JPH0652824A - Ion implanting device - Google Patents

Abstract

PURPOSE:To surely prevent an ion implanting device from being involved in ill effect such as dielectric breakdown resulting from electric charge by stably and surely neutralizing a semiconductor substrate charged phenomenon as a result of ion implantation. CONSTITUTION:An ionized gas generator 21 is provided which is formed in one with a Faraday gauge 15. The ionized gas generator 21 consists of a silica container 17 in which rare gas such as Ar is filled and filaments 18a, 18b provided at both ends inside thereof. The filament 18 is electrified and 50-200V voltage is applied between both filaments 18a, 18b to generate discharge in the silica container 17. Low-energy electrons of 20eV or lower are developed by such discharge through gas ionization, emitted from a hole 20 made in the silica container 17 and supplied to a semiconductor substrate 5 to neutralize its positive electric charge.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion implantation apparatus, and more particularly to an ion implantation apparatus used when forming an impurity layer on a semiconductor substrate in a semiconductor process.

[0002]

2. Description of the Related Art Ion implantation is one of the methods for forming an impurity layer on a semiconductor substrate. FIG. 6 is a schematic configuration diagram showing a conventional ion implantation apparatus. First, a high density plasma is generated by supplying a dopant gas or solid vapor to the ion source 1 and performing arc discharge. Next, a high voltage (generally 20 to 80K) is applied to the extraction electrode (not shown).
V) is applied so that ions are extracted from the ion source 1 and at the same time, desired energy is applied to form an ion beam 2. The magnetic field is deflected by the mass analyzer 3 from the ion beam 2 to which constant energy is given, and ions having a predetermined mass and charge determined by the magnetic flux density, energy, and the radius of curvature of the mass analyzer 3 are selected.

Then, the ion beam 2 passes through the analysis slit 4 and is guided to the target semiconductor substrate 5 with a higher resolution. At this time, a plurality of semiconductor substrates 5 are placed on the disk 6 having a disk shape, and the disks 6 are rotated A and translated B so that the ion implantation is uniformly performed on the semiconductor substrates 5.

When the ion implantation is performed, a pattern is usually already formed on the semiconductor substrate 5. An example of the patterned semiconductor substrate 5 is shown in FIG. In the figure, the semiconductor substrate 5 is of P conductivity type, for example, and a thick field insulating film 7 is selectively formed on the main surface of the semiconductor substrate 5. A thin insulating film 8 serving as a gate insulating film is formed in the active region sandwiched by the field insulating film 7, and a gate electrode 9 is formed on the insulating film 8.
Note that the insulating film 8 is extremely thinned with the miniaturization of the device.

Further, in the case of forming a normal CMOS transistor, the P channel region 11 is masked with a photoresist 10 as shown in FIG. In this case, ion implantation is performed so that the source / drain of the n-channel region is formed to have the N conductivity type. At this time, the ion beam 2 is, for example, an ion beam of phosphorus, arsenic, or the like.

As described above, when ion implantation is performed with the semiconductor substrate 5 covered with the insulating films 7 and 8 and the photoresist 10, the surface of the semiconductor substrate 5 is positively charged and the thickness of the semiconductor substrate 5 is greatly reduced. There is a high possibility that dielectric breakdown will occur in the insulating film 8.

The charge neutralizer 12 is generally used as one of the means for preventing this dielectric breakdown. FIG. 8 is a schematic configuration diagram illustrating the operation of the neutralizer 12. In the figure, a charge neutralizer 12 accelerates primary electrons 14 emitted from a filament of an electron gun 13 with an electric field of about 300 V and irradiates the opposing Faraday cage 15 with the secondary electrons 1.
6 is generated. By supplying the secondary electrons 16 to the semiconductor substrate 5 during ion implantation, the semiconductor substrate 5 charged with positive ions is electrically neutralized.

[0008]

Since the conventional ion implanter is constructed as described above, this charge neutralizer 1 is used.
When the ion implantation is performed using 2, some of the primary electrons 14 reach the semiconductor substrate 5 with energy of about 300 eV. It is believed that this is due to the design and surface condition of the Faraday cage. The primary electrons exceed the positive potential of the semiconductor substrate 5 which is positively charged with the ion beam 2 and reach an electrically neutral portion of the semiconductor substrate 5 to cause negative charging.

As described above, when the charge neutralizer 12 is used to perform ion implantation, positive and negative charges are repeated, and the insulating film 8 is extremely thinned without being electrically neutralized. There is a high possibility of causing dielectric breakdown. In addition, the primary electron 14
Therefore, the controllability is poor because the amount of secondary electrons 16 changes with time depending on the surface state of the Faraday cage 15.

The present invention has been made in order to solve such problems, and an object thereof is to obtain an ion implanter capable of reliably neutralizing the charge of a semiconductor substrate without causing negative charge. .

[0011]

An ion implantation apparatus according to claim 1 of the present invention is provided with an ionization gas generator for emitting electrons by discharge in a sealed gas near a semiconductor substrate and irradiating with an ion beam. Thus, the charging phenomenon that occurs in the semiconductor substrate is electrically neutralized by the electrons.

The ion implanting apparatus according to the second aspect of the present invention further detects the charge amount of the semiconductor substrate and controls the output of the ionized gas generator according to the detected amount.

[0013]

The ionized gas generator emits relatively low-energy electrons, which are supplied to the semiconductor substrate to neutralize the positive charge due to ion implantation. Further, the neutralization effect becomes more reliable by detecting the charge amount of the semiconductor substrate and controlling the output of the ionized gas generator.

[0014]

【Example】

Example 1. FIG. 1A is a schematic sectional view showing a main part of an ion implantation apparatus according to an embodiment of the present invention, and FIG. 1B is a sectional view taken along the line CC ′ of FIG. The same parts as those in the conventional case are designated by the same reference numerals, and the description thereof will be omitted as appropriate. In the figure, 17 is a container for generating ionized gas, which is made of quartz. The quartz container 17 surrounds the outer circumference of the Faraday cage 15. The Faraday cage 15 has a cylindrical shape, and the quartz container 17 has the same structure. The quartz container 17 has a structure in which the ends thereof abut against each other at the center of the lower portion of FIG. 1B, and a pair of filaments 18a and 18b are provided at both ends thereof. Reference numeral 19 is a gas introduction pipe, and 20 is a hole having an inner diameter of 1 mm. And above 17
˜20 constitute an ionized gas generator 21.

Next, the operation of neutralizing the charge on the semiconductor substrate 5 by the ionized gas generator 21 will be described. First, gas is introduced into the quartz container 17. At this time, the gas is
A rare gas such as Ar, Kr, Xe is the most suitable. The gas flow rate can be up to 5 sccm, but it is usually 0.
Use at 1-0.3 sccm. Next filament 18
Apply a direct current to and heat. Further, a voltage of 50 to 200 V is applied between the two filaments 18a and 18b to generate a discharge in the quartz container 17. in this way,
When ion implantation is started in a state where electric discharge is generated in the quartz container 17, two holes 20 provided in the quartz container 17 are provided.
Emits electrons. Since the electrons are emitted into the Faraday cage 15 with low energy of 20 eV or less, the positive charge of the semiconductor substrate 5 is effectively neutralized without negative charge. In the above example, the quartz container 17 has two
Two holes were prepared, but when implanting ions into a large-diameter target, increasing the number of holes to three or four increases the effect.

Example 2. Second Embodiment FIG. 2 is a schematic sectional view showing a main part of an ion implantation apparatus according to a second embodiment of the present invention. Here, the Faraday cage 15 is formed in a so-called cone shape as shown in the figure, and the ionized gas generator 21 is also formed in a shape corresponding thereto. In this case, the direction in which the electrons generated in the quartz container 17 are emitted through the hole 20 is 45 ° with respect to the surface of the semiconductor substrate 5, and the electrons generated in the quartz container 17 are directed to the semiconductor substrate 5. Is effectively supplied, so that the neutralizing action is more reliably and smoothly performed.

Embodiment 3. In the above embodiment, the quartz container 1
The electron density of the ionized gas in 7 is kept almost constant because the discharge voltage and current are constant during the injection, but the electron density can be controlled by providing the circuit shown in FIG. . That is, the charge amount detector 22 detects the charge amount of the semiconductor substrate 5, the preamplifier 23 amplifies the detected amount, and the A / D converter 24 converts it into a digital signal and inputs it to the microprocessor 25. On the other hand, the photodetector 26
Detects the light of a photodiode provided on the disk 6 to generate a signal synchronized with the time when the ion beam 2 implants the semiconductor substrate 5 in the microprocessor 25.
To enter.

And this microprocessor 25
Controls the arc power supply 28 by calculating a control parameter from the input charge detection amount and the input synchronization signal and outputting the control parameter to the arc voltage / current control circuit 27. Further, when the charge amount exceeds a certain value, the microprocessor 25 outputs a beam cutoff signal to the beam cutoff device 29 to interrupt the injection. Therefore, even when the energy level of the ion beam 2 fluctuates significantly, the neutralization function is accurately and surely performed.

Example 4. FIG. 4 shows still another embodiment, in which a DC voltage 30 of 5 to 10 V is applied between the disk 6 and the Faraday cage 15 integrally formed with the ionized gas generator 21. . in this case,
The electrons emitted from the quartz container 17 of the ionized gas generator 21 are attracted to the disk 6 side by the electric field due to the DC voltage, and the neutralizing effect is enhanced.

Example 5. FIG. 5 shows a Faraday cage 15.
The insulating film 31 is formed by, for example, alumite treatment on the inner wall of the. In this case, most of the electrons emitted from the ionized gas generator 21 are supplied to the semiconductor substrate 5 without being trapped by the Faraday cage 15, so that the efficiency of the neutralizing action is improved.

Example 6. Although the ionized gas generator 21 is formed integrally with the Faraday cage 15 in each of the above embodiments, it is not always necessary to form the ionized gas generator 21 integrally with the Faraday cage 15 as long as the ionized gas generator 21 is not separated from the semiconductor substrate 5. It may be arranged.

[0022]

As described above, according to the present invention, the predetermined ionized gas generator is provided, and the relatively low energy electrons emitted therefrom neutralize the charging phenomenon of the semiconductor substrate. There is no adverse effect of the negative charging phenomenon caused by the mixture of electrons, and a reliable neutralizing effect can be obtained.

If the charge amount of the semiconductor substrate is detected and the output of the ionized gas generator is controlled based on the detected charge amount, an accurate and stable neutralization effect can be obtained even if the energy level of the ion beam varies. can get.

[Brief description of drawings]

FIG. 1 is a sectional view showing a main part of an ion implantation apparatus according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a main part of an ion implantation apparatus according to a second embodiment of the present invention.

FIG. 3 is a block circuit diagram showing a main part of an ion implantation device according to a third embodiment of the present invention.

FIG. 4 is a sectional view showing a main part of an ion implantation apparatus according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view showing a main part of an ion implantation apparatus according to a fifth embodiment of the present invention.

FIG. 6 is a configuration diagram showing a conventional ion implantation apparatus.

FIG. 7 is a diagram showing a charged state of an insulating film formed on a semiconductor substrate.

FIG. 8 is a diagram for explaining the operation of a charge neutralizer in a conventional ion implanter.

[Explanation of symbols]

 1 Ion source 2 Ion beam 5 Semiconductor substrate 6 Disk 17 Quartz container 18 Filament 19 Gas introduction tube 20 Hole 21 Ionizing gas generator 22 Charge amount detector 27 Arc voltage / current control circuit

Claims (2)

[Claims] 1. An ion implanter for extracting ions from an ion source to form an ion beam, irradiating the ion beam on a semiconductor substrate to implant the ions, and discharging electrons in an enclosed gas. An ion implantation apparatus, wherein an ionized gas generator is provided in the vicinity of the semiconductor substrate, and a charging phenomenon generated in the semiconductor substrate by the irradiation of the ion beam is electrically neutralized by the electrons. 2. The ion implanter according to claim 1, wherein the charge amount of the semiconductor substrate is detected, and the output of the ionized gas generator is controlled according to the detected amount.