JPH02306614A - Electron beam aligner - Google Patents

Abstract

PURPOSE:To improve uniformity and prevent aperture damage and the like by applying voltages respectively between a cathode and a cutting aperture and between the cutting aperture and an anode, which voltages have values respectively proportional to the distances and polarity to accelerate electron. CONSTITUTION:The following are provided; an LaB6 rod 11, a cathode constitut ed a graphite block 12 retaining the rod 11 and executing electric current heating, a cutting aperture 19, and an electronic gun 10 with an anode 17. The tip of the rod 11 is a plane (100 face). The peripheral. end surface of at least the rod 11 of the graphite block 12 is also a plane, and is made the same plane as the tip plane of the rod 11. Voltages are applied respectively between the cathode and the cutting aperture 19 and between the cutting aperture 19 and the anode 17, which voltages have values proportional to the respective distances (L1-L2, L2) and polarity to accelerate electron. Thereby bits colliding against the cutting aperture are reduced, uniform electric field is applied, electrons are lead out, and the maximum luminance 10<6>A/cm<2> of an LaB6 chip can be achieved.

Description

[Detailed Description of the Invention] (Summary of the Invention) Regarding an electron beam exposure apparatus that uses a beam patterned in a variable rectangle, a part of electrode wiring, etc., the diode gun is improved to be suitable for the exposure apparatus. , with the aim of providing an electron gun with high uniformity and no problems such as damage to the aperture, the electron beam generated from the electron gun is applied to the opening of an aperture for beam patterning, and passes through the opening of the aperture. In an electron beam exposure apparatus that performs drawing using an electron beam, the electron gun is equipped with a cathode, a cutting aperture, and an anode, which are composed of a rod of electron-generating material and a block that supports it and heats it with electricity. The electron emitting tip surface is finished flat and coplanar with the end surface of the block, and the opening of the cutting aperture is narrower than the tip plane of the rod (and is mounted with the centers of both aligned, so that there is no gap between the cathode and the cutting aperture). , a voltage is applied between the cutting aperture and the anode, the value of which is proportional to the respective distances, and the polarity of which accelerates electrons.

(Industrial Application Field) The present invention relates to an electron beam exposure apparatus that uses a beam patterned into a variable rectangle, the shape of a part of electrode wiring, or the like.

Electron beam exposure devices used to draw semiconductor integrated circuit patterns include: ■ Those that use a point beam, ■ Those that use a variable rectangular shaped beam, ■ Those that use a beam patterned in the shape of the stencil through a stencil mask, and ■ Blanking. Some use a dot-patterned beam passed through an aperture array, and so on. The present invention relates to an exposure apparatus using patterned electron beams as described in (1) to (4) above.

[Conventional technology]

Exposure equipment that uses a point beam uses a relatively sharp thermionic emission cathode with a curvature of about 10 μm, such as tungsten (W) used in scanning electron microscopes or lanthanum boride (LaB6). Thermionic electrons emitted from the tip are extracted by an extraction voltage applied between the cathode and anode, and a blocking potential is applied to Wehnelt to create an electron lens effect, forming a crossover near the cathode. A reduced image of is formed on the wafer using two to four stages of magnetic field or electric field lenses, and this is raster or vector scanned using an electrostatic or electromagnetic deflector to draw a pattern. Since the crossover image is a point, this method is called a point drawing method.

An electron gun for pointillism is made by sharpening the tip of a W or LaB6 rod with a curvature of about 1000 degrees, concentrating the electric field on this point to create a strong electric field of 10'V/cm or more, and collecting electrons by field emission. There are some types that can be used to draw out the .

However, it is hopeless to perform high-speed writing on a wafer using point beam type exposure. If a 1 cm" opening is drawn with a 0.01 μm beam, there will be 10" dots, so the resist sensitivity will be lO/, which is the limit for fine pattern drawing.
Ic/cI112, even though the current density is 100OA/cI11", which is the limit for field emission type, 10
It takes an exposure time of 10 seconds, and it is impossible for such an exposure apparatus to be used in a semiconductor IC manufacturing line.

In the variable rectangular beam type, the beam is irradiated onto an aperture having a first aperture, and the beam that has passed through the aperture of the aperture is imaged onto the aperture of a second aperture using an electron lens, and is deflected (usually by electrostatic deflection). ) over the aperture to change the shape and size of the beam passing through the aperture of the second aperture. 1st. The opening of the second aperture is often rectangular, but may also have a shape with 45 degree diagonal edges or a more complex shape. In short, this method has the following advantages: By changing the degree of overlap of the second apertures, a shaped beam of variable size, such as a rectangle, is obtained.

In the stencil mask type, the second aperture is a stencil mask with apertures in various patterns necessary for IC drawing, and the deflector is deflected so that any one of these apertures can be selected. Make the width larger. In IC, there are more repeated patterns,
For example, in an IC memory, identically shaped transistors, capacitors, and wiring patterns are repeated hundreds of thousands or even millions of times on a chip. The various patterns that form this repeated basic unit are arranged to form one block pattern, and a frequently used basic unit pattern is selected and used as a second block pattern. The stencil masks are arranged on an aperture plate made of a thin silicon crystal plate with a thickness of 10 μm to several tens of μm, and can be used to quickly and efficiently draw a pattern of a certain layer of a certain product.

However, stencil masks are not suitable for manufacturing other types of ICs. This is because the pattern shapes of ICs of different types do not necessarily have commonality, and one stencil mask is usually made for each layer of one type.

In the blanking aperture array type, an aperture plate in which a large number of fine openings are arranged on a plane is used at the position of the second aperture. Each of these apertures has two electrodes, one of the electrodes is at ground potential and the other is set to 0V or 5V, allowing the beam passing through the aperture to go straight or deflect, allowing the straight beam to pass through but cutting off the deflected beam. A third aperture is provided to turn on and off the beam projected onto the wafer for patterning. Since the beam pattern (mask pattern) can be changed arbitrarily by changing the voltage applied to the electrodes of each aperture, one mask is not required for each layer of each type of IC, and can be used in common.

Exposure equipment that uses patterned beams as described in ■ to It needs to be uniform, but
It is difficult to obtain such a beam.

FIG. 4 shows a conventional example of an electron gun for a beam exposure apparatus. 11
is a single-crystal LaB rod, and the tip has a curved surface with a curvature of 30 μm to 200 μm.

12 is a graphite block and LaBa rod 11
is supported and heated with electricity. 13 is its power source.

Reference numeral 15 denotes a grid, to which a negative voltage is applied by voltages ri and 16, and 17 an anode, which is connected to ground.

The cathode block 12°11 is connected to the grid by a high resistance 14 and kept negative by a so-called auto-bias. In this electron gun 10, an electric field that suppresses the electron beam acts between the cathode and the grid.
An electric field that accelerates the electron beam acts between the anodes, and a power supply 13 causes the graphite block 12 and La86
When the rod 11 is heated with electricity, electrons are emitted from the tip of the rod, and the electrons that pass through the openings in the grid are connected to the crossover 2.
1 is formed and then projected through an aperture of the anode toward a wafer (not shown). The end face of the LaB6 rod 11 may be a flat surface that protrudes from the graphite block 12.

Since this type of electron gun 10 uses LaB6, it has a high current and a long life. Even if the device is repeatedly used in a high vacuum state, and after the vacuum is broken, it is used again in a high vacuum state, there is no problem with electron emission, and therefore it is suitable for a beam exposure device. Barium oxide-impregnated cathodes used in electron guns such as cathode ray tubes cannot withstand such usage, and cannot be reused once the vacuum is broken.

However, in this electron gun IO, the beam intensity distribution is not exactly uniform. Electrons not only come from the tip of the rod 11 but also from the base (the graphite block 12 side of the rod 11)
It's also coming from. This is not without reason, since the root is closer to the heating part and has a higher temperature. However, these electrons are suppressed by the suppressing electric field between the cathode and the grid,
Therefore, the intensity distribution of the beam emitted from the rod 11 (particularly that seen through the apertures of the grid 15) is non-uniform. In this electron gun, an electrostatic lens is formed due to the electric field distribution unique to a three-pole electron gun, and the electrons are converged near the center to form a crossover 21, which changes the angular distribution of the irradiation of the electrons that have passed through the crossover. It has a Gaussian distribution expressed by the following equation.

f −exp (−θ2/A) where θ is an angular parameter and A is a constant. Usually, in a variable rectangular beam type exposure apparatus, uniformity of 5% or more is required within the rectangular beam, and if such conditions are imposed, only about 2% of the beam (total emitted current) can be used.

In the future, uniformity of 5% will be unsatisfactory in order to expose even finer patterns, and therefore it will be necessary to further increase the uniformity, which will further narrow the range of use. Although the uniformity is slightly improved by making the rod end surface flat, there is not a significant difference in quality.

The fact that only a small portion of the emitted current is utilized means that
This means that the total emission current needs to be increased inversely proportionally, which poses problems such as power loss and wear and tear on various parts. L
aB, consumption of the rod tip, dissolution of the first rectangular forming aperture, etc.

Typically, the first rectangular shaped aperture is made from a silicon wafer. In the case of silicon, rectangular openings can be made with high precision by exposing the <111> plane using anisotropic alkaline etching on a <100> substrate, but if the total emission current is 30 KV and 700 μA to 1 mA, there is a risk of melting. The sex is coming out.

Tungsten (W), tantalum (Ta), molybdenum (
When the second aperture is formed with a high melting point metal such as MO),
Although it is resistant to melting, the accuracy of the rectangular opening remains unsatisfactory.

To solve such damage and wear problems, it is necessary to reduce the current emitted from the cathode. If the emission current is larger than the current passing through the rectangular aperture, the wasted electron flow will gather at the crossover, causing the electrons to repel each other.
Because of the scattering, the energy distribution of the beam is broadened. When the energy distribution becomes wider, the chromatic aberration caused by the electron lens on the wafer surface increases, making it impossible to obtain a sharp beam and making it impossible to expose fine patterns.

LaB, the temperature of the rod is 1500°C-1600°C
However, during use, LaB near the surface evaporates and the <100> crystal plane becomes exposed, resulting in a change in shape and a change in the intensity and distribution of the emission current. However, the lifespan is not very long (1000 to 2000 hours).The situation is much the same with LaB rods with flat tips: the uniformity of the beam intensity is not sufficient, and there is a high risk of melting the second aperture. As the root also wears out, it gradually becomes thinner and the tip area becomes smaller, so the electron beam irradiation characteristics change.

There is a type of electron gun called a diode gun, which is widely used in the television field. The diode gun has a cathode 18, a cutting aperture 19, and an anode 17 as shown in FIG.
(2) Since the aperture is set at +20V and the anode is set at +300V, both accelerate the thermionic electrons emitted from the cathode. The beam 20 is as shown, with no crossovers, no particular broadening of the energy distribution, and a high degree of uniformity. However, diode guns used in televisions have barium oxide impregnated cathodes, have low apertures and low anode voltages, and cannot be used for electron beam exposure.

[Problem to be solved by the invention]

As described above, although conventional electron guns using LaB6 are suitable for point beam type exposure equipment, patterned beam type exposure equipment has problems such as insufficient uniformity, wear and tear of the cathode and aperture, etc. be. Furthermore, diode guns for television cannot be used in exposure equipment.

However, diode guns are attracting attention as electron guns for patterned beam exposure equipment because of their high uniformity.

The purpose of this study is to improve the diode gun so that it is suitable for exposure equipment, and to provide an electron gun with high uniformity and no problems such as aperture damage. be.

[Means to solve the problem]

As shown in FIG. 1, in the present invention, an electron gun 10 is provided with a cathode composed of a LaB rod 11 and a graphite block 12 that supports and heats the rod, a cutting aperture 19, and an anode 17.

The end surface of the rod 11 is a plane (100 plane), and the end surface of the graphite block 12 at least around the rod 11 is also a plane and the same plane as the end surface of the rod 11. The diameter of the rod 11 is 100 μm to 500 μm.

The opening of the cutting aperture 19 is narrower than the tip plane of the rod 11, and is arranged so as to be located in the middle of the tip plane. The aperture of the anode 17 is made wider than the cross section of the beam so that the beam 20 passes through the center of the aperture without colliding with the anode, and the anode is installed with the aperture 15 and the beam center aligned.

The anode 17 is at a ground potential, the cathode is at a negative potential v1, for example -30KV, and the potential ■2 of the aperture 19 is ■2.
=v1·L, /L2. This is a uniform electric field condition, whereby the potential lines run equidistantly from the cathode to the anode, parallel to the anode, etc., and the electric field runs at right angles thereto, so that the beam 20 becomes a parallel beam as shown.

The voltage between the aperture 19 and the cathode is preferably IOV to IKV, and the amount of heating heat due to the electron flow incident on the aperture 19 is preferably less than IOW.

Further, it is preferable that the portion of the beam passing through the opening of the aperture 19 that is incident on the rectangular forming aperture is 80% or less.

[Function] In the electron gun having this configuration, the electron beam 20 has high uniformity (the beam intensity at each point in the cross section of the electron beam is uniform). This is because: (1) if the tip end surface of the LaB60 rod 11 is flat, (2) the end surface of the graphite block 12 for support and heating is also flat and the same plane as the tip end surface of the rod 11, so there is no edge effect, and (2) the electric field It depends on the fact that all of the fields are accelerating electric fields, parallel, and uniform.

Since electron emission is carried out by the LaB60 tube 11, a large current can be obtained and there is no problem in reusing it after breaking the vacuum. Since the tip surface from which electrons are emitted is flat and the electric field is uniform, even if the tip surface is worn out during use, there is no particular effect on electron emission.

The beam 20 is a parallel beam, and if it is shaped into a required rectangle by the aperture 19, the rectangular aperture 2
2, the area to be cut is reduced (I would like to make it zero, but it is difficult to make it zero considering the misalignment of each element of the exposure device), so the rectangular aperture 22 is heated and damaged. can be reduced. 23 is the aperture 22
2 shows the intensity distribution of the beam 20 at .

The cutting aperture 19 sends electrons emitted from the surface of the rod 11 corresponding to the opening to the anode side through the aperture, but electrons emitted from the surface of the rod 11 corresponding to the plate portion around the opening are attracted to the plate portion. However, this electron flow heats the aperture 19. At this point, aperture 1
It is best to make the aperture 9 the same size as the end face of the rod 11 (if it is made larger, there will be problems with beam intensity and uniformity), but if positional deviation is taken into consideration, making it the same size is a problem, so it has to be made slightly smaller. I don't get it. Therefore, the electron flow from the rod 11 to the aperture 19 is unavoidable, but the distance between this (LI
Since L2) is small and the electric field is not so strong, the electron collision energy is small and the problem of overheating of the aperture 19 is not serious.

〔Example〕

With the electron gun in Figure 1, L+=10mm, LI-Lz=100
μm, Vt = 30KV, therefore V2-V, = +30
0V, the tip surface of the LaBb rod is a <100> plane and the area is 300μmφ, the current density of LaB6 is 10A
/am2, the total emission current will be about 7 mA. Aperture 1
The energy applied to the aperture 9 is 2W, the aperture diameter of the aperture 19 is lOOμmφ, and the current passing through the aperture is 700μA. The toughness β is J・V,/ΔE, ΔE=0.3 e
When V, V+ = 30KV, β = lO6A/Ω2. Brightness 106A/cm” is the conventional round head L
3X1 at 20-30KV, the value obtained with the aB6 electron gun
It is considerably larger than 05A/mark 2.

If LaBa is made too thin, it may easily cause a breakage accident during polishing (
, Therefore, it is difficult to manufacture one with a diameter of 300 μm or less. Furthermore, the distance between the cathode and the aperture of 100 .mu.m is close to the limit, and if the cathode and the aperture are made closer than this, contact and discharge accidents are likely to occur due to thermal expansion when the cathode is heated.

The opening of the cutting aperture 19 is LaB.

If it is made significantly smaller than the end face of the rod 11, the uniformity of the beam will be better, but more electrons will enter the aperture and overheating will become a problem. For example, when I made a 1000μmΦ one (made of Ta) and operated it instead of the 300μmΦ one mentioned above, the aperture current reached 70mA, the final energy reached 21W, and the Ta-made, 50μm thick aperture melted. .

FIG. 2 shows the electron gun of the present invention in a concrete form.

As in all figures, the same parts are given the same reference numerals. 25.26 is a support pillar, Mo.

It is made of Ta and supports the graphite block 12,
Supply current to this. Reference numeral 27 is a support member that mechanically connects the support columns 25 and 26, and is made of ceramic (A2□03). (b) is an end view of the cathode portion of (a). 19
a is the opening of the aperture 19;

To attach the LaB60 rod 11 to the graphite block 12, make a hole in the block 12, insert the rod 11 of the same diameter into it, cut off the unnecessary part of the rod 11,
A method is used in which the end face is polished together with the end face of the block 12 to make the same plane, but the graphite block 12
Even if the hole to be drilled is shallow (in this case, the hole to be drilled into the rod 1
The length of 1 may be shortened) or deeper or even penetrated. FIGS. 3(a) and 3(b) show an example of the latter. 12a
is a through hole drilled into the block 12, which has a length of 1 m.
Insert the mLaB60 screw 11 as shown in the same figure (b).

Another good method is to split the graphite block in two. An example of this is shown in FIG. 3(C). After drilling the hole in the block 11, the block 12 is split into two and the LaB and rod 11 are held between the wire holes. Note that the hole may be formed in the form of a groove after dividing into two. The heating of LaB60 11 is
Generally, the graphite block 12 is heated by applying electricity, and the heat is transferred to the LaB rod to heat the rod 11. The same is true in FIG. 3(C), and when the contact resistance of the two-split block 12.12 is large, current flows through the rod 11, but this has almost no heating effect on the rod 11.

La860 tube is IOA/cm from the tip at 1550'C
2 current flows. The total current from the cathode is 7 mA, and electrons exit from the tip at a current density of 10 A/cTII2. The total current coming out of the cathode is less than 70mA, and the power consumption of the cutting aperture is 2. IW does not dissolve at this level.

The beam exiting the 50 μm hole in aperture 19 is 70 μA
Then, the brightness was 10'A/cm'', and the first silicon rectangle forming aperture was irradiated.

The uniformity of this beam is 98% even at a distance of 25 μm from the center.
%, and the beam intensity distribution is rectangular. Therefore, a rectangular beam of about 30 μm can be formed with an aperture opening of 25 μm. The amount cut by the silicon aperture is 40 μA, and 1.2 W of heat is generated at an accelerating voltage of 30 KV, which does not melt the silicon.

If a magnetic field lens is placed in the space up to the anode and a 4x image of the cutting aperture is created on the first rectangular forming aperture, the 100 μm silicon aperture can be uniformly irradiated.

When the electron gun of the present invention is used in a blanking aperture array type exposure apparatus, a current density of 100 A/cm'',
Minimum pattern size of 0.02μm, 10μc/cm”
Using this resist, 1120 areas can be exposed in 1.3 seconds with any pattern rule. Therefore lG
B) DRAM (minimum pattern 70.1am) 8-inch wafer can be exposed within 5 minutes.

〔Effect of the invention〕

As explained above, in the present invention, 1) the number of bits hitting the cutting aperture is reduced, and 2) a uniform electric field is applied to draw out electrons to achieve the maximum brightness LO of the La86 chip.
6A/cmz can be achieved, ■ A relatively small amount of current is taken out into the drift space, so energy dispersion due to electron-electron interaction is suppressed, ■ Dissolution of the first rectangular aperture is suppressed, and ■ The rectangular shape is This has the effect of increasing the uniformity and edge sharpness of the beam, and making it possible to expose ultra-large scale LSIs with a fine beam.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is a detailed explanatory diagram of the invention, Fig. 3 is an explanatory diagram of the method for attaching the rod 11 to the block 12, and Figs. 4 and 5 are conventional illustrations. It is an explanatory diagram of an example. In FIG. 1, 11 is a rod of electron-generating material, 12 is a supporting current heating block, 19 is a cutting aperture, 17 is an anode, and 22 is a rectangular forming aperture. 10: It sub-gun Ll Explanation of the principle of the present invention Lot l to block 12! The installation method is shown in the 3rd explanatory diagram.
figure

Claims (1)

[Claims] 1. An electron beam exposure apparatus that applies an electron beam generated from an electron gun to an aperture opening for beam patterning and performs drawing using the electron beam that passes through the aperture opening. The electron gun consists of a rod (11) of electron-generating material and a block (12) that supports it and heats it with electricity.
) consisting of a cathode and a cutting aperture (19)
, and an anode (17), the electron-emitting tip surface of the rod is finished flat and flush with the end surface of the block, the opening of the cutting aperture is narrower than the tip plane of the rod, and the center of both The distances (L_1-L_2,
An electron beam exposure apparatus characterized in that a voltage having a value proportional to L_2) and a polarity that accelerates electrons is applied.