JP4369787B2 - Photomask white defect correction method - Google Patents

Description

  The present invention relates to a technique for correcting white defects in a photomask used for manufacturing a semiconductor device.

  The photomask serves as a transfer master, and if there is a defect in the mask, the defect is reflected in all of the transferred wafers and the performance of the device is degraded. Therefore, the mask is strongly required to be defect-free, and if the mask has a defect, the defect must be corrected. Conventionally, this correction processing is called a mask repair technique and occupies an important position in the semiconductor manufacturing field.

  With recent mask repair technology, fine defects in the most advanced photomask are being corrected by FIB processing. That is, black defects are removed by using a FIB gas-assisted etching technique, and white defects are corrected by forming a light shielding film by using a carbon-based FIB-CVD technique. In photomask defect correction, it is natural that the optical characteristics and accuracy of correction are important, but not only that, but also a cleaning process for removing foreign matter and resist residue is indispensable in photomask manufacturing. Therefore, it is required that the optical characteristics of the mask correction portion do not deteriorate even after cleaning. Cleaning is performed by chemical cleaning using acid, alkali or ozone, or physical cleaning using ultrasonic waves. Once modified, the mask must withstand the cleaning process with multiple chemical and wear resistances. The light shielding film by FIB-CVD can be shielded with a thin film thickness by using a metal-based light shielding film, but the film attached by FIB-CVD is peeled off by cleaning. Therefore, even when the film thickness is increased, the film is not peeled off by cleaning, and is used as a carbon-based FIB-CVD light shielding film with little film loss.

Lithography has been supported by increasing the NA of the exposure apparatus lens and shortening the exposure wavelength as the design rule becomes finer. At present, an exposure apparatus using a KrF excimer laser having a wavelength of 248 nm is used for device manufacture, and an exposure apparatus using a KrF excimer laser having a wavelength of 193 nm is being used at the research and development level. Furthermore, development of an exposure apparatus using an F2 excimer laser having a short wavelength of 157 nm is also in progress. As the exposure wavelength is shortened, transmittance is obtained by injecting gallium, which is an ion source of the primary beam that is irradiated when scanning microscope (SIM) is used for defect recognition and when FIB defect correction is performed. The decline is becoming a problem. Under such circumstances, instead of FIB-CVD, a defect correction method by CVD using an electron beam that does not cause a decrease in transmittance is being studied for an exposure apparatus using an F2 excimer laser (Patent Literature). 1, Patent Document 2). Since the electron beam can realize a beam diameter smaller than that of the FIB, it has an adaptability to a generation of fine patterns that are exposed using an F2 excimer laser.
Japanese Laid-Open Patent Publication No. 2004-12806 “Defect Correction Method for Levenson Type Phase Shift Mask” Published on January 15, 2004 Japanese Laid-Open Patent Publication No. 2001-185479 “Lithography Mask Substrate and Method of Manufacturing the Same” Released on July 6, 2001 EWMcDaniel, Collision phenomena in ionized gases, John Wiley & Sons Inc., 1964

  Regarding the light-shielding film formed by correcting the white defect by the electron beam, it is necessary to form a CVD film in which the film is peeled off in the subsequent cleaning process or the film thickness is small, but the electron beam has a shorter history than the FIB-CVD. CVD has a problem that it is difficult to form a firm deposition.

  This invention solves the above-mentioned problems, and forms a light-shielding film that can withstand practical use, has chemical resistance in the cleaning process, does not cause film peeling, and can withstand practical use in correcting white defects in photomasks. It is an object to provide a technique for performing the above.

In the photomask white defect correction method of the present invention, when phenanthrene is used as the source gas and the acceleration voltage of the electron beam irradiated to the defective portion is 1 kV, the product of the time during which the beam stays at the irradiation point and the current density is , The electron beam CVD is performed so as to be in the range of 40 to 10,000 (μsec · pA / μm ² ), and when the acceleration voltage is other than 1 kV, the secondary voltage with respect to the acceleration voltage at the acceleration voltage of 1 kV is obtained. The ratio of the electron generation efficiency was obtained, and the range was set by changing the upper and lower limit values of the setting range to one time the value of the ratio. The supply of phenanthrene, which is a raw material gas, was performed at a heating temperature in the reservoir of 40 ° C. or higher.

In the photomask white defect correcting method of the present invention, when naphthalene is used as a source gas and the acceleration voltage of the electron beam irradiated to the defective portion is 1 kV, the product of the time during which the beam stays at the irradiation point and the current density is , The electron beam CVD is performed so as to be in the range of ^{20 to} 10,000 (μsec · pA / μm ² ), and when the acceleration voltage is other than 1 kV, the secondary voltage with respect to the acceleration voltage at the acceleration voltage of 1 kV is obtained. The ratio of the electron generation efficiency was obtained, and the range was set by changing the upper and lower limit values of the setting range to one time the value of the ratio. The supply of naphthalene, which is a raw material gas, was performed at a heating temperature in the reservoir of 10 ° C. or higher.

In the photomask white defect correction method of the present invention using phenanthrene as a source gas, the product of the time during which the beam stays at the irradiation point of the electron beam with an acceleration voltage of 1 kV irradiated to the defective portion and the current density of the electron beam is Electron beam CVD is performed at 40 to 10,000 (μsec · pA / μm ² ), and the supply of phenanthrene, which is a raw material gas, is performed at a heating temperature of 40 ° C. or higher in the reservoir. And processing without peeling of film was realized.

In the photomask white defect correcting method of the present invention using naphthalene as the source gas, the product of the time during which the beam stays at the irradiation point of the electron beam with an acceleration voltage of 1 kV and the current density is 20 to 00 00 By performing electron beam CVD at (μsec · pA / μm ² ) and using naphthalene as the source gas so that the heating temperature in the reservoir is 10 ° C. or higher, there is no film loss or film peeling due to cleaning. Processing was realized.

  When the acceleration voltage of the electron beam is set to an acceleration voltage other than 1 kV in the above method, the secondary electron generation efficiency from the sample with respect to the acceleration voltage is compared with the secondary electron generation efficiency in the case of 1 kV. By adjusting the range of the product of the beam staying time at the irradiation point and the current density, it was possible to realize processing without film loss or film peeling by cleaning.

In the photomask white defect correcting method of the present invention, as shown in FIG. 1, a white defect portion 4c of a photomask in which a pattern 4a is formed of a light-shielding material on a transparent glass substrate 4b is transferred from a gas nozzle 2 to a source gas 3. This is a modification process by CVD that irradiates the processed part with the electron beam 1 while being jetted, and was born in a research to realize a solid electron beam CVD that does not cause peeling or film loss in the subsequent cleaning process. . In the processing conditions of the electron beam 1 that irradiates the defect portion 4c from trial and error, the product of the time during which the electron beam 1 stays at the irradiation point (Dwell Time) and the beam current density of the electron beam 1 is greater than a certain threshold value. It was found that by forming a film under conditions, a light shielding film similar to a carbon-based FIB-CVD light shielding film in which the film thickness hardly changes before and after cleaning can be formed. FIG. 2 (a) shows a carbon film produced by conventional FIB-CVD, and FIG. 2 (b) shows a carbon film produced by electron beam CVD (film produced under film formation conditions that do not satisfy the conditions of the present invention). (c) shows a Raman spectrum having a Raman shift wave number in the range of 600 to 2300 cm ^{−1 with} the intensity on the vertical axis for a carbon film produced by electron beam CVD (film produced under the conditions of the present invention). The processing conditions in (b) and (c) are as shown in Table 1 below. The intensity is not numerically displayed in the graph, but what is important here is the shape of the Raman spectrum, and is therefore an arbitrary unit.

(a)のスペクトルに比べ、(b)のスペクトルにはバックグラウンドに高波数側に上昇するピークがあるのがわかる。これは膜中に水素が含まれている場合に見られるものであり、この条件で作製した膜は洗浄により大きく膜減りした。それに対して(c)のスペクトルは(b)に比べて、(a)に近い形状となっており、この条件の膜は洗浄してもほとんど膜減りは見られなかった。また、この電子ビームＣＶＤ遮光膜は波長193ｎｍや157ｎｍの電子ビームに対して遮光膜として十分な遮光率を持っている。また、電子ビームＣＶＤを用いれば、微細な遮光膜を所望の位置に形成できるので、微細な欠陥にも対応でき、高精度な白欠陥修正を行える。

Compared with the spectrum of (a), it can be seen that the spectrum of (b) has a peak rising in the background on the high wavenumber side. This is seen when hydrogen is contained in the film, and the film produced under these conditions was greatly reduced by washing. On the other hand, the spectrum of (c) has a shape closer to that of (a) than that of (b), and the film under these conditions showed almost no film loss even after washing. Further, this electron beam CVD light shielding film has a sufficient light shielding rate as a light shielding film for an electron beam having a wavelength of 193 nm or 157 nm. Further, if electron beam CVD is used, a fine light-shielding film can be formed at a desired position, so that it can cope with fine defects and can correct white defects with high accuracy.

  In CVD where aromatic hydrocarbons such as phenanthrene are used as the source gas, charged particles are irradiated to sublimate hydrogen, and carbon is deposited on the sample surface, a firm film is formed. Means to grow a grown film. If hydrogen sublimation is not sufficient and remains, the density of carbon atoms contained in the film decreases, resulting in a brittle film. It is understood that sufficient charged particle irradiation is necessary to completely sublimate hydrogen in electron beam CVD.

From the experimental results so far, it was found that the film having cleaning resistance is “a film formed under the condition that the deposition generation amount is 0.003 (μm ³ / nC) or less”. Here, nC is nanocoulomb, and the amount of deposition generated here indicates the volume of the product generated per unit of charge amount irradiated. This means that the deposition amount with respect to the amount of charged particles (in this case, electrons) irradiated, that is, the one where carbon is tightly bonded becomes a deposition film that can withstand cleaning more. The method of forming this film is “film formation by irradiating a large amount of electron beams to the source gas supplied to the sample surface”. The processing conditions for forming a film by this method are as follows.

Dose amount (μC / m ² ) = Dwell Time (μSec) × Current Density (pA / μm ² )
Is a condition equal to or greater than the threshold. However, it should be noted that this threshold varies depending on the gas supply conditions. FIG. 3 is a graph showing data of the deposition amount (Deposition Yield: μm ³ / nC) with respect to the dose amount: Dwell Time × Current Density (μSec · pA / μm ² ). The source gas used here is phenanthrene, but the gas concentration is changed by setting the temperature of the gas reservoir in three stages. The value of 0.003 μm ³ / nC indicated by the thick line in the graph of FIG. 3 is the experimentally obtained threshold value for the amount of deposition generated to determine whether or not cleaning is possible, but in the state in which phenanthrene is injected at 40 ° C. It is shown that a resistant deposition film is formed when the amount is 40 μSec · pA / μm ² or more. In addition, when the phenanthrene is injected at 60 ° C, the dosage is 80 µSec · pA / µm ² or more, and when the phenanthrene is injected at 75 ° C, the dosage is 150 µSec · pA / µm ² or more. It can be seen that is formed. That is, when the source gas is supplied in a rich state, it is necessary to irradiate so many electron beams in order to completely decompose the gas and sublimate hydrogen.

  Although it has been stated that the concentration of the injected gas differs depending on the temperature of the reservoir, the relationship between temperature and vapor pressure is shown in the graph of FIG. This graph is data using phenanthrene and naphthalene as source gases. Although phenanthrene and naphthalene have different values depending on the gas type, they agree with each other in the tendency that when the temperature is increased, the vapor pressure is increased and the vaporization is facilitated. That is, it can be seen that the gas supply amount (supply speed) increases as the temperature of the reservoir increases. In actual work, the gas supply amount is controlled by the set temperature of the reservoir. Therefore, the temperature-vapor pressure characteristic corresponding to this gas type must be accumulated as preparation information.

  In order to effectively form a deposition film with high cleaning resistance, it is not necessary that the amount of deposition generated is small, so the peripheral problem will be described. One problem is that the amount of gas supplied is too small.

  If the refresh time (time until the beam returns to the same beam irradiation point when scanning the processing area) is too short, the gas supply to the sample surface becomes insufficient, and there is no head gas in the absence of source gas. Will be supplied. This is a so-called air shot state, that is, a dose supply that does not contribute to film formation, and cannot be defined under the above processing conditions. Therefore, it is necessary to define a lower limit value of the refresh time. However, it should be noted that this lower limit value varies depending on the gas type and the gas introduction system (nozzle diameter, distance between the nozzle tip and the sample surface). Incidentally, when the distance between the nozzle tip (tip diameter 0.5 mmφ) and the sample defect portion is 330 μm and the source gas is phenanthrene or naphthalene, the refresh time needs to be 5 msec or more. However, the amount of gas supplied to the sample surface decreases in proportion to the cube of the distance between the gas nozzle and the sample defect portion. That is, as the distance increases, the lower limit of the refresh time increases accordingly.

Another problem is that the dose to be irradiated may be too much compared to the amount of gas supplied. In this case, as in the previous problem, when there is no source gas, it is an empty shot to supply a dose, and a dose that does not contribute to film formation occurs. Again, it cannot be defined under the above processing conditions. Therefore, it is necessary to define the upper limit value of the dose amount from this viewpoint. However, it should be noted that this upper limit value varies depending on gas supply conditions. FIG. 5 is a graph showing the relationship between Current Density and Deposition Yield under the condition that the phenanthrene reservoir temperature is set to 75 ° C. and the Dwell time is 2 μsec. Increasing the Current Density increases the irradiation dose with respect to the supplied gas and decreases the Deposition Yield. From this tendency, it can be estimated that Deposition Yield saturates when it reaches a certain Current Density. Increasing the Current Density beyond this value does not make sense because the dose is supplied to a place where there is no source gas. That is, the dose amount at this time (10000 μSec · pA / μm ^{2 in} FIG. 5) is the upper limit of the processing conditions.

Although the upper limit may be greater than this value depending on the raw material gas supply conditions, considering the actual throughput and charge-up problems due to electron irradiation, the upper limit in the case of phenanthrene and naphthalene is determined from the results of previous experiments. In the present invention, it is 10000 μSec · pA / μm ² .

  If the above conditions are suppressed, it is considered that practical conditions for white defect correction using phenanthrene and naphthalene can be covered. However, the conditions of the present invention are formally related to the relationship between the “beam diameter” and the irradiation pixel size. Since satisfying may not meet the intended purpose, we will touch on that point. If the diameter of the irradiated electron beam is larger than the beam irradiation pixel size set on the system, the beam irradiation to the corresponding pixel will also irradiate the adjacent pixels, so even when the pixels on both sides are irradiated. Effective Dwell time is increased by electron irradiation. Taking this into consideration, in order to obtain an appropriate dose amount, a method for determining an effective dwell time by subtracting the influence at the time of adjacent pixel irradiation on the left and right and upper and lower sides, and thinning scanning for thinning and scanning the beam irradiation pixels By performing the above, it is possible to control the effective dwell time even when the beam diameter is larger than the beam irradiation pixel size.

By the way, in the thin film formation process by electron beam CVD, it is generally considered that secondary electrons generated by electrons incident on the sample affect the thin film formation. (Refer nonpatent literature 1) The efficiency of the secondary electron which generate | occur | produces in a sample changes with the material of a sample, and the incident acceleration voltage. FIG. 6 is a graph showing “Relationship between incident electron acceleration voltage and secondary electron yield when irradiated with an electron beam” described in FIG. 13-3-2 in Non-Patent Document 1. FIG. 6 shows the secondary electron generation efficiency with respect to the acceleration voltage of the irradiation electron beam. There is a peak at an acceleration voltage of 1 kV or less, and the secondary electron yield decreases as the acceleration voltage increases. Δmax, E _{p +} , E _p0 , and E _{p− in} FIG. 6 are different depending on the material to be irradiated with the electron beam. It is considered that secondary electrons contribute to the film formation process, that is, to sublimate hydrogen from the source gas to form a close bond of carbon atoms. Therefore, when the acceleration voltage of the electron beam is used at a voltage other than 1 kV, the processing conditions for processing without film loss or film peeling due to cleaning are set at the irradiation point of the electron beam in consideration of secondary electron generation efficiency. Shifts the range of product of time spent and current density. For example, when processing is performed at an acceleration voltage of 2 kV, where the generation efficiency of secondary electrons is about half that when the acceleration voltage is 1 kV, the range of the product of the time during which the beam stays at the irradiation point of the electron beam and the current density ranges from 80 to Processing is performed by shifting to 20000 (μsec · pA / μm ² ).

In this embodiment, phenanthrene is heated as a source gas to 40 ° C. or higher in a gas reservoir, and the electron beam is accelerated under processing conditions in which the electron beam is irradiated while being supplied to the photomask white defect portion as shown in FIG. The voltage is 1 kV, the time that the electron beam stays at the irradiation point (Dwell time), the product of the beam current density of the electron beam is 44 μsec · pA / μm ² or more, and the time until the beam returns to the same point in the processing area (Refresh time) was set to 36 msec or more, and a film was formed on the defective portion. At this time, the degree of vacuum in the sample chamber was 7.7 × 10 ⁻⁵ Pa, and the distance between the gas nozzle tip and the sample defect portion was 330 μm. It was confirmed that the sample produced under this condition hardly loses its film even if it was washed several times by a normal cleaning chemical process.

The product of the electron beam staying time (Dwell time) and the beam current density of the electron beam is 40 μsec · pA / μm ² or more, and the beam is the same in the processing area to control the supply amount of the source gas. If the time to return to one point (Refresh time) is set to 5 msec or more, a film having a strong cleaning resistance can be obtained.

  The product of the dwell time and current density, and the refresh time threshold are adjusted according to the temperature of the gas reservoir, the gas type, the gas flow rate, the material of the workpiece, and the surface condition.

In the case of naphthalene, the gas reservoir temperature is 10 ° C. or higher, the threshold of the product of the electron beam residence time and the current density is 20 μsec · pA / μm ² , and the refresh time threshold is 5 msec.

It is a figure which shows the form of this invention which corrects a photomask white defect by electron beam CVD. It is the Raman spectrum which compared film | membrane intensity | strength by conventional FIB-CVD, electron beam CVD which satisfy | filled the conditions of this invention, and CVD which does not satisfy | fill the conditions. It is a graph which shows the relationship between a dose amount and a deposition production amount. It is a graph which shows the relationship between the temperature of phenanthrene and naphthalene, and vapor pressure. It is a figure which shows the relationship between a current density and the amount of deposition production. It is a graph which shows the relationship between an incident electron acceleration voltage at the time of irradiating an electron beam, and a secondary electron yield.

Explanation of symbols

1 electron beam 2 gas nozzle 3 source gas 4 photomask
4a Shading pattern 4b Transparent area
4c White defect

Claims (4)

A photomask white defect correction method using electron beam CVD using phenanthrene as a source gas,
The phenanthrene is supplied at a heating temperature in the reservoir of 40 ° C or higher ,
When the acceleration voltage of the electron beam is 1 kV, the product of the time during which the electron beam stays at the irradiation point and the current density is in the range of 40 to 10,000 (μsec · pA / μm2),
Wherein when the acceleration voltage is other than 1kV, obtains the ratio of the secondary electron generation efficiency in the accelerating voltage 1kV and the secondary electron generation efficiency in the accelerating voltage other than the 1kV, time of the electron beam to stay on irradiation point A method for correcting a white defect in a photomask , wherein processing is performed in the product range obtained by multiplying the upper and lower limit values of the product of current density by the reciprocal of the ratio. A photomask white defect correction method using electron beam CVD using naphthalene as a source gas,
The supply of the naphthalene is performed by setting the heating temperature in the reservoir to 10 ° C or higher,
When the acceleration voltage of the electron beam is 1 kV, the product of the time during which the electron beam stays at the irradiation point and the current density is in the range of 20 to 10,000 (μsec · pA / μm2),
When the acceleration voltage is other than 1 kV, the ratio of the secondary electron generation efficiency at an acceleration voltage other than 1 kV and the secondary electron generation efficiency at the acceleration voltage of 1 kV is obtained, and the time during which the electron beam stays at the irradiation point; A method for correcting a white defect in a photomask, wherein processing is performed in the product range obtained by multiplying the upper and lower limit values of the product of current density by the reciprocal of the ratio. When the diameter of the electron beam is larger than the target irradiation pixel size, the product of the time during which the beam stays at the irradiation point of the electron beam and the current density is irradiated to the pixel adjacent to the target irradiation pixel. 3. The method for correcting a white defect in a photomask according to claim 1, wherein adjustment is performed in consideration of the influence of time. A photomask white defect correction method using electron beam CVD using phenanthrene as a source gas,
The phenanthrene is supplied at a heating temperature in the reservoir of 40 ° C or higher ,
When the acceleration voltage of the electron beam is 1 kV, the product of the time during which the electron beam stays at the irradiation point and the current density is in the range of 40 to 10,000 (μsec · pA / μm2),
When the acceleration voltage is other than 1 kV,
If the secondary electron generation efficiency is higher than the secondary electron generation efficiency when the acceleration voltage is 1 kV, the product of the time over which the electron beam stays at the irradiation point and the current density is increased by the amount of secondary electron generation efficiency. Shift the range to be set in the direction of decreasing the value,
If the secondary electron generation efficiency is smaller than the secondary electron generation efficiency when the acceleration voltage is 1 kV, the product of the product of the time during which the electron beam stays at the irradiation point and the current density by the amount of the secondary electron generation efficiency. A method for correcting a white defect in a photomask, characterized in that processing is performed in the product range obtained by shifting the set range in a direction in which the value increases.

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