WO2005086222A1

WO2005086222A1 - Method for revealing dislocations emerging in a crystalline material

Info

Publication number: WO2005086222A1
Application number: PCT/FR2005/050134
Authority: WO
Inventors: Yann Bogumilowicz; Jean-Michel Hartmann; Yves Campidelli
Original assignee: Commissariat A L'energie Atomique
Priority date: 2004-03-02
Filing date: 2005-03-01
Publication date: 2005-09-15
Also published as: FR2867309A1; FR2867309B1

Abstract

The invention relates to a method for revealing dislocations emerging in a surface layer made of crystalline material of a substrate by etching this surface layer. The crystalline material of the surface layer consists of Si1-xGex in which 0 = x = 1, and the etching is effected by means of a gas that etches said crystalline material.

Description

METHOD FOR REVELATION OF EMERGING DISLOCATIONS IN A CRYSTALLINE MATERIAL

DESCRIPTION

TECHNICAL FIELD The present invention relates to a process for revealing emerging dislocations in a crystalline material. It relates in particular to the revelation of emerging dislocations in a thin film of semiconductor material secured to a support.

STATE OF THE PRIOR ART There are several techniques for determining the density of the defects existing in a monocrystalline material. These techniques include transmission electron microscopy, X-ray topography and chemical revelation. Transmission electron microscopy (TEM) gives very detailed information on the nature of the defects present in a monocrystalline film. In particular, it is a technique which will make it possible to observe all the defects which one can find in a crystal, that is to say gaps, interstitials, dislocations ... This technique makes it possible to observe the dislocations as a whole. We can therefore observe the emerging parts of the dislocations, which pass through the upper layers of the sample, and are harmful for the electrical properties. We can also observe the parts buried, known as the mesh parameter agreement, which have little influence on the electrical properties of the upper layers. This makes it more difficult to interpret the results obtained and to count them. The statistics of these defects can also be biased by the very small volume of material observed. Indeed, the sample must be transparent to electrons in at least one dimension to be observable. Therefore, the samples typically measure 100 μm x 100 μm x some 100 nm. The volume probed is not always typical of the starting material. The measurement time is typically a few days, mainly due to the preparation of the sample. The subtlety of this technique also requires having dedicated staff. This technique is destructive. X-ray topography consists of a projection of all the defects present in the sample on a plane (the plane of a photographic film or a CCD sensor). The principle of fault observation is similar to that of transmission electron microscopy. So, as in transmission electron microscopy, we observe the dislocations as a whole. As X-rays penetrate matter much more easily than electrons, the measurement can be made directly on the sample to be observed without any special preparation. The spatial resolution obtained with this technique is typically from 1 to 10 μm. The measurement time varies from a few minutes to a few hours. The subtlety of this technique requires having dedicated staff. This technique is non-destructive. The chemical revelation of the defects gives information only on the surface of the sample. It does not allow direct observation of the defect itself but of the relief that the revelation will have created. The revelation takes place by exposing the sample to a chemical solution which will etch it. All chemical fault revealing solutions work on the same principle. They contain one or more oxidizing agents (the most used are HON ₃ , Cr0 ₃ , K ₂ Cr ₂ 0 ₇ ..) which will transform (for example if the monocrystalline material is silicon) silicon into Si0. This Si0 ₂ is then etched by dissolution in hydrofluoric acid (HF). If the solution is judiciously chosen, it must engrave with defective zones the zones with defects and the zones without defects. This is due to the stress field created by the dislocation and / or the segregation of impurities at the level of the dislocation, which will modify the surface potential between the dislocation and the perfect crystal surrounding it. The engraving speeds observed will therefore be different for an area with or without defects. In the case of dislocations, we will observe the intersection of these with the surface of the sample, ie points. The revelation time is typically a few minutes. The revelation does not require any special preparation of the sample. This technique is relatively simple, and can be practiced by anyone authorized to handle chemicals. This technique is destructive. Depending on the densities of defects present in the films, certain techniques are more suitable than others. It is indeed well known that the current state of the art does not make it possible to obtain SiGe films (C) (that is to say SiGe films with or without carbon) relaxed free of dislocations . In particular, these show densities of emerging dislocations typically 10 ⁶ cm ^"2. Such densities are difficult to observe in transmission electron microscopy because they are too low, but are on the other hand too high to be observed by X-ray topography. Therefore, there remains only the chemical revelation which is fully adapted to qualify the films of SiGe (C). There are various chemical preparations, well known in the microelectronics industry, for effecting a revelation. SECCO solution (see F. Secco d'Aragona, J. Electrochem. Soc. 119 (1972), 948). Mention may also be made of the SCHIMMEL solution (see DG Schimmel, J. Electrochem. Soc, 126 (1979), 479) All of these preparations use wet chemistry and use chemicals that are harmful to humans and the environment (HF, chromium and its derivatives, etc.), and the chemistry is fairly dependent on the experimenter. The latter may for example choose to use a different dilution of the development solution, to use a different development time, to use a different volume of solution, whether to use agitation or not ... This can make it difficult to compare the results obtained by different teams. It explains in particular the poor communication on the number of dislocations present in the films of SiGe (C), and the large variations in densities announced from one team to another. In addition, this chemistry is apparently not available in automatic machines with chemical baths (cleaning machine, resin removal ...), which prevents its use on full plates, therefore complicates the counting defects and makes it very difficult to optimize and monitor the quality of the layers online. The article “Dislocation generation of GaAs on Si in the cooling stage” by M. TACHIKAA et al., Applied Physics Letters USA, Vol. 56, No. 22, May 28, 1990, pages 2225 to 2227, discloses the evaluation of the dislocations generated in a layer of GaAs deposited on silicon, during the cooling step. This evaluation is carried out at growth temperature using vapor phase etching. An etching of epitaxial surfaces of GaAs and GaP is reported by a vapor phase of HCl, at growth temperature. The article “Characterization of threading dislocations in GaN epiaxial layers” by T. HINO et al., Applied Physics Letters, American Institute of Physics, New York, USA, Vol. 76, No. 23, June 5, 2000, pages 3421 to 3423, discloses the characterization of dislocations in epitaxial layers of GaN in using an HCl vapor etching technique. These last two documents relate to III-V materials (GaN, GaAs, GaP) which are materials very different from category IV materials (Si, Ge, SiGe), even if all of them are semiconductor crystalline materials. These two categories refer to different worlds of microelectronics. For problems of contamination, pollution, etc., materials III-V and IV-IV do not coexist in clean rooms and in filing, etching equipment, etc. Furthermore, these materials do not react at all in the same way to chemical attacks. Thus, a person skilled in the art specializing in III-V materials is not the same as that of materials IV-IV. Furthermore, the epitaxy frames are equipment which makes it possible to deposit films respecting the atomic arrangement of the substrate on which they are deposited. The frames used industrially carry out the deposits by means of gaseous precursors (SiH, SiH ₂ Cl ₂ , Si ₂ He ... as precursors of silicon). These frames also use gaseous hydrochloric acid to clean the process chamber between each epitaxy. In fact, HCl is a gas which etches silicon, SiGe (C) and germanium among others. The gaseous HCl can also be used during the deposits to allow selective epitaxies to be carried out with respect to a dielectric or as a degree of freedom on the germanium concentration and the growth rate during epitaxy of SiGe (C) films. PRESENTATION OF THE INVENTION To remedy the drawbacks of the prior art, a new method is disclosed here for revealing emerging dislocations in a crystalline material. This revelation is made by gaseous chemical means. This new technique overcomes the main defects of the state of the art indicated above. In particular, the present invention allows a more reproducible revelation from one sample to another, but also from one team to another. The invention can advantageously take advantage of an epitaxy frame, the role of which is usually to deposit monocrystalline films of Si, Ge, SiGe, SiGe (C) .... It therefore benefits from all the advantages to use a machine rather than an experimenter, in terms of standardization and reproducibility in particular. This new process, unlike the processes usually used (chemical attacks such as SECCO etching for example) does not require cleaving the plate of crystalline material. Once the revelation has been obtained, the dislocations are thus directly observable on any device for automatic detection and counting of defects on a full plate such as those used on production lines, or simply by optical or electronic microscopy. Knowledge of the presence of defects in a SiGe film (C) for example, as well as their density and their distribution is very important, in particular for the relaxed SiGe (C) layers (used in CMOS applications with constrained silicon channel, but also in optoelectronics). It is in fact these defects which will determine the electrical and optical properties of the SiGe films (C). The subject of the invention is therefore a method of revealing emerging dislocations in a surface layer of crystalline material of a substrate by etching of said surface layer, characterized in that the crystalline material of the surface layer is made of Siι- _x Ge _x with 0 <x <1 and in that the etching is carried out by means of a gas etching said crystalline material. Advantageously, the etching takes place in the process chamber of an epitaxy frame. If the surface layer is an epitaxial layer on a support epitaxy comprising the remainder of the substrate and if the epitaxy takes place in the process chamber, etching the surface layer ^• can be performed directly after the epitaxy of the surface layer. The etching gas can comprise an acid gas chosen from HC1, HF, HBr and HI. It can be an acid gas diluted in hydrogen. The surface layer may in particular be made of monocrystalline material. The surface layer can be the surface layer of a solid substrate, a crystalline film secured to a support or the silicon film of an SOI substrate. The surface layer can be the SiGe film of an SGOI substrate or the strained silicon film of an SSOI substrate.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and other advantages and particularities will appear on reading the description which follows, given by way of nonlimiting example, accompanied by the appended drawings among which: FIG. 1 is a dark field image of the surface of a pseudo-substrate of SiGe (C) 20% after revelation by a SECCO solution according to the prior art, - Figure 2 is a dark field image of the surface of a pseudo- 20% SiGe (C) substrate after development by the process according to the invention; - Figure 3 is a diagram representing the etching speed as a function of the etching temperature for some compositions of Siι_ _x Ge _x .

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

The following description will mainly relate, by way of example, to the revelation of dislocations in a monocrystalline layer of SiGe (C) epitaxially grown on a monocrystalline silicon support. A preliminary step of preparing the sample to be revealed may be necessary if the SiGe layer (C) is oxidized. It is well known that when a film of SiGe (C) is exposed to air, it tends to oxidize. In order to be able to reveal the films of SiGe (C), it will therefore be necessary to overcome the native oxide. This can easily be done by wet chemical cleaning. In particular, immersion of the sample in a bath of dilute hydrofluoric acid will allow this native oxide to be removed. This immersion also prevents it from reforming for a few hours by passivation of the surface by hydrogen or fluorine atoms. This preliminary step is not necessary if the revelation (etching) takes place directly after the growth of the SiGe layer (C), that is to say without discharging the sample from the epitaxy frame. The epitaxy frame makes it possible to control the temperature and the environment to which the sample is subjected. The revelation is implemented using dry chemistry. It takes place advantageously at high temperature (over 400 ° C.) and at reduced pressure. The sample can first be heated to a temperature above 775 ° C to remove any surface contamination. It is then heated to a temperature of 750 ° C. for example under a stream of hydrogen (a few tens of liters per minute) under a pressure of 2660 Pa (or 20 Torr). Once 750 ° C is reached, a few hundred cubic centimeters per minute of gaseous HCl are introduced in addition to the hydrogen in the process chamber of the epitaxy frame. After an exhibition of typically a few minutes, the sample is discharged from the epitaxy frame. Other gravitational gases such as HF, HBr, HI ... can also be used, diluted in hydrogen. Usually, HCl gas is used in epitaxy for cleaning the quartz domes which make up the deposition chamber, or for allowing selective epitaxy to be carried out with respect to a dielectric, but in no case for revealing defects. After a certain time (depending mainly on the germanium concentration of the sample), the exposure to the etching gas is stopped. The sample is then cooled and discharged from the epitaxy frame. An observation in grazing light should normally show a film of milky appearance. Under the microscope (optical or electronic), the presence of inverted pyramids is observed on the surface of the sample. Each inverted pyramid reflects the presence of an emerging dislocation. The present invention allows the use of an epitaxy frame to reveal the dislocations in a SiGe film (C). It therefore benefits from the intrinsic advantages of this type of tool. We can cite among them a very good uniformity of the process of revelation on the whole of the sample, a great reproducibility from one sample to another, an excellent control of the parameters of the process. HCl gas is already used on epitaxy machines. The implementation of the technique is therefore done without modification of existing equipment. The fact of using a CVD frame and the fact that the revelation is necessarily carried out in a controlled environment makes it possible to drastically limit the presence of particles on the surface of the sample. Particles can disturb the counting statistic during observations, because they can be confused with the pyramids corresponding to the defects. The present invention enables revelations to be made over the entire surface of a standard substrate currently used in microelectronics (ie 100, 150, 200 or 300 mm in diameter). This allows excellent counting statistics, but also makes it easy to make observations on the entire substrate. The revelation on a full plate allows the subsequent use of standard equipment for automatic counting of faults already present on them. production lines. From an industrial point of view, this technique therefore means considerable time savings in the characterization of the SiGe (C) layers (relaxed layers, in particular), and therefore constitutes significant progress for optimization, characterization and online monitoring. such layers which are becoming increasingly important in the industry. The present invention makes it possible to reveal a film of SiGe (C) in situ, just after the end of growth. It is in this way sure that the defects are introduced during growth and not by processes occurring afterwards. The present invention does not use chromium or chromium-based products. It's a advantage because products containing chromium are very toxic for humans and the environment. With the present invention, there is no need to directly handle hazardous chemicals such as hydrofluoric acid HF. This is an advantage in terms of security. The present invention consumes very little material to reveal the defects (typically 20 nm). This is an advantage for characterizing ultra thin films, but also thick films for which we are sure to characterize defects close to the surface. FIG. 1 is an image of the surface of a pseudo-substrate of SiGe (C) 20% after revelation by a SECCO solution. The film to be characterized is a relaxed film Sio, Ge ₈ ₀ ₂ 1.2 .mu.m thick. The image was obtained by a dark field optical microscope. It corresponds to a field of 240 μm x 180 μm. The edges of the image are oriented along the crystallographic directions [110]. The bright points are the signature left by the revelation of the dislocations which cross the film. A count gives 426 dislocations, ie a density of 9.9 × 10 ⁵ cm ⁻² . FIG. 3 is an image of the surface of a pseudo-substrate of Si _{0 /} 8Ge _0/2 after revelation by the present invention. characterized is a relaxed Si film _0, 8GE _0, ₂ of 1.2 .mu.m thick. the sample is identical to that of Figure 1. the image was obtained by an optical microscope dark field. It corresponds at a field of 240 μm x 180 μm. The edges of the image are oriented along the crystallographic directions [110]. Brilliant are the signature left by the revelation of the dislocations which cross the film. A count gives 442 dislocations, ie a density of 10 ⁶ cm ^"2. This process therefore makes it possible in particular to characterize the crystalline quality of SiGe (C) layers. The crystalline quality of SiGe (C) layers will depend on the quality of electrical structures produced using these layers. The realization of electrical structures is very long and costly. It requires many steps which will complicate the interpretation of results. In this context, a revelation of the defects present in the SiGe film (C) , using the method presented here, makes it possible to very quickly obtain information on the quality of the epitaxy film The present invention relates to the revelation of emerging dislocations in SiGe (C) films whatever their germanium concentration. However, it requires an adaptation of the parameters of the development process to the germanium concentration of the sample. feel invention may also be considered on germanium films. The revelation is also effective whether the SiGe film (C) is deposited on silicon, or on an insulator (SGOI). It can also be envisaged that the present technique makes it possible to reveal dislocations in silicon either on solid substrates, or on SOI or constrained silicon substrates on SSOI substrate (for “Strained SOI”). In this case, the very low material consumption with the present technique would characterize the ultra-thin SOI layers. The present invention can also be envisaged for substrates of orientation other than (001), for example substrates (111), (110) ... The present invention can also be envisaged for other families of semiconductors than IV-IV, like the family of III-V type GaAs, or II-VI type CdSe ... We can envisage the realization of a network of holes if we manage to create a network of dislocations. In fact, it is well known that when a silicon film is bonded to a silicon substrate with a slight disorientation between the crystal orientations of the two substrates, we will create a network of dislocations. With the present invention, an array of holes can be created by revealing the dislocations. FIG. 3 is a diagram representing the etching speed V as a function of the etching temperature for some compositions of Siι- _x Ge _x . Advantageously, the etching temperature to reveal the defects is adapted as a function of the respective proportions of Si and Ge in the material Siι_ _x Ge _x . Thus, the etching temperature can be chosen so that the etching speed is typically between 1 and 10 nm / min. Thus, for silicon (curve 1), it is preferable to work around 800 ° C. For Si ₀ .33 ₀ 67Ge (curve 2), it is preferable to work around 700 ° C. For Si ₀ , _s Ge ₀ , 5 (curve 3), it is preferable to work around 650 ° C. For germanium, it is preferable to work around 400 ° C. The diagram in FIG. 3 illustrates the evolution, for different proportions of Si and Ge, of the etching speed as a function of the etching temperature with gaseous HCl. A person skilled in the art can, for the desired proportions of Siι- _X Ge _x , obtain the corresponding curve and deduce therefrom the suitable temperature range. Unlike most of the methods of the prior art, the process according to the invention can be applied to very thin films (typically less than 100 nm or even 20 nm), for example to the germanium thin film of a SGOI structure. Thin films are very sensitive to the temperatures to which they are subjected. The method according to the invention allows a very fine adaptation of the set of temperature / time parameters so as not to damage the thin films.

Claims

1- Method for revealing emerging dislocations in a surface layer of crystalline material of a substrate by etching of said surface layer, characterized in that the crystalline material of the surface layer is in Siι- _x G _e with 0 < x <1 and in that the etching is carried out by means of a gas etching said crystalline material.

2- Revelation method according to claim 1, characterized in that the etching takes place in the process chamber of a frame of epitaxy.

3- Disclosure method according to claim 2, characterized in that, the surface layer being an epitaxial layer on an epitaxy support constituting the rest of the substrate and the epitaxy taking place in said process chamber, the etching of the surface layer is produced directly after the epitaxy of said surface layer. 4- Disclosure method according to any one of claims 1 to 3, characterized in that the etching gas comprises an acid gas chosen from HF, HBr and HI. 5- Disclosure method according to any one of claims 1 to 3, characterized in that the etching gas is HCl. 6- Revelation method according to any one of claims 1 to 5, characterized in that the etching gas is an acid gas diluted in one hydrogen. 7- Revelation method according to any one of claims 1 to 6, characterized in that the surface layer is made of monocrystalline material. 8- Disclosure method according to any one of claims 1 to 7, characterized in that the surface layer is the surface layer of a solid substrate. 9- Disclosure method according to any one of claims 1 to 7, characterized in that the surface layer is a crystalline film secured to a support. 10- Disclosure method according to any one of claims 1 to 7, characterized in that the surface layer is the silicon film of an SOI substrate. 11- Disclosure method according to any one of claims 1 to 7, characterized in that the surface layer is the SiGe film of an SGOI substrate.

12- Disclosure method according to any one of claims 1 to 7, characterized in that the surface layer is the strained silicon film of an SSOI substrate.