Plasma generator

Abstract: A plasma-processing method used in processes for manufacturing semiconductor devices. During plasma processing, ultraviolet radiation is emitted from a region where a plasma is created. An ultraviolet radiation-blocking means blocks the ultraviolet radiation from impinging on the sample surface to protect it. The blocking means passes particles forming a plasma onto the sample surface. The particles passed through the ultraviolet radiation-blocking plates are implanted into the sample. Alternatively, the processed surface of the sample is etched, or a film is deposited on the processed surface of the sample.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma generator for processing semiconductor devices with a plasma during processes for fabricating the devices. 2. Description of the Related Art In processes for fabricating semiconductor devices, various kinds of processes are performed, using a plasma generator such as a plasma doping system, a plasma-enhanced CVD system, a plasma etching system, and a plasma ashing system. In any of these kinds of processes, a plasma is generated, and processing is performed, using the generated plasma. In a plasma doping system, a glow discharge plasma is generated, for example, inside a gaseous ambient containing impurity atoms to be doped, to implant the impurity atoms into a sample. In a plasma-enhanced CVD system, an r.f. glow discharge plasma is generated, for example, in a reactive gas ambient. The reactive gas species is decomposed, thus obtaining atoms. These atoms are deposited as a thin film. In a plasma etching system, a plasma is generated, for example, in a reactive gas ambient. The etching process is made to proceed by the action of neutral active species. This system includes a plasma ashing system. Alternatively, the etching process is made to proceed by the combined effect of the neutral active species and reactive gas ions. Or, a diverging magnetic field is formed by a magnetic field, and a plasma is radiated from an ion source along the diverging field. As a result, a sample placed in the plasma flow is etched. In the above-described plasma generator, when a plasma is generated, ultraviolet radiation is emitted from the region where the plasma is created. Therefore, the ultraviolet radiation impinges on the sample under plasma processing. Consequently, the sample is damaged. One example of this is described by taking hydrogenation using plasma doping as an example. Plasma hydrogenation is a technique consisting of implanting hydrogen into a poly-crystalline silicon film to remove crystal grain boundaries from the silicon film. In this processing, energetic ultraviolet radiation having wavelengths ranging from 110 nm to 180 nm is emitted from the plasma generation region. When a poly-crystalline silicon device is exposed to such UV radiation, the device is readily damaged. As an example of characteristic of plasma hydrogenated TFT (thin-film transistor), drain current-gate voltage curve (Id-Vg curve) is shown in Fig. 3. In this graph, the drain current is plotted on the vertical axis, whereas the gate voltage is on the horizontal axis. The device whose characteristic is indicated by the solid-line curve (a) of Fig. 3 was obtained by hydrogenation. This characteristic is considerably better than the characteristic of a device undergone no hydrogenation. However, the characteristic is not very excellent because of damage caused by ultraviolet radiation produced by a glow discharge and because of damage sustained by energetic particles. Then, the surface of the device to be processed was covered with quartz glass obstructing hydrogen flux. Thereafter, the surface was exposed to ultraviolet radiation emitted from the plasma generation region at 285°C. As a result, a characteristic curve indicated by the broken line of (b) in Fig. 3 was derived. As can be seen from this characteristic curve, the device characteristic was greatly deteriorated by the exposure to the ultraviolet radiation. The device was then annealed at 285°C for 1 hour. We checked if this annealing could repair the damage caused by the UV irradiation. As indicated by the characteristic curve (c) indicated by the dot-and-dash line, the device characteristic was healed to some extent, not completely. Accordingly, when the device was exposed to UV radiation, it was damaged, so that the characteristics were deteriorated. The DE-A-3336064 discloses a CVD plasma deposition process and apparatus for forming a layer on a sample, wherein the region of the chamber where the layer is produced is shielded from the region of the chamber where the plasma is produced so that light rays may not pass to the sample. According to the US-A-4,836,902 a method and apparatus is provided for plasma stripping a polymer photoresist coating from a semiconductor substrate wherein ultraviolet radiation generated as a byproduct of plasma generation is absorbed by a baffle placed between a plasma source and the substrate. The JP-6-244159 describes an apparatus wherein a gaseous starting material which is excited by ultraviolet rays is supplied to the surface of an object to be treated. To prevent the object from being damaged by the irradiation light intercepting means are provided between the light source and the sample. It is an object of the present invention to provide a plasma generator capable of excellently eliminating the effects of UV radiation emitted by the plasma generator and at the same time decreasing the processing time and increasing the troughput of the abovementioned processing methods. A plasma generator for achieving the above-described object is provided according to the features of the appended claims 1 and 2. Other objects and features of the invention will appear in the course of the description thereof, which follows. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic cross section of a plasma generator according to a first embodiment of the invention; Fig. 2 is a schematic cross section of a further UV radiation-blocking means according to a second embodiment of the invention; and Fig. 3 is a graph showing the Id-Vg characteristics of devices undergone the prior art plasma hydrogenation processing, illustrating the problems with the prior art processes. DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the invention is described by referring to the schematic cross section of Fig. 1. It is to be noted that like components are indicated by like reference numerals in figures 1 and 2. In Fig. 1, a plasma generator, generally indicated by reference numeral 2, produces a plasma P along the side wall 11S of a chamber 11. A sample 101 positioned inside the chamber 11 has a surface 101S to be processed. The plasma P is generated from the side of the processed surface 101S to the top to plasma-etch the processed surface 101S. The positional relation among a plasma region 51 where the plasma P is generated, the sample 101, and an ultraviolet radiation-blocking means 61 is shown. Means for generating the plasma is not shown. Specifically, the plasma region 51 is produced along the side wall 11S of the chamber 11. A sample 101 is placed on a stage 111 on the side of the bottom of the chamber 11. The ultraviolet radiation-blocking means 61 is mounted between the plasma region 51 and the sample 101 to pass the plasma P and to block the ultraviolet radiation UV released from the plasma region 51. The ultraviolet radiation-blocking means 61 consists of two cylindrical blocking plates 62a and 62b which are located substantially coaxially about the sample 101. The cylindrical blocking plates 62a and 62b are spaced from each other by a given spacing d3, for example. The blocking plates 62a and 62b are provided with plural holes 63a and 63b, respectively, which are located in a staggered relation to each other. That is, where the side wall of the chamber 11 is viewed from above the sample 101, the holes 63b do not register with the holes 63a. The ultraviolet radiation-blocking means 61 is mounted to the side wall of the chamber 11 via an insulator 64 in such a way that a plasma region 51 is secured between the side wall 11S of the chamber 11 and the ultraviolet radiation-blocking means 61. In the plasma generator 2 described above, the ultraviolet radiation-blocking means 61 is mounted between the sample 101 and the plasma region 51 created inside the chamber 11 to pass the plasma P and to block the ultraviolet radiation UV. Therefore, the plasma P is guided onto the processed surface 101S of the sample 101 but the ultraviolet radiation UV does not impinge on the processed surface 101S. Hence, the sample 101 is not damaged by the ultraviolet radiation UV during the plasma processing. In the ultraviolet radiation-blocking means 61 described above, the ultraviolet radiation UV generated in the plasma region 51 travels straight and thus blocked by the plural ultraviolet radiation-blocking plates 62a and 62b. Even if the radiation passes through the holes 63a in the first ultraviolet radiation-blocking plate 62a, the radiation is almost totally blocked by the second ultraviolet radiation-blocking plate 62b, because the two sets of holes 63a and 63b are located in a staggered relation to each other. On the other hand, the plasma P passes through the holes 63a and 63b and reaches the processed surface 101S of the sample 101. The position at which the ultraviolet radiation-blocking means 61 is mounted is not limited to the side wall of the chamber 11. The ultraviolet radiation-blocking means 61 may be mounted at any arbitrary position as long as the plasma region 51 is secured. An ultraviolet radiation-blocking means 71 of a further configuration according to a second embodiment of the invention is described next by referring to the schematic cross section of Fig. 2. The ultraviolet radiation-blocking means 71 comprises a plurality of (e.g., n) substantially annular ultraviolet radiation-blocking plates 72a, 72b, ..., 72n which are spaced a given spacing of d4 from each other. The blocking plates 72a-72n are inclined to the side wall 11S of a chamber 11. The blocking plates 72a-72n are arranged along the side wall 11S via the plasma region 51. For example, the blocking plates 72a-72n are laid to overlap each other successively, for example, from the side wall 11S of the chamber 11 toward the center. In the ultraviolet radiation-blocking means 71 of the configuration described above, the ultraviolet radiation-blocking plates 72a-72n are inclined to the processed surface 101S of the sample 101 and spaced the given spacing of d4 from each other. Furthermore, the radiation-blocking plates 72a-72n are laid to overlap each other. Therefore, the ultraviolet radiation UV traveling straight is blocked by the ultraviolet radiation-blocking plates 72a-72n. On the other hand, the plasma P passes between the successive ultraviolet radiation-blocking plates 72a-72n and arrives on the processed surface 101S of the sample 101.

Claims: A plasma generator (2) for generating a plasma inside a chamber (11) to process a sample (101) placed inside the chamber (11), the plasma generator (2) comprising: a plasma region (51) formed inside the chamber (11); and an ultraviolet radiation-blocking means (61) acting to pass the plasma but block ultraviolet radiation, characterized in that the sample is placed such that the sample surface (101S) to be processed extends parallel to a bottom side of the chamber (11), the plasma region (51) extends along a sidewall (11S) of the chamber (11) and comprises the shape of a tube surrounding the sample (101), the tube axis being perpendicular to the sample surface (101S), and the ultraviolet radiation-blocking means (61) is comprised of ultraviolet radiation-blocking plates (62a, 62b) which extend parallel to the sidewall (11S), inside of the tube-shaped plasma region (51) and substantially coaxially with the tube axis, so that the plasma region (51) is enclosed between the sidewall (11S) and the ultraviolet radiation-blocking plates (62a, 62b), wherein the ultraviolet radiation-blocking plates (62a, 62b) are each provided with plural holes and spaced at a given spacing (d3) from each other so that the holes are located in a staggered relation to each other. A plasma generator (2) for generating a plasma inside a chamber (11) to process a sample (101) placed inside the chamber (11), the plasma generator (2) comprising: a plasma region (51) formed inside the chamber (11); and an ultraviolet radiation-blocking means (71) acting to pass the plasma but block ultraviolet radiation, characterized in that the sample is placed such that the sample surface (101S) to be processed extends parallel to a bottom side of the chamber (11), the plasma region (51) extends along a sidewall (11S) of the chamber (11) and comprises the shape of a tube surrounding the sample (101), the tube axis being perpendicular to the sample surface (101S), and the ultraviolet radiation-blocking means (71) is comprised of a plurality of substantially annular ultraviolet radiation-blocking plates (72a - 72n) which extend parallel to the sidewall (11S), inside of the tube-shaped plasma region (51) and substantially coaxially with the tube axis, so that the plasma region (51) is enclosed between the sidewall (11S) and the ultraviolet radiation-blocking plates (72a, 72b), wherein the ultraviolet radiation-blocking plates (72a, 72b) are each provided with plural holes and spaced at a given spacing (d4) from each other so that the holes are located in a staggered relation to each other.

Inventors: GOSAIN PAL DHARAM, JIYONASAN UESUTOOTAA, USUI SETSUO, GOSAIN, PAL DHARAM, JIYONASAN, UESUTOOTAA, USUI, SETSUO, Gosain, Pal Dharam, c/o Sony Corporation, Jiyonasan, Uesutootaa, c/o Sony Corporation, Usui, Setsuo, c/o Sony Corporation
Applicants: SONY CORP, SONY CORPORATION
Application year: 1995
Main classification: C23C16
IPC codes: H01L21, C23C16, C23C14, H01J37