WO2004086844A2

WO2004086844A2 - Multilayer substrate implanted with a low dose

Info

Publication number: WO2004086844A2
Application number: PCT/FR2004/000739
Authority: WO
Inventors: Laurent Roux; Bernard Vidal; Jacques Perrocheau; Hasnaa Faik
Original assignee: Ion Beam Services
Priority date: 2003-03-28
Filing date: 2004-03-25
Publication date: 2004-10-14
Also published as: FR2853140A1; WO2004086844A3; FR2853140B1

Abstract

The invention relates to a substrate (1) which is provided with a stack of deposited layers (11, 12, 21, 22, , 71, 72). According to the invention, at least one of the aforementioned layers comprises created point defects at a concentration of between 3.1020/cm3 and 3.1023/cm3 in an adjustment zone. The stack of layers preferably comprises a stack of pairs of layers, each pair consisting of an odd layer (11, 21, 71) and an even layer (12, 22, 72) having different compositions. The invention also relates to a method of preparing said substrate.

Description

The present invention relates to a substrate provided with a stack of deposited layers.

This invention therefore relates to thin film technology and finds a particularly interesting application in the field of optics. In fact, in this field, many devices are produced from multilayer substrates, that is to say substrates on which a plurality of thin layers are stacked.

A typical example of these devices is the interference mirror. Such a mirror is composed of a stack of layers which can take different forms. The waves reflected by each layer produce a constructive interference governed by Bragg's law, which justifies providing a certain number of layers. This interference only occurs when the thickness of the layers, taking into account their refractive indices, are of the same order of magnitude as the wavelength to be reflected. Thus, for high energy X-rays whose wavelength is between 0.1 and 1 nanometer, a monocrystalline substrate can be used, the reflective layers here being constituted by the crystal planes parallel to the substrate. On the other hand, when the wavelength increases, there is no satisfactory single crystal.

To treat the spectral range covering low energy X-ray and extreme UV radiation, ie approximately between 1 and 30 nanometers, it is thus known to produce a stack of thin layers deposited under vacuum. The layers are alternately composed of a heavy, rather absorbent material, such as molybdenum or tungsten, and a light, rather transparent material, such as silicon or carbon. The higher the difference in the refractive indices of the two materials, or in other words, the greater the index shock at the interface of two successive layers, the better the resulting reflection. Naturally, the quality of the mirror depends closely on the precision that can be obtained on the different parameters characterizing the deposited layers, and first of all on the thickness of these layers. However, the production methods currently available do not guarantee sufficient precision on this dimensional characteristic when the optical specification of the mirror is very restrictive. The object of the present invention is in particular to adjust the thickness of the deposited layers.

According to the invention, a substrate is provided with a stack of deposited layers and, at least one of these layers has in a setting area n a concentration of point defects created between 3.10 / cm and 3.10 ²³ / cm ³ .

Indeed, it is possible to create point defects by performing an ion implantation on this stack, which makes it possible to reduce the thickness of the layer or layers concerned at the level of the adjustment zone. According to an embodiment adapted to optics, the stack comprises a superposition of pairs each formed by an odd layer and an even layer distinguished by their compositions.

Often, an odd layer and an even layer are further distinguished by their thicknesses. As an example, the composition of an odd layer belongs to the group comprising molybdenum and tungsten.

Likewise, the composition of an even layer belongs to the group comprising silicon and carbon.

Preferably, the thickness of the odd layers and the even layers is less than 30 nanometers.

According to an additional characteristic, the adjustment zone extends over all of the pairs of layers.

For some applications, the adjustment zone presents a variable concentration of point faults created. If necessary, the adjustment zone covers the entire surface of the substrate.

The invention also relates to a method for preparing a substrate provided with a stack of deposited layers, this method comprising a step of ion implantation in a zone for adjusting at least one of these layers, the dose of implantation being between 5.10 / cm and 5.10 / cm oxygen equivalent, so that the concentration of point defects created is between 3.10 ²⁰ / cm ³ and 3.10 ²³ / cm ³ .

The method optionally includes additional steps to obtain the characteristics of the substrate mentioned above. Advantageously, it comprises, following the implantation step, a step of annealing the substrate.

The present invention will now appear in more detail in the context of the following description of an exemplary embodiment given by way of illustration with reference to the single appended figure which represents a substrate.

With reference to this figure, a first reflective layer 11 is deposited on a substrate which is here made of silicon. A second layer 12 is then deposited on the first 11, these two layers forming a first pair. A second pair is then deposited which is composed of a third 21 and a fourth 22 layer. There is thus successively deposited a plurality of pairs, 7 for example, the last being formed of a thirteenth 71 and a fourteenth 72 layers.

The layers of odd rows are preferably identical as regards their compositions and their thicknesses. The material of these layers is advantageously absorbent in the spectral range considered, ie from 1 to 20 nanometers. Mention will be made, by way of example, of molybdenum and tungsten.

The layers of even rows are preferably identical as regards their compositions and their thicknesses. The material of these layers is advantageously transparent in this same spectral range. By way of example, mention will be made of silicon and carbon.

Optionally, a buffer layer or even several layers can be provided which are deposited directly on the substrate 1 before the first reflective layer 11.

The substrate thus provided with a stack of deposited layers is then subjected locally or globally to an ion implantation step. Ion implantation is a technique commonly used for doping semiconductor materials. According to this technique, atoms are ionized then they are accelerated by means of an electric field to provide them with a well defined energy and to project them on the substrate which becomes a target. The ions thus produced are slowed down by energy transfer to the electrons and / or the nuclei of the target atoms. According to the ratio between the mass of the implanted ion and the atomic mass of the target, we pass from the transfer of electronic energy to the transfer of atomic energy to higher or lower energies. The implantation can cause deterioration of the stack of the deposited layers 11, 12, ..., 72, all the more so since the implanted ions are heavy and of low energy.

The implantation of oxygen at high doses, greater than 5.10 / cm, and at medium or high energy tends to damage the stack, thereby considerably reducing any possibility of reflection.

The implantation at high dose and at low energy leads to a spraying of the target, that is to say to an ablation of the deposited layers.

The invention therefore provides for implantation at low dose in a range extending substantially, for oxygen, from 5.10 / cm to 5.10 / cm.

These implantation parameters make it possible to minimize the loss of reflectivity of the stack, while producing a reduction in thickness of the implanted area of the order of 12%.

Thus, for a dose of 10 / cm of oxygen ions of energy equal to 180 keV, an odd layer of molybdenum goes from 2.76 to 2.60 nanometers and an even layer of silicon goes from 4.06 to 3, 35 nanometers.

The penetration depth of the implanted ions, which can be estimated at around 500 nanometers, guarantees a substantially identical treatment of the different pairs of layers deposited. The reduction in thickness of the different layers, which depends on the implantation dose, is closely linked to the number of point defects created. By point defect, we mean a disturbance of the atomic order, a gap for example, created by the shock of the incident ions with the atoms of the target.

The concentration of point defects created is proportional to the implanted dose for a given incident ion, but the proportionality factor very strongly depends on the mass of this ion and the mass of the target atoms.

Thus, for a given concentration of point defects created, the implantation dose will depend on the nature of the incident ion. An object of the invention being to limit the number of these defects, it is therefore preferable to characterize the implantation by the concentration of point defects rather than by the dose.

The following table gives the doses necessary to obtain a concentration of point defects created of 3.10 ²³ defects / cm ³ in the case of a molybdenum-silicon stack implanted with O ions at a dose of 5.10 ¹⁵ / cm ² : Incident ion Energy (keV) Dose (ion / cm ² ) Defect factor (defect / cm. ion) O 180 5.10 ¹⁵ 6.10 ⁷

Ar 320 1.25.10 ¹⁵ 2.4.10 ⁸

N 160 6.10 ¹⁵ 5.10 ⁷

He 60 3.75.10 ¹⁶ 8.10 ⁶

H 30 3.10 ¹⁷ 1.10 ⁶

To establish the equivalence between a reference ion, oxygen in this case, and all the possible ions, the calculation code "SRIM" is used. On this subject, one can refer to the book “Ion Implantation, Science and Technology” published by JF Ziegler (2000 Ion Implantation Technology Co.), Chapter 3 “Ion Implantation Physics”, pages 175 to 238. In addition, one can consult this calculation code, in particular version 2000-39, on the Internet site "www.srim.org/srim/srimlegl.htm", by downloading the program "srim.exe" (protected by copyright 1984-2002 , James F. Ziegler):

"The Shopping and Range of Ions in Matter" (J. F. Ziegler, IBM Research, Yorktown, NY, 10598 USA and J. P. Biersack, Hahn-Meitner Inst., 1 Berlin 39, Germany).

It turns out that a concentration of point defects created greater than 3.10 ²³ defects / cm ³ greatly degrades the optical properties of the stack. The implantation dose will therefore be determined to avoid exceeding this value. It is however advisable to create a minimum of specific faults because otherwise the layout would be pointless. The concentration of defects thus created will therefore be greater than 3.10 ²⁰ defects / cm ³ . In addition, two methods make it possible to demonstrate implantation at low doses. The first method, specular reflection analysis, provides information on interfacial roughness. The second method, transverse measurements (“Rocking Curve” in English), analyzes the light scattered around the different Bragg peaks of the stack of layers.

The implantation can be practiced globally, over the entire surface of the substrate. It can be practiced locally, in an adjustment zone, either by using a photolithography technique, or by using a beam of directed ions. Preferably, after implantation, the substrate is subjected to annealing to reduce optical losses. For example, the temperature is between 100 and 200 ° C, the atmosphere is controlled or it is open air, while the duration is of the order of a few tens of hours. The invention thus makes it possible to carry out the following operations:

- frequency setting of a stack of layers by global layout, for mirrors or masks;

- localization to correct defects in the uniformity of the stack;

- localized repair of defects in the substrate-stack structure; - Realization of a reflection gradient to obtain a range of usable wavelengths, this by varying one of the implantation parameters;

- manufacture and repair of masks or reticles by localization of reflective areas.

Apart from these examples of implementation, the invention applies when it comes to modifying the thickness of any layer.

Furthermore, to protect the substrate, a covering layer can be deposited on the implanted layers.

The embodiment of the invention presented above was chosen for its explicit character. However, it would not be possible to exhaustively list all the embodiments covered by this invention.

In particular, any step or any means described may be replaced by a step or equivalent means without departing from the scope of the present invention.

Claims

1) Substrate 1 provided with a stack of deposited layers 11, 12, 21, 22, ..., 71, 72 characterized in that at least one of these layers has a concentration of defects in an adjustment zone punctuals created between 3.10 / cm and 3.10 ²³ / cm ³ .

2) Substrate according to claim 1, characterized in that said stack comprises a superposition of couples each formed by an odd layer 11, 21, 71 and an even layer 12, 22, 72 distinguished by their compositions. 3) Substrate according to claim 2, characterized in that an odd layer 11, 21, 71 and an even layer 12, 22, 72 are further distinguished by their thicknesses.

4) Substrate according to claim 3, characterized in that the composition of an odd layer 11, 21, 71 belongs to the group comprising molybdenum and tungsten.

5) Substrate according to any one of claims 3 or 4, characterized in that the composition of a pair layer 12, 22, 72 belongs to the group comprising silicon and carbon.

6) Substrate according to any one of claims 2 to 5, characterized in that the thickness of said odd layers 11, 21, 71 and pairs 12, 22, 72 is less than 30 nanometers.

7) Substrate according to any one of claims 2 to 6, characterized in that said adjustment zone extends over all of said pairs of layers.

8) Substrate according to any one of claims 2 to 7, characterized in that said adjustment zone has a variable concentration of point defects created.

9) Substrate according to any one of claims 2 to 8, characterized in that said adjustment zone covers the whole of its surface.

10) Method for preparing a substrate 1 provided with a stack of deposited layers 11, 12, 21, 22, ..., 71, 72 characterized in that, it comprises a step of ion implantation in a zone of adjustment of at least one of these layers, the implantation dose being between 5.10 / cm and 5.10 / cm oxygen equivalent so that the concentration of

20 "i 23 3 point defects created is between 3.10 / cm and 3.10 / cm. 11) Method according to claim 10, characterized in that said stack comprises a superposition of couples each formed of an odd layer 11, 21, 71 and an even layer 12, 22, 72 distinguished by their compositions. 12) Method according to claim 11, characterized in that an odd layer 11, 21, 71 and an even layer 12, 22, 72 are further distinguished by their thicknesses.

13) Method according to claim 12, characterized in that the composition of an odd layer 11, 21, 71 belongs to the group comprising molybdenum and tungsten.

14) Method according to any one of claims 12 or 13, characterized in that the composition of a pair layer 12, 22, 72 belongs to the group comprising silicon and carbon.

15) Method according to any one of claims 11 to 14, characterized in that the thickness of said odd layers 11, 21, 71 and pairs 12, 22, 72 is less than 30 nanometers.

16) Method according to any one of claims 11 to 15, characterized in that said adjustment zone extends over all of said pairs of layers. 17) Method according to any one of claims 11 to 16, characterized in that said adjustment zone has a variable concentration of implanted ions.

18) Method according to any one of claims 11 to 17, characterized in that said adjustment zone covers the entire surface of the substrate. 19) Method according to any one of claims 10 to 18 characterized in that, following said implantation step, it comprises a step of annealing the substrate.