Patent Application
20050118823
1. Field of the Invention
The present invention relates to method and apparatus for processing a wafer when a semiconductor is manufactured.
2. Description of the Related Art
In the semiconductor manufacturing field, the size of a wafer tends to increase year after year. In order to improve a packing density, the thickness of a wafer tends to be reduced. In order to reduce the thickness of a wafer, an underside grinding operation is carried out, i.e., a surface protection tape is adhered to a front surface of a wafer, on which semiconductor devices are formed, to draw and hold the wafer and, then, the underside of the wafer is ground. However, as the thickness of a wafer is reduced, it is more difficult to handle the wafer, and the reliability of a chip mounting operation, after the wafer is cut into chips, is reduced. Accordingly, the ground surface (underside) obtained after the underside grounding operation is carried out, is polished, so that a fracture layer occurring on the ground surface, in the underside grounding operation, is removed.
In some cases, a plasma-processing operation is carried out on a wafer when a semiconductor is manufactured. In Japanese Unexamined Patent Publication (Kokai) No. 5-182935, Kokai No. 5-299385, Kokai No. 8-167595, Kokai No. 9-293876, Kokai No. 11-260793, WO98/33362, Kokai No. 2000-216140, Kokai No. 2001-127016, Kokai No. 2001-160551, Japanese Examined Patent Publication (Kokoku) No. 7-111965, Japanese Patent No. 2534098, Japanese Patent No. 2594448, Japanese Patent No. 2673526, Japanese Patent No. 3093445 and Japanese Patent No. 3231202, various plasma devices used when a semiconductor is manufactured or various processing methods of a wafer to be plasma-processed are disclosed.
Usually, in order to improve the level of cleanliness of a wafer, for example, a gettering method, in which the level of cleanliness of a device active region on the front surface of a wafer is maintained by forming a site to collect heavy metal pollutants on the underside of the wafer, is adopted. However, as described above, if the thickness of a wafer is reduced, it is necessary to provide a process, subsequent to the grinding process, in which a layer damaged by grinding is removed. Accordingly, the effect of the gettering cannot be expected, and ion contamination sometimes occurs. Especially, in recent years, a further reduction in the thickness of a wafer is required. Thus, it is difficult to obtain the effect of gettering, and there is a high possibility that an electrical failure may occur due to ion contamination of a manufactured semiconductor.
When dicing a wafer, a dicing tape is applied to the underside of the wafer, and a dicing saw cuts halfway through the dicing tape, from the front surface of the wafer, so that a part of the dicing tape remains and, thus, the separated dies can be prevented from scattering. However, when the dicing tape is directly applied to a polished surface of the wafer immediately after polishing, an adhesion force between the dicing tape and the polished surface is increased because the polished surface is activated. Therefore, it is difficult to pick up the dies from the dicing tape in a die bonding operation.
Further, when a wafer is not sufficiently cleaned, a natural oxide layer having a nonuniform thickness is partly formed on the underside of the wafer. Accordingly, there is a possibility that the underside of the wafer may be mottled in a later thin film forming process due to the above natural oxide layer. In this case, not only a problem of appearance but also a variation in electrical properties of the semiconductor may occur.
Further, when discrete devices are formed from a wafer, it is preferable that a polishing process is adopted to obtain an excellent uniform thickness of the wafer. However, the underside of the wafer is flattened more than necessary after the polishing process. Accordingly, when the polished surface of the wafer is coated with a metal coating in a later metalizing process, an adhesion force between the metal coating and the polished surface of the wafer is reduced, and the metal coating may be stripped.
In view of the above problems, the object of the present invention is to provide a wafer processing method in which a wafer can be processed while the occurrence of an electrical failure is restricted even if the thickness of the wafer is reduced and to provide a wafer processing apparatus in which the wafer processing method is carried out.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a wafer processing method comprising the steps of grinding an underside of a wafer which is provided, on its front surface, with a plurality of semiconductor devices; polishing a ground surface formed by the grinding operation; and carrying out a plasma-processing for a polished surface formed by the polishing operation under a predetermined gaseous atmosphere in a plasma chamber, to form an oxide layer on the polished surface.
Namely, in the first aspect of the present invention, the oxide layer is formed on the polished surface on the underside of the wafer and, accordingly, the occurrence of ion contamination can be prevented. Therefore, the wafer can be processed while the occurrence of an electrical failure is restricted even if the thickness of the wafer is reduced. The plasma-processing operation can be carried out immediately after the polishing process. Accordingly, the first aspect is different from a situation when it is necessary to transfer the wafer from a polishing machine to a plasma-processing machine, the mixing of contamination from a polluted atmosphere to the wafer can be prevented and, thus, the occurrence of an electrical failure can be further restricted. Further, in the first aspect, even if the dicing tape is applied, an adhesion force between the dicing tape and the wafer is not extremely large because the oxide layer is formed. Therefore, the difficulty of picking up of dies can be prevented. Also, in the first aspect, the wafer can be prevented from being mottled in a later thin film forming process because the oxide layer can be formed on the entire surface of the wafer. Oxygen is supplied to the plasma chamber to provide an oxygen atmosphere in the plasma-processing operation to form the oxide layer.
According to a second aspect of the present invention, there is provided a wafer processing method comprising the steps of grinding an underside of a wafer which is provided, on its front surface, with a plurality of semiconductor devices; polishing a ground surface formed by the grinding operation; carrying out a first plasma-processing for a polished surface formed by the polishing operation under a first gaseous atmosphere in a plasma chamber, to clean the polished surface; and carrying out a second plasma-processing for the polished surface after the washing operation under a second gaseous atmosphere in the plasma chamber, to form an oxide layer on the polished surface.
Namely, in the second aspect of the present invention, the oxide layer is formed on the polished surface on the underside of the wafer and, accordingly, the occurrence of ion contamination can be prevented. Also, in this case, the oxide layer is more uniform and excellent because the oxide layer is formed after a cleaning operation and, thus, the wafer can be processed while the occurrence of an electrical failure is further restricted even if the thickness of the wafer is reduced. The first and second plasma-processing operations can be carried out immediately after the polishing process, and can be carried out in the same plasma chamber. Accordingly, the second aspect is different from the situation, when it is necessary to transfer the wafer from a polishing machine to a first plasma-processing machine, and from the first plasma-processing machine to a second plasma-processing machine, the mixing of contamination from a polluted atmosphere to the wafer can be prevented and, thus, the occurrence of an electrical failure can be further restricted. Further, in the second aspect, even if the dicing tape is applied, an adhesion force between the dicing tape and the wafer is not extremely large because the oxide layer is formed. Therefore, the difficulty of picking up of dies can be prevented. Also, in the second aspect, the wafer can be prevented from being mottled in a later thin film forming process because the oxide layer can be formed on the entire surface of the wafer. Carbon tetrafluoride (CF4) or sulfur hexafluoride (SF6) is supplied to the plasma chamber to provide an atmosphere of CF4 or SF6 in the first plasma-processing operation to clean the wafer, and oxygen is supplied to the same plasma chamber to provide an atmosphere of oxygen in the second plasma-processing operation to form the oxide layer.
According to a third aspect of the present invention, there is provided a wafer processing method comprising the steps of grinding an underside of a wafer which is provided, on its front surface, with a plurality of semiconductor devices; polishing a ground surface formed by the grinding operation; and carrying out a plasma-processing for a polished surface formed by the polishing operation under a predetermined gaseous atmosphere in a plasma chamber, to roughen the polished surface.
Namely, in the third aspect of the present invention, the underside of the wafer is appropriately roughened by plasma-processing and, accordingly, a metal coating coated in a later metalizing process bites into the roughed portion. Thus, even on a thin wafer the metal coating can be prevented from being stripped. Carbon tetrafluoride (CF4) or sulfur hexafluoride (SF6) is supplied to the plasma chamber to provide an atmosphere of CF4 or SF6 in the plasma-processing operation to roughen the surface.
According to a fourth aspect of the present invention, there is provided a wafer processing apparatus comprising grinding means for grinding an underside of a wafer whose front surface has a plurality of semiconductor devices formed thereon; polishing means for polishing a ground surface formed by the grinding means; and plasma-processing means for carrying out a plasma-processing for a polished surface formed by the polishing operation under a predetermined gaseous atmosphere in a plasma chamber, to form an oxide layer on the polished surface.
Namely, in the fourth aspect of the present invention, the oxide layer is formed on the polished surface on the underside of the wafer and, accordingly, the occurrence of ion contamination can be prevented. Therefore, the wafer can be processed while the occurrence of an electrical failure is restricted even if the thickness of the wafer is reduced. The plasma-processing operation can be carried out immediately after the polishing process. Accordingly, the fourth aspect is different from a situation when it is necessary to transfer the wafer from a polishing machine to a plasma-processing machine, the mixing of contamination from a polluted atmosphere to the wafer can be prevented and, thus, the occurrence of an electrical failure can be further restricted. Further, in the fourth aspect, even if the dicing tape is applied, an adhesion force between the dicing tape and the wafer is not extremely large because the oxide layer is formed. Therefore, a difficulty in picking up of dies can be prevented. Also, in the fourth aspect, the wafer can be prevented from being mottled in a later thin film forming process because the oxide layer can be formed on the entire surface of the wafer. Oxygen is supplied to the plasma chamber to provide an atmosphere of oxygen in the plasma-processing operation to form the oxide layer.
According to a fifth aspect of the present invention, there is provided a wafer processing apparatus comprising grinding means for grinding an underside of a wafer whose front surface has a plurality of semiconductor devices formed thereon; polishing means for polishing a ground surface formed by the grinding means; and plasma-processing means in which, after a first plasma-processing is carried out on a polished surface formed by the polishing operation under a first gaseous atmosphere in a plasma chamber, to clean the polished surface, a second plasma-processing is carried out on the polished surface under a second gaseous atmosphere in the plasma chamber, to form an oxide layer on the polished surface.
Namely, in the fifth aspect of the present invention, the oxide layer is formed on the polished surface on the underside of the wafer and, accordingly, the occurrence of ion contamination can be prevented. Also, in this case, the oxide layer is more uniform and excellent because the oxide layer is formed after the cleaning operation and, thus, the wafer can be processed while the occurrence of an electrical failure is further restricted even if the thickness of the wafer is reduced. The first and second plasma-processing operations can be carried out immediately after the polishing process, and can be carried out in the same plasma chamber. Accordingly, the fifth aspect is different from the situation when it is necessary to transfer the wafer from a polishing machine to a first plasma-processing machine, and from the first plasma-processing machine to a second plasma-processing machine, the mixing of contamination from a polluted atmosphere to the wafer can be prevented and, thus, the occurrence of an electric failure can be further restricted. Further, in the fifth aspect, even if the dicing tape is applied, an adhesion force between the dicing tape and the wafer is not extremely large because the oxide layer is formed. Therefore, a difficulty of picking up the dies can be prevented. Also, in the fifth aspect, the wafer can be prevented from being mottled in a later thin film forming process because the oxide layer can be formed on the entire surface of the wafer. Carbon tetrafluoride (CF4) or sulfur hexafluoride (SF6) is supplied to the plasma chamber to provide an atmosphere of CF4 or SF6 in the first plasma-processing operation to clean the wafer, and oxygen is supplied to the same plasma chamber to provide an atmosphere of oxygen in the second plasma-processing operation to form the oxide layer.
According to a sixth aspect of the present invention, there is provided a wafer processing apparatus comprising grinding means for grinding an underside of a wafer whose front surface has a plurality of semiconductor devices formed thereon; polishing means for polishing a ground surface formed by the grinding means; and plasma-processing means for carrying out a plasma-processing for a polished surface formed by the polishing operation under a predetermined gaseous atmosphere in a plasma chamber, to roughen the polished surface.
Namely, in the sixth aspect of the present invention, the underside of the wafer is appropriately roughened by plasma-processing and, accordingly, a metal coating coated in a later metalizing process bites into the roughened portion. Thus, the metal coating can be prevented from being stripped even from a thin wafer. Carbon tetrafluoride (CF4) or sulfur hexafluoride (SF6) is supplied to the plasma chamber to provide an atmosphere of CF4 or SF6 in the plasma-processing operation to roughen the surface.
According to a seventh aspect of the present invention, there is provided a wafer processing apparatus comprising grinding and polishing means for grinding an underside of a wafer which is provided, on its front surface, with a plurality of semiconductor devices and polishing a ground surface formed by the grinding operation; plasma-processing means for carrying out a plasma-processing for a polished surface formed by the polishing operation under a predetermined gaseous atmosphere in a plasma chamber, to form an oxide layer on the polished surface; applying means for applying a DAF tape and/or a dicing tape to the underside of the wafer; and stripping means for stripping the DAF tape and/or the dicing tape or releases thereof from the underside of the wafer, wherein the grinding and polishing means, the plasma-processing means, the applying means and the removing means are integral with one another; and the wafer can be transferred between the grinding and polishing means, the plasma-processing means, the applying means and the stripping means.
Namely, in the seventh aspect of the present invention, time management for grinding and polishing operations in the grinding and polishing means, a plasma-processing operation in the plasma-processing means, an applying operation in the applying means, and a stripping operation in the stripping means, can be controlled together.
a to 2e are views of processes showing a wafer processing method according to the present invention; and
Embodiments of the present invention will be described below with reference to the accompanying drawings. In the following drawings, the same members are designated by the same reference numerals. For ease of understanding, the scale is changed as necessary in the drawings.
a to 2e show processes of a wafer processing method according to the present invention. A wafer processing method according to the present invention will be described with reference to
As shown in
The wafer 20 in the above state is introduced to the grinding and polishing machine 100 of the wafer processing apparatus shown in
As can be seen from
With reference to
The wafer 20, ground and polished in the grinding and polishing machine 100, is transferred to the plasma chamber 31 though an inlet (not shown) thereof, and is placed on the lower planar electrode 33, with the ground surface 23 being upwardly oriented. Then, the inlet is closed and sealed. The open/close valve 36 is opened, and the pump 38 is activated, to decompress the inner space 32 of the plasma chamber 31 by discharging gas through the pipe 37. Then, the open/close valve 44 is opened to supply CF4 or SF6 to the inner space 32 of the plasma chamber 31, and through the planar electrode 34, via the pipe 47. A voltage is applied, by the power source 35, between the lower planar electrode 33 and the upper planar electrode 34, in the plasma chamber 31 which is slightly decompressed. The CF4 or SF6 supplied to the plasma chamber 31 functions as a reactive gas and, accordingly, plasma is formed in the inner space 32 of the plasma chamber 31. The plasma is a low temperature plasma having a temperature of about 60 to 90° C. and, accordingly, the retaining layer 40 of the wafer 20 is not damaged. The plasma impinges on the polished surface 23 of the wafer 20 by a flow of CF4 gas or SF6 gas through the upper planar electrode 34 and, thus, the polished surface 23 is plasma-processed. If, for example, CF4 is adopted as a reactive gas, the CF4 is decomposed into carbon trifluoride (CF3) and fluorine (F), and the F is applied to the polished surface 23 of the wafer 20 made of silicon. On the surface of the wafer 20, silicon (Si) of the wafer 20 reacts with F to form silicon tetrafluoride (SiF4) and, then, is removed from the polished surface 23 of the wafer 20. Therefore, the underside of the wafer 20 is removed by, for example, about 20 Å to 40 Å, to produce a new surface of the wafer 20. The same is almost true in other cases in which SF6, etc. is adopted as a reactive gas. Therefore, an effect similar to that of cleaning of the polished surface can be obtained by such plasma processing. Nitrogen dioxide NO2 together with CF4 and SF6 may be supplied to the plasma chamber 31, as necessary. Thus, a cleaning operation using plasma processing can be efficiently carried out.
After carrying out plasma processing for a predetermined time, the open/close valve 44 is closed, and the pump 38 is activated while the open/close valve 36 is opened, to discharge a gas in the inner space 32, i.e., CF4, SF6 or the like. Then, the open/close valve 45 is opened while the open/close valve 36 is closed, to supply an inert gas in the source 42, for example, helium to the inner space 32 of the plasma chamber 31, through the upper planar electrode 34, via the pipe 48. Once the inner space 32 of the plasma chamber 31 is charged with helium, the open/close valve 36 is opened while the open/close valve 45 is closed, to discharge the helium. Thus, the remaining gas such as CF4 or SF6 in the inner space 32 of the plasma chamber 31 is almost completely discharged, and the inner space 32 of the plasma chamber 31 can be cleaned.
After closing the open/close valve 36, the open/close valve 46 is opened to supply oxygen in the source 43 to the inner space 32 of the plasma chamber 31, and through the upper planar electrode 34, via the pipe 49. A voltage is applied, by the power source 35, between the lower planar electrode 33 and the upper planar electrode 34, in the plasma chamber 31 which is slightly decompressed. In this case, oxygen functions as a reactive gas and, accordingly, plasma is formed in the inner space 32 of the plasma chamber 31. The plasma is a low temperature plasma having a temperature of about 60 to 90° C. and, accordingly, the retaining layer 40 of the wafer 20 is not damaged. The plasma impinges on the polished surface 23 of the wafer 20 by a flow of oxygen gas through the upper planar electrode 34 and, thus, the polished surface 23 is plasma-processed and, thus, an oxide layer is formed on the polished surface 23 of the wafer 20. In
With reference to
As illustrated, a die attach film tape (DAF tape) attaching machine 300 may be provided between the plasma-processing machine 200 and the dicing tape applying machine 400. Thus, the DAF tape may be applied to the plasma-processed underside of the wafer 20 and, then, the dicing tape may be applied to the DAF tape in the dicing tape applying machine 400. The DAF tape provided between the dicing tape and the underside of the wafer 20, functions as an adhesive provided on the bottom surface of the die in the die bonding operation.
As described above, in the present invention, the DAF tape applying machine 300 for applying the DAF tape and the dicing tape applying machine 400 for applying the dicing tape are provided adjacent to or integral with the grinding and polishing machine 100 and the plasma-processing machine 200. Thus, the mixing of contamination can be prevented when the wafer is transferred. Further, with the above structure, time management of the grinding and polishing machine 100, of the plasma-processing machine 200, of the DAF tape applying machine 300 and of the dicing tape applying machine 400 can be controlled together. Thus, throughput in all processes can be improved, and a defective fraction can be reduced to a minimum. Further, a tape detaching machine (not shown) for detaching the DAF tape and/or the dicing tape or releases of these tapes, may be provided. Namely, the grinding and polishing machine 100, the plasma-processing machine 200, the DAF tape applying machine 300, the dicing tape applying machine 400 and the tape stripping machine (not shown) may be integral with one another, and the wafer may be freely transferred among the grinding and polishing machine 100, the plasma-processing machine 200, the DAF tape applying machine 300, the dicing tape applying machine 400 and the tape stripping machine, by transferring means (not shown). In such a case, time management of the grinding and polishing machine 100, of the plasma-processing machine 200, of the DAF tape applying machine 300, of the dicing tape applying machine 400 and of the tape stripping machine can be controlled together. Thus, throughput in all processes can be improved, and a defective fraction can be further reduced.
In the above-described embodiments, a cleaning operation for the polished surface 23 of the wafer 20 and a forming operation of an oxide layer have been described. However, the wafer processing apparatus according to the present invention can be used for another application that will be described later. The underside of the wafer, which is ground and polished in the grinding and polishing machine 100 is flattened more than usual. However, if, for example, the underside of the wafer is metalized in a later process, an adhesion force between the polished surface and a metal coating formed by metalizing is reduced and, accordingly, the metal coating may be stripped. However, in the present invention, the wafer 20 discharged from the grinding and polishing machine 100 is transferred to the plasma-processing machine 200 and, then, is placed in the manner described above. The above-described plasma-processing operation (under an atmosphere of CF4 or SF6) functioning as a cleaning operation, is carried out for a longer time than the above-described plasma-processing operation. Accordingly, the polished surface 23 of the wafer 20 can be removed so that the wafer has a thickness of, for example, about 2 to 3 micrometer. In this case, the roughness of a new surface precipitated after the plasma-processing operation is larger than that before the plasma-processing operation. Accordingly, the metal coating formed by metalizing, bites into the rough underside of the wafer 20 and, thus, the adhesion force between the metal coating and the polished surface is increased. Therefore, in the present invention, even if the metalizing operation is carried out in a later process, the metal coating of a thin wafer can be prevented from being stripped.
In the embodiment which has been described with reference to
| Number | Date | Country | Kind |
|---|---|---|---|
| 102003-403247 | Dec 2003 | JP | national |
