JP4589838B2 - Ion implantation method - Google Patents

Description

  The present invention relates to an ion implantation method, and more particularly to an ion implantation method using a low energy ion beam.

  Along with the high integration of CMOS semiconductor integrated circuit devices, MOS transistor performance degradation, drain current degradation, threshold shift, and the like due to the short channel effect are becoming problems. In order to suppress the short channel effect, it is effective to form the source and drain regions shallowly. In order to form the source and drain regions shallow, it is desired to reduce the energy of the ion beam used for ion implantation.

  When ion implantation is performed with low energy, the processing time per unit implantation amount becomes longer due to the decrease in the amount of ion beam current. In order to avoid an increase in processing time, it is necessary to increase the amount of current of the low energy ion beam. When the amount of current is increased, the ion beam is likely to diverge due to the space charge effect. In order to prevent the divergence of the ion beam, a method of converging the beam by arranging an electrostatic lens in the beam line has been proposed.

  The inventors of the present application have converged a low-energy ion beam using an electrostatic lens and performed ion implantation, and found that it is insufficient for forming shallow source and drain regions.

  An object of the present invention is to provide an ion implantation method suitable for forming a shallow impurity implantation region.

According to one aspect of the invention,
Obtaining an ion beam including ions of impurities to be implanted and accelerated with an energy of 5 keV or less in acceleration energy;
Injecting the ion beam into an internal cavity of a beam line, and converging the incident ion beam with an electrostatic lens disposed in the internal cavity;
The space in the vicinity of the portion where the ion beam is converged by the electrostatic lens passes, a step of electrically neutralized,
Among the internal cavities of the beam line through which the ion beam passes, the internal cavities of the beam line are evacuated so that the degree of vacuum at the position where the electrostatic lens is arranged is higher than the degree of vacuum downstream thereof. And a process of
The ion beam that has passed through the electrically neutralized space is irradiated to a single crystal semiconductor substrate without passing through an amorphous layer made of an element constituting the semiconductor substrate, and ions are implanted into the semiconductor substrate. And an ion implantation method.

  By using an ion beam having an energy of 5 keV or less, shallow implantation can be performed. Since the ion beam is converged by the electrostatic lens, it is possible to suppress a decrease in implantation amount due to the divergence of the ion beam. Further, when a crystal substrate on which an amorphous layer is not formed is used, even if an electrostatic lens is used, it is possible to obtain an impurity distribution almost equivalent to that when not using it.

  Before describing the embodiments of the present invention, an ion implantation evaluation experiment conducted by the present inventors and the results thereof will be described.

  FIG. 1 shows a schematic diagram of an ion implantation apparatus used in an ion implantation evaluation experiment. The configuration of the ion implantation apparatus is basically the same as that of the ion implantation apparatus according to the embodiment of the present invention, and FIG. 1 is referred to in the description of the embodiment.

As shown in FIG. 1, the ion implantation apparatus includes an ion beam generator 10, a mass analyzer 20, a beam line 30, and an ion implantation chamber 40. An ion source 11 and an extraction electrode 12 are disposed inside the ion beam generator 10. The ion source 11 generates ions of impurity elements to be implanted into the substrate. Ions generated in the ion source 11 are extracted to the outside by the extraction electrode 12 to form an ion beam. The inside of the ion beam generator 10 is evacuated to about 1 × 10 ⁻³ Torr by the vacuum pump 13.

  The ion beam emitted from the ion beam generator 10 enters the mass analyzer 20. The mass analyzer 20 includes a deflecting electromagnet, extracts only ions having a desired mass and kinetic energy from an incident ion beam, and emits an ion beam having the desired kinetic energy consisting of the desired ions.

  The ion beam emitted from the mass analyzer 20 passes through the aperture 35 disposed in the vicinity of the incident end of the beam line 30 and enters the internal cavity. An electrostatic lens 31 is disposed in the internal cavity of the beam line 30. The side wall of the beam line 30 is grounded, and a negative voltage is applied to the electrostatic lens 31 by a DC voltage 32.

  The ion beam traveling in the beam line 30 is once accelerated and converged when entering the electrostatic lens 31. The ion beam converges while traveling through the electrostatic lens 31. When the converged ion beam is emitted from the electrostatic lens 31, it returns to its original energy even when it is decelerated and undergoes a diverging action. As a whole, the convergence effect is stronger, and the ion beam is converged by passing through the electrostatic lens 31.

  Plasma generating means 33 is attached to the side wall of the beam line 30 on the downstream side of the electrostatic lens 31. The plasma generating means 33 generates Ar or Xe plasma 33a and electrically connects the space near the portion through which the ion beam passes and the ground potential. Thereby, electrons stay in the space near the portion through which the ion beam passes, and this space is electrically neutralized. Electrons staying in this region are attracted to the surface of the substrate that is positively charged by the implantation of ions, thereby preventing the substrate from being charged.

The ion beam emitted from the beam line 30 enters the ion implantation chamber 40. The inside of the ion implantation chamber 40 is evacuated by a vacuum pump 41 to 1 × 10 ⁻⁵ to 1 × 10 ⁻⁴ Torr. A substrate holding mechanism 43 that holds a substrate 42 to be ion-implanted is disposed in the ion implantation chamber 40. The substrate holding mechanism 43 holds the substrate 42 so that the incident ion beam is irradiated onto the substrate 42. The substrate holding mechanism 43 holds a plurality of substrates along a certain circumference and makes a circular motion along the circumference. When the rotating substrate 42 crosses the irradiation position of the ion beam, ions are implanted into the substrate.

FIG. 5 shows an impurity concentration distribution in the depth direction when boron ions (B ⁺ ) are implanted into a silicon substrate using the ion implantation apparatus shown in FIG. The acceleration energy is 5 keV, and the dose is 1 × 10 ¹⁵ cm ⁻² . A solid line a ₅ in the figure indicates a case where a voltage of −15 keV is applied to the electrostatic lens 31 in FIG. 1, and a solid line b ₅ indicates a case where a voltage is not applied to the electrostatic lens 31. A silicon substrate having a surface layer made pre-amorphous before ion implantation was used. Pre-amorphization was performed by implanting Ge ⁺ ions under conditions of an acceleration energy of 40 keV and a dose amount of 5 × 10 ¹⁴ cm ⁻² and an acceleration energy of 80 keV and a dose amount of 1 × 10 ¹⁵ cm ⁻² .

  It can be seen that when the electrostatic lens 31 is made to function, the boron concentration in a region deeper than 50 nm is higher than when the electrostatic lens 31 is not made to function. The reason why the boron concentration in the deep region becomes high is considered as follows.

  Some of the ions once accelerated by the electrostatic lens 31 become neutral boron atoms due to the influence of the gas staying in the beam line 30. The neutral boron atoms are not decelerated when they are emitted from the electrostatic lens 31. For this reason, boron atoms having an energy higher than the desired energy are directly implanted into the substrate 42. It is considered that the boron concentration in the deep region is increased by the implantation of high-energy boron atoms.

  Next, a first embodiment for solving the above problem will be described. FIG. 1 shows a schematic diagram of an ion implantation apparatus according to a first embodiment. A vacuum pump 34 is attached to the beam line 30. The vacuum pump 34 is, for example, a turbo molecular pump. Since other configurations are the same as those of the ion implantation apparatus used in the evaluation experiment, the description thereof is omitted here.

In the case of the evaluation experiment, the pressure in the internal cavity of the beam line 30 was about 1.3 × 10 ⁻⁵ Torr, whereas in the case of the first embodiment, the pressure was 1.7. × 10 ⁻⁶ Torr. Since the degree of vacuum of the space where the electrostatic lens 30 is arranged is increased, the in-beam passing through the space is not easily affected by the gas staying in the space. For this reason, it is considered that ions are not easily neutralized electrically.

FIG. 2 shows the boron concentration distribution in the substrate depth direction when ion implantation is performed using the ion implantation apparatus according to the first embodiment. The ion implantation conditions are the same as in the evaluation experiment. A solid line a ₂ indicates a case where a voltage of −15 kV is applied to the electrostatic lens 31, and a solid line b ₂ indicates a case where the electrostatic lens 31 does not function. Compared to the case of FIG. 5, the boron concentration in a region deeper than 50 nm is reduced when the electrostatic lens 31 is functioned, and is closer to the case where the electrostatic lens 31 is not functioned. I understand.

As described above, by attaching a vacuum pump to the beam line 30 in which the electrostatic lens 31 is disposed and increasing the degree of vacuum inside the beam line 30, it is possible to perform shallow implantation using a low energy ion beam. In the first embodiment, the space in which the electrostatic lens 31 is disposed is evacuated to about 1.7 × 10 ⁻⁶ Torr, but the above effect can be achieved by reducing the pressure to 5 × 10 ⁻⁶ Torr or less. Will be obtained.

  After being decelerated after passing through the electrostatic lens 31, the kinetic energy does not change even if ions become neutral. For this reason, the degree of vacuum in the space downstream of the electrostatic lens 31 may be made worse than the degree of vacuum at the position where the electrostatic lens 31 is disposed. Therefore, it is preferable that the plasma generating means for electrically neutralizing the space in the vicinity of the ion beam is attached downstream of the position where the electrostatic lens 31 and the vacuum pump 34 are attached.

  Next, a second embodiment of the present invention will be described. In the evaluation experiment, the voltage applied to the electrostatic lens 31 is −15 kV, but in the second embodiment, it is −5.5 kV. Other conditions are the same as those in the evaluation experiment.

FIG. 3 shows a boron concentration distribution in the substrate depth direction when ion implantation is performed by the method according to the second embodiment. A solid line a ₃ in the figure indicates a case where ion implantation is performed by the method according to the second embodiment, and a solid line b ₃ indicates a case where no voltage is applied to the electrostatic lens 31. There is almost no difference in the boron concentration distribution between the two. Even if ions once accelerated by the electrostatic lens 31 become neutral atoms and are injected into the substrate with the same energy, the energy is at most about twice the desired energy, and the impurity concentration distribution is large. This is thought to be because it has no effect.

  In the second embodiment, the voltage applied to the electrostatic lens 31 is set to −5.5 kV, and the case of accelerating to about twice the initial ion beam energy of 5 keV has been described. In order not to have a large influence on the impurity concentration distribution, the energy of the ion beam once accelerated by the electrostatic lens 31 should be less than three times the energy of the ion beam before acceleration. Is preferable, and it is more preferable to make it 2.5 times or less.

  In the evaluation experiment and the first and second embodiments, the case where the surface layer of the substrate into which ions are to be implanted is preamorphized has been described. Next, a third embodiment in which pre-amorphization is not performed will be described.

  When ion implantation is performed in a shallow region using a low-energy ion beam, in order to prevent impurities from reaching a deep region due to the channeling effect, the crystal of the surface layer of the single crystal semiconductor substrate is used before ion implantation. Pre-amorphization is performed to break the structure. However, when pre-amorphization is performed, the impurity concentration distribution is easily affected by the electrostatic lens, as shown in FIG.

FIG. 4 shows the boron concentration distribution in the depth direction when boron ions are implanted into the silicon substrate without pre-amorphization. The solid line a ₄ in the figure, when a voltage is applied to the -15keV the electrostatic lens 31 shown in FIG. 1, a solid line b ₄ indicates the case where did not function electrostatic lens 31. Note that the vacuum pump 34 did not evacuate the beam line 30.

  There was no significant difference in the boron concentration distribution between when the electrostatic lens 31 was made to function and when it was not made to function. That is, when ion implantation is performed on a crystal substrate that is not preamorphized, the impurity concentration distribution is not easily affected by the electrostatic lens.

  Therefore, by irradiating the ion beam focused by the electrostatic lens to the single crystal semiconductor substrate without passing through the amorphous layer made of the elements constituting the semiconductor substrate, there is no adverse effect by the electrostatic lens. , Ion implantation can be performed. In this case, impurities are distributed to a deeper region than when pre-amorphization is performed, but since the pre-amorphization process is not performed, it is possible to improve productivity by reducing the number of processes. Note that, when ions are implanted into a shallow region, the energy of the ion beam is preferably 5 keV or less.

In the above embodiment, the case where boron ions are implanted into the silicon substrate has been described. However, a semiconductor substrate other than silicon may be used, or ions other than boron may be used. For example, a SiGe substrate or a substrate obtained by epitaxially growing a SiGe layer on the surface of the Si substrate may be used. Further, As ⁺ , P ⁺ , or BF ₂ ⁺ may be used as impurity ions to be implanted.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

It is the schematic of the ion implantation apparatus by the Example of this invention, and the ion implantation apparatus used by evaluation experiment. It is a graph which shows boron concentration distribution regarding the depth direction of a board | substrate at the time of ion-implanting by the method by a 1st Example. It is a graph which shows the boron concentration distribution regarding the depth direction of a board | substrate at the time of ion-implanting by the method by a 2nd Example. It is a graph which shows the boron concentration distribution regarding the depth direction of a board | substrate at the time of ion-implanting by the method by a 3rd Example. It is a graph which shows the boron concentration distribution regarding the depth direction of a board | substrate for demonstrating the evaluation experiment result of ion implantation.

Explanation of symbols

10 ion beam generator 11 ion source 12 extraction electrodes 13, 34, 41 vacuum pump 20 mass analyzer 30 beam line 31 electrostatic lens 32 DC power supply 33 plasma generating means 40 ion implantation chamber 42 substrate 43 substrate holding means

Claims (1)

Obtaining an ion beam including ions of impurities to be implanted and accelerated with an energy of 5 keV or less in acceleration energy;
Injecting the ion beam into an internal cavity of a beam line, and converging the incident ion beam with an electrostatic lens disposed in the internal cavity;
The space in the vicinity of the portion where the ion beam is converged by the electrostatic lens passes, a step of electrically neutralized,
Among the internal cavities of the beam line through which the ion beam passes, the internal cavities of the beam line are evacuated so that the degree of vacuum at the position where the electrostatic lens is arranged is higher than the degree of vacuum downstream thereof. And a process of
The ion beam that has passed through the electrically neutralized space is irradiated to a single crystal semiconductor substrate without passing through an amorphous layer made of an element constituting the semiconductor substrate, and ions are implanted into the semiconductor substrate. And an ion implantation method.

Images