JPH0837144A - Method and apparatus for pattern transfer exposure - Google Patents

Abstract

PURPOSE:To stabilize temperature during exposing process by executing the pattern transfer exposing while the coolant of which temperature can be controlled freely is circulated and coolant temperature is adjusted to keep constant the temperature of the pattern transfer substrate from the start to the end of exposing process. CONSTITUTION:A mask substrate 1 is moved to a stage 4 via a gate valve 13 and is then fixed to the stage 4 by a mechanical clamp 5. The stage 4 is temperature-controlled to 20 deg.C by a coolant. The stage 4 can be freely moved during the transfer exposing process because the piping for transferring the coolant and the piping for heat conductive gas are composed of a bellow type flexible tube. In the case of electron beam lithographic exposure, temperature of the mask substrate 1 for starting evacuation is lowered to 15 deg.C as in the case of the prior art. Thereafter, the stage 4 for supporting the mask substrate 1 is set to about 20 deg.C and temperature of the stage 4 and mask substrate 1 is kept at 20 deg.C from the start to the end of the electron beam lithographic exposing process by means of the coolant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor integrated circuit (hereinafter abbreviated as an integrated circuit) and a manufacturing apparatus therefor, in which an integrated circuit pattern (hereinafter abbreviated as a pattern) is transferred to a pattern transfer substrate (hereinafter referred to as a pattern transfer substrate). Explain with mask substrate)
The present invention relates to an exposure method and an exposure apparatus for exposing and exposing the above photosensitive resist (hereinafter abbreviated as resist).

[0002]

2. Description of the Related Art Conventionally, when manufacturing an integrated circuit, a mask (reticle) having a pattern consisting of several kinds of combinations according to its use such as etching or ion implantation is sequentially passed through a resist by a reduction exposure apparatus such as a stepper. A pattern forming method by a so-called photolithography method is used in which a pattern is transferred onto a semiconductor substrate by repeating exposure and baking. Therefore, since a plurality of patterns are superposed on the same semiconductor substrate, it is necessary to minimize the superposition error.

In particular, with the recent increase in the degree of integration of integrated circuits, the device elements themselves are miniaturized, and the patterns themselves are miniaturized accordingly, so that the patterns are required to have higher precision in overlay. It has started to be done. The causes of the overlay error are mainly classified into those caused by the reduction exposure apparatus, those caused by the mask substrate, and those caused by the photomask.

Regarding the first reduction exposure apparatus, in addition to the improvement of the mechanical position accuracy for superposition of the reduction exposure apparatus itself, the improvement of the method of reading the registration mark is adopted. On the other hand, on the user side of the reduction exposure apparatus, various measures have been taken to address this problem, such as designating a specific machine as a dedicated machine for each lot unit and preventing the error between lots peculiar to the specific machine. ing.

Further, regarding the second mask substrate, in addition to devising the process flow, the position of the reading mark, the layer, etc., so that the shape of the overlay mark does not deteriorate, RSA {Rear Surface Alignment
Law; S.Katagiri, et al., The6th international Mic
There is also proposed a method of arranging overlay marks on the back surface of a mask substrate, as in roProcess conf., B-8-6, (1993)}. As another method, the exposure apparatus is provided with a chip leveling function to minimize the influence of the warp of the mask substrate.

Regarding the final third photomask, there are one that occurs when the photomask is manufactured and one that occurs when pattern exposure printing is performed by an exposure device using the photomask. The former is largely due to the temperature drop of the mask substrate due to adiabatic expansion in which the mask substrate is loaded into the electron beam drawing apparatus and evacuated. In order to suppress this temperature change, Japanese Patent Application Laid-Open No. 60-171725 proposes a method of controlling the temperature by providing a heating device in the load lock chamber in front of the electron beam drawing processing chamber.

The latter is caused by temperature instability in the use environment, and as a method for avoiding this, a method of controlling the temperature of the mask substrate or wafer is proposed in Japanese Patent Laid-Open No. 53-98782. There is. The present technique is also an effective method for suppressing the temperature rise of the mask particularly when high energy irradiation is performed as in X-ray lithography.

Further, JP-A-60-1717 for the same purpose as the present invention.
The method disclosed in Japanese Patent No. 25 is an effective method provided with a mechanism for heating a sample in a preliminary chamber, but it does not take into consideration temperature change during exposure. That is, this method cannot correct the influence of the expansion of the mask substrate due to the temperature rise caused by the electron irradiation energy. Among the causes of the overlay error described above, the error caused by the first reduction exposure apparatus is very small and can be ignored because the alignment accuracy of the reduction exposure apparatus itself is improved.

For example, a commercially available reduction exposure apparatus NSR2005
When using {Nikon Corp.} as an overlay mark on the active layer and overlaying on the same active layer, overlay error is 3σ = 0.05 μm
It was below. This is a value close to the measurement error, and the influence of the reduction exposure apparatus itself is very small in the production of the current integrated circuit.

Further, it is a very difficult problem at present to reduce the overlay error caused by the second mask substrate.
The mask substrate itself may warp as the manufacturing process progresses,
This is because it is inevitable that the side wall of the etched overlay mark becomes rough and it becomes difficult to read the mark. The overlay error caused by the third photomask is a problem that can be most efficiently reduced at present.

[0011]

The present invention is based on the above-mentioned third aspect.
The object of the present invention is to reduce the overlay temperature due to the photomask of (1) and further reduce the positional deviation error of the transfer pattern caused by the temperature change of the mask substrate due to the pattern transfer exposure at the time of manufacturing the mask substrate.

The extent to which the mask substrate is affected by the temperature rise that occurs during exposure will be described below by taking a concrete example. First, taking a 5 × reduction type exposure apparatus as an example, the maximum allowable temperature change ΔT due to exposure is calculated in order to suppress the positional deviation of the pattern due to transfer exposure within a certain allowable value.

The exposure area is set to 20 mm, and the maximum positional deviation at the time of exposure is 0.05 μm or less, that is, 0 on the mask (reticle).
It should be set within 25 μm. When a quartz glass mask substrate is used, its linear expansion coefficient is 5.0E-7 / K
Therefore, the temperature change ΔT during electron beam writing is 0.05E-6.
(M) * 5 ≧ 5.0E-7 (/ K) * ΔT (K) * 20E-
By 3 (m) * 5, ΔT ≦ 5K.

Therefore, it is necessary to suppress the temperature rise to 5 K or less when the positional deviation during exposure is to be 0.05 μm or less. The requirement for reducing the temperature rise becomes stricter as the chip size of the integrated circuit becomes larger and as the device becomes finer. T. Matsusaka et al., The 6th i
nternational MicroProcess conference, PC-3 (1993)
However, there is a view that it will be necessary to keep it below 0.1K in the near future.

Further, when a mask made up of several kinds of combinations to be used in superposition is manufactured by the conventional exposure method, the positional deviation of the pattern due to the unstable temperature exists on each of the plurality of mask substrates. The displacement is amplified as a whole. Therefore, when the combined mask patterns are sequentially transferred and exposed on the same mask substrate, the positional deviations are superimposed and further amplified and transferred and exposed on the mask substrate. In production
It becomes more and more disadvantageous to the miniaturization.

The temperature rise during drawing exposure is estimated as follows using a 5 inch square mask substrate as an example. The irradiation energy is 10 (μA) * 10 (kV) * 7200 (sec) = 72, assuming that an electron beam of 10 μA on average is irradiated for 2 hours at 10 kV.
The mask substrate has received Joule heat of 0 (joule). In addition, the temperature rise of the mask substrate is 0.2cal / (gK),
If it is made of quartz glass with a specific gravity of 4.0 and a thickness of 2 mm, then 720 / 4.1855 (cal) = ΔT (K) * 0.2 {cal / (gK)}
* 12.5 (cm) * 12.5 (cm) * 0.2 (cm) * 4.0 The temperature rise ΔT is estimated to be 6.9K.

Therefore, in the conventional electron beam drawing exposure method,
Even if the influence of heat radiation is taken into consideration, a considerably large temperature rise is expected under the above condition (ΔT ≦ 0.1K), which may be a major obstacle to miniaturization of integrated circuits in the future. Although the above has been described as a problem relating to mask substrate fabrication, the same problem also exists in the case of direct electron beam drawing on a semiconductor substrate.

Therefore, according to the present invention, in order to reduce the overlay error caused by the photomask as much as possible and to manufacture a mask substrate with higher accuracy, the temperature rise ΔT of the mask substrate during the electron beam drawing exposure process is set to 0.1 K or less. It is an object of the present invention to provide a method for suppressing the above-mentioned problems, preventing the instability of the temperature during exposure, and an exposure apparatus therefor.

[0019]

According to the present invention, when pattern transfer exposure is performed by an electron beam drawing apparatus, a temperature-adjustable cooling medium is circulated through a stage on which a pattern transfer substrate coated with a photosensitive resist is placed, and Adjust the temperature of the refrigerant,
It is a pattern transfer exposure method characterized by performing pattern transfer exposure while keeping the temperature of the pattern transfer substrate constant from the start of exposure to the end of exposure. When exposing a set of masks to be used, a temperature-adjustable cooling medium is circulated through the stage on which the pattern transfer substrate is placed, and the temperature of the cooling medium is adjusted so that pattern transfer exposure is performed while keeping all the masks at a constant temperature. And a mechanism for arranging a coolant pipe on the stage on which the pattern transfer substrate is mounted and for freely adjusting the temperature of the coolant in the electron beam drawing apparatus. It is a characteristic exposure apparatus.

[0020]

According to the present invention, since the temperature-adjustable coolant is circulated through the stage on which the mask substrate for pattern transfer exposure is placed in the electron beam drawing apparatus, the temperature of the stage, that is, the mask substrate is kept at a constant temperature. The temperature from the start of the pattern exposure to the end of the pattern exposure can be maintained at a constant temperature while maintaining the temperature. Therefore, the influence of the expansion of the mask substrate due to the temperature rise caused by the electron beam irradiation energy can be corrected.

Therefore, it is possible to manufacture a mask substrate having a transferred and exposed pattern with higher accuracy than the conventional method. In addition, regarding the production of a set of multiple photomasks that are used in superposition to produce the same type of integrated circuit, all the masks were exposed at the same temperature. If so, amplification of positional deviation due to the synergistic effect between the masks does not occur.

[0022]

An embodiment of the present invention will be described with reference to the drawings.
FIG. 2 is a cross-sectional view showing the outline of the entire electron beam drawing apparatus according to the present invention. The mask substrate 1 opens the gate valve 3 and is carried into the load lock chamber 2. After that, the gate valve 3 is closed and the load lock chamber 2 is evacuated by the vacuum pump. At this time, since air molecules are removed from the load lock chamber 2, ideally, adiabatic expansion does not occur and the temperature of the mask substrate 1 does not drop.

However, the exhaust is not performed instantaneously, and adiabatic expansion occurs during the exhaust process, and the mask substrate 1 is actually cooled. Since the cooled mask substrate 1 does not exchange heat with gas in a vacuum, heat is exchanged mainly by heat conduction due to contact between the mask substrate 1 and the stage 4, and the temperature of the stage 4 gradually approaches. To go.

The mask substrate 1 is transferred to the stage 4 via the gate valve 13 and fixed to the stage 4 by the mechanical clamp 5. In this embodiment, as shown in FIG. 3, a space 14 is provided between the mask substrate 1 and the stage 4 and filled with He gas 17 having a high thermal conductivity.
This technique is frequently used in dry etching, and compensates for heat transfer with the stage, which is insufficient with solid contact alone, by gas contact.

The temperature of the stage 4 is adjusted to 20 ° C. by the refrigerant 15. If the temperature of the stage at this time is significantly different from room temperature, it is difficult to precisely control the temperature, or the temperature rises to cause distortion when returning to room temperature.
The stage temperature should be as close as possible to room temperature. Further, in order to allow the stage 4 to freely move in the XY axis directions during transfer exposure, the pipe 6 for passing the refrigerant and the pipe for heat transfer gas 7 are made of bellows-shaped flexible tubes. The material of the flexible tube may be metal such as stainless steel or resin such as Teflon.

Further, in order to improve the control accuracy of the position of the stage 4, as shown in FIG. 4, cooled He gas is directly supplied to the space 14 in contact with the back surface of the mask substrate 1 without using these flexible tubes. Any method may be used. Alternatively, a cooling laser may be used. FIG. 1 shows the temperature change of the mask substrate at the time of exposure by the electron beam drawing exposure apparatus according to the method of the present invention and the conventional method.

FIG. 1A shows the temperature change of the mask substrate when the method of the present invention is used, and FIG. 1B shows the temperature change of the mask substrate when the conventional method is used. First, in the case of electron beam drawing exposure according to the conventional method, as shown in FIG. 1 (b), after being carried into a load lock chamber at room temperature of 25 ° C., when a vacuum is started, adiabatic expansion occurs in the load lock chamber and the mask substrate is heated to 15 ° C. Then, 1 hour after recovering to about 23 ° C., electron beam drawing exposure is started. The temperature of the mask substrate gradually rises due to the electron beam irradiation energy, and the temperature of the mask substrate rises to 27 ° C. at the end of the electron beam drawing exposure after 2 hours.

Therefore, the expansion of the mask substrate from the start of the exposure of the electron beam drawing to the end of the exposure of the electron beam drawing is 5 inches square, and in the case of the mask substrate, if the effective area is 100 mm square, the maximum displacement of the transfer pattern is , 5.0E-6 (/
K) * 100 (mm) * 4 (K) / 5 = 4E-4 (mm) = 0.4μ
m.

On the other hand, when the electron beam drawing exposure according to the present invention is started, the temperature of the mask substrate is lowered to 15 ° C. as in the conventional method when the vacuum is started. After that, the stage on which the mask substrate is placed reaches about 20 ° C., and the temperature of the stage and the mask substrate is kept at 20 ° C. by the action of the coolant from the start of the electron beam drawing exposure to the end of the electron beam drawing exposure. Therefore, according to the present invention, the problem of positional displacement of the transfer pattern due to the thermal expansion of the mask substrate by the above-mentioned conventional method does not occur.

In the present invention, the method of keeping the temperature of the stage at the time of exposure, that is, the temperature of the pattern transfer substrate constant by cooling by the action of the cooling medium has been shown. However, the method of keeping the temperature of the pattern transfer substrate constant. As a result, maintaining the heating temperature is not suitable for the following reasons. This is because in the case of heating, it is necessary to heat to a temperature sufficiently higher than room temperature, in which case the resolution of the photosensitive resist is lowered and the beam spot is increased due to the vacuum deterioration of the processing chamber.

[0031]

According to the present invention, the stage for mounting a mask substrate to be subjected to electron beam drawing exposure is provided with a function of circulating a cooling medium and keeping the stage temperature constant. Since the correction is performed and the temperature of the mask substrate is always maintained at a constant temperature from the start to the end of the pattern exposure, the mask substrate with high dimensional accuracy can be manufactured.

As a result, the mutual alignment accuracy of a plurality of photomasks having an integrated circuit pattern composed of several kinds of combinations for manufacturing integrated circuits of the same type is also improved, and a more miniaturized integrated circuit is manufactured. Can now easily cope.

[Brief description of drawings]

FIG. 1A is a characteristic diagram showing the temperature of a mask substrate during electron beam writing by the method of the present invention. (B) is a characteristic diagram showing the temperature of the mask substrate at the time of electron beam drawing by the conventional method.

FIG. 2 is a schematic cross-sectional view of an electron beam drawing apparatus using a stage according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a stage according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view of another stage according to the embodiment of the present invention.

[Explanation of symbols]

1 Mask Substrate 2 Load Lock Chamber 3 Gate Valve 4 Stage 5 Mechanical Clamp 6 Refrigerant Pipe 7 Heat Transfer Gas Pipe 8 Electron Gun 9 Stop Valve 10 Chrome 11 Photosensitive Resist 12 O Ring 13 Gate Valve 14 Space 15 Refrigerant 16 N ₂ Gas 17 He gas

Claims (3)

[Claims] 1. When performing pattern transfer exposure by an electron beam drawing apparatus, a temperature-adjustable refrigerant is circulated through a stage on which a pattern transfer substrate coated with a photosensitive resist is placed, and the temperature of the refrigerant is adjusted, A pattern transfer exposure method comprising performing pattern transfer exposure while maintaining the temperature of the pattern transfer substrate constant from the start of exposure to the end of exposure. 2. For manufacturing integrated circuits of the same type,
When exposing a set of masks to be used by overlapping,
A mask manufacturing method characterized in that a temperature-adjustable cooling medium is circulated through a stage on which a pattern transfer substrate is placed, the temperature of the cooling medium is adjusted, and pattern transfer exposure is performed while keeping all masks at a constant temperature. 3. An electron beam drawing apparatus, characterized in that a coolant pipe is disposed on a stage on which a pattern transfer substrate is mounted, and a mechanism for freely adjusting the temperature of the coolant is provided.