JPH0534250A - Method for preparing sample for transmission electron microscope - Google Patents

Abstract

PURPOSE:To obtain a method for fabricating a sample for a transmission electron microscope at a desired position by performing composition analysis in a depth direction by means of secondary ion masses, Auger electrons or the like while etching and by stopping the etching at a desired depth position on a desired region. CONSTITUTION:Semiconductor laser of AlGaInP crystal-grown on a GaAs substrate is fixed to a reinforcing ring 8 made of stainless steel with a square hole opened, and GaAs is etched out by sulfuric etching solution. This structure is put into a secondary ion detector where Cs+ ions are used to start sputter etching. If a transmission electron microscope image only of an active layer of 0.06mum is to be observed, as the active layer does not contain Al, it is possible to stop etching on a P-AlGaInP interface of the active layer by stopping the etching at a time when no more Al ions are generated. Then a fixing jig is put upside down and Cs ions are used from a substrate side to start sputter etching, and the etching is stopped at a time when no more Al ions are detected.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention provides a method for producing a sample for a transmission electron microscope by stopping etching at a desired position in a transmission electron microscope for producing an ultrathin film and observing the layer structure, crystal defects and the like. To do.

[0002]

2. Description of the Related Art Recent remarkable progress in semiconductor crystal growth technology has enabled crystal growth at the monoatomic layer level. In particular, a metal-organic vapor phase epitaxy method (MOVPE method) or a molecular beam epitaxy method (MBE method) is used to form a superlattice structure in which extremely thin layers having different compositions are stacked, or these superlattices are used in an active region. Optical devices such as semiconductor lasers and photodetectors and high-speed electronic devices such as HEMTs using a heterostructure have been developed one after another.

Conventionally, a transmission electron microscope has been used as a method for evaluating deterioration of these devices. As a method for producing a sample for observation with a transmission electron microscope, a method as shown in FIG. 6 has been used so far. The sample to be observed is sandwiched between dummy glasses 71 and 77 and adhered, and mechanically cut to a thickness of 1 mm or less. After cutting, it is thinned to a thickness of 30 μm or less using a polishing jig. After that, the sample was put in an ion milling machine and a small hole was ion-etched to a region of several Å or less or a region other than the observed region to prepare a sample for a transmission electron microscope.

[0004]

However, this ion etching may take a considerable amount of time,
In many cases, even if a sample is manufactured over 2 to 3 days, the observed region is entirely removed by etching and only the non-observed region remains, so that an observation sample cannot be obtained in the end. Especially InP
It is very difficult to prepare a sample for mixed crystals of the system. further,
It is almost impossible to stop etching at a desired position in order to observe a predetermined area, and while observing with a transmission electron microscope whether or not observation is possible with a little etching, a sample for observation is prepared. Is the current situation. Even in this case, it is difficult to thin the region to be observed, although it takes time to prepare the sample.

[0005]

The gist of the present invention is to prepare a sample for a transmission electron microscope by stopping the etching of a desired minute region at a desired depth position, and monitor the depth position. A method of performing etching while being provided. In a semiconductor device having a laminated structure of different composition, after selective chemical etching removal to a predetermined thickness with a predetermined chemical etching solution, the mass of secondary ions is detected while etching away with Cs + ions to etch at a desired position. Method of stopping and preparing sample for transmission electron microscope observation Sputtering with neutral particles such as Ar in low vacuum, suspending to high vacuum and irradiating electron beam on sample surface to secondary electron and Auger electron The method of producing a sample for a transmission electron microscope by repeatedly detecting whether a desired region and a desired depth position by composition analysis are repeated, and stopping the etching when the desired depth position is reached. Element content of particles sputtered using a quadrupole mass spectrometer installed in the exhaust line while sputtering with Ar in high vacuum or high vacuum. It was carried out, to provide a method of producing by stopping etching the transmission electron microscope specimen when it reaches the desired position.

[0006]

The semiconductor device normally has a crystal growth on a substrate having a thickness of 300 μm or more and a maximum of 10 μm from the surface.
When the composition of the crystal-grown semiconductor and the substrate are different and there is selectivity in etching, the region with the thickness of is used as the active region. While sputter etching with Cs + ions or Ar, secondary electron mass and electron beam irradiation detect secondary electrons, Auger electrons or elements of sputtered particles and etch to a desired depth to prepare a sample for transmission electron microscope. can do. Therefore, sputter etching with Cs + ions or Ar not only has a high etching rate, but also the etching surface is extremely flat, and a region that can be observed over a large area can be formed.

[0007]

【Example】

(Example 1) The present invention will be described below with reference to examples.
For example, the structure of a semiconductor device is a crystal on a GaAs substrate.
In the case of grown AlGaInP semiconductor laser
And explain. FIG. 1 shows Se-doped on an n-type GaAs substrate 1.
N-type GaAs buffer layer 2 is 0.5 μm, Se doped
N-type AlGaInP cladding layer 3 is 1 μm, undoped
GaInP active layer 4 is 0.06 μm, Zn-doped P-type A
lGaInP clad layer 5 is 1 μm, Zn-doped p-type G
The aInP layer 6 is 0.2 μm and the p-type GaAs layer 7 is
Red semiconductor laser structure with 0.5 μm stacked, size
Is 350 μm in length, 350 μm in width, and 100 μm in height.
It As shown in FIG. 2 (a), this is a medium with a thickness of 20 μm.
Stainless steel with a square hole of 400 μm × 400 μm in the heart
Fix it to the reinforcement ring 8 made of LES with epoxy adhesive,
Sulfuric acid type etching solution (H₂SO_Four: H ₂O₂: H₂O =
GaAs is etched away at 1: 8: 1 (Fig. 2).
(B)).

The pressing ring 1 as shown in FIG.
It is fixed to a fixing jig composed of 1, a screw 10, and a supporting jig 12, and is put in a secondary ion detecting device, and sputter etching is started using Cs + ions from the direction of the arrow shown in the figure. The reason why the fixing jig is used is that the reinforcing ring 8 alone is not easy to handle, and the epi film 13 is in contact with one surface of the reinforcing ring, so that it is installed in the secondary ion detector after selective chemical etching. This is because there is a risk of damage due to shock during installation or warpage of the reinforcing ring when installed. When an attempt is made to observe a transmission electron microscope image of only the 0.06 μm active layer, the active layer does not contain Al. For example, when etching from the surface, Al ions are no longer generated as shown in FIG. When the etching is stopped, it is possible to stop the etching at the P-AlGaInP interface of the active layer. Next, the fixing jig shown in FIG. 3 is turned upside down to start sputter etching using Cs ions from the substrate side, and stop etching when Al ions are no longer detected. By doing so, only the 0.06 μm-thick active layer can be thinned to prepare a sample for a transmission electron microscope.

(Embodiment 2) Next, etching takes a considerably longer time than in the above-mentioned embodiment, but since a sample for a transmission electron microscope is produced while observing the measurement point, the result is almost certain. A method for producing a sample with a yield of 100% will be described. The sample used is the same as that described in Example 1. As shown in FIG. 3, the substrate is removed by chemical etching to form only the epi film 13, and the epitaxial film 13 is placed in a sputter etching device on which an Auger electron detection device is mounted. Ideally, the Auger electron detector is incorporated into the scanning electron microscope. Since the degree of vacuum is not good during sputter etching with Ar, the surface of the sample cannot be analyzed by irradiating the sample surface with accelerated electrons. Therefore, during composition analysis by Auger electron, high vacuum (10 ^-8 torr)
r) or less) and a low vacuum (about 10 ⁻⁴ torr) during sputter etching requires a considerable amount of time to prepare a desired sample, but the surface condition and the sputter position are observed with a scanning electron microscope. However, it has the advantage of being able to perform etching, and it has become possible to prevent contamination by etching unnecessary areas and to prepare transmission electron microscope samples in minute areas.

In the ion etching by the conventional ion milling apparatus, it was hardly known in the initial stage of etching which region was irradiated with ions, but in the present invention, the etching is performed while confirming the secondary electron image from the initial stage. Since it can be done, there is no needless etching. Further, in the conventional ion milling device, the ions are irradiated at an angle that is very shallow as the surface of the sample slides, but in the present invention, it is not necessary to care about the irradiation angle of neutral particles or ions.

(Embodiment 3) In the above-mentioned two embodiments, the depth position can be determined with a high degree of accuracy, and some samples require precision, but the position may be approximately the same. In this case, the depth position can be obtained by installing a quadrupole mass spectrometer in the exhaust line of the sputtering device and performing elemental analysis of the sputtered particles. Examples will be described below. The sample used is the same as that described in Example 1. As shown in FIG. 3, the substrate is removed by chemical etching to form only the epi film 13, and the epitaxial film 13 is placed in an exhaust line 52 as shown in FIG. 5 in which a quadrupole mass spectrometer 51 is placed. , And mount it on the sample table 54. Since the mother crystal of the semiconductor is analyzed, the degree of vacuum need not be so high, but 10 ^-6 in consideration of contamination and the like.
A vacuum degree of torr or higher is necessary.

The sample surface is irradiated with Ar ions from the direction shown in the figure. The acceleration energy at this time is adjusted so that the etching rate is, for example, about 1 μm / h, although it depends on the material to be measured. If the etching rate is too high, the surface may be roughened, or the etching may not be stopped at a desired depth position and may be overetched. Since the thickness of the sample that can be observed with the transmission electron microscope is about 50 nm or less, it is easier to control if the etching rate is slower to some extent.

Also in this case, the etching is quickly stopped when Al is no longer detected as in the first embodiment, and the etching on the opposite side is started. In this way, etching can be stopped at a desired depth position, and only the active layer can be taken out and observed with a transmission electron microscope.

[0014]

As described above, according to the present invention, since it is possible to etch a desired region to a desired depth position, it is possible to observe defects and deteriorated states of a specific layer, and
As a method for producing an observation sample, since it can be produced with a yield of almost 100%, there is almost no waste of sample preparation, and it is very effective in shortening the time until observation.

[Brief description of drawings]

FIG. 1 is a perspective view of a layer structure of a semiconductor device used in the present invention.

FIG. 2 is a reinforcing ring and a fixing method for fixing the sample to be measured used in the present invention.

FIG. 3 is a sectional view of a reinforcing ring fixing base of the present invention.

FIG. 4 is a diagram showing positions in the depth direction from the surface obtained by using the present invention.

FIG. 5 is a cross-sectional view of the device of the present invention.

FIG. 6 shows a conventional sample preparation method.

[Explanation of symbols]

1 n-GaAs substrate 2 n-GaAs buffer layer 3 N-AlGaInP clad layer 4 GaInP active layer 5 P-AlGaInP clad layer 6 p-GaInP layer 7 p-GaAs cap layer 8 Reinforcement ring 9 Epoxy adhesive 10 screws 11 Press ring 12 Support jig 13 Epi film 14 Cs 50 chambers 51 Quadrupole mass spectrometer 52 Exhaust line 54 sample table 55 ion gun 56 peep windows 71 dummy glass 72 Adhesive 74 Epi film 75 GaAs substrate 76 Adhesive 77 Dummy glass

Claims (4)

[Claims] 1. A semiconductor device having a laminated structure having different compositions is etched and removed to a predetermined thickness by selective chemical etching, and then the mass of secondary ions is detected while etching and removing with Cs + ions to etch at a desired position. A method for producing a sample for a transmission electron microscope, which comprises: 2. A semiconductor element having a laminated structure of different composition is removed by selective chemical etching to a predetermined thickness, then sputter-etched with Ar at a first vacuum degree, and then etching is stopped. The transmitted electron is characterized in that the degree of vacuum is set to 2, and the etching portion is irradiated with electrons to detect secondary electrons and Auger electrons, and the etching and the Auger electron detection are repeated up to a predetermined position. Method for preparing sample for microscope. 3. A semiconductor element having a laminated structure having a different composition is etched and removed to a predetermined thickness by selective chemical etching, and then the mass of the element is detected using a quadrupole mass spectrometer while sputter etching with Ar. And a method for producing a sample for a transmission electron microscope, which is characterized in that etching is stopped at a desired position. 4. The sample to be measured is fixed to a stainless steel reinforcing ring having a hole larger than that of the sample to be measured with an epoxy adhesive, and the reinforcing ring is fixed to a fixing base composed of a holding ring, a screw, and a supporting jig. And a method for producing a sample for a transmission electron microscope.