JPH0131660B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to improvements in electron beam annealing equipment.

[Technical background of the invention and its problems] Recently, an electron beam annealing apparatus has been developed that irradiates a sample with an electron beam and anneals the sample by scanning the beam. By annealing a semiconductor film on an insulator using this equipment, it was found that the characteristics of devices such as MOS transistors formed on the semiconductor film became close to those of devices formed on bulk semiconductors, and The usefulness of beam annealing equipment is attracting attention.

Insulators, such as _SiO2 films, are amorphous,
Polycrystalline Si deposited on this SiO ₂ film by the usual method
The crystal grain size of the film is only about a few hundred Å, and the carrier mobility of a MOS transistor formed on this polycrystalline Si film is about 10 [cm ² /ν.sec], and the leakage current is also large. . However, when the polycrystalline Si film is irradiated and scanned with a high-energy-density electron beam, the Si melts and recrystallizes as the film is scanned. Then, the crystal grain size is several thousand [Å] to several [μm],
The carrier mobility of the MOS transistor formed on this is on the order of 100 [cm ² /ν.sec]. Also,
When a Si single crystal is used as a substrate and a part of the SiO ₂ film is opened and a polycrystalline Si film is partially in contact with the substrate and deposited on the SiO ₂ film, the polycrystalline Si melted by the electron beam annealing described above first solidifies in the area in contact with the Si single crystal and grows epitaxially. Single crystallization
Proceeding to molten Si on a SiO ₂ film results in a single crystal film, and when a MOS transistor is formed on this, the device characteristics become closer to those of a device formed on a bulk semiconductor. In this way, by melting and solidifying the polycrystalline Si on the SiO ₂ film using an electron beam annealing device, it is possible to obtain crystal grains larger than the crystal grain size at the time of deposition.

However, this type of method has the following problems. In other words, although the crystal grains of polycrystalline Si grow by electron beam annealing,
Despite the fact that Si is melted at all costs, at most a few [μm]
The crystal grains remain at a certain level. In addition, some of the polycrystalline Si
Even when it is brought into contact with a Si single crystal, the part that becomes single crystal extends only about 20 [μm] from the contact area. In other words, there is a limit to the ability to improve the characteristics of a semiconductor film on an insulator, and it has been impossible to expect a significant improvement in the element characteristics of devices formed on this semiconductor film.

[Purpose of the invention]

An object of the present invention is to provide an electron beam annealing apparatus that can make a semiconductor film such as polycrystalline silicon into a film with excellent characteristics by electron beam annealing, and that can contribute to improving the element characteristics of devices formed on this semiconductor film. Our goal is to provide the following.

[Summary of the invention]

The gist of the present invention is to improve the beam shape on the sample so that the liquid phase-solid phase boundary is convex toward the liquid phase side with respect to the solid phase. That is, when a sample of polycrystalline Si or the like is subjected to electron beam annealing, the shape of the electron beam is usually circular (Gaussian distribution), so the melted portion solidifies from the outside. In other words,
It was found that crystal nuclei were generated from the edges of the melted zone, and this was a factor that hindered recrystallization. Therefore, if the resolidification of the molten zone is directed outward from the center, that is, if the liquid phase-solid phase boundary is convex toward the liquid phase side with respect to the solid phase, recrystallization and grain size increase can be achieved. It is effective for It was also confirmed that the liquid phase-solid phase boundary described above can be realized by selecting the beam shape on the sample.

Focusing on these points, the present invention provides an electron beam that focuses and accelerates an electron beam emitted from an electron emitter, irradiates the sample onto the sample, and also moves the beam and the sample relatively to anneal the sample. In the annealing apparatus, the beam shape on the sample is shaped so that it has at least one concave portion outward, and the direction of movement of the sample with respect to the shaped beam is directed toward the open side of the concave portion. It is.

Further, in the present invention, the beam intensity on the sample is controlled so that the beam intensity on the sample is stronger at the outer periphery than at the center.

〔Effect of the invention〕

According to the present invention, the liquid phase-solid phase boundary of a sample formed by electron beam annealing can be made convex toward the liquid phase side with respect to the solid phase. Therefore, when a polycrystalline Si film or the like on an insulator is used as a sample, resolidification of the melted portion occurs from the center outward. That is, since the grain boundaries included in the resolidified portion extend toward the outside of the melted portion, only a single crystal is selected, and a long single-crystal film can be obtained. That is, a semiconductor film such as polycrystalline Si can be made into a film with excellent characteristics by electron beam annealing, and it is possible to improve the element characteristics of a device formed on this semiconductor film.

[Embodiments of the invention]

FIG. 1 is a schematic configuration diagram showing an electron beam annealing apparatus according to a first embodiment of the present invention. In the figure, reference numeral 1 denotes a cathode (electron emitter) made of tungsten, and this cathode 1 is formed by cutting out a part of a cylindrical body with a diameter of 2 mm in a fan shape at 90 degrees with respect to the central axis. Further, the cathode 1 is arranged so that its central axis coincides with the optical axis of an optical system, which will be described later, and can be rotated about the optical axis. A tungsten wire 2 having a diameter of 0.5 mm is welded to the upper part of the cathode 1, and a filament 3 for heating the cathode 1 is provided around the outer periphery of the cathode 1. Further, in the figure, 4 is a Wehnelt electrode for controlling the electron beam emitted from the cathode 1, and 5 is an anode for accelerating the electron beam. An electron gun is constructed from these.

Below the electron gun, electromagnetic lenses 6 and 7 for focusing the electron beam and x- and y-direction deflection plates 8 and 9 for deflecting the electron beam are arranged, respectively. The electron beam emitted from the electron gun is focused and irradiated onto the sample surface 10 by electromagnetic lenses 6 and 7, and deflected by deflection plates 8 and 9.
It is designed to be scanned above. Here, the shape of the electron beam focused on the sample surface 10 is approximately the same as the lower end surface (radiation end surface) of the cathode 1,
As shown in Figure 2, 1/4 of the circular image is cut out into a fan shape. This shaped beam is directed toward the side of the notch of the beam (in the direction of arrow A in FIG. 2) toward the sample surface.
Scanning is performed in a direction opposite to the A direction so that 0 moves relatively. Note that although the beam on the sample surface 10 rotates due to the settings of the electromagnetic lenses 6, 7, etc., this rotation is corrected by rotating the cathode 1.

Using this device configured in this way, polycrystalline Si
When the film was annealed, the following results were obtained. First, as a sample, a single crystal Si wafer was wet oxidized to form a SiO ₂ film of 5000 [Å] thick, a polycrystalline Si film of 5000 [Å] thick was deposited on top of this by low pressure CVD, and then a low pressure CVD 1000 SiO ₂ film by method
[Å] deposited material was used. Accelerating voltage is 10
[kV], the beam current was 4 to 7 [mA], and the beam diameter on the sample was ~250° [μm]. The polycrystalline Si film was annealed under the above conditions (one beam scan), the SiO ₂ film on the surface was etched, and the crystal grain growth of the polycrystalline Si film was investigated. As a result, it was found that a single crystal thin film with a width of about 100 [μm] and a length of several [mm] was obtained.

On the other hand, when a polycrystalline Si film was annealed under the same conditions as above using a conventional device using a tungsten cylinder with a diameter of 2 mm as the cathode 1, the crystal grains were at most several μm in diameter. Ta.
This is because when scanning with a circular electron beam, the shape of the molten pool is circular, and the outer part of the molten zone solidifies faster than the center part due to linear scanning. This is because grain boundaries are generated from both sides and proceed inward. On the other hand, when the device of this embodiment is used, the center of the molten zone solidifies faster than the outside, and the grain boundaries generated from the center advance to both sides, so large crystal grains can be obtained as described above. A large single crystal thin film can be obtained.

Thus, according to the method of this embodiment, by annealing a polycrystalline Si film deposited on an insulator such as a SiO ₂ film, it is possible to increase the crystal grains and recrystallize the film, resulting in a film with excellent properties. I can do it. Therefore, it is possible to improve the device characteristics of semiconductor devices such as MOS transistors formed on this film.
Further, compared to conventional devices, the present invention can be easily realized by simply changing the shape of the cathode 1.

Figures 3a and 3b are for explaining the second embodiment; Figure 3a is a perspective view showing the cathode configuration, and Figure 3b is a schematic diagram showing the beam shape on the sample. This embodiment differs from the first embodiment described above in that the cathode 1 has a part of the cylinder cut out.
Instead, two tungsten cylinders were used. That is, the cathode 11 of the device of this embodiment has a diameter of 1.5 [mm] as shown in Fig. 3a.
It is composed of tungsten cylindrical bodies 11a and 11b. Note that these tungsten cylinder bodies 11a and 11b have a diameter of 0.5 [μm] centered on the optical axis.
They are spaced apart and arranged axially symmetrically.

With such a configuration, the shape of the electron beam irradiated onto the sample surface 10 is 2 as shown in FIG. 3b.
It is a superposition of parts of two circles. In other words, the two opposing parts of the beam are concave outward. Therefore, by scanning with an electron beam such that the sample surface 10 moves relatively toward the opening side of the recess (direction B in the figure), the same effect as in the first embodiment can be obtained.

By the way, when a polycrystalline Si film was annealed using this device, the following results were obtained. first,
As a sample, a groove with a width of 3 [μm] was formed in the <110> direction on a SiO ₂ film on a (100) Si single crystal substrate, and a polycrystalline Si film of 7000 [Å] thick was deposited on this by low-pressure CVD method. ,
Furthermore, a 1500 [Å] SiO ₂ film was deposited on top of this. Conditions such as accelerating voltage and beam current were the same as in the previous example, and the polycrystalline Si film was annealed at a scanning speed of 50 to 150 [cm/sec]. As a result, it was found that a single crystal film had grown to a length of several millimeters on the SiO ₂ film from most of the areas that were in contact with the Si single crystal in the groove. When this was done using a conventional device, the single crystal film could only extend from the groove by about 10 [μm].

FIG. 4 is a plan view showing the shape of an aperture mask for explaining the third embodiment.
The difference between this embodiment and the first embodiment is that instead of defining the shape of the cathode 1, a dumbbell-shaped aperture 12a as shown in FIG. 4 is provided between the anode 5 and the electromagnetic lens 6. This is due to the arrangement of the aperture mask 12. In this case, a tungsten cylinder similar to the conventional one was used as the cathode 1.

With such a configuration, the beam shape on the sample surface will be approximately the same as in the second embodiment. Therefore, the same effects as in the first embodiment can be obtained.

Figures 5a and 5b are for explaining the fourth embodiment; Figure 5a is a perspective view showing the cathode shape, and Figure 5b is a schematic diagram showing the beam shape on the sample surface. This embodiment differs from the first embodiment in that the cathode 1 has a cylindrical shape as shown in FIG. 5a. That is, the cathode 1 has a diameter of 0.7 mm at the axis of a tungsten cylinder with a diameter of 2 mm.
It is formed by drilling a [mm] hole.

With such a configuration, the shape of the electron beam irradiated onto the sample surface 10 will be donut-shaped as shown in FIG. 5b. In other words, the beam intensity on the sample surface 10 is stronger on the outer circumferential side than on the inner side.
When this donut-shaped beam is scanned in one direction,
Near the center of the scanning area, the initially heated area will be cooled and heated again in the beamless or sparse area at the center of the beam, and as a result, the average amount of heating will be greater on the inside than on the outside. It becomes less. Therefore, as in the first embodiment, crystal grains generated from the center grow on both sides.

Therefore, this embodiment also provides the same effects as the first embodiment. Further, since the scanning direction of the beam is not defined by the beam shape, there is no need for a rotation mechanism or the like for rotating the cathode 1, and there is an advantage that the configuration can be simplified.

Note that the present invention is not limited to the embodiments described above. For example, in the first embodiment, the electron emitter may have any shape as long as its emission end face has at least one outwardly concave portion. Furthermore, in the third embodiment, the arrangement position of the aperture mask, the shape of the aperture, etc. can be changed as appropriate according to specifications. In addition, in the fourth embodiment, the shape of the electron emitter is not necessarily limited to a cylinder, but a circular hole centered at the axis of the cylinder at an appropriate depth from the radiation end surface side as shown in FIG. 6a. It may be formed by In other words, it suffices if the radiation end face shape is donut-shaped. Furthermore, it is also possible to use, as the electron emitter, a tungsten rod 21 as shown in FIG. 6b whose outer periphery is coated with a material 22 having a high electron emissivity such as ThO ₂ . Furthermore, the material of the electron emitter is not limited to tungsten, _TiO2, etc., and can of course be changed as appropriate according to specifications. Furthermore, instead of deflecting and scanning the electron beam, the sample may be moved. Furthermore, the present invention can be applied to various semiconductor films in addition to polycrystalline Si as a sample. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an electron beam annealing apparatus according to the first embodiment of the present invention, FIG. 2 is a schematic diagram showing the beam shape for explaining the operation of the above embodiment, and FIG. 3 is a schematic diagram showing the beam shape. Figures a and b are for explaining the second embodiment, Figure 3 a is a perspective view showing the shape of the electron emitter, Figure 3 b is a schematic diagram showing the beam shape, and Figure 4 is the third embodiment. Figures 5a and 5b are for explaining the fourth embodiment, and Figure 5a is a perspective view showing the shape of the electron emitter; Figure 5b
6 is a schematic diagram showing the beam shape, and FIGS. 6a and 6b are perspective views showing the shape of the electron emitter, respectively, for explaining a modified example. DESCRIPTION OF SYMBOLS 1... Cathode (electron emitter), 2... Tungsten wire, 3... Filament, 4... Wehnelt electrode, 5... Anode, 6, 7... Electromagnetic lens, 8, 9... Deflection plate, 10... ...sample surface, 11
a, 11b...Tungsten cylindrical body, 12...Aperture mask.

Claims (1)

[Scope of Claims] 1. A means for focusing and accelerating an electron beam emitted from an electron emitter and irradiating it onto a sample, and a beam shape such that the beam shape on the sample has at least one outwardly concave portion. and means for relatively moving the sample and the beam so that the direction of movement of the sample with respect to the shaped beam is toward the open side of the recess of the beam. Electron beam annealing equipment. 2. The means for shaping the beam shape is such that the electron emitter has a radiation end face shape of at least 1.
The electron beam annealing apparatus according to claim 1, wherein an electron beam annealing apparatus is used that has a concave portion outwardly. 3. The means for shaping the beam shape uses two electron radiators having circular or polygonal radiation end faces as the electron radiators, and arranges these electron radiators symmetrically with respect to the optical axis and spaced apart from each other. An electron beam annealing apparatus according to claim 1, wherein the electron beam annealing apparatus is arranged as follows. 4. The electron beam annealing apparatus according to claim 2 or 3, wherein the electron emitter is rotatably provided around an optical axis. 5. The means for shaping the beam shape is provided with an aperture mask on the path of the electron beam that defines the shape of the beam, and the aperture shape of the aperture mask has at least one portion that is concave outward. An electron beam annealing apparatus according to claim 1, wherein the electron beam annealing apparatus is configured as follows. 6. The electron beam annealing apparatus according to claim 5, wherein the aperture mask has a dumbbell-shaped aperture. 7 means for focusing and accelerating the electron beam emitted from the electron emitter and irradiating it onto the sample; means for controlling the beam intensity on the sample so that it is stronger at the outer periphery than at the center; An electron beam annealing apparatus comprising a controlled beam and means for relatively moving a sample. 8. The electron beam annealing apparatus according to claim 7, wherein the means for controlling the beam intensity is to use a cylindrical object as the electron emitter. 9. The electron emitter according to claim 7, wherein the means for controlling the beam intensity is to use, as the electron emitter, an electron emissivity at a radiation end face of which is higher at the outer circumference than at the center. Beam annealing equipment. 10. Claim 9, wherein the electron emitter is a cylindrical first electron emitter with a second electron emitter having a higher electron emissivity applied to the outer circumference of the first electron emitter. electron beam annealing equipment.