JPH01155619A - Electron flood system - Google Patents

Abstract

PURPOSE:To prevent the accumulation of the quantity of excessive electron beam as well as to bring the application voltage to dielectric withstand voltage or less by a method wherein a retaining part is grounded through a capacitor, and the dielectric capacitance of the capacitor is selected at a specific value. CONSTITUTION:Ionized impurities are accelerated into high energy and implanted into the semiconductor substrate 6 which is retained by a grounded retaining part 11 and a capacitor is formed thereon. A secondary electron is generated by the irradiation of the electron beam generated by an electron beam generating part 2, and the secondary electron generating part 4 with which the secondary electron will be projected is provided. At that time, the retaining part 11 is grounded through the intermediary of a capacitor 15. The dielectric capacitance CX of the capacitor 15 is CX< C0.VB.(Vmax-VS)<-1>. C0 is the dielectric capacitance of the capacitor 15 formed on the substrate 6, and VB is the withstand voltage of the insulating material in the substrate 6, and e.Vmax (e is the primary quantity of electric charge) is the maximum energy viewed from the retaining part 11 of the secondary electron. As a result, the accumulation of excessive quantity of electron beam can be prevented, and the applied voltage can be brought to the dielectric withstand voltage or less.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is used to prevent charging of a semiconductor substrate caused by ion beam irradiation in ion implantation technology used in the manufacture of semiconductor devices, etc. This invention relates to an electron flood system that irradiates a semiconductor substrate with an electron beam.

(Prior Art) Ion implantation technology is a technology for adding impurities to a semiconductor substrate, has good controllability of the amount of added impurities, and is widely used in manufacturing semiconductor devices. This ion implantation technique is performed by creating a plasma state in an ion source, usually called an ion source, extracting positive ions from the ion source, accelerating them, and irradiating the semiconductor substrate on which the semiconductor element is to be formed with the positive ions. It will be done.

On the other hand, an insulator formed by S102 or the like is present in a semiconductor substrate, and a positive ion beam consisting of desired impurity ions is irradiated onto the semiconductor substrate with such an insulator formed using ion implantation technology. The need often arises.

In such a case, positive charges of positive ions brought to the semiconductor substrate by the ion beam accumulate on the insulator, and electrical stress is applied to the insulator. If the amount of charge accumulated in the insulator increases and the voltage applied to the insulator exceeds the withstand voltage of the insulator, the insulator will suffer electrostatic breakdown. When such electrostatic breakdown occurs, the insulator cannot be repaired, and therefore loses its original function, causing a serious problem in that it leads to failure of the semiconductor device.

For this reason, in recent years, in ion implantation technology, the semiconductor substrate is irradiated with an electron beam during ion implantation, and the static charge is alleviated or canceled by the negative charge of the electrons. Generally, electron flood or electron It's called a shower.

Figure 4 shows a conventional electron flood system.

This electron flood system is used in an ion implantation device that irradiates an ion beam 13 onto a semiconductor substrate 6 held in a holder 1 provided in an ion beam irradiation chamber 12, and heats a filament 2a of a thermionic generation section 2. Thermionic electrons 3 are generated, and these thermionic electrons 3 are accelerated with energy E (usually 200 to 500 eV) and irradiated to the secondary electron beam generating section 4 to generate a secondary electron beam 5. The holder 1 is made of a conductor and has a conductor wire 14b.
It is grounded to earth 17 via. In addition, the semiconductor substrate 6
In order to form a capacitor, an insulating film 6a is formed on this.
A conductive film 6b is further formed on this insulating film 6a. The semiconductor substrate 6 on which such a capacitor is formed is irradiated with secondary electrons 5 to cancel out the positive charges accumulated in the capacitor made of the insulating film 6a and the conductive M6b. Note that the secondary electron beam generating section 4 is grounded to the earth 17 via a conducting wire 14b.

(Problems to be Solved by the Invention) The energy distribution of the secondary electron beam 5 obtained by the above-mentioned electron flood system has the characteristics shown in FIG. In Figure 5, the horizontal axis shows the electron energy (e
V) and the number of electrons is plotted on the vertical axis. The energy of the secondary electron beam 5 is distributed in a range from zero to the energy E given to the thermoelectron 3. And 5 (e
There are peaks near V) and E (eV), respectively. When the semiconductor substrate is irradiated with the secondary electron beam 5 having such energy distribution, the insulator film 6a becomes -E
A voltage up to (V) will be applied. In recent semiconductor devices, oxide films made of SiO2 with a thickness of 200A or less are used, and a voltage of about 30V or more is applied to such an oxide film with a thickness of 200A or less. Electrostatic damage occurs, and defects occur due to excessive electron dose. This phenomenon is generally called overflood, and the energy of the secondary electron beam 5 used to cancel positive charges is transferred to the conductor 6b formed on the semiconductor substrate 6.
This is due to the fact that the potential energy of That is, when the energy of the secondary electron beam 5 is larger than the potential energy of the conductor 6b on the semiconductor substrate 6, the secondary electron beam 5 reaches the semiconductor substrate 6 and is applied to the insulator 6a on the semiconductor substrate 6. Voltage increases. When this applied voltage exceeds the withstand voltage of the insulator 6a, electrostatic breakdown occurs.

Further, electrons having energy around E shown in FIG. 5 are those that have been accelerated and backscattered. As can be seen from the characteristic graph shown in FIG. There is an electron beam with an energy of 30 eV or more, which causes overflooding. Furthermore, it is quite difficult to appropriately control the amount of electron beam irradiation to prevent this overflooding due to problems such as the properties of the ion beam 13 and the semiconductor substrate 6, and the stability of the filament 2a of the thermionic generation section 2. .

The present invention provides an electron flood system that can prevent excessive electron beams from accumulating on a semiconductor substrate and prevent the voltage caused by the electron beam applied to the semiconductor substrate from exceeding a set voltage that is lower than the dielectric withstand voltage. The purpose is to

[Structure of the invention]

(Means for Solving the Problems) The present invention is used in an ion implantation device that accelerates and implants ionized impurities into a semiconductor substrate on which a capacitor is formed, which is held by a grounded holding part, and which emits electrons. An electron beam generating section that generates a beam, and a secondary electron generating section that generates secondary electrons by irradiation with the electron beam generated by the electron beam generating section and irradiates the semiconductor substrate with the secondary electrons. In an electron flood system, the holding part is grounded via a capacitor, and the capacitance MC of this capacitor is defined as C, the capacitance of the capacitor formed on the semiconductor substrate, VB, and 2, the withstand voltage of the insulator in the semiconductor substrate. When the maximum energy of the next electron seen from the holding part is e*V (e is the charge element), +1ax C<C*V-(v -v)-'tonal function x
It is characterized by satisfying the following requirements.

(Function) In the electron flood system according to the present invention configured as described above, the holding part is grounded via a capacitor, and the capacitance C of this capacitor is set to a predetermined value c - v.
-(v -v)'woX OB
Select so that it does not exceed max B. Then,
Even if the semiconductor substrate is irradiated with an excessive amount of electron beam, the potential energy of the conductor on the semiconductor substrate is larger than the maximum energy of secondary electrons e−■11a
X, the excess secondary electrons do not reach the semiconductor substrate,
It is possible to prevent excessive accumulation of electron beams, and also to prevent the voltage applied to the semiconductor substrate from exceeding a set voltage that is lower than the dielectric strength voltage.

(Example) FIG. 1 shows an example of an electron flood system according to the present invention. In the electron flood system of this embodiment, a capacitor 5 is newly provided between the holder 1 and the ground 17 of the conventional electron flood system shown in FIG. Descriptions of the components other than the capacitor 5 will be omitted since they will be explained in the prior art section. Here, when the holder 1 is a conductor, the capacitance EiC of the capacitor 5 needs to be as shown below. Now, the capacitance of the capacitor formed from the insulator film 6a and the conductor film 6b of the semiconductor substrate 6 held in the holder 1 is determined by the voltage allowed between the holder 11 and the conductor film 6b. Let e*V (eV) be the maximum energy of the secondary electrons that irradiate the VB1 semiconductor substrate 6.

In such a max configuration, the capacitance is C8 as shown in FIG.
, Cx can be considered as a series connection of capacitors 10.15. During ion implantation, the ion beam 13 and secondary electron beam 5 are used to form an insulator film 6a and a conductor film 6.
When a charge of -Q is accumulated in the capacitor 10 consisting of the capacitor 10, the same amount of charge of -Q is also induced in the capacitor 15. Considering the case of negative charging in which the amount of electricity of the secondary electron beam 5 per unit time is large, x voltages that are IQI/C and IQI/C are applied to capacitors 10 and 15, respectively. If the sum of these voltages is vl, that is, Co C8, then v>lv 1 (2)
Under the condition of First, excessive accumulation of electrons is prevented.

Furthermore, since the voltage applied to the capacitor 10 (capacitance) needs to be equal to or lower than VB, the following condition (3) is required.

From equations (1), (2), and (3), the capacitance c of the capacitor 5 must satisfy the following conditions.

Therefore, the capacitance C of capacitor 5 is (4)
By selecting the equation so as to satisfy the equation, the electron flood system of this embodiment can prevent the accumulation of excessive electron dose and prevent the voltage applied to the semiconductor substrate from exceeding the set voltage below the dielectric withstand voltage. You can avoid it.

In the above embodiment, the holder 1 was described as a conductor, but if the holder 1 is an insulator, if the capacitance C of the capacitor 0 includes the main static capacitance of the insulator, then (4) It can be applied without changing the formula.

Further, a modification of the electron flood system of the above embodiment is shown in FIG. This modified electron flood system has a power supply 16 newly installed between the capacitor 15 and the ground 17 in the electron flood system embodiment shown in FIG. This improves the utilization efficiency of the electron beam 5. This electric? When the voltage across 1g and 16 is vl,
The capacitance C8 of the capacitor 15 is adjusted to satisfy the following equation in which VIlax in equation (4) is replaced with Vllax+v1.
By selecting , the same effect as the embodiment shown in FIG. 1 can be obtained.

〔Effect of the invention〕

According to the present invention, an electron flood that can prevent accumulation of an excessive amount of electron beam on a semiconductor substrate and prevent the voltage caused by the electron beam applied to the semiconductor substrate from exceeding a set voltage lower than the dielectric withstand voltage is possible. system can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of an electron flood system according to the present invention, FIG. 2 is a block diagram of a modification of the embodiment shown in FIG. An explanatory diagram used to find the conditions for capacitance C to satisfy. Figure 4 is a configuration diagram of a conventional electron flood system. Figure 5 shows the energy of the secondary electron beam generated by the secondary electron beam generator. It is a line diagram showing distribution. 2... Thermionic generation part, 2a... Filament, 3.
・Thermionic electron, 4 ・Secondary electron beam generation part, 5 ・・
Secondary electron beam, 6... Semiconductor substrate, 6a... Insulator film, 6b... Conductor film, 11... Holder, 12...
...Ion beam irradiation chamber, 13...Ion beam, 1
4a. 14b...Conducting wire, 15...Capacitor, 17...
Earth. Applicant's agent Mr. Sato Figure 1 Figure 2 Figure 3 971

Claims (1)

[Claims] An electron beam generating section that is held by a grounded holding section and is used in an ion implantation device that accelerates and implants ionized impurities to high energy into a semiconductor substrate on which a capacitor is formed, and that generates an electron beam. and a secondary electron generating unit that generates secondary electrons by irradiation with the electron beam generated by the electron beam generating unit and irradiates the semiconductor substrate with the secondary electrons, the electron flood system comprising: The holding part is grounded via a capacitor, and the capacitance of this capacitor C_X is the capacitance of the capacitor formed on the semiconductor substrate, C_O is the withstand voltage of the insulator in the semiconductor substrate, and the secondary electron The maximum energy seen from the holding part of is e・V_m_a_x (e is the elementary charge)
When, C_X<C_O・V_B・(V_m_a_
An electron flood system characterized by satisfying the relationship: x-V_s)^-^1.