JPH06196121A - Ion implanting method - Google Patents

Abstract

PURPOSE:To provide an ion implanting method capable of realizing a high vacuum state in a vacuum chamber. CONSTITUTION:An ion source 12 produces an ion beam 20 from material gas composed of phosphine including phosphorus as dopant substance and phosphine- diluting argon. A pump 21 removes electrically neutral substance in argon. Since phosphine-diluting gas is argon, the gas is heavy due to its high molecular weight. Consequently, it is possible to sufficiently remove the diluting gas by degassing so as to realize a high vacuum state in a vacuum chamber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion implantation method, and more particularly to an ion implantation method used for manufacturing semiconductor devices.

[0002]

2. Description of the Related Art In an ion implantation method widely used for manufacturing semiconductor devices, generally, monovalent positive ions are accelerated to high energy to implant impurities into an object to be irradiated such as a silicon wafer. 200 KV of monovalent ion commercially
Ion implanters that can accelerate to such an extent are widely used. On the other hand, when manufacturing a semiconductor device, it is sometimes necessary to perform ion implantation with an energy of 200 KV or more and about 400 KV or less.

In such a case, a monovalent ion is 2
An ion implanter having an accelerating voltage of 00KV to 400KV is required. However, the acceleration voltage is 200KV
Ion implanters of a certain size or higher require a special consideration for high-voltage insulation, and have a drawback that the implanter becomes large and expensive.

In order to solve such a drawback, there is a method of using divalent ions in an ion implanter having a maximum acceleration voltage of 200 KV. That is, if the valence of the ions is q and the acceleration voltage is V, the energy E of the ions at the time of ion implantation
Is given by E = qV, so if q = 2 doubly charged ions are used, the maximum acceleration voltage V is 200 KV and maximum 400
Ion implantation with KV energy is possible. Such an ion implantation method has an advantage that it does not require a device cost, but has a problem that not only divalent ions but also unnecessary monovalent ions are mixed in a considerable amount. Hereinafter, this problem will be described with reference to the drawings by using an example of P ⁺⁺ (divalent ion of phosphorus). FIG. 3 is a diagram schematically showing a general ion implantation apparatus.

The material gas is supplied from a cylinder 10 through a flow controller 11 to an ion source 12 for ionization. In order to generate P ⁺⁺ ions, the material gas is phosphine (PH ₃ ) diluted with hydrogen (H ₂ ) approximately in the range indicated by PH ₃ : H ₂ = 15-20%: 85-80%. Is often used.

In the ion source 12, in addition to P ⁺⁺ ions, P
⁺ Ion (monovalent ion of phosphorus), P ₂ ⁺ Ions (monovalent ions of phosphorus molecules) are also generated, but P ⁺ The ions are identified by the mass spectrometer 13 and P ⁺ Since the ions cannot pass through the mass analysis slit 14, they are not injected into the wafer 15. On the other hand, P ₂ ⁺ The ions take the same orbit in the mass spectrometer 12 as the P ^{+ +} ions, so they can pass through the slit 14. However, a positive high voltage is applied to the vicinity of the slit 14 to set the electrostatic potential to P ₂ ^+. By making it larger than the kinetic energy of the ions, P ₂ ⁺ Ions can be repelled, and wafer 15 has P ⁺ It is not implanted like ions. In addition, P ₂ ⁺ A method of repelling ions is called a beam filter method and is disclosed in the following document. REKaim et al. "Solid State Technology" April
1989, p65. R. Simonton et al. "Nucl.Instr.and.Meth.B37 / 38" 1
989, p616. According to the above implantation method, the P generated by the ion source 12 is
⁺ Ion and P ₂ ⁺ Ions can be excluded theoretically.

However, the P ⁺⁺ ions are in the slit 1
There is a phenomenon that it is converted into monovalent in the process from passing through 4 to being injected into the wafer 15. This divalent P ⁺⁺ ions, by get electrons from the residual gas 16 in the neutral area indicated by reference numeral A and B, monovalent P ⁺ It is a phenomenon that it is converted into ions. The chemical reaction formula of the above phenomenon is as follows. P ⁺⁺ + A ^o → P ⁺ + A ⁺ … (1)

In equation (1), A ^o Is residual neutral gas 16
Is. As the residual neutral gas 16, it is considered that most of the material gases supplied to the ion source 12 reach the regions A and B without hydrogen (H ₂ ) being ionized.

P ⁺ converted to monovalent by the reaction represented by the formula (1) The ions pass through the acceleration tube 17 and the ion beam scanning system 18 in the same manner as the divalent P ^{+ +} ions, and the wafer 15
Will be injected into. This one price P ⁺ Ions can amount to about 10% of the regular divalent ions in terms of the number of elements. Also, this monovalent P ⁺ Ions have different energies depending on where the reaction represented by the formula (1) has occurred. For example, what happened in region B has the same energy as doubly charged P ⁺⁺ ions, but what happened in region A has a lower final energy than ^doubly charged P ⁺⁺ ions, and so on. Thus, one-value P ⁺
Since the energy of ions varies, the problem of energy contamination such as increase of dose in-plane non-uniformity of ion-implanted wafer, fluctuation of junction depth, and dose measurement. Cause Energy and contamination
The problem of application is disclosed in the following documents. K. Bvack et al. "Nucl.Instr.and.Meth.B21" 1987,
p405.

[0010]

In order to solve the above problems, a turbo molecular pump or a cryopump is newly installed in the area A or the area B to lower the pressure,
The probability of occurrence of the reaction represented by the equation (1) is lowered to reduce the divalent P
⁺⁺ A method of reducing the conversion amount of ions into monovalent ions is being considered.

However, the material mixed gas (PH ₃ + H
_{In 2} ), since it contains hydrogen molecules (H ₂ ) having a small molecular weight and a small pumping speed, it is difficult to create a high vacuum state. In order to create a high vacuum state, the turbo molecular pump or cryopump must be made larger and have higher performance.
There is a problem. The present invention has been made in view of the above points, and an object thereof is to provide an ion implantation method capable of bringing a vacuum chamber into a high vacuum state.

[0012]

The ion implantation method according to the present invention comprises a step of producing an ion beam from a material comprising a compound containing a dopant substance and a diluent for diluting the compound, and a diluent. Among these, a step of removing electrically neutral ones from the vacuum chamber by degassing is provided, and the diluent is a rare gas.

[0013]

According to the above-mentioned ion implantation method, since the diluent is a rare gas, the molecular weight is large and heavy as compared with, for example, hydrogen. Therefore, the diluent can be sufficiently removed by degassing, and the vacuum chamber can be brought to a high vacuum state.

Furthermore, if the inside of the vacuum chamber is set to a high vacuum state, it is possible to reduce the probability of collision between the ion beam containing divalent ions and the diluent when the divalent ions are implanted. Therefore, the probability that divalent ions are converted to monovalent ions is reduced, and an ion beam containing divalent ions at a high rate can be obtained.

[0015]

EXAMPLES The present invention will be described below with reference to examples.
FIG. 1 is a diagram schematically showing the configuration of an ion implantation apparatus used in an embodiment of the present invention. An embodiment of the ion implantation method will be described with reference to FIG.

As shown in FIG. 1, the material gas is a cylinder 10
Is supplied to the ion source 12 through the flow controller 11 and is ionized by the ion source 12. The material gas used in this example is phosphine (PH ₃ ) diluted with argon (Ar). Phosphine is a compound containing phosphorus (P) which is a dopant element.
The ratio of phosphine to argon is PH ₃ : Ar = 15.
%: 85% The diluent gas is selected from gases that do not react with hydrogen (H) contained in phosphine. The diluent gas is preferably selected from inert gases, especially rare gases. In the ion source 12, in addition to the P ⁺⁺ ions (phosphorus divalent ions), P ⁺ Ion (monovalent ion of phosphorus), P ₂
⁺ Ions (monovalent ions of phosphorus molecule) are generated. The ion beam 20 is filtered by the following method in order to extract only divalent P ⁺⁺ ions effective for implantation from the mixed atmosphere. First, P ⁺ Ions are P ⁺⁺ ions and P ₂ ⁺ Since the mass is different from that of the ions, they are identified by the mass analyzer 13. That is, P ⁺ Ions cannot pass through the mass analysis slit 14. This gives P
⁺ Ions are eliminated. Next, a positive high voltage is applied to the vicinity of the slit 14 to change the electrostatic potential of P ⁺⁺ ions to P ₂ ^+.
It is made larger than the kinetic energy of ions. This allows
P ₂ ⁺ near the slit 14 Ions are repelled and P ₂ ⁺
Ions are eliminated.

When performing such a series of processes, the vacuum chamber is degassed by a pump 21 such as a turbo molecular pump or a cryopump to sufficiently lower the pressure. Particularly, the pressure in the vicinity of the inlet of the acceleration tube 17 shown in the region A is sufficiently lowered. At this time, argon has a large molecular weight as compared with hydrogen and has a high evacuation speed, so that it is sufficiently sucked and eliminated. Therefore, including the P ⁺⁺ ions ion beam - with the probability of collision between the arm 20 and the diluent gas as compared to the hydrogen can be sufficiently low, P ⁺⁺ ions P ⁺ The probability of conversion to ions is reduced.

The ion beam 20 thus obtained
Is P ⁺ The amount of mixed ions becomes small, and P ⁺⁺ ions are contained in a high proportion. The ion beam 20 is injected into the wafer 15 via the ion beam scanning system 18.

In the above divalent ion implantation method, the diluent gas is selected from substances that do not react with hydrogen contained in phosphine. In the above embodiment, argon, which is one of the rare gases, is selected. Argon has a larger molecular weight than hydrogen used as a diluting gas, and is easily sucked by the pump 21. Therefore, a high vacuum state can be created. Also, if a high vacuum state is created,
The reaction described by the equation (1) is reduced as compared with the case where the material gas diluted with hydrogen is used. Therefore, a highly pure divalent ion beam containing a very small amount of monovalent ions can be produced.

In addition to argon, rare gases such as helium (He), neon (Ne), krypton (Kr), and xenon (Xe) may be selected as the diluent gas. Since none of these substances reacts with hydrogen contained in phosphine and has a larger molecular weight than hydrogen used as a diluent gas in the past, it is easily sucked by the pump 21. Therefore, it is possible to obtain the same effect as that of the above-mentioned embodiment using argon as the diluent gas.

In addition to phosphine, arsine (AsH ₃ ) or stibine (SbH ₃ ) can be used as the compound containing the dopant element. Arsine contains arsenic (As) as a dopant element, and stibine contains antimony (Sb) as a dopant element. Like a phosphine, arsine and stibine are each a substance in which a dopant element and hydrogen are combined, and hydrogen has been conventionally used as a diluent gas. This diluent gas is mixed with helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (X).
By using a rare gas such as e), it is possible to obtain the same effect as that of the above-mentioned one embodiment.

FIG. 2 is a diagram showing the effect of the above-mentioned embodiment, and particularly shows the effect of extracting divalent ions. In FIG. 2, the number of mixed monovalent ions for each sample of the material gas is shown by a ratio. 2, sample A in which phosphine was diluted with hydrogen, sample B in which phosphine was diluted with argon (one example), sample C in which phosphine was used alone, and sample D in which material gas was generated from solid phosphorus Each one is shown.

As shown in FIG. 2, the number of monovalent ions mixed in the sample B according to the present invention is lower than the number of monovalent ions mixed in the sample A, which is almost equal to the undiluted sample C or sample D. Is the number of From this result, it can be judged that the ion implantation method according to the present invention can obtain a high vacuum state, reduce the collision between the ion beam and the neutral gas, and reduce the number of monovalent ions mixed.

The advantage of the present invention (Sample B) over Samples C and D is that, firstly, Sample B contains phosphine with argon as compared with Sample C containing only phosphine which is self-combustible and combustible. It is safe because it is diluted to a low concentration. Secondly, sample D using solid phosphorus requires heating time for heating up to 400 ° C. with a heater and setup time such as cooling time after ion implantation. Since no setup time is required, the operating rate of the ion implantation apparatus can be increased.

[0025]

As described above, according to the present invention, it is possible to provide an ion implantation method capable of bringing a vacuum chamber into a high vacuum state.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an ion implantation apparatus used in an embodiment of the present invention.

FIG. 2 is a diagram showing an effect of an embodiment of the present invention.

FIG. 3 is a diagram schematically showing a general ion implantation apparatus.

[Explanation of symbols]

12 ... Ion source, 13 ... Mass spectrometer, 14 ... Analysis slit, 15 ... Wafer, 17 ... Accelerator tube, 18 ... Ion beam
Scanning system, 20 ... Ion beam, 21 ... Pump.

Claims (3)

[Claims] 1. A step of producing an ion beam from a material comprising a compound containing a dopant substance and a diluent for diluting the compound, and degassing an electrically neutral one of the diluents. And a step of removing it from the vacuum chamber by means of a step of removing the diluent from the vacuum chamber, wherein the diluent is a rare gas. 2. A step of producing an ion beam from a material comprising a compound containing a dopant substance and a diluent for diluting the compound, and degassing an electrically neutral one of the diluent. A step of removing monovalent ions of the dopant substance from the ion beam; a step of removing monovalent ions of the dopant substance molecule from the ion beam; A step of extracting divalent ions of the dopant substance from an ion beam and injecting the divalent ions into an object to be irradiated, wherein the diluent is a rare gas. 3. The compound is selected from one of phosphine, arsine, and stibine, and the diluent is selected from one of helium, neon, argon, krypton, and xenon. The ion implantation method according to claim 1 or claim 2.