Semiconductor device manufacturing: process – Bonding of plural semiconductor substrates – Subsequent separation into plural bodies
Reexamination Certificate
2001-02-28
2002-10-15
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Bonding of plural semiconductor substrates
Subsequent separation into plural bodies
C438S506000, C438S455000, C438S691000
Reexamination Certificate
active
06465327
ABSTRACT:
TECHNICAL FIELD
The present invention concerns a method for producing a thin membrane and the membrane structure so obtained. This membrane may be made up of one or more materials, monocrystalline materials in particular. It may be self-supporting or fixed to a supporting substrate to rigidify the structure so obtained.
This type of membrane offers many advantages. By way of example, mention may be made of compliant substrates which may use a membrane of the invention, or any other application in which a thin film is required (silicon film on a glass or plastic substrate). By compliant substrate is meant a structure able to accept the stresses induced by a structure adhering to it, and which may be a layer deposited on a surface of this substrate by heteroepitaxy for example.
PRIOR ART
FR-A-2 681 472 describes a method for fabricating thin films in semiconductor material. This document discloses that the implanting of a rare gas or of hydrogen into a substrate in semiconductor material is able to create microcavities or microbubbles called “platelets” at a depth close to the average penetration depth of the implanted ions. If this substrate is placed in intimate contact, via its implanted surface, with a stiffener, and if heat treatment is applied at a sufficient temperature, an interaction occurs between the microcavities or platelets leading to separation of the semiconductor substrate into two parts: firstly a thin semiconductor film adhering to the stiffener, and secondly the remainder of the semiconductor substrate. Separation occurs at the site where the microcavities or platelets are present. Heat treatment is such that the interaction between the microcavities or platelets formed by implantation causes the separation of the thin film from the remainder of the substrate. A transfer therefore takes place of a thin film from an initial substrate to a stiffener acting as a support for this thin film.
This method may also be applied to the fabrication of a thin film in solid material other than a semiconductor material (a conductor or dielectric material), whether crystalline or not.
With the methods described in FR-A-2 681 472 (corresponding to U.S. Pat. No. 5,374,564) already cited and FR-A-2 767 416, it is possible to transfer a thin film in homogeneous material or made up of homogeneous or heterogeneous multilayers to a mechanical support also called a stiffener. This transfer is advantageously conducted using heat treatment. However, this heat treatment may be associated with or entirely replaced by mechanical separation, for example by using tensile and/or shearing and/or flexion forces applied in separate or combined manner. Such process is described in FR-A-2 748 851.
It has also been shown that this technique could be used without a stiffener if the implanted ions are located at a sufficient depth to induce fracture over the entire substrate with no blister formation at the implanted surface. In this respect, reference may be made to FR-A-2 738 671 (corresponding to U.S. Pat. No. 5,714,395). In this case, to obtain a fracture, the microcavity zone needs to be at a minimum depth relative to the implanted surface so that the thin film may be sufficiently rigid. This rigidity may also be obtained through the use of one or more layers deposited on the thin layer with fracture.
The documents cited above describe methods with which it is possible to obtain a thin layer of material. This layer may be homogeneous, contain all or part of a microelectronic or optoelectronic component, or even be heterogeneous. By heterogeneous is meant that it may be made up of several elements stacked on top of each other. These stacks of layers are generally obtained by epitaxial growth. With epitaxial growth the problem is raised of compatibility between the different layers. These compatibility problems may for example relate to widely varying mesh parameters leading to dislocations in at least one of the layers. On this account, some structures appear impossible to obtain.
Also, document FR-A-2 738 671 already cited, indicates that implantation must be conducted at an energy such that the ion penetration depth is at least equal to a minimum depth for the film to be rigid. It is indicated that, for silicon, the minimum penetration depth is in the order of 5 &mgr;m even 4 &mgr;m. This relates to an implanting energy of approximately 500 keV. For silicon carbide, which is a much more rigid material than silicon, the minimum possible thickness of the thin film is in the order of 1 &mgr;m. With this method, it is therefore possible to obtain thin films or layers whose thickness is greater than a minimum thickness needed to provide the thin layer with some extent of rigidity. It is indicated that a rigid thin layer is a layer whose mechanical properties are sufficient during the second step (which corresponds to heat and/or mechanical treatment) to avoid the onset of swelling, platelets or platelet burst and hence are sufficient for application of the second step to achieve surface detachment. However, with this method, it is impossible, depending upon the mechanical nature of the required film, to obtain self-supporting thin films using standard commercially available implanters, that is to say using implanters having a maximum implanting energy of 200 keV. For example, it is impossible to obtain a silicon film having a thickness of 4 &mgr;m with such energy.
Another problem is raised if it is desired to use a standard implanter (energy less than 200 keV) to transfer a thin film onto an ordinary support, that is to say a support which does not have sufficient rigidity to obtain a stiffening effect. For example, it is not possible to transfer a monocrystalline silicon film onto a flexible support such as a plastic support without using an intermediate support of handle-type such as disclosed in FR-A-2 725 074. However, it would be advantageous to have available a method with which it is possible a overcome the need for this handle-type support and which enables direct transfer of the thin film onto its final support.
DISCLOSURE OF THE INVENTION
The invention provides a solution to the above-cited problems. The solution is put forward to fix two substrates to one another via their implanted surface, implantation being conducted such that the substrate cleavage phenomenon may occur at the implanted zones. It is then possible to obtain a membrane formed by the joining of the two thin layers. This membrane may be transferred onto any type of support (semiconductor, metal, plastic, ceramic) with no condition as to adhering force (strong or weak) between the membrane and the support.
The subject matter of the invention is therefore a method for producing a thin membrane, characterised in that it comprises the following steps:
implanting gas species through one surface of a first substrate and through one surface of a second substrate which, in such substrates, are able to create microcavities delimiting for each substrate a thin layer lying between these microcavities and the implanted surface, the microcavities being able, after their implantation, to cause detachment of the thin layer from its substrate;
assembly of the first substrate onto the second substrate such that the implanted surfaces face one another;
detaching each thin layer from its substrate, the thin layers remaining assembled together to provide said thin membrane.
By gas species is meant elements, hydrogen or rare gases for example, in their atomic form (H for example) or in their molecular form (H
2
for example) or in their ionic form (H
+
, H
+
2
. . . for example) or in their isotopic form (deuterium for example) or in isotopic and ionic form.
Also, by implantation is meant any means of inserting the previously defined species, either alone or in combination, such as ion bombardment, diffusion, etc.
According to one variant of embodiment, the steps are conducted in the following order:
implanting the first substrate and the second substrate,
assembly of the first substrate onto the second substrate via the implante
Aspar Bernard
Bruel Michel
Jaussaud Claude
Lagahe Chrystelle
Commissariat a l'Energie Atomique
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Rocchegiani Renzo N.
Smith Matthew
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