Abstract:
The invention relates to an installation for treating wafers made of materials serving as microelectronics substrates including a tank for containing a treatment bath, a wafer support device capable of receiving at least one wafer of a first size, and an element for grasping and placing each wafer of the first size in the bath and for removing it therefrom. The installation further includes a support for receiving at least one wafer of a second size that is smaller than the first size, the shape of the support allowing it to be grasped by the grasping element and received by the wafer support device in the tank.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of microelectronics. It relates more particularly to the field of installations for treating wafers of materials used as substrates for the fabrication of microelectronic components and in particular chemical treatment installations. 
     BACKGROUND ART 
     To be more precise, the present invention relates to the field of installations and methods for treating and manipulating wafers, in particular in the context of methods of manipulating wafers without using a cassette, which type of installation is often referred to as a “cassetteless” installation. It is nevertheless also directed to certain manipulations using cassettes that receive wafers. 
     The document U.S. Pat. No. 5,657,879 discloses a cassette for receiving wafers including plates for adjusting the capacity of the cassette and sleeves, also in the form of cassettes, for adapting the cassette to receive wafers with different dimensions. 
     The document DE 45 00 205 discloses a cassette for receiving wafers including an adaptor for receiving wafers with different dimensions. 
     Chemical treatment of wafers for microelectronics generally necessitates the immersion of the wafers in baths of chemical products, some of which are corrosive. 
     In cassetteless installations for manipulating and treating wafers, the wafers are initially disposed in batches of 25 in a manipulation and storage cassette, for example, and are removed from the cassettes and immersed successively in different chemical baths. Between the baths, the wafers are grasped by special combs in order to be transferred from one chemical bath to another. In each bath the wafers are disposed on wafer supports which are intended to remain permanently in the chemical bath. 
     The wafers are deposited on wafer supports specific to each tank and the combs do not remain in the tanks during treatment. This type of installation enables the chemical treatment to be optimized by adapting the wafer supports in each tank. The wafer supports can have a very small volume and surface area to interfere with the treatment as little as possible. 
     This type of installation avoids contamination of the baths by the chemical products which remain on the baskets or cassettes if baskets or cassettes are used to transfer wafers from one tank to another. What is more, there can be a multiplicity of transfer combs, for example, to avoid the combs being dipped successively into chemically incompatible baths. They can also be rinsed while the wafers are undergoing chemical treatment. However, this type of installation is unable to treat several sizes of wafers using the same system. The comb system is already difficult to adjust mechanically to guarantee proper holding of wafers of a single type, and therefore there is no question of achieving an adjustment enabling satisfactory holding of wafers of several types, i.e. several sizes. 
     SUMMARY OF THE INVENTION 
     The present invention provides an economic way of treating more than one type of wafer in the above type of installation. 
     This is achieved by an installation for treating wafers of a material used as a substrate for microelectronics, the installation comprising: 
     a tank adapted to contain a treatment bath and provided with wafer support means, preferably in the form of a wafer support device that is adapted to receive at least one wafer of a first size; 
     holding means, preferably in the form of a grasping element that is adapted to grasp each first size wafer to place it in the tank and withdraw it therefrom; and 
     a support that is adapted to receive at least one wafer of a second size less than the first size, which support has a geometry such that it can be grasped directly by the holding means and received by the wafer support means of the tank. 
     Thus, even if an installation according to the invention is dedicated to treating wafers of a first size, it is possible to effect chemical treatment of wafers of a second size smaller than the first size. 
     BRIEF DESCRIPTION OF THE INVENTION 
     For example, if the installation is dedicated to treating 20 cm diameter wafers, the grasping means, for example combs, are adjusted for that diameter and the tanks are provided with wafer supports adapted to receive wafers of that size. 
     The installation can nevertheless also be used to treat 10 cm diameter wafers, for example, because all that is required is to place the 10 cm diameter wafers in a support having a geometry such that it can be grasped by the combs. 
     That geometry is advantageously determined by manipulator plates whose shape is similar to that of a wafer of the first size, i.e. has a diameter of 20 cm, in the example described above. 
     It is even more advantageous for the support to include two manipulator plates joined together by strips adapted to hold a batch of wafers of the second size, either directly or through the intermediary of a cassette. 
     In another aspect, the invention proposes a method of treating wafers of materials used as substrates for microelectronics, including a step of employing holding means originally designed to grasp at least one wafer of a first size and to immerse each wafer in a treatment bath contained in a tank provided with wafer support means adapted to receive at least one wafer of said first size, characterized in that it alternately includes a step of using the same holding means to grasp a support adapted to receive at least one wafer of a second size, less than the first size, and to immerse the second size wafers in the treatment bath by depositing said support in said tank so that it cooperates with said wafer support means. 
    
    
     Other aspects, objects and advantages of the invention will become apparent after reading the following detailed description, which is given by way of non-limiting example only and with reference to the accompanying drawings, in which: 
     FIG. 1 is a diagrammatic sectional representation of a wafer storage box; 
     FIG. 2 is a diagrammatic representation of the transfer of wafers from a storage and manipulation cassette to a support according to the invention; 
     FIG. 3 is a schematic representation in end elevation of two variants (FIGS. 3 a  and  3   b ) of means of manipulating the support according to the invention; 
     FIG. 4 is a schematic representation of the wafer support members and various embodiments of the edge of the means of manipulating supports according to the invention; FIGS. 4 a  and  4   b  respectively show, in section, multiple and single support members; FIGS. 4 c  to  4   e  show in section various shapes of edge adapted to cooperate with the support members; and FIG. 4 f  shows a support according to the invention in end elevation, with an edge of the type shown in FIG. 4 e , and interengaged with transfer combs; 
     FIG. 5 is a perspective view of one non-limiting example of a support according to the invention; 
     FIG. 6 is a perspective view of another non-limiting example of a support according to the invention; 
     FIG. 7 is a diagrammatic partial end view of the support according to the invention shown in FIG. 6; 
     FIG. 8 is a perspective view of another embodiment of a support according to the invention; 
     FIG. 9 is a diagrammatic partial end-view of the support showing FIG. 8; and 
     FIGS. 10 and 11 are diagrammatic representations of different embodiments of utilizing supports according to the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to the skilled artisan from this detailed description. 
     Manufacturers of microelectronic components use wafers of materials such as silicon, quartz, glass, etc. Generally speaking, although this is not limiting on the invention, the material can be a semiconductor, ceramic or plastics material. The wafers are usually round and thin. For silicon, for example, the diameter of the wafers  1  is typically 10 cm (4 inches), 12.5 cm (5 inches), 15 cm (6 inches), 20 cm (8 inches) or 30 cm (12 inches). However, the present invention is compatible with other shapes of the wafers  1 . For example, the wafers can have shapes of the kind used to fabricate flat screens. 
     According to the invention, the wafers undergo a number of technological process steps to form electronic, optical or opto-electronic components. Such processes comprise one or more operations in which the wafers are chemically treated in liquid chemical baths  21 . 
     The baths  21  are typically mixtures of acids, bases, solvents or de-ionized water and rinsing solutions. The baths  21  are contained in tanks  20  fed automatically with chemical products from a centralized product distribution system. The tank  20  can be heated and activated by ultrasound or megasound. The tanks  20  are generally grouped together on a chemical treatment system for automatically transporting the wafers from one tank to another, starting from a loading and/or transfer station and ending at an offloading station. 
     The wafers are advantageously chemically treated in batches, for example batches of 25. Before and after the chemical treatment steps the batches of wafers are manipulated and stored in first storage boxes  5 . 
     FIG. 1 shows that the first storage boxes  5  are closed by a lid  7  and contain a manipulation and storage cassette or box  4  in which the wafers are stored. The manipulation and storage cassettes  4  are made from a plastics material that is incompatible with the nature of the chemical treatment baths generally employed. 
     In one particular embodiment of the method according to the invention an installation dedicated to 20 cm diameter wafers is used for chemical treatment of 10 cm diameter wafers using a support  10  described below. 
     The following detailed description refers to 10 cm diameter wafers  1  and 20 cm diameter wafers  2 . 
     FIG. 2 shows how a transfer system  30  removes the 10 cm diameter wafers  1  from the manipulation and storage cassette  4 . The transfer means  26  then interengage with and move the 10 cm diameter wafers  1  and deposit them in a support  10 . The support  10  can then be deposited in a second manipulation and storage cassette  3  which can itself be stored in another box to await chemical treatment of the wafers  1 , for example. 
     The second manipulation and storage cassette  3  is advantageously identical to those adapted to receive the 20 cm diameter wafers  2 . 
     As a general rule, the support  10  must be compatible with the physical and/or chemical treatments mentioned above and must not contaminate the wafers  1 . The support  10  is advantageously made from a very pure and chemically inert material such as quartz or various plastics material and fluorinated products. A support  10  of this kind comprises holding members  11  and members  14  for retaining the wafers  1  on the support  10 . By way of non-limiting example, the holding members  11  comprise a pair of holding plates  12  and the retaining members  14  consist of bars  15 . 
     In accordance with the present invention, the support  10  is intended to enable equipment for manipulating 20 cm diameter wafers  2  to be used to treat 10 cm diameter wafers  1 . The holding members  11  must therefore have a shape compatible with that equipment, since it is the holding members  11  that manipulate the supports  10 . For example, if two transfer combs  27  are adapted to interengage with two diametrally opposite areas of the 20 cm diameter wafers  2 , the transfer combs  27  must also be able to interengage with the holding members  11 , which must also have two diametrally opposed holding areas  47  separated by a distance of approximately 20 cm (FIGS. 3 a  and  3   b ). Similarly, for it to be possible for the support  10  to be deposited on the bottom of the tanks  20 , on wafer supports  22  designed to receive 20 cm diameter wafers  2 , the holding members  11  must have bearing areas  48  such that the support  10  can rest on the wafer supports  22  (FIGS. 3 a  and  3   b ). 
     In a basic embodiment, the holding members  11  have dimensions (diameter and thickness) identical to those of the wafers  2  so that they can be grasped by the transfer combs  27  originally designed to grasp such wafers  2  and locate in storage boxes originally designed to receive such wafers  2 . 
     However, the shape of the holding members  11  can be different, and optimized so that the chemical treatments are effective and homogeneous, while complying with the disposition and the geometry of the holding areas  47 , the bearing areas  48  and the retaining members  14 . FIGS. 3 a  and  3   b  show two embodiments of such holding members  11 A,  11 B. FIGS. 3 a  and  3   b  also show in dashed outline the position that a larger wafer  2  to be treated would assume in the transfer combs  27 . 
     If the holding members  11  are thicker than the wafers  2 , they advantageously have, at least in the holding areas  47  and bearing areas  48 , an edge  43  adapted to cooperate with the storage and manipulation cassettes  3 , the transfer means  26 , the cransfers combs  27  and the wafer supports  22 . 
     The storage and manipulation cassettes  3 , the transfer means  26 , the transfer combs  27  or the wafer support members  22  generally have grasping parts  40  provided with notches  41 . There can be a series of notches  41  on each grasping part  40  (FIG. 4 a ) or a single notch  41  on each grasping part  40  (FIG. 4 b ). 
     As shown in FIG. 4 b  in particular, a notch  41  has a profile adapted to locate a wafer  1 . Chamfers  42  are provided on each side of each notch  41  to guide the wafers  1  towards the notch  41 . If the holding members  11  are thicker than a wafer  2 , they cannot enter directly into the notches  41  of the transfer combs  27 . The edge  43  of the holding members  11  is then shaped to cooperate closely and securely with the grasping parts  40 . Thus the edge  43  can also be chamfered to cooperate with the chamfers  42  on the grasping parts  40  (FIG. 4 c ). In one variant the edge  43  can also be flat and comprise a projecting member  44  (FIG. 4 d ). The projecting member  44  then has a thickness equal to that of a wafer  1 . In another variant, the edge  43  of the holding members  11  can comprise a groove  45  which the whole of the grasping part  40  can enter (FIG. 4 e ). FIG. 4 f  shows a holding plate  12  interengaged with transfer combs  27 , in conformance with the latter variant. The edges of the groove  45  overlap the transfer combs  27  locally, in the area  47  where the holding plate  12  is held by the transfer combs  27 . 
     In one particular but non-limiting embodiment of the support  10 , shown in FIG. 5, the support comprises a single vertical holding plate  12  and three horizontal bars  15 . The holding plate  12  is placed in the middle of the bars  15  and perpendicular to them. The bars  15  are rigidly joined to the holding plate  12 . The 10 cm diameter wafers  1  are disposed on the three bars  15  on each side of the holding plate  12  and parallel to the holding plate  12 . The three bars  15  have notches  41  regularly spaced along their length. 
     The preferred embodiment of the support  10 , as described in outline above, is shown more clearly in FIGS. 6 and 7, which show the two vertical holding plates  12  and the three horizontal retaining bars  15 , forming a rigid assembly. The first type wafers  1  are disposed on  35  the bars  15  between and parallel to the two holding plates  12 . 
     In another embodiment of the support  10 , shown in FIGS. 8 and 9, the support comprises two holding plates  12  and four bars  15 . Each end of a bar  15  is on the inside face  13  of a holding plate  12 , at one of four corners of a trapezium. Disposed in this way, the bars  15  constitute a cassette support member  16  adapted to receive and retain a cassette  6  grouping a series of wafers  1  for treatment. 
     Supports  10  comprising one or two holding plates  12  and three or four bars  15  are described above. Obviously other variants of the support  10  can comprise more than two holding plates  12  or a different number of bars  15 , or other types of bearing members  14 ,  15  for the wafers  1 , for example continuous or discontinuous concave surfaces. 
     Two embodiments of a method in accordance with the present invention utilizing supports  10  as described above will now be described. 
     The first embodiment is shown diagrammatically in FIG.  10  and uses a support as described with reference to FIGS. 8 and 9. In a first step A the first type wafers  1  are removed from the manipulation and storage cassettes  4  by transfer means  26 ,  30  known in the art. The first type wafers  1  are raised by the means  30 , grasped by the means  26  and deposited in a treatment cassette  6  (step A). A cassette transfer system  28  engages with and moves the treatment cassette  6  and deposits it in a support  10 , as shown in FIGS. 8 and 9 (step B) . Transfer combs  27 , originally designed for grasping and moving larger wafers  2 , can then interengage with the holding plates  12  in a step C to move the support  10  carrying the cassette  6  containing the wafers  1  toward a tank  20 . The tank  20  contains a chemical treatment bath  21 . The support  10  is put down on the bottom of the tank  20  with its holding plate  12  resting on wafer support rods  22  originally designed to receive larger wafers  2 . The transfer combs  27  are advantageously withdrawn from the tank  20  during the chemical treatment and can be rinsed if necessary. After the chemical treatment is finished, the transfer combs  27  grasp, raise and move the support  10 . The support  10  can be moved towards a new chemical treatment tank. At the end of the chemical treatment operations, steps A, B and C described above can be repeated in the reverse chronological order, before offloading and/or storing the first type wafers  1 . 
     A second embodiment of a method according to the present invention is described below with reference to FIG.  11 . It comprises two main steps G and H. During step G, 10 cm diameter wafers  1  are transferred from a manipulation and storage cassette  4  to a support  10  using transfer means  26 ,  30 . Transfer combs  27  originally designed to grasp and move larger wafers  2  then interengage with the holding plates  12  to lift and move the support  10  towards a tank  20  on the bottom of which the support  10  is placed, resting on wafer support rods  22 , which were also originally designed to receive larger wafers  2  (step H) The tank  20  contains a chemical treatment bath. The transfer combs  27  are preferably withdrawn from the tank  20  and rinsed while the treatment of the wafers  1  is taking place. Then either the operations G and H are repeated in reverse order to store the 10 cm diameter wafers  1  in storage and manipulation boxes  4  or the support  10  is moved into a new tank for further chemical treatment or rinsing. 
     The use of the invention has been illustrated by way of example with reference to 10 cm diameter wafers  1  treated in an installation initially dedicated to treating 20 cm diameter wafers  2 , but the invention can obviously be used with any other two dimensions of the wafers  1 . 
     It follows from the foregoing description that a treatment installation and method according to the invention enable the use of several types of wafers  1  with different dimensions without having to change or adjust the transfer combs  27 , the tanks  20  fitted with their wafer support rods  22 , etc. 
     The invention being thus described, it will be apparent that the same may be varied In many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be recognized by the skilled artisan are intended to be included within the scope of the following claims.