JPS6315740B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a transfer mask, and particularly to a method for manufacturing a transfer mask using electron beam exposure. Recently, with the expansion of the range of applications of semiconductor devices, a higher degree of integration is required, and there is also a strong desire to shorten the development period. Generally, when manufacturing exposure masks for semiconductor devices, a master mask is first manufactured using electron beam exposure technology, and then the mask is transferred directly or through another mask based on this master mask. An exposure mask is manufactured by. Then, using this transferred exposure mask, a desired pattern is formed on each semiconductor substrate by optical exposure. The transfer mask in the present invention is a master mask in which a pattern that selectively absorbs light and X-rays is formed on a structure that transmits light and X-rays. The electron beam exposure method used to manufacture masks for semiconductor devices involves deflecting an electron beam according to a program stored in advance in an electronic computer.
This is applied to a mask material coated with electron beam resist to draw a predetermined pattern, and compared to conventional optical exposure methods, it is capable of forming much finer patterns with higher precision. Furthermore, this method has the advantage that the drawing pattern can be easily modified or changed, and is therefore attracting attention as a method that can meet the above-mentioned requirements. In order to form a transfer mask with high precision using this type of electron beam exposure technology, it is necessary to use polysilicon as a violet light material (hereinafter simply referred to as a light shielding material) for ultraviolet and far ultraviolet light, and to use polysilicon along the mask surface during etching. It is desirable to use a dry etching method that is less likely to erode the grain direction. A thickness of 800 Å is sufficient for the light shielding layer of the transfer mask. Therefore, visible light is also sufficiently transmitted through this light-shielding layer, making it easy for an operator to align the mask with the underlying pattern previously formed on the semiconductor substrate. Now, when pure polysilicon is used as a light-shielding material as has been used in the past, its sheet resistance is as high as 10 MΩ/□ or more, so the charge generated by the electron beam during electron beam exposure accumulates. This caused the electron beam to be repelled and become extra polarized, resulting in the problem that accurate drawing could not be achieved. Next, this phenomenon will be explained using FIG. The mask material 110 of the transfer mask is generally made of polysilicon 112 (film thickness of 500 Å to 2000 Å) as an ultraviolet shielding layer on a mask base of quartz or glass plate.
is deposited. An electron beam resist 111 is deposited on the mask material 110. A predetermined magnetic field is applied to the electron beam deflection coil 100 according to a program stored in advance in an electronic computer to deflect the electron beam 101 that has been focused by an electron lens or the like in the previous stage. The deflected electron beam 101 is applied to the mask material 11
0, the portion 50 of the resist 111 on the surface of the mask material 110 is destroyed. After this, part 5 of this destroyed resist 111
The light shielding layer 112 under the layer 0 is etched and removed, and the remaining resist 111 is also removed. Then, only the portion 50 hit by the electron beam has a property of transmitting ultraviolet light and the like, and can be used for optical exposure. Now, if we try to operate the electron beam 101 from the position of the linear irradiation 70 to the position of the polarized irradiation 71 with a predetermined change, the electron beam 101 should hit the light shielding layer from the position 1 to the desired position 2. However, in reality, it is extra deflected and irradiated and moves to position 3. The reason for this is that, for example, beam shots 4 and 5 are already charged by the electron beam.
This is thought to be due to the fact that the electron beam is deflected to an unexpected position 3 due to the repulsion between the two positions, causing the position 5 to move slightly to the right, and the cumulative distance of this small movement to the unexpected position 3. Therefore, this phenomenon is
This is very similar to the phenomenon that occurs when an extra magnetic field is applied to the electron beam polarizing coil 100 in advance. Since this phenomenon is also related to the speed of deflection operation of the electron beam 101, it is difficult to program in advance the amount of this extra deflection. The characteristic diagram in FIG. 2 shows the actual value of the error in the line segment dimension, which was determined experimentally in relation to the amount of charge injected by the electron beam. The vertical axis shows the error in the line segment dimensions, that is, the value [%] obtained by dividing the distance Δl of the extra deflection by the previously desired distance l, and the horizontal axis shows the amount of charge injected per unit area [ coulomb/cm ² ]. The sheet resistance value of the mask material 110 used here is
It is 100MΩ/□ or more. Characteristic curve 10,
11, 12, and 13 have beam position movement frequencies of 1MHz, 15KHz, 1500Hz, and 1500Hz, respectively, as parameters.
This is the characteristic when the frequency is 150Hz. Here, the beam position movement frequency is defined as the time required for the electron beam to move in one direction from a fixed point, move in the opposite direction from a certain point, and return to the original fixed point. This is the desired frequency. As is clear from the figure, the error in the line dimension increases as the amount of charge injected per unit area increases. It was also found that even with the same amount of injected charge, the higher the frequency of movement of the beam position, the larger the error in the line segment dimension. Next, how the influence of the error in the line segment dimension appears on the planar figure actually drawn will be explained with reference to FIGS. 3 and 4. Now, in an attempt to draw a desired figure 6 (the part indicated by the chain double-dashed line), the electron beam 101 is directed to the first operating line 1.
It has been found that if the lines are applied sequentially from 02 to the next operating line 103, the figure 6 becomes a trapezoidal figure 6' with a bulge at the bottom.
That is, the vertical and horizontal dimensions W and l of the desired figure 6
It was found that gradually expands and becomes W′, l′.
It has also been found that when attempting to draw two desired figures 7 and 8, the electron beam 101 is influenced by the accumulated charge of the previously drawn figure 7, causing figure 8 to move toward 8'. In this way, we have discovered that there are phenomena in which figures expand and the distance between figures that are next to each other increases. It was also found that this phenomenon is related to the beam position movement frequency, beam scanning method, etc. In addition, as another means of solving the above problem, it is possible to simply deposit metals such as gold or Al by vacuum evaporation on a mask material on which polysilicon is deposited as a light-shielding layer on the surface, but this method does not Depending on the type and thickness of the metal to be etched, the etching conditions for polysilicon may change, and the transmittance of visible light may decrease, resulting in a problem that the characteristics of the transfer mask are greatly reduced. An object of the present invention is to provide a method for manufacturing a transfer mask that can reduce such phenomena. The present invention is characterized by a mask equipped with a polysilicon mask having, for example, a metal layer having a predetermined sheet resistance value corresponding to resist sensitivity, and a process for forming the mask pattern using a position movement frequency, an electron beam This is because acceleration, etc., are limited to an effective range. According to the present invention, when sensitizing a resist film in a mask with an electron beam, the sheet resistance required to reduce the accumulation of charged electrons to the extent that it does not affect the writing accuracy can be adjusted to resist sensitivity and writing speed. Since a corresponding determination can be made, it is possible, for example, to reduce as much as possible the amount of metal deposited in order to obtain electrical conductivity. Furthermore, since it is possible to minimize changes in etching conditions and decreases in the amount of visible light transmitted, it is possible to provide a more practical method for manufacturing a mask (transfer mask). Next, the structure of the mask material of the transfer mask used in the embodiment of the present invention and the method of manufacturing the transfer mask by forming a mask pattern on this mask material will be explained in order of steps. FIGS. 6a to 6e are cross-sectional views illustrating the structure of a transfer mask material and the process of forming a mask pattern according to the present invention. As shown in FIG. 6a, the transfer mask material includes a polysilicon film 602 with a thickness of 500 Å to 1000 Å on a glass or quartz substrate 601 with a thickness of 0.2 mm to 5 mm, and a polysilicon film 602 having a predetermined sheet resistance value. It has a three-layer structure including a metal layer 603. The metal layer 603 is, for example, a Ta, Cr, Ni or Al layer with a thickness of 20 Å to 200 Å. Therefore, as shown in FIG. 6b, an electron-sensitive resist 604 is coated on the metal layer 603, and the resist film is removed in a predetermined shape by the above-mentioned electron beam exposure, and the structure shown in FIG. 6c is obtained. get. Using this resist film 604 as a mask, the metal layer 603 and polysilicon 602 are selectively removed by sputtering in an atmosphere of hydrocarbon gas containing halogen.
The structure shown in FIG. 6d is obtained. Then, Figure 6e
By removing the resist 604 as shown in , a desired transfer mask can be obtained. FIG. 5 is a graph of the upper limit of the sheet resistance value of the metal layer required to suppress the error in line dimension within 0.1 μm, which was experimentally determined in relation to the beam position movement frequency. Here, the characteristic curves 31, 32, 33, 34 are
The electron beam sensitivity [coulomb/cm ² ] as a parameter was set to 10 ⁻⁷ , 10 ⁻⁶ , 10 ⁻⁵ , and 10 ^−4, respectively. The test pattern used in this experiment has a shape that can generally represent the pattern of an actual LSI product. From the figure, the limits of the characteristics that the transfer mask material should have are determined as shown in Table 1 below.

[Table] This data was obtained when a mask pattern was manufactured under the conditions shown in Table 2 below.

[Table] Figure 7 shows the upper limit of the sheet resistance of the metal layer required to suppress the line dimension error within 0.1 μm in relation to the electron beam sensitivity. This is a summary. For example, if we are going to use a resist film 604 with a sensitivity [coulomb/cm ² ] of approximately 10 ^-7 and 10 ^-5 , as shown in Tables 3 and 4 below, as is clear from FIG. Metal layers each having a sheet resistance value are formed on the polysilicon film.

【table】

[Table] In the above examples, a three-layer structure was explained as a transfer mask material, but it is not limited to this, and for example, a structure in which impurities are injected into a polysilicon film to obtain an appropriate sheet resistance value. The same effect as described above can be obtained even with a mask having a two-layer structure, such as one in which a mixture of silicon, Cr, and Ni is deposited on glass by sputtering. Further, alloying the metal layer and the polysilicon layer by heat treatment at about 200 to 450°C is effective in increasing the bonding strength between the two. Such metallization is preferably carried out in a vacuum chamber immediately after the deposition of the metal layer;
It is also possible to heat the substrate during metal evaporation, or to perform it outside the vacuum system after evaporation. By using such a method of manufacturing a transfer mask for photoetching which is patterned by electron beam exposure, the following characteristics can be obtained. First, the deposited metal layer for improving conductivity is extremely thin, so it has good visible light transparency, which is a characteristic of polysilicon masks, and reactive sputtering using a hydrocarbon gas containing halogen. - Electron beam exposure can be used without sacrificing the good patterning properties of etching. For example, approximately 10 ^-4
When performing high-speed exposure at approximately 20 MHz using a low-sensitivity resist of [coulomb/cm ² ] on the surface, the sheet resistance of the metal layer required is 200 Ω/□. When this is achieved by chromium vapor deposition, the etching time of dry etching using _CF4 increases by approximately 30%, and the transmittance of polysilicon increases by approximately 30% due to optical density.
Although it is 1.5, there is no problem in practice, and if the sheet resistance of the metal layer can be higher, there will be no problem because the amount of metal to be deposited or added will be smaller. The second feature is that the method of imparting conductivity to the transfer mask can be changed depending on the writing speed.
For example, if the drawing speed is low, about 1 MHz or less, the sheet resistance may be higher than 200Ω/□, which reduces the thickness of the metal deposited film, making etching easier and improving visible light transmittance. . Also, instead of metal, polysilicon with boron,
Low-resistance polysilicon, which can be achieved by implanting impurities such as phosphorus and annealing at several hundred degrees without affecting mask parallelism, is sufficient.
There is a point that the range of manufacturing methods becomes wider. Furthermore, by using the transfer mask manufacturing method of the present invention, the problem of charge accumulation can be practically solved. For example, it is possible to suppress the thickness to 0.1 μm or less.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a state in which a transfer mask material is irradiated with an electron beam of an electron beam exposure device,
FIG. 2 is a characteristic diagram showing experimental data obtained by irradiating the transfer mask material with the electron beam of FIG.
3 and 4 show the desired mask and
FIG. 3 is a plan view showing the relationship between a pattern shape and an actually drawn mask pattern shape. FIG. 5 is a characteristic diagram showing the characteristics that the transfer mask material based on the present invention should have, and FIGS. 6 a to 6 e are cross-sectional views sequentially explaining the steps of manufacturing the transfer mask based on the present invention. . Figure 7 shows the line segment dimension error of 0.1μ.
FIG. 3 is a diagram showing the upper limit value of the sheet resistance value necessary to suppress the value within m in relation to the electron beam sensitivity. In the figure, 1, 2, 3, 4, 5...Positions hit by the electron beam, 50...Destroyed resist film portion, 70, 71, 72...Locus of the electron beam, 100...Electron lens. Coil, 101...
Incident electron beam, 10, 11, 12, 13...Characteristic curves experimented at different beam position movement frequencies, 6, 7, 8... Desired mask pattern shape, 6', 8'... obtained Mask pattern shape, 102, 103... Electron beam operation line, 11
1... Transfer mask material, 31, 32, 33, 34
. . . Characteristic curves tested at different electron beam sensitivities, 601 . . . quartz or glass, 602 . . . polysilicon, 603 . . . metal layer, 604 . . . resist film.

Claims (1)

[Claims] 1 A transfer process that includes the step of forming a material that reacts to electron beams on a mask material that has a material that suppresses the charge effect caused by electron beam irradiation, and irradiating this material with electron beams to draw a predetermined pattern. In the method for manufacturing a mask, when the sensitivity [coulomb/cm ² ] of the material that reacts with the electron beam is 10 ^-7 to 10 ^-6 , 10 ^-6 to 10 ^-5 , or 10 ^-5 to 10 ^-4 In this case, the resistance value [Ω/□] of the material to be suppressed is set to 10 ⁶ to 10 ⁴ and 2× corresponding to these ranges, respectively.
Using an electron beam of 10 ⁵ to 2×10 ³ or 3×10 ⁴ to 200, an electron beam with an accelerating voltage of 10 KV to 25 KV is deflected at a position movement frequency of 200 KHz to 20 MHz and applied to a material that reacts to the electron beam. A method for manufacturing a transfer mask, comprising the steps of: