JP2008292351A - Dopant profile measuring thin piece sample preparing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a scanning capacitance microscope dopant profile measurement or an electron beam holography dopant profile measurement for a cross section of a thin piece cut from a desired region in a semiconductor device by a focused ion beam apparatus. <P>SOLUTION: A residual gallium layer 3 on the surface of the thin piece 6 cut by the focused ion beam apparatus is removed by sputtering a gas cluster ion beam 1 such as argon. If the dopant profile measurement is implemented by using an electron beam holography, the thin piece 2 is thinned down by sputtering the gas cluster ion beam 1 after an removal of the residual gallium layer 3 until an electron beam of 100-200 kV passes through it. If the dopant profile measurement is implemented by using a scanning capacitance microscope, a surface of the thin piece 2 is oxidized by an oxygen gas cluster ion beam after the removal of the residual gallium layer 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to the preparation of a flake sample for measuring a dopant profile of a semiconductor device.

  The profile measurement of the dopant of the MOS structure is performed by measuring the capacitance change in a very small region immediately below the metal probe with a scanning capacitance microscope (SCM) (Non-patent Document 1). The scanning capacitance microscope measurement can detect not only the dopant distribution but also spike defects. Dopant profile measurement is performed by converting a phase image of a cross section including a pn junction into a potential distribution image using electron beam holography (Non-patent Document 2).

  In the preparation of a sample for a conventional scanning capacitance microscope, a method including cutting a region including a defective portion or a portion where a dopant profile is desired to be measured with a wire saw, and thinning by precision polishing using diamond abrasive grains or colloidal silica is employed. Even when a region including a defective portion or a portion where a dopant profile is desired to be measured is cut out by a focused ion beam apparatus (FIB), precision polishing using diamond abrasive grains or colloidal silica is used to remove the gallium implantation region. Therefore, it is difficult to pinpoint a defective portion or a portion where a dopant profile is desired to be measured. Here, cutting out at a pinpoint means cutting out with a sample amount as small as possible so that the target position is included and less shaving is required. In addition, the scanning capacitance microscope measurement requires an appropriate oxide film between the probe and the silicon in the measurement region. This oxide film is formed in a state where the silicon in the measurement region is heated to 300 ° C. It was performed by irradiating ultraviolet light for about minutes.

  It has been practiced to cut out a failed portion at a pinpoint with a focused ion beam apparatus and evaluate the cut-out portion with a transmission electron microscope (TEM) (Non-patent Document 3). In the evaluation of a transmission electron microscope, the composition was found by structural problems and electron energy loss spectroscopy (EELS) analysis, but electrical properties such as dopant distribution could not be known. There is a need for a method for measuring whether the dopant distribution is designed as designed in the cross-section of the device cut out with a focused ion beam device, and a method for examining the electrical characteristics of the failure point cut out with a focused ion beam. (Patent Document 1).

In order to realize the above-mentioned demand and perform reliable scanning capacitance microscope measurement, in addition to forming an appropriate oxide film on the silicon surface in the measurement region, gallium implanted into the cut-out part accompanying cut-out with a focused ion beam or It is necessary to remove the damaged layer formed in the cutout portion. In addition, since the unevenness also affects the capacity, it has to be reduced. In order to perform dopant profile measurement using electron beam holography, the implanted gallium must be removed, and the sample must be made thin with little irregularities so that the electron beam can be transmitted. In order to obtain highly reliable data, the damaged area of the thinned sample must be reduced.
XD Wang, CL Liu, A. Thean, E. Duda, R. Liu, Q. Xie, S. Lu, A. Barr, T. White, BY Nguyen, M. Orlowski, J. Vac. Sci. Technol. B22 373-376 (2004) Oeda Osamu, Applied Physics 72 539-549 (2003) Yoshimasa Kondo, O plus E 25 899-903 (2003) JP2004-226079

  An object of the present invention is to enable measurement of a dopant profile of a desired cross section of a semiconductor device or measurement of a dopant profile by electron holography.

  In order to solve the above-described problems, in the present invention, a gas sample ion beam is used to cut a thin sample from a semiconductor device with a focused ion beam apparatus, and to reduce the cross-section of the cut thin sample and to remove implanted gallium. Then, removal processing with less damage and less unevenness is applied to the narrow region of the cut-out cross section. If a gas cluster ion beam device is used, the combination of the cluster size and the incident energy per atom can be optimized, so that removal processing with less damage and less unevenness can be performed in a narrow area.

Also the use of the oxygen gas cluster ion beam, its by controlling the cluster size and the incident energy per atom, good stoichiometry, i.e. chemical composition closer to Si0 ₂ of the formed oxide film thickness control A good silicon oxide film can be obtained. If a thin oxide film with good reproducibility is obtained, reliable dopant profile data can be obtained with a scanning capacitance microscope.

  When the dopant profile is measured using electron holography for the device cross-section, the cross-section of the slice cut from the semiconductor device with a focused ion beam device is cut into the thickness of the electron beam of 100 to 200 kV. Thin by sputtering.

  The cluster ion beam has a low energy per atom and is not implanted deep into the sample. If noble gas cluster ions are used, the dopant profile measurement is not affected unlike gallium because it is inactive even if ions are implanted. The cluster ion beam has a lateral sputtering effect (the gas cluster ion beam has an effect of being easily sputtered (prone to flatten) when protruding from the plane, which is referred to as a lateral sputtering effect), and a removal cross section with less unevenness can be obtained.

  By optimizing the conditions with an oxygen gas cluster ion beam, an oxide film with good stoichiometry and a moderately thin thickness can be formed with good reproducibility. In this case as well, an oxide film surface with less unevenness can be obtained with an oxygen gas cluster ion beam.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

  FIG. 1 illustrates a case where a cross section of a thin piece 6 cut out from a semiconductor device by a focused ion beam apparatus is etched using a gas cluster ion beam to prepare a sample for measuring a dopant profile for electron holography. FIG. 6 is a schematic cross-sectional view (a cross-sectional view when cut from a direction perpendicular to the measurement cross-section of the thin piece 6 and parallel to the surface of the semiconductor device) for each processing step of the thin piece 6.

  The focused ion beam is irradiated to form a cross section at a desired position of the semiconductor device, and the slice 6 including the cross section is taken out from the focused ion beam apparatus. When the thin ion beam 6 is irradiated with the focused ion beam, gallium is implanted and the residual gallium layer 3 is present. The extracted slice 6 is introduced into a gas cluster ion beam apparatus in order to perform pre-processing necessary to enable measurement of a dopant profile with a scanning capacitance microscope or electron beam holography. While observing with an optical microscope or a scanning electron microscope combined with a gas cluster ion beam apparatus, the position is adjusted so that the residual gallium layer 3 on the surface of the thin piece 6 comes to the irradiation position of the gas cluster ion beam.

A gas cluster ion beam 1 of a rare gas such as argon with an ion dose of 10 ¹⁴ ions / cm ² to 10 ¹⁶ ions / cm ² and an acceleration voltage of 10 to 20 kV optimized for the combination of cluster size and incident energy per atom. The thin piece 6 is irradiated (FIG. 1 (a)), and the surface is sputtered until the residual gallium layer 3 of about 30 nm implanted on the surface of the thin piece 6 cut out by the focused ion beam apparatus can be removed (FIG. 1 (b)). ). When measuring the dopant profile using electron holography, the thin piece 6 is turned over and the residual gallium layer 3 of about 30 nm implanted on the back surface is also removed (FIG. 1 (c)). After turning the sample over, while observing with an optical microscope or scanning electron microscope combined with a gas cluster ion beam device again, adjust the position so that the surface of the thin piece 2 after removal of residual gallium is at the irradiation position of the gas cluster ion beam To do.

When measuring the dopant profile using electron holography, after removing the residual gallium layer 3 on both sides, the ion dose is optimized by combining the cluster size and incident energy per atom 10 ¹⁴ ions / cm The surface of the thin piece 2 after removing the residual gallium layer is irradiated and scanned with a gas cluster ion beam 1 of a rare gas such as argon having ² to 10 ¹⁶ ions / cm ² and an acceleration voltage of 10 to 20 kV (FIG. 1 (d)), It is further thinned to 100 nm or less through which an electron beam of 100 to 200 kV is transmitted (FIG. 1 (e)). The film thickness is confirmed by taking it out with an atomic force microscope or the like.

Residual gallium layer removal and slicing roughing are performed by sputtering with the effect of accelerating reactive gas cluster ion beams such as SF ₆ and CF ₄ , and finishing processing is performed by a gas cluster ion beam of rare gas such as argon 1 If this is done, the processing time can be shortened.

  FIG. 2 is a schematic cross-sectional view for each processing step of the thin piece 6 when a sample for measuring a dopant profile for a scanning capacitance microscope is produced from the thin piece 6 cut out by the focused ion beam apparatus using a gas cluster ion beam.

In order to remove the residual gallium layer 3, an ion dose of 10 ¹⁴ ions / cm ² to 10 ¹⁶ ions / cm ² with optimized combination of cluster size and incident energy per atom, argon with an acceleration voltage of 10 to 20 kV, etc. Irradiate the gas cluster ion beam 1 of the rare gas (Fig. 2 (a)).

After the removal of the residual gallium layer 3, the surface of the thin film 2 after the removal of the residual gallium 2 is irradiated with an oxygen gas cluster ion beam 5 having a cluster ion size of 250 or more, an ion dose of about 5 × 10 ¹⁵ ions / cm ² and an acceleration voltage of 5 to 10 kV. (FIG. 2 (b)), a 5 to 10 nm surface oxide layer 4 is formed on the cross section of the thin piece 2 after the removal of residual gallium (FIG. 2 (c)).

  A thin sample including a cross section of a failure portion of the semiconductor device is cut out by the focused ion beam apparatus. The failure location of a semiconductor device is measured with an LSI tester, an electron beam tester or the like on the target chip. The cause of a failure such as a spike defect can be clarified by measuring the dopant profile of the cut-out slice sample with a scanning capacitance microscope or electron holography.

  This method can be used not only for preparing a sample for measuring a dopant profile with a scanning capacitance microscope but also for preparing a sample for measuring a dopant profile with a scanning nonlinear dielectric microscope (SNDM), which is more sensitive than a scanning capacitance microscope.

It is a schematic sectional drawing of the thin piece in the case of producing the sample for a dopant profile measurement for electron holography by etching the thin piece cut out from the semiconductor device with the focused ion beam apparatus using a gas cluster ion beam. It is a schematic sectional drawing of the thin piece in the case of producing the sample for dopant profile measurement for a scanning capacitance microscope by etching the thin piece cut out from the semiconductor device with the focused ion beam apparatus using a gas cluster ion beam.

Explanation of symbols

1 Argon gas cluster ion beam
2 Thin section from which residual gallium layer has been removed
3 Residual gallium layer
4 Oxide film
5 Oxygen gas cluster ion beam
6 Thin section cut out by focused ion beam device

Claims (5)

Cutting out a slice including a desired cross section from a semiconductor device using a focused ion beam apparatus;
A method for preparing a flake sample for measuring a dopant profile, comprising a step of removing residual gallium from the cut flake with a gas cluster ion beam.   2. The method for preparing a thin film sample for measuring a dopant profile according to claim 1, wherein the residual gallium is removed from the thin film on both surfaces of the thin film.   3. The method for preparing a flake sample for measuring a dopant profile according to claim 2, wherein after the residual gallium is removed, the gas cluster ion beam is further used for thinning.   4. The method for preparing a slice sample for measuring a dopant profile according to claim 3, wherein the residual gallium removal is performed with a reactive gas cluster ion beam, and further thinning after the residual gallium removal is performed with a rare gas cluster ion beam.   2. The thin film for measuring a dopant profile according to claim 1, wherein after removing the residual gallium in the cross section of the thin film, the surface of the thin film is irradiated with an oxygen gas cluster ion beam to form a surface oxide layer on the surface of the thin film after removing the residual gallium. Sample preparation method.

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