JPH0750678B2 - Wafer edge exposure method - 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. 5 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. 6 is a diagram 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. 5 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 this 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 peeled off or scattered, or is rubbed on a wafer cassette or the like and adhered to the pattern forming portion of the wafer, causing the above-mentioned problem of the 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 method that can improve productivity in wafer peripheral exposure by shortening the irradiation time and does not cause resist foaming.

〔Constitution〕

In order to achieve such an object, the wafer edge exposure method of the present invention is a wafer edge exposure method in which light guided by a light guide fiber is applied to the wafer edge while the wafer coated with the resist is rotated to expose the wafer. A first exposure step and a second exposure step. In the first exposure step, the wafer is exposed while rotating the wafer for two or more rotations, and then in the second exposure step. The wafer is exposed while the illuminance is higher than that in the exposure step and the temperature of the wafer is lower than the temperature of the wafer in the first exposure step.

[Action]

In the first exposure step, the wafer is exposed by rotating it twice or more, so that the resist at the fixed point on the peripheral portion of the wafer can release gas while it is not irradiated with light. Therefore, while suppressing foaming of the resist, the resist is provided with an irradiation amount of light necessary for gas release in the first exposure step such that foaming does not occur even when light irradiation is performed with strong illuminance in the second exposure step. be able to. Further, since the wafer is heated, the gas generated by the light irradiation diffuses quickly in the resist and is quickly released to the outside of the resist. Therefore, even if the rotation speed of each rotation is increased, the gas can be sufficiently released during the time when the light irradiation is not performed, and the entire irradiation time in the first exposure step can be shortened.

In the second exposure step performed after the first exposure step, the gas is sufficiently released from the resist in the first exposure step, so that the resist does not foam even when irradiated with light with strong illuminance. Further, by increasing the illuminance, in the second exposure step, the irradiation amount required for removing the resist in the developing step can be given in a short time. Also,
Since the temperature of the resist is lower than the temperature of the first exposure step, even if the resist is irradiated with strong illuminance, the gas is not abruptly generated from the remaining gas releasing medium.

[Specific explanation of action]

FIG. 3 is a perspective view for explaining an irradiation amount in the present invention. W is a wafer, Wp is a wafer peripheral portion, A is a fixed point on the wafer peripheral portion, and E is a light emitted from the light guide fiber 6. The exposed area is shown. In the present invention, 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, and the time t ₀ when the fixed point A passes through the exposure area E is rotated. When the number of rotations is n, the irradiation 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 is known to have a relationship.

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. In other words, a small I to suppress foaming
When trying to expose from the beginning to the end, the rotation speed of the wafer would have to be considerably slowed down. However, if the gas-releasing medium in the resist has been sufficiently reacted and decomposed and discharged in advance, foaming will not occur even if light irradiation with a large I is performed.

Therefore, in the present invention, the exposure is divided into a first exposure step and a second exposure step, and in the first exposure step, exposure is performed with a weak illuminance to sufficiently react / decompose and release the gas releasing medium (hereinafter referred to as gas releasing). After that, the wafer is irradiated with strong illuminance in the second exposure step to increase the rotation speed of the wafer and shorten the irradiation time.

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 exposure is performed with I and T that satisfy the following relationship, the rotation speed of the wafer must be considerably slowed down, and the irradiation time (t ₀ × n, hereafter referred to as t ₁ ) in the first exposure step becomes long. It does not contribute much to improving productivity.

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. If the foaming time tb is the time from the start of light irradiation under the condition of vr> vd until the filling gas reaches a certain level and foaming occurs, the passage time t ₀ <foaming time tb does not cause foaming. . Further, the amount of gas generated by one pass is determined by the product I ₁ × t ₀ of the illuminance (hereinafter referred to as I ₁ ) in the first exposure step and the passage time 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, the number of rotations n 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 pass and given to the resist to reduce the passage time t ₀ , that is, to increase the rotation speed. , Transit time t ₀ <foaming time tb. Then, the gas generated by the light irradiation is released to the outside of the resist during the time period until the wafer rotates once and the light is irradiated to the same place next time. At this time, if the wafer is heated,
According to the formula, the gas is quickly released to the outside of the resist.
Further, since I ₁ can be increased by decreasing t ₀ as described above, the total irradiation time t ₁ (= t of the first exposure step is t ₁ (= t by the relationship of H ₁ = I ₁ × t ₀ × n. ₀ × n) can be shortened.

Next, referring to FIG. 4, the mechanism of gas release in the first exposure step will be described. FIG. 4 is a diagram schematically showing the mechanism of gas release in the first exposure step. R represents resist and G represents gas.

In FIG. 3 and FIG. 4, when the wafer W rotates and the fixed point A on the peripheral portion of the wafer enters the exposure area E and starts receiving light irradiation, as shown in FIG. Gas G is generated. As described above, in the first exposure step, when the generation rate of the gas G is faster than the release rate of the gas G, as the fixed point A passes through the exposure area E of FIG. As shown in, the gas G gradually fills the resist. However, in this state, the gas G has not collected yet and has not foamed. And Fig. 4 (C)
Since the fixed point A has finished passing through the exposure area E of FIG. 3 before the gas G as shown in FIG.
Before the foaming, the light irradiation of the fixed point A through the first rotation is completed. After that, the wafer W continues to rotate, and the fixed point A in FIG.
In the time period during which the light irradiation to the next exposure area E is not received, as shown in FIG. 4D, the gas G generated by the irradiation light passing through the first rotation is released to the outside of the resist R. It
This outgassing occurs because the resist R is heated,
It is done efficiently from the formula ii. The temperature of the resist at this time is set as the resist temperature T _{1 in} the first exposure step. When the fixed point A in FIG. 3 reaches the exposure area E at the second rotation, most of the gas G generated by the light irradiation at the time of the first passage is released, so the fixed point A is again exposed. Even if the gas passes through E, the gas G does not fill more than the amount of gas generated at the time of the first rotation, and the gas G is not filled, as shown in FIG.
By repeating the same cycle as the first rotation shown in (d), the first exposure step is continued while suppressing the foaming of the resist R. Then, after a certain number of rotations, when the predetermined irradiation amount is reached, the gas releasing medium is sufficiently reacted and decomposed and released, and the first exposure step is completed.

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.

〔Example〕

 Examples of the present invention will be described below.

FIG. 1 is a graph for explaining a wafer peripheral exposure method according to an embodiment of the present invention, in which the upper axis of the vertical axis represents the illuminance I, the lower axis of the vertical axis represents the resist temperature T, and the horizontal axis represents the time t. FIG. 2 is a schematic explanatory view of a wafer peripheral exposure apparatus used for carrying out the wafer peripheral exposure method of the above embodiment.

In FIG. 2, 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 drive mechanism, and 9 is a controller.

In FIG. 2, a heater 71 and a water cooling pipe 72 are provided inside the rotary stage 7, and the heating temperature of the heater 71 and the cooling temperature of the water cooling pipe 72 are controlled by the controller 9.

In FIGS. 1 and 2, while the rotary stage 7 is heated to, for example, 70 ° C. by the heater 71, the resist-coated wafer W is transferred to the rotary stage 7 by a transfer system (not shown). After the wafer W is vacuum-sucked on the rotary stage 7, the rotary stage 7 starts to rotate at the same time as the shutter 5 is opened by the signal from the controller 9.
Light irradiation in the first exposure step is started. In the first exposure step, the neutral density filter 4 is arranged on the optical path, and light irradiation is performed with a weak illuminance of, for example, I ₁ = 1200 mW / cm ² . Then, the wafer W is rotated 6 times at a speed of 5 seconds / revolution so that the total irradiation amount H ₁ becomes, for example, 275 J / cm ² .

Then, when the first exposure process is completed, the controller 9
The rotation of the rotary stage 7 is stopped and the shutter 5 is closed by the signal from the. Then, the cooling by the water cooling pipe is started by the signal from the controller 9. 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 the shutter is stronger than I ₁ , for example.
The exposure of the second exposure step is performed with the illuminance of I ₂ = 3000 mW / cm ² .

[Experimental example]

The numerical values given in the above examples are the most preferable ones as examples in which exposure is completed in a short time while suppressing foaming of the resist, but experimental examples in which the temperature in each exposure step is changed are as follows: Explained.

In the above table, the illuminance is mW / cm ² , the temperature is ° C, and the rotation time is shown in seconds / revolution. Further, except No5 and No6, the upper row of each No shows the data in the first exposure step, and the lower row shows the data in the second exposure step. The resist used was OFPR-800 manufactured by Tokyo Ohka Kogyo Co., Ltd. and was applied in a thickness of 2 μm.

In the above experimental example, in the case of No. 1, although foaming of the resist was not recognized, it was found that the resist was not dissolved in the developing solution and was not preferable in practical use. It is considered that this is because the resist undergoes a crosslinking / polymerization reaction by being irradiated with light while being kept at a high temperature. According to known literature, generally, a phenol novolac / naphthoquinone diazide-based resist undergoes crosslinking / crosslinking when exposed to light at a high temperature of about 80 ° C. or higher.
It is said that a polymerization reaction is caused, and it is desirable to carry out exposure at the periphery of the wafer of the present invention at a temperature not higher than the temperature at which the crosslinking / polymerization reaction is caused. This temperature needs to be appropriately determined depending on the type of resist.

The experimental example of No2 is the same as the data of the above-mentioned example.
In this example as well, no foaming of the resist was found and the resist did not remain after development, which is the most preferable in practice. However, it goes without saying that the numerical values of the respective parameters are appropriately changed depending on the characteristics of the resist used.

According to the experimental example of No3, in the first exposure step, the foaming of the resist did not occur, but after the second exposure step,
Many foaming occurred. It is considered that this is because gas was rapidly generated from the small amount of the gas releasing medium that was not released in the first exposure step because the exposure was performed with a high illuminance while maintaining the temperature at a high temperature.

In the case of the No. 4 experimental example, about 20 to 30 resist bubbles were found after the second exposure step. It is considered that this is because the gas generation rate was rather low due to the low temperature in the first exposure step, and the reaction / decomposition release of the gas release medium was insufficient in the first exposure step. However, also in this case, if the number of rotations is increased, it is considered that the foaming can be prevented although the total irradiation time becomes longer.

The No. 5 experimental example is an example in which the first exposure step is omitted and only the second exposure step is performed. In this case, a large amount of foaming occurs, which is practically unusable.

The experimental example of No. 6 is an example in which the exposure is not divided into the first exposure step and the second exposure step, and the exposure is performed by only one rotation, and the illuminance is reduced so that foaming does not occur. Although no bubbling occurred, irradiation for a long time of 900 seconds / revolution was necessary to irradiate the irradiation amount required for removing the resist in the developing step, and productivity was remarkably poor and practically unusable.

〔The invention's effect〕

As described above with reference to the examples and the experimental results, the wafer edge exposure method of the present invention includes the first exposure step and the second exposure step, and the wafer is heated in the first exposure step. Exposure is performed while rotating the wafer two or more times, and then in the second exposure step, the illuminance is higher than that in the first exposure step and the wafer is lower in temperature than the wafer temperature in the first exposure step. Since the exposure is a feature, the resist is not foamed and the processing time can be shortened, which can contribute to a great improvement in productivity in the wafer peripheral exposure.

[Brief description of drawings]

FIG. 1 is a graph for explaining a wafer peripheral exposure method according to an embodiment of the present invention, and FIG. 2 is a schematic explanatory view of a wafer peripheral exposure apparatus used for carrying out the wafer peripheral exposure method according to the embodiment.
FIG. 3 is a perspective view for explaining the irradiation dose in this embodiment, FIG. 4 is a view schematically showing the mechanism of gas release in the first exposure step, and FIG. 5 is a view showing the back side of this wafer. Partial cross-sectional view of wafer showing embedded resist, 6th
The figure shows the shape of the circuit pattern exposed on the wafer. In the figure, I ... Illuminance T ... Resist temperature W ... Wafer Wp ... Wafer periphery 1 ... Light source lamp 4 ... Dimming filter 6 ... Light guide fiber 7 ... Rotating stage

Claims (1)

[Claims] 1. A wafer peripheral exposure method for exposing a wafer peripheral portion by irradiating light guided by a light guide fiber to a wafer while rotating a resist-coated wafer, the first exposing step and the second exposing step. In the first exposure step, the wafer is exposed while rotating it while rotating the wafer twice or more. Then, in the second exposure step, the illuminance is stronger than that in the first exposure step. And a wafer peripheral exposure method, which comprises exposing the wafer to a temperature lower than the temperature of the wafer in the first exposure step.