the central portion,
It may be about 5 μm. In order to expose such a thick resist and remove it in the developing step, it is necessary to expose it at a certain dose or more. Since the irradiation amount is the product of the illuminance and the time, in order to increase the irradiation amount, the illuminance is increased or the irradiation time is lengthened.

Here, in order to increase the productivity, the irradiation time is required to be as short as possible, and it is impossible to increase the irradiation amount by increasing the irradiation time.

However, on the other hand, if the illuminance is increased to obtain a required irradiation amount above a certain level, there are the following problems. That is, when the resist is irradiated with light with strong illuminance, gas is rapidly generated due to photochemical reaction of the resist itself and decomposition of solvent and additives in the resist, and the generated gas is not released to the outside of the resist, May result in bubbles. When the resist is foamed, the resist in the foamed portion is rubbed against the wafer cassette or the like and adheres to the pattern forming portion of the wafer, causing the problem of the above-mentioned pattern defect.

[Object of the Invention]

The present invention has been made in consideration of such problems,
It is an object of the present invention to provide a wafer peripheral exposure apparatus which can improve productivity in wafer peripheral exposure by shortening the processing time and which does not cause resist foaming.

〔Constitution〕

In order to achieve such an object, a wafer peripheral exposure apparatus of the present invention includes a rotary stage on which a resist-coated wafer is placed, and a wafer temperature adjusting mechanism including a heating mechanism and a cooling mechanism provided on the rotary stage. A light guide fiber and a light source lamp for irradiating the peripheral portion of the wafer mounted on the rotating stage and rotating, and a controller for controlling the rotation and illuminance of the heating mechanism, the cooling mechanism, and the rotating stage. To do.

[Action]

The wafer peripheral exposure apparatus having the above-described configuration can first perform exposure with weak illuminance and high temperature of the resist, then cool the wafer, and then perform exposure with high illuminance and low temperature of the resist. As will be described, the exposure can be completed in a short time without the foaming of the resist.

〔Example〕

 Examples of the present invention will be described below.

FIG. 1 is a schematic explanatory view of a wafer peripheral exposure apparatus of an embodiment of the present invention.

In FIG. 1, 1 is a light source lamp such as an ultra-high pressure mercury lamp,
2 is an elliptical focusing mirror, 3 is a plane reflecting mirror, 4 is a neutral density filter,
Reference numeral 5 is a shutter, 6 is a light guide fiber, W is a resist-coated wafer, 7 is a rotary stage, 8 is a stage driving mechanism such as a motor, and 9 is a controller.

In FIG. 1, a motor 71 as a heating mechanism and a water cooling pipe 72 as a cooling mechanism are provided inside the rotary stage 7, and a vacuum suction hole (not shown) for fixing the wafer W is further provided. Power supply to heater 71 and water cooling pipe
The amount of water supplied to 72 is controlled by the controller 9.

As the heater 71, a sheet-shaped heater, a cartridge-shaped heater, a sheath heater, or the like can be used, and the heater is embedded in the rotary stage 7 to be mounted. Although it is possible to heat the wafer W by disposing a ring-shaped lamp surrounding the rotary stage 7, the embedded type heater 71 is superior in terms of cost and life.

In FIG. 1, the wafer W coated with the resist is transferred to the rotary stage 7 by a transfer system (not shown) while the rotary stage 7 is heated to, for example, 70 ° C. by the heater 71. After the wafer W is vacuum-sucked on the rotary stage 7, the rotary stage 7 is driven by a signal from the controller 9.
At the same time as the rotation starts, the shutter 5 opens, and exposure with weak illuminance (hereinafter referred to as the first exposure step) is performed first. The weak illuminance is, for example, a weak illuminance of 1200 mW / cm ² , and the neutral density filter 4 as an illuminance adjusting mechanism is arranged on the optical path. Then, the wafer W is rotated 6 times at a speed of 5 seconds / revolution so that the total irradiation amount becomes 275 mJ / cm ² , for example. A well-known rotation reading mechanism such as a rotary encoder is used for controlling the rotation, and when a predetermined number of rotations is reached, a signal from the controller 9 is used to drive the stage drive mechanism 8
The rotation of the rotary stage 7 is controlled to stop.

Then, when the first exposure process is completed, the controller 9
The rotation stage 7 stops rotating and the shutter 5 closes. Then, the signal from the controller 9 starts cooling by the water cooling pipe.
Then, the heater 71 and the cooling pipe 72 are controlled by the controller 9, and the wafer W is held at, for example, 25 ° C. lower than the temperature in the first exposure step. Then, as the rotary stage 7 starts to rotate, the neutral density filter 4 is removed from the optical path, the shutter 5 is opened, and exposure is performed with an illuminance stronger than the illuminance in the first exposure step (hereinafter referred to as the second exposure step). Will be done. The exposure is completed by one rotation, and the strong illuminance is, for example, an illuminance of 3000 mW / cm ² .

Under the above conditions, the actual OF of Tokyo Ohka Kogyo Co., Ltd.
When a resist coated with PR-800 having a thickness of 2 μm was exposed and an experiment was carried out, no foaming of the resist was found and it was found to be suitable.

Hereinafter, the reason why the resist does not bubble and the exposure is completed in a short time in this embodiment will be specifically described.

FIG. 2 is a perspective view for explaining the irradiation amount in this embodiment, where W is the wafer, Wp is the wafer peripheral portion, A is the fixed point of the wafer peripheral portion, and E is the light emitted from the light guide fiber 6. The exposure area is shown. In this embodiment,
The irradiation amount is the total amount of light received while the fixed point A passes through the exposure area E. For example, the illuminance is I, the time for the fixed point A to pass through the exposure area E is t ₀ , and the number of rotations for rotating the wafer is When n is set, the dose is I × t ₀ × n.

Specifically, the bubbling phenomenon of the resist occurs when the amount of gas generated per unit time (hereinafter, generation rate) is larger than the amount of gas released per unit time (hereinafter, release rate). That is, since the amount of generated gas is larger than the amount of gas released to the outside of the resist, the gas fills the inside of the resist, and the increase and concentration of the filled gas lead to foaming.

Gas production rate is the rate of photochemical reaction (hereinafter, reaction rate)
The release rate of the gas is determined by the rate at which the generated gas diffuses in the resist (hereinafter referred to as the diffusion rate).
Therefore, in general, in order to perform light irradiation while suppressing foaming of the resist, it is sufficient to reduce the reaction rate, increase the diffusion rate, and set the generation rate to be equal to or lower than the release rate.

Here, if the reaction rate is vr, the diffusion rate is vd, the illuminance is I, and the resist temperature is T, then vr I, exp (−Ea / kT) …… i vd exp (−Q / kT) …… ii Known to be related.

Ea is the activation energy of the reaction, k is the gas constant, and Q is the activation energy of the diffusion.

Therefore, in order to establish the relationship of vr <vd, it is conceivable to lower I and reduce vr. However, if I is lowered, the irradiation time must be lengthened in order to give a certain irradiation amount necessary for removing the resist in the developing process. However, the gas releasing medium in the resist is sufficiently reacted and decomposed and released in advance (hereinafter referred to as gas releasing).
If it is in the state of being foamed, the foaming does not occur even if the light is irradiated with a large I. Therefore, if exposure is performed with a weak illuminance in the first exposure step so that the gas releasing medium is sufficiently outgassed, bubbling does not occur even if irradiation is performed with a high illuminance in the second exposure step, and the rotation speed of the wafer is reduced. The irradiation time can be shortened by increasing the speed.

Here, in order to sufficiently release gas in the first exposure step so that bubbling does not occur even when light irradiation with strong illuminance is performed in the second exposure step, irradiation at a certain level or more is also performed in the first exposure step. The amount of irradiation required for this sufficient gas emission (hereinafter referred to as gas emission irradiation amount H ₁ ) is vr <vd
When I and T that satisfy the following relation are used for exposure, the rotation speed of the wafer must be considerably slowed down, and the irradiation time (hereinafter referred to as t ₁ ) in the first exposure step becomes long, so that the actual production Does not contribute much to the improvement of sex.

Here, even if vr> vd, foaming does not occur immediately, and it is necessary to collect the filled gas in a certain amount or more. Letting the time from the start of light irradiation under the condition of vr> vd until the filled gas reaches a certain amount or more to aggregate and foam to be the foaming time tb, the passage time t ₀ <foaming time
If it is tb, it will not foam. Further, the amount of gas generated by one pass is determined by the illuminance of the first exposure step (hereinafter, I ₁
And ) And the transit time t ₀ , I ₁ × t ₀ . In other words, even if I ₁ is increased, the gas generation amount does not change if t ₀ is decreased. In other words, I ₁ can be increased by decreasing t ₀ .

Therefore, in the present embodiment, the number n of rotations of the wafer in the first exposure step is set to be plural and the gas emission irradiation amount H ₁ is divided into each passing and given to the resist to reduce the passing time t _0. The rotation speed is increased so that the passage time t ₀ <the foaming time tb. Then, the gas generated by the light irradiation is released to the outside of the resist during a time period when the wafer is rotated once and the light is not irradiated to the same place next time. At this time, since the wafer is heated, according to the above formula (ii), the gas is promptly released to the outside of the resist in the time period when the light irradiation is not performed. Further, as described above, I ₁ can be increased by decreasing t ₀ ,
Due to the relationship of H ₁ = I ₁ × t ₀ × n, the total irradiation time t ₁ (= t ₀ × n) in the first exposure step can be shortened.

In the second exposure step, light irradiation is performed with a higher illuminance (hereinafter referred to as I ₂ ) than in the first exposure step, but the gas release medium is sufficiently reacted and decomposed and released in the first exposure step. Therefore, foaming does not occur. That is, since the light irradiation is performed with the illuminance I ₂ which is stronger than that in the first exposure step, the irradiation time t ₂ in the second exposure step which gives the irradiation amount (hereinafter referred to as H ₂ ) necessary for resist removal in the development step is set. Can be shortened. Further, if a small amount of the gas releasing medium remains in the resist in the first exposure step, it will be irradiated with light of the above-mentioned strong illuminance I ₂ , but the remaining amount of the gas releasing medium is very small. Since the temperature of the resist (hereinafter, the temperature of the resist in the second exposure step is T ₂ ) is lower than that in the first exposure step, the gas generation rate from the above i-th equation is sufficiently smaller than the gas release rate, Does not lead to foaming.

In the above embodiment, the cooling mechanism using the water cooling pipe is described, but the cooling mechanism is not limited to this. For example, forced cooling may be performed by a fan or the like, or a rotating stage may be provided with a cooling fin or the like. Further, although the illuminance adjusting mechanism that is applied to the neutral density filter is used, the illuminance adjusting mechanism is not limited to this, and the power supplied to the light source lamp may be controlled, for example.

〔The invention's effect〕

As described above, the wafer periphery exposure apparatus of the present invention is
A rotating stage on which the resist-coated wafer is placed, a wafer temperature adjusting mechanism including a heating mechanism and a cooling mechanism provided on the rotating stage, and a light beam on the wafer peripheral portion of the rotating wafer placed on the rotating stage. Since it is equipped with a light guide fiber for irradiating and a light source lamp, and a controller for controlling the heating mechanism, the cooling mechanism, the rotation of the rotary stage and the illuminance, it is first exposed to a low illuminance and after exposing the resist to a high temperature to a high illuminance. In addition, the wafer peripheral exposure apparatus can perform exposure with the resist at a low temperature, the exposure of the wafer can be completed in a short time without foaming of the resist.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a wafer peripheral exposure apparatus of an embodiment of the present invention, FIG. 2 is a perspective view for explaining an irradiation amount in the present embodiment, and FIG. 3 is a resist which wraps around the back side of the wafer. Is a partial cross-sectional view of the wafer, and FIG. 4 is a view showing the shape of the circuit pattern exposed on the wafer. In the figure, W ... Wafer Wp ... Wafer periphery 1 ... Light source lamp 4 ... Attenuation filter 6 ... Light guide fiber 7 ... Rotating stage 71 ... Heater 72 ... Water cooling pipe.

Claims (1)

[Claims] 1. A rotary stage on which a wafer coated with a resist is placed, a wafer temperature adjusting mechanism including a heating mechanism and a cooling mechanism provided on the rotary stage, and a wafer mounted on the rotary stage and rotating. Wafer peripheral exposure comprising a light guide fiber for irradiating the peripheral portion of the wafer and a light source lamp, an illuminance adjusting mechanism, and a controller for controlling the heating mechanism, the cooling mechanism, the rotation of the rotary stage and the illuminance adjusting mechanism. apparatus.