JP2894660B2 - Ion implantation amount measuring method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of semiconductor device manufacturing, and more particularly to a method and apparatus for measuring the amount of ion implantation.

[0002]

2. Description of the Related Art An ion implantation technique, which is an impurity introduction technique in a semiconductor device manufacturing technique, is widely used because an implantation amount can be accurately controlled.

In the ion implantation technique, after ionizing an impurity element, a desired ion species is selected by mass spectrometry and extracted. Next, the semiconductor substrate is accelerated to a desired acceleration energy, and impurities necessary for the semiconductor substrate are implanted at a desired implantation amount and acceleration energy. Thereafter, heat treatment is performed at a predetermined temperature for a predetermined time. In this manner, this is a technique for forming an impurity layer having a desired conductivity type and an impurity distribution that provides conductivity. At this time, it is necessary to know whether or not the desired ion implantation amount has been correctly introduced.

As a conventionally known method of measuring the amount of ion implantation, a semiconductor substrate into which ions have been implanted is subjected to a heat treatment to activate the introduced impurities. Thereafter, there is a method of measuring the sheet resistance of the impurity layer. In this method, after heat treatment, four probes are electrically contacted on the same line, a current is applied to two points at both ends, and a voltage at two points inside is measured. The resistance value is calculated from this voltage, and the ion implantation amount is estimated.

As another method, there is a thermal wave method utilizing a heat wave propagating in a semiconductor substrate. In the thermal wave method, a substrate is irradiated with a pumping laser beam to generate a thermal wave in which the temperature and the carrier density of the semiconductor substrate surface periodically change. As a result, the reflectivity changes periodically. Here, when a reflectance detection laser beam is irradiated, a modulated reflected wave is obtained, from which the ion implantation amount is estimated.

[0006]

However, the conventional method as described above has a disadvantage that the spatial resolution of the ion implantation dose distribution measurement is low. For example, in the method of measuring the sheet resistance, the spatial resolution is 500 μ
m, about 1 μm in a method using a thermal wave. This value was generally insufficient as the spatial resolution of the distribution measurement in the depth direction of the ion implantation amount of the impurity layer having a distribution within a depth of about 1 μm.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide an ion implantation dose measuring method and an ion implantation dose measuring method capable of improving the spatial resolution of an ion implantation dose distribution measuring method and knowing the depth distribution.

[0008]

In order to achieve the above object, the present invention provides a method for measuring the amount of ion implantation according to the present invention, which comprises applying a laser beam modulated at a predetermined pulse width and a predetermined pulse repetition frequency to a desired position on a semiconductor substrate. Irradiating the, the tip of the probe is disposed at a position separated by a predetermined distance from the desired position on the semiconductor substrate, a current flowing between the probe and the semiconductor substrate is measured, The amount of ions implanted into the semiconductor substrate is estimated from the amount of change.

In order to achieve the above object, an ion implantation dose measuring apparatus according to the present invention comprises a mechanism for generating a laser beam and a mechanism for modulating the laser beam so as to have a predetermined pulse width and a predetermined pulse repetition frequency. A mechanism for irradiating the modulated laser beam to a desired position on the semiconductor substrate, a mechanism for disposing a probe tip at a position separated by a predetermined distance from the desired position on the semiconductor substrate, A mechanism for measuring a current flowing between the probe and the semiconductor substrate,
The probe serves as a mechanism for scanning the semiconductor substrate.

[0010]

According to the present invention, a pulse-modulated laser beam is irradiated to an ion-implanted region on a semiconductor substrate by using the above-described means, and the coefficient of thermal expansion of the semiconductor substrate depends on the ion implantation amount. Change. For this reason, the distance between the probe arranged near the semiconductor substrate and the semiconductor substrate changes depending on the ion implantation amount, and the current flowing between the two (tunnel current)
The ion implantation amount can be measured by utilizing the fact that changes occur.

A current (tunnel current) flowing between the probe arranged near the semiconductor substrate and the semiconductor substrate is measured in advance, and then the tunnel current is measured again while irradiating pulse-modulated laser light. The difference between the two corresponds to the ion implantation amount. At this time, the distribution of the ion implantation amount in the scanning direction can be known by scanning the probe with respect to the semiconductor substrate.

[0012]

FIG. 1 shows a configuration diagram of an ion implantation dose measuring apparatus according to an embodiment of the present invention. In the figure, 1
Reference numeral 0 denotes a laser pulse generator, 11 denotes a polarizer, 12 denotes an optical lens, 13 denotes a semiconductor substrate, 14 denotes an XY movable fixed base, 15 denotes an XY moving mechanism, 16 denotes a probe, and 17 denotes a current.
A voltage converter, 18 is a lock-in amplifier, 19 is a wave memory, and 20 is an image monitor.

The laser pulse generator 10 uses an Ar ion laser, a wavelength of 488 nm, a pulse width of 1 msec, and a repetition frequency of 200 Hz. First, the portion to be measured of the semiconductor substrate 13 is brought close to the probe 16. Next, the distance between the semiconductor substrate 13 and the probe 16 is reduced to about 10 ° so that a tunnel current flows between the semiconductor substrate 13 and the probe 16. After that, the laser light emitted from the laser pulse generator 10 is applied to the polarizer 11 and the optical lens 1.
After that, the semiconductor substrate 13 is irradiated with a diameter of 1 μm. Then, the p-type silicon substrate which is the semiconductor substrate 13 expands because it is heated by the laser light. Therefore, the semiconductor substrate 13 approaches the tungsten needle which has been subjected to electrolytic polishing, which is the probe 16. Thus, the tunnel current flowing between the semiconductor substrate 13 and the probe 16 changes. From this, when the tunnel current flowing between the probe 16 arranged near the semiconductor substrate 13 and the semiconductor substrate 13 is measured in advance, and the tunnel current is measured again while irradiating the pulse of the laser light, The difference between the two corresponds to the amount of ion implantation.

At this time, if a pulse beam of a laser beam is irradiated from directly above the probe 16, a shadow of the probe 16 is generated on the semiconductor substrate 13, so that the pulse beam of the laser beam is irradiated obliquely. I have.

FIG. 2 is a view for explaining ion implantation conditions of a sample measured by the ion implantation amount measurement of the present invention. The figure shows a P-type silicon substrate 22 in which P ⁺ ions are vertically implanted from above a photoresist mask 21 having a thickness of 0.6 μm and an opening width of 2 μm. Here, ion implantation conditions are an acceleration energy of 140 keV and an implantation amount of 2 × 10 ¹³ cm ⁻² . FIG. 3 shows the results of ion implantation dose distribution measurement in the depth direction obtained by using the ion implantation measuring apparatus of the present invention with the cross section of the semiconductor substrate having undergone ion implantation.

FIG. 3 is a diagram showing the ion implantation dose distribution of the portions indicated by the respective line segments A, B and C in FIG. In FIG. 3, the vertical axis indicates the ion implantation amount, and the horizontal axis indicates the distance from the silicon substrate surface. Here, the unit of the injection amount was an arbitrary unit. In FIG. 3, A has the largest injection amount, and C, the surface of which is covered with the photoresist 21, has the least amount.

Next, two-dimensional measurement will be described. The laser beam pulse beam and the probe 16 are scanned over the semiconductor substrate 13. Here, the scanning area is 3 μm × 3 μm, the scanning speed is 10 μm / sec, and the scanning line interval is 100 °. The signal obtained as a result is stored in the wave memory 19 and displayed on the image monitor 20. Thus, a two-dimensional distribution of the ion implantation amount is displayed. The scanning at this time is performed by moving the XY movable fixed base 14 supporting the semiconductor substrate 13 to the XY moving mechanism 15 composed of a PZT ceramic actuator.
This was performed using FIG. 4 shows a two-dimensional measurement result. FIG.
Then, the injection conditions are also shown. In FIG. 4, 4
0 is a silicon substrate, 41 is a two-dimensional distribution of implantation dose, 42
Is a photoresist mask having a thickness of 0.6 μm and an opening width of 2 μm.

In the prior art, it is difficult to know such a distribution of the injection amount in the depth direction.

In this embodiment, the laser light is pulse-modulated. Therefore, the tunnel current fluctuates periodically. This tunnel current is lock-in amplified. Here, lock-in amplification is used for the following reason. When the sample is irradiated with a periodically intermittent laser beam, the sample is heated and the sample expands periodically according to the repetition frequency of the laser beam. As a result, the tunnel current between the semiconductor substrate and the probe fluctuates periodically, and the tunnel current is AC-modulated. After narrow band amplification of the AC modulated tunnel current output, phase detection is performed. As a result, unmodulated noise and dark current are not amplified, so that the signal / noise ratio is improved.

In the embodiment of the present invention, a process is used in which a probe is arranged near a certain region on a semiconductor substrate and a current (tunnel current) flowing between the probe and the semiconductor substrate is measured. Alternatively, an atomic force or magnetism may be used. Further, in the present embodiment, the laser beam is irradiated to cause a small displacement, but other than that, a microwave or the like may be used.

In this embodiment, the amount of ion implantation is measured. However, the same measurement principle can be applied to the measurement of strain and stress of a semiconductor substrate having a uniform impurity concentration.

[0022]

As described above, according to the present invention, the resolution of the implantation dose measurement in the lateral direction of the ion-implanted semiconductor substrate can be significantly improved, and the distribution in the depth direction can be known. The industrial effect is great.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an ion implantation amount measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating ion implantation conditions of the present invention.

FIG. 3 is a diagram showing an ion implantation amount measurement result using the ion implantation amount measuring method of the present invention.

FIG. 4 is a diagram showing an ion implantation amount measurement result using the ion implantation amount measuring method of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 laser pulse generator 11 polarizer 12 optical lens 13 semiconductor substrate 14 XY movable fixed base 15 XY moving mechanism 16 probe 17 current-voltage transformer 18 lock-in amplifier 19 wave memory 20 image monitor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/66 G01N 27/00 H01L 21/265

Claims (2)

(57) [Claims] 1. A method according to claim 1 , further comprising the steps of:
The tip of the probe is placed at a predetermined distance from the semiconductor substrate.
At a predetermined pulse width and pulse repetition frequency.
The modulated position is irradiated with the modulated laser light to the desired position.
While scanning the needle on the desired position, the probe and the half
Measure the tunnel current flowing between the conductor board and the
An ion implantation amount measuring method, comprising measuring an ion implantation amount at the desired position from a change amount of the channel current . 2. A method according to claim 1 , further comprising the steps of:
The tip of the probe is placed at a predetermined distance from the semiconductor substrate.
And a mechanism to generate laser light
The pulse width and the number of pulse repetitions.
A mechanism for modulating laser light, and the modulated laser light
A mechanism for irradiating the probe with the desired position, and
A mechanism for scanning on a position, the probe and the semiconductor substrate
And a mechanism for measuring a tunnel current flowing between the two .