JP2610264B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a method of manufacturing a semiconductor device using a semiconductor crystal substrate such as GaAs, and more particularly, to a technique for forming a conductive layer by ion implantation. .

(Prior Art) In manufacturing a semiconductor device, it is well known that a predetermined conductivity type layer is formed by ion-implanting impurities into a semiconductor substrate. For example, in a GaAs integrated circuit, a semi-insulating GaAs substrate is generally used, an active layer is formed by ion implantation, and a high concentration layer of source and drain is formed by ion implantation. In these methods, the demand for controllability of the ion implantation process has been increased along with the demand for higher speed and higher integration of the semiconductor device.

When a predetermined conductivity type layer is formed by ion implantation, there is a surface channeling phenomenon in which impurity atoms are implanted deeper in a specific direction in relation to the crystal structure of the substrate. In a normal semiconductor crystal substrate having, for example, a (100) plane as a main surface, axial channeling occurs due to a large crystal lattice gap when ions are implanted perpendicularly to the substrate surface. For this reason, conventionally, during ion implantation, the substrate main surface is tilted several degrees with respect to the ion implantation direction to avoid axial channeling, and a rotation angle of several degrees to several tens degrees within the substrate surface is used to avoid surface channeling. Have been.

However, in an actual ion implantation apparatus, variations in characteristics between elements cannot be eliminated only by a measure for channeling. For example, when there is a problem in adjustment of the ion beam sweep system and the ion beam current has non-uniformity on the sweep axis, the ion implantation varies.

FIG. 6 shows an example of such a variation in ion implantation, in which an impurity concentration distribution in a wafer surface is shown by a contour line pattern. The numbers indicate the variation in concentration in%. Such a problem is particularly serious in a semiconductor device having a fine circuit structure, for example, an ultra-high-speed digital IC or a high-frequency analog IC in which a MESFET is integrated and formed using a GaAs substrate.

(Problems to be Solved by the Invention) As described above, the conventional method of forming the conductive layer by the ion implantation method has a problem that there is a non-uniformity of the ion implantation that cannot be suppressed only by preventing the channeling. .

An object of the present invention is to provide a method of manufacturing a semiconductor device which solves such a problem.

[Configuration of the invention]

(Means for Solving the Problems) According to the present invention, when a predetermined conductivity type layer is formed on a semiconductor substrate by ion implantation, the substrate holder has a rotation axis coinciding with the central axis of the ion beam amplitude, In addition, a substrate having a substrate holding surface slightly inclined from a direction perpendicular to the rotation axis is used, and ion implantation is performed while holding and rotating the substrate in the holder. Here, the inclination of the substrate holding surface is preferably set in the range of 4 ° to 12 °.

(Operation) According to the method of the present invention, since the substrate surface to be ion-implanted is inclined with respect to the ion beam axis, axial channeling can be avoided. By rotating the substrate surface within the substrate holding surface by a predetermined angle, surface channeling can also be prevented. By performing ion implantation on the substrate while rotating the substrate together with the holder, even if there is non-uniformity in the ion beam itself, the influence of the non-uniformity is canceled out, and ion implantation with little variation in the substrate surface is performed.

(Example) Hereinafter, an example of the present invention will be described.

FIG. 1 shows a substrate holding state in one embodiment. The substrate holder has a rotating shaft 3 connected to a rotation driving mechanism (not shown).
And a substrate holding surface 1 inclined by a predetermined angle from a direction orthogonal to the rotation axis 3. The rotation axis 3 is set in a direction coinciding with the center axis of the ion beam 4. In this embodiment, ions were implanted into such a substrate holding surface 1 while holding a substrate 2 of a (100) main surface of a semi-insulating GaAs single crystal having a cubic unit cell.

FIG. 2 shows the inclination direction A of the substrate holding surface 1 and the GaAs substrate 2
(0) shows the relationship with the direction B of the orientation flat 5.

The state in which the direction B and the direction A coincide with each other is (0
And (2) a state in which the direction is inclined to the maximum with respect to a plane orthogonal to the rotation axis 3. By tilting the substrate 2 around the center of the substrate within the substrate holding surface 1 with this state as the origin, the angle λ
Get.

Hereinafter, the angular relationship between the substrate and the center of the ion beam will be represented using an angle and an angle λ.

FIG. 3 shows a current amount distribution of the ion beam used in this embodiment. This shows that the beam adjustment of the ion implantation apparatus is insufficient and the ion beam has a two-dimensionally uneven distribution.

Under the above conditions, Si ions were implanted into a semi-insulating GaAs substrate, an active layer was formed, and the uniformity of the ion implantation was evaluated. In addition, the angle of FIG.
The uniformity of the ion implantation was expressed in terms of the variation (ΔVp) of the pinch-off voltage (Vp) of the MESFET by taking the angle λ and the rotation of the rotating shaft 3 in FIG. Table 1 shows the results.

From the above results, by performing ion implantation in the range of 4 ° to 12 ° and λ = 30 ° while rotating the substrate, excellent ion implantation uniformity in which ΔVp is within 6% can be obtained. You can see that it is obtained.

FIG. 4 shows the concentration distribution of ion implantation for the sample 2 corresponding to FIG.

In the above, an example in which λ is fixed to 30 ° has been described.
Next, from the range of angles where this good result was obtained, =
This shows a case where ion implantation is performed similarly while changing λ from 22 ° to 30 ° with the angle fixed at 10 °. The measurement parameters were the same as in the previous measurement. Table 2 shows the results of examining the uniformity of ion implantation from the variation of ΔVp at this time.

From the above results, by performing ion implantation in the range of = 10 ° and λ = 24 ° to 28 ° and while rotating the substrate, excellent ion implantation uniformity in which ΔVp is within 2% can be obtained. You can see that it is obtained.

FIG. 5 shows the ion implantation concentration distribution for sample 2;
This is shown in correspondence with FIG.

Also in this case, the variation of Vp is concentric and 2%
Only to the extent. Accordingly, an element having similar characteristics can be formed over the entire surface of the substrate as compared with the case where only λ is specified.

In general, λ is an inclination set to avoid channeling in ion implantation, so that an appropriate angle can be selected within a target range. In setting the angle, a plurality of substrate holders having different fixed angles may be exchanged, or a substrate holder having a variable mechanism may be used. Although one substrate holder can hold a plurality of substrates, it is desirable to hold one substrate in one substrate holder in order to improve the uniformity of ion implantation. In the embodiment, an example has been described in which ions are implanted to form a predetermined conductivity type layer on a semi-insulating GaAs substrate. However, similar effects can be expected when applied to other semiconductor crystals, particularly compound semiconductor crystals. In the embodiment, the case of a GaAs substrate having a cubic (100) main surface has been described.
A substrate having (010) or (001) as the main surface may be used.
It is also possible to prepare and use a GaAs single crystal substrate having a plane inclined from, for example, about 7 ° from 0). In this case, by rotating the substrate holder at a setting of = 0 °, The same effect as that of the embodiment can be obtained.

In addition, the present invention can be variously modified and implemented without departing from the spirit thereof.

〔The invention's effect〕

As described above, according to the present invention, by holding a substrate on a substrate holder having a predetermined inclination angle and performing ion implantation while rotating the substrate, channeling can be prevented and, at the same time, unevenness in ion beam adhesion can be prevented. Even if it is, the conductivity type layer excellent in the uniformity of the ion implantation distribution can be obtained without being affected by the influence. And using this conductive type layer,
A semiconductor device having excellent element characteristics can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a substrate holder in one embodiment of the present invention, FIG. 2 is a diagram for explaining the setting of the angle of a substrate on a substrate holding surface, and FIG. 3 is ion implantation used in the embodiment. 4 and 5 show the ion implantation concentration distribution in the substrate surface according to the embodiment, and FIG. 6 shows the ion implantation concentration distribution example in the substrate surface according to the conventional method. FIG. 1 ... substrate holding surface 2 ... GaAs substrate 3 ... rotation axis 4 ... ion beam 5 ... orientation flat.

Claims (5)

(57) [Claims] 1. A method of manufacturing a semiconductor device, comprising the step of forming a layer of a predetermined conductivity type by ion implantation of impurities into a semiconductor substrate, comprising: a rotating axis coinciding with a central axis of an ion beam amplitude; To the first angle θ
Using a substrate holder having an inclined substrate holding surface, the second angle λ is provided between the direction of the inclination of the substrate holding surface by the first angle and the direction of the orientation flat of the semiconductor substrate. A method for manufacturing a semiconductor device, comprising: holding a semiconductor substrate in a substrate holder; and performing ion implantation while rotating the semiconductor substrate around the rotation axis. 2. The method according to claim 1, wherein said semiconductor substrate is a GaAs substrate. 3. The method according to claim 2, wherein said first angle θ is 4 ° to 12 °. 4. The method according to claim 2, wherein said GaAs substrate is a {100} plane substrate. 5. The direction of the orientation flat is a <001> direction of the substrate, and the second angle λ is 24
5. The method for manufacturing a semiconductor device according to claim 4, wherein the length is not less than {28}.