JPH0712778A - Analysis method and analysis device for admolecule on surface of semiconductor substrate - Google Patents

Abstract

PURPOSE:To analyze an admolecule or the like on the surface of a semiconductor substrate with high sensitivity by providing the substrate in gas and irradiating the surface thereof with a laser beam while scanning. CONSTITUTION:A semiconductor substrate 105 is laid in a chamber a106. Then, inert gas such as N2 flows from the side 107a to the side 107b of piping, and a part thereof is introduced to a chamber b111. When a laser beam 102 irradiates the surface of the substrate 105 in that state, molecules absorbed to the surface are desorbed and carried on N2 gas to an ionization section 112. In this section 112, corona discharge is generated due to an electrode 108 at atmospheric temperature, and admolecules desorbed from the N2 gas are ionized. The admolecules are also ionized due to ionized gas and, therefore, nearly all of the admolecules are ionized. Also, a part of the ions so generated enters a differential evacuation chamber 113 and only ions are selectively introduced to a mass spectrograph 110 via a lens 114 for mass analysis. As a result, admolecules on the surface of the substrate 105 can be identified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an analyzer for analyzing adsorbed molecules on a semiconductor substrate.

[0002]

2. Description of the Related Art Conventionally, as a surface analysis method and a surface analysis apparatus using this type of laser beam, for example, Japanese Patent Application Laid-Open No. 61-61160
There is a laser mass spectrometer shown in -285649. FIG. 4 shows a schematic configuration diagram thereof. Here, 401 is a vacuum chamber, 402 is a sample, 403 is a laser beam, 404 is a first laser device, 405a and 405b are condenser lenses,
406 is a window, 407A is a neutral particle, 407B is an ion,
Reference numeral 408 is a mass spectrometer, 409 is a sample fine movement device, 410 is a second laser device, 411 is a laser beam, and 412 is a nozzle. Next, the operation of this laser mass spectrometer will be described. The laser beam 403 emitted from the laser device 404 is condensed by the condenser lens 405a, and the vacuum chamber 401
Is irradiated on the surface of the sample 402 which is placed outside. Neutral particles 407A are ejected from the sample 402 by laser irradiation. The neutral particles 407A are introduced into the vacuum chamber 401 through the nozzle 412 provided in the vacuum chamber 401, and the laser beam 411 from the second laser device 410 is supplied.
Is ionized by the irradiation. This ion 407B was subjected to mass analysis by a mass analyzer 408 installed in the vacuum chamber 401, and elemental analysis of the sample 402 was performed.

[0003]

Since the conventional laser mass spectrometer has the above-mentioned structure, it has the following problems. First, the neutral particles 407A from the sample 402 pass through the nozzle 412 and the vacuum chamber 401.
Since it is introduced into the vacuum chamber 401, air is mixed in the vacuum chamber 401. Therefore, neutral particles 407A and neutral particles 407A
There is a problem in that the components in the atmosphere are mixed in the ionized ions 407B, resulting in an error in the elemental analysis of the sample 402. Secondly, by irradiating the neutral particles 407A with the laser beam 411, the neutral particles 407A
Are ionized and mass-analyzed as ions 407B. In order to keep the vacuum chamber 401 in a vacuum of a certain constant pressure, it is necessary to reduce the number of neutral particles 407A by the nozzle 412, and 407A is not completely ionized to ions 407B. Therefore, sample 4
When the No. 02 adsorbed molecule is analyzed, there is a problem that the number of ions detected by the mass spectrometer 408 is extremely small, and an adsorbed molecule having a small number of atoms cannot be detected.

[0004]

The present invention provides an analysis method for analyzing an impurity gas contained in a gas by using atmospheric pressure ionization mass spectrometry, in which a semiconductor substrate is placed in the gas and the surface of the semiconductor substrate is placed. The method for analyzing an adsorbed molecule on the surface of a semiconductor substrate is characterized by irradiating a laser beam on a semiconductor substrate, and the analyzer for an adsorbed molecule on the surface of a semiconductor substrate of the present invention places the semiconductor substrate in a gas. Means and means for irradiating the semiconductor substrate surface with a laser beam,
Means for scanning the laser beam on the surface of the semiconductor substrate;
It is provided with means for ionizing the gas by the atmospheric pressure ionization method and means for mass spectrometric analysis of the ionized gas.

[0005]

In the present invention, the adsorbed molecules adsorbed on the surface of the semiconductor substrate are desorbed by irradiating the surface of the semiconductor substrate with a laser beam. The desorbed adsorbed molecules are carried to the atmospheric pressure ionization section by the gas and ionized together with the gas. The ionized gas and adsorbed molecules are mass-analyzed and mass-analyzed by a mass spectrometer. When the atmospheric pressure ionization method is used here, all the desorbed adsorbed molecules are ionized, so that even if the number of atoms is very small, they can be detected with high sensitivity.

[0006]

Embodiments of the present invention will now be described with reference to the drawings. [Embodiment 1] FIG. 1 shows a first embodiment of the present invention. Here, 101 is a laser, 102 is a laser beam, 103 is a laser scanning device, 104 is a window, and 105.
Is a semiconductor substrate, 106 is a chamber a, 107a, 10
7b and 107c are piping, 108 is an electrode, 109 is a vacuum pump, 110 is a mass spectrometer, 111 is a chamber b, 1
12 is an ionization unit, 113 is a differential pumping unit, and 114 is a lens. Next, the operation will be described. The semiconductor substrate 105 is installed in the chamber a of 106. At this time, the pipe 1
An inert gas such as Ar or N ₂ flows at about 1 to 3 SLM from the 07a side to the 107b side. About 10 of this gas
0 sccm is introduced into the chamber b of 111, and the rest is discharged to the outside of the chamber b of 111 through the pipe 107c. In this state, the laser 101 is formed on the surface of the semiconductor substrate 105.
When the laser beam 102 from the
The surface of 05 is locally heated, and the adsorbed molecules are desorbed from the surface of the semiconductor substrate 105. Then, the gas is carried to the ionization unit 112. In the present invention, the laser 101
Laser scanning device 10 for scanning the laser beam 102 on
3, the laser beam 102 is applied to the semiconductor substrate 10
5 can be scanned over the entire surface. Therefore, when analyzing the adsorbed molecules on the surface of the semiconductor substrate 105, it is possible to analyze the entire area of the surface of the semiconductor substrate 105 or an arbitrary portion even if it is a local portion.

In the ionization section 112, the atmospheric pressure (10
Corona discharge is generated by applying a voltage of 1 to 3 KV to the electrode 108 at ⁵ Pa).
The gas passing through 07b is ionized by the corona discharge. When the adsorbed molecules desorbed from the semiconductor substrate 105 are introduced into the ionization section 112, the adsorbed molecules are ionized by the corona discharge, and at the same time, the adsorbed molecules are also ionized by the ionized gas. Here, the atmospheric pressure ionization method will be described. The ionization potential of an inert gas such as Ar or N ₂ is 15 eV or more, and when atoms or molecules having an ionization potential smaller than 15 eV collide with the ionized inert gas, the atoms or molecules are ionized by the collision and are ionized. The gas is neutralized.
Therefore, in a state where the mean free path of atoms and molecules is short, such as under atmospheric pressure, and the mutual collisions of about 10 ⁷ times / sec occur, the impurity gas in the gas has an ionization potential of the impurity gas. If it is smaller than the potential, almost all is ionized by the corona discharge and the ionized gas. That is, since the ionization potential of the adsorbed molecules is approximately 10 eV or less on average, the adsorbed molecules desorbed from the semiconductor substrate 105 are not ionized by the ionization section 112.
Almost all are ionized by. Part of the gas generated in the ionization section 112 and the ions of the adsorbed molecules are in the differential exhaust chamber 11.
3, and only the ions are selectively introduced into the mass spectrometer 110 by the lens 114 for mass analysis, so that adsorbed molecules on the surface of the semiconductor substrate 105 can be identified.

2a and 2b are the results of analyzing the adsorbed molecules on the surface of the semiconductor substrate by using the analysis method and the analysis apparatus of the present invention. Using nitrogen gas as a carrier gas, two types of samples having different treatment methods were measured. 2a shows a semiconductor substrate washed with water and dried by nitrogen blow, FIG. 2b.
Is a semiconductor substrate washed with water and dried with vapor of IPA (isopropyl alcohol), and the entire surface of the semiconductor substrate was scanned with a laser beam. 2a and 2b, the horizontal axis represents the detected ion mass number and the vertical axis represents the signal intensity. In FIG. 2a, the mass numbers 18, 28,
42 and 56 peaks are detected. 18 is due to the water adsorbed on the surface of the semiconductor substrate.
2, 56 are due to nitrogen as a carrier gas. Figure 2
Peaks of mass numbers 28, 42, 56 and 60 are detected in b, 28, 42 and 56 are due to nitrogen as a carrier gas, and 60 is IPA adsorbed on the surface of the semiconductor substrate.
It is due to. Even when the sample used in FIG. 2a and the sample used in FIG. 2b are analyzed by the surface analyzer of the related art, only nitrogen and oxygen, which are components of air, are detected, and signals due to adsorbed molecules on the semiconductor surface are detected. Not done. As described above, using the analysis method and analysis apparatus of the present invention,
It is possible to detect the adsorbed molecules adsorbed on the surface of the semiconductor substrate with high sensitivity, which was impossible with the conventional technique.

[Second Embodiment] FIG. 3 shows a second embodiment of the present invention. Here, 301 is a laser, 3
02 is a laser beam, 303 is a laser scanning device, 304
Is a window, 305 is a semiconductor substrate, 306 is a chamber a, 30
7a, 307b, 307c are pipes, 308 is an electrode, 30
9 is a vacuum pump, 310 is a mass spectrometer, 311 is a chamber b, 312 is an ionization part, 313 is a differential evacuation part, 3
Reference numeral 14 is a mirror and 315 is a lens. In this embodiment,
Since the reflection by the mirror 314 is used for scanning the laser beam 302, there is an advantage that the laser scanning device can be downsized.

[0010]

As described above, according to the present invention, means for placing a semiconductor substrate in a gas, means for irradiating the surface of the semiconductor substrate with a laser beam, means for scanning the surface of the semiconductor substrate with the laser beam, Since a means for ionizing the gas by the atmospheric pressure ionization method and a means for mass spectrometric analysis of the ionized gas are provided, the adsorbed molecules adsorbed on the surface of the semiconductor substrate can be analyzed with high sensitivity.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus according to a first embodiment of the present invention.

FIG. 2 is analytical data using the apparatus of the present invention.

FIG. 3 is a schematic diagram of an apparatus according to a second embodiment of the present invention.

FIG. 4 is a schematic view of a conventional device.

[Explanation of symbols]

 101 Laser 102 Laser Beam 103 Laser Scanning Device 104 Window 105 Semiconductor Substrate 106 Chamber a 107a, 107b, 107c Piping 108 Electrode 109 Vacuum Pump 110 Mass Spectrometer 111 Chamber b 112 Ionization Section 113 Differential Exhaust Section 114 Lens 301 Laser 302 Laser Beam 303 Laser Scanning Device 304 Window 305 Semiconductor Substrate 306 Chamber a 307a, 307b, 307c Piping 308 Electrode 309 Vacuum Pump 310 Mass Spectrometer 311 Chamber b 312 Ionization Section 313 Differential Exhaust Section 314 Mirror 315 Lens 401 Vacuum Chamber 402 Sample 403 Laser Beam 404 1st laser apparatus 405a, 405b Condensing lens 406 Window 407A Neutral particle 407B Ion 408 Mass spectrometer 409 Fee fine movement apparatus 410 second laser device 411 laser beam 412 nozzles

Claims (2)

[Claims] 1. An analytical method for analyzing an impurity gas contained in a gas by using atmospheric pressure ionization mass spectrometry,
A method for analyzing adsorbed molecules on the surface of a semiconductor substrate, comprising placing a semiconductor substrate in the gas and irradiating the surface of the semiconductor substrate with a laser beam while scanning. 2. A means for placing a semiconductor substrate in gas,
A means for irradiating the surface of the semiconductor substrate with a laser beam, a means for scanning the surface of the semiconductor substrate with the laser beam, a means for ionizing the gas by an atmospheric pressure ionization method, and a mass analysis of the ionized gas. And means for analyzing adsorbed molecules on the surface of a semiconductor substrate.