GB2241250A

GB2241250A - RF plasma CVD employing an electrode with a shower supply surface

Info

Publication number: GB2241250A
Application number: GB9101619A
Authority: GB
Inventors: Masahiko Doki; Makoto Toraguchi; Shigeru Suzuki
Original assignee: Fuji Electric Co Ltd; Fujitsu Ltd
Current assignee: Fuji Electric Co Ltd; Fujitsu Ltd
Priority date: 1990-01-26
Filing date: 1991-01-24
Publication date: 1991-08-28
Also published as: KR940000909B1; DE4102198A1; GB9101619D0

Abstract

An RF plasma CVD apparatus comprises a vacuum chamber 1, a substrate mount 4 having a built-in heater and having a flat upper surface for mounting thereon a substrate 2 on which a film is to be formed, and an R electrode 5 having a surface opposite to the substrate mount 4, the surface being formed as a shower supply surface 51 having a large number of pores 52 for supplying film-forming gas as a shower into a space between the shower supply surface 51 and the substrate mount 4. The pores 52 are formed such that the diameter d of each of the pores 52 is set to be not larger than 0.4 times as large as the distance D between the substrate 2 and the shower supply surface 51 and to be not larger than 0.75 times as large as the distance p between the respective centers of adjacent pores 52. As illustrated in Fig 1a each of the pores is disposed at the vortex position of an equilateral triangle. <IMAGE>

Description

RF PLASMA CVD APPARATUS AND THIN VILM FORMING METHOD USING THE APPARATUS

BACKGROUND OF THE INVENTION

The present Invention relates to an RP plasma apparatus, which in used In a stop of forming a thin film on a surf ace of a substrate In a serlea ot stops of producing a semiconductor. comprising a vacuum chamber, a substrate mount having a built-in heater and having a flat upper cuziace for mounting thareon a substrata on which a film is tQ be formed, and an RP electrode having a surface opposite to the aubstrate mount, the surface being formed as a shower supply surf ace having a large number of pores for supplying film-forming gas an a shower Into a space opposite to the subatrate mount, and more particularly relatee to the structure of the apparatus Improved, in film forming rate, uniformity of film thickness and uniformity of film quality, and to a thin film forming method for forming a thin film on a substrate by using this apparatus.

conventionally, In this type RP plasma CVD apparatust a thin film having uniform film thickness and uniform film quality In formed as follows. The distance between a substrata, which Is mounted on a substrate mount having a bultin heater and constitutes a ground electrode, and a shower supply surface of an RP electrode opposite to the substrate is cat to be In a range of 20 to 40 =. After the pressure of gas in a vacuum chamber which houses the electrode& Is cot to be In a range of the order of several torrp an RP voltage Is applied to the RP electrode to generate uniform and stable glow discharge between the two electrodes. At the same time, while a film-fornting gas Is uniformly supplied from the shower supply surface of the RP electrode to the whole surface of the substrata which 10 to be subjected to film formation, the gas in the vacuum chamber is exhausted by a vacuum exhaust system, so that the pressure of the gas In the vacuum chamber is kept constant. An example of the arrangement of pores for bringing uniform gas flow onto the substrate surface to attain uniform film thiess is disclosed in Japanese Patent Unexamined Publication No. Eel-1-149964.

in the conventional RP plasma MD apparatus, to generate uniform and stable glow discharge between the electrode&, the distance (hereinafter referred to an welectrode distance,,) between. the heated substrata as a ground electrode and the shower supply surface of the RP electrode Is out to be In a range of 20 to 40 mm and the pressure of gas is act to be in a low range of the order of several torr. Therefore, the density of plasma derived from glow discharge Is small, so that the density of active seeds contributing to film formation is small. Therefore, a problem arises In that the film forming rate is low and the productivity attained by the apparatus is low. Further, because the electrode distance is large, the distribution of neutral active seeds free from restriction of the electric field Is formed easily In a flow of gas which goes from the shower supply surface onto the substrata. Therefore, there arises another problem In that both the uniformity of film thickness and the uniformity of film quality deteriorate when the substrata surface becomes large.

SUY OF W51 INVEXTION An object of the present Invention Is therefore to provide an RF plasma CVD apparatus in which high-dencity unif orm plasma can be generated stably in a space between an RP electrode and a ground electrode by using a given RP electric power source and In which the distribution of active &ado becomes uniform, and to provide a thin film f orming method In which not only the film forming rate can be Improved when a substrata is subjected to thin film formation by using this apparatus but both the uniformity of film thickness and the uniformity of film quality can be attained oven when the substrate has a large area to be subjected to film formation.

In order to solve the problems, according to the present Invention, the RP plasma CVD apparatus compriiwoa a vacuum chamber, a substrata mount having a built-in heater and having flat upper surface for mounting thcreon a substrata on which film is to be formed, and an RP electrode having a surface opposite to the substrata mount, the surface being formed as a shower supply surface having a large number of pores for supplying film-forming gas as a shower into a space opposite to the substrato mount, wherein the pores are formed such that the diameter of each of the pores in the shower supply surface is act to be not larger than 0.4 times as large as the distance between the substrate mounted on the substrata mount and the shower supply surface and to be not larger than 0,75 times as large as the distance between the respective centers of adjacent pores.

In the RP plasma CVD apparatus In which the diameter of each of the pores In the shower supply surface Is determined as described above, the distance between the substrata to be subjected to film formation and the shower supply surface of the RP electrode Is preferably cot to be not larger than 20 mm.

Further, the pores formed In the shower supply surface of the RP electrode are preferably formed at the vortex positions of each of a large number of regular triangles formed by three groups of equidistant parallel lines, three lines, each contained in dif f rent groups p passing a comon point and being shifted-by 60 from one another.

in forming a thin film on a substrata by using the apparatus in which the diameter of each of the pores In the shower supply surface of the RP electrode# the distance between the shower supply surface and the substrata to be subjected to film formation,, and the distance between the respective canters of adjacent pores have the aforementioned relations, the thin film Is formed under a pressure of the film-forming gas dischargeable under an RP voltage supplied to the RP electrode.

To attain high-density plasma by using a given RP electric power source, It Is necessary to generate uniform and stable glow discharge by increasing the pressure of the film-forming gas and reducing the electrode distance. According to experiments by the inventors, It Is found to be very important to avoid induction of concentrated discharge by flattening of alectrodeer In partloulart flattening of a cathode surface for generating uniform and stable glow discharge under a high gas pressure, that In, low vacuum degree, and In a short gap. That is, because the pores In the shower eupply surface form the irregularity of the electrode surface, stable glow discharge can be generated only when the diameter of each of the pores, the electrode distance, and the dietance between the respective canters of adjacent pores have predetermined relations. Specifically, when the diameter 5L of each of the pores in relatively large compared with the electrode distance D, the electric field intensity 2 at the peripheral portion of the pore becomes abnormally large compared with average electric field intensity BezV/D (V: voltage applied between the substrata to be subjected to film formation and the R? electrode) so that uniform glow discharge cannot be generated. when the distance between the canter@ of adjacent pores, that in, pitch la. approaches the diameter A. the portion between adjacent pores serves an a projecting electrode. Accordingly, the electric field is concentrated In this portion to generate a filament- shaped arc, so that uniform glow discharge cannot be generated. The experiments have proved that uniform glow discharge is generated only when the pore diameter Sk, the distance D between the substrate and the shower supply surface and the porm pitch p have the following relations.

d < 0.4 X D and d < 0.75 X p Accordingly, by constructing an electrode system while keeping the aforementioned relations, uniform and stable glow discharge can be generated between the electrodee, so that high-density plasma can be generated stably oven it the gas pressure Is increased and the electrode distance Is reduced under a given RP electric power source.

in this caser plasma density is remarkably increased even under the same gas pressure by reducing the electrode distance D from the conventional range of 20 to 40= to a new range of not larger than 20 mm, Neutral active seeds In high-density plasma generated as described above have no opportunIty of forming the distribution thereof because the electrode distance is sufficiently short. Accordingly.. all active woods are distributed unitormlyi so that a thin f Ilm uniform In both f Ilm thickness and film quality can be formed on a substrata though the substrata may have a large area.

if the pores formed In the shower supply surface are disposed at the vortex positions of a largo number of regular triangles formed by three groups of equidistant parallel lines ' three lines, each separately contained in the groups, passing a contron point on the shower supply surface and being shifted by 60 from on another, a maxim= number of pores can be 1.

1 1 dieposed on the shower supply surface having a predetermined area in case that the minimum pore pitch is constant, and the gas flow can be uniformized. Further, according to this arrangement of poree, the pore diameter can be reduced to obtain a predetermined gee flow.. so that the electrode distance sufficient to generate uniform glow discharge can be reduced. Accordingly, plasma density can be Increased more.

Thus,, by using a thin film forming method of forming a thin film on a substrate in which the electrode distance is kept at a small value in a range satisfying the aforementioned relations and the pressure of the film-forming gas Is met to a dischargeable pressure under an RP voltage supplied to the RP electrode, plasma density in the plasma generation space (the space between the electrode&) can be incroaeed so that the film forming rate can be Increased. Furthermore, neutral active seeds in high-density plaema generated as described above have no opportunity of forming the distribution thereof because the electrode distance in sufficiently short. Accordingly. all active &ado are dletributed uniformly, so that a thin film uniform in both film thickness and film quality can be formed on a substrate though the eubetrate may have a large area.

BRIEF DESCRIPTION OF THE DRAWINGS

Pigs. 1(a) and 1(b) show a structure of a shower supply surface of an RP electrode according to an embodiment of the present inventionf In which Fig. 1(a) Is a plan view thereof, and Fig. 1 (b) Is a sectional view taken along the line A - A of rig. 1 (a), rig. 2 in a vertical sectional view showing an example of construction of an RP plaema M apparatus including an RP electrode having a shower supply isurface of the structure depicted In Fig. li Pig. 3 is a graph showing the change of discharge state according to the combination of the diameter of each of the porea in the shower supply surface of the RP electrode and the distance between the shower supply surface and the substrata to be subjected to film formation, rig. 4 is a graph showing the change of discharge state according to the combination of the diameter of each of the pores in the shower supply surface of the RP electrode and the distance between the canters of adjacent pores, and rig. 5 is a graph showing the relationship of the distance between the shower supply surface of the R? electrode and the substrata to be subjected to film formation and the plasma density with use of the gas pressure as a parameter. DETAILED DESCRIPTION OF THE INVENTION

An example of the structure of a shower supply surface of an RP electrode according to the present Invention Is shown in Pig. 1. An example of configuration of an RP plasma M apparatus using the RP electrode having the shower supply surface in shown in Pig. 2.

- a - 1 i 1 i 1 i i j i i j Gatg valves 3a and 3b used for carrying-inlout a substrata 2 to bO subjgcted to film formation are provided in opposite walls of a vacuum chamber 1, by which the vacuum chamber 1 can be scaled to a vacuum state. The substrata 2 to be subjected to film formation Is placed on a substrata mount 4 having a built-in heater so as to be in contact with an upper surface thereof. The substrata mount 4 is provided in the vacuum chamber 1 and can be moved up and down by the operation of an actuator (not shown) from the outside of the vacuum chamber.

An RP electrode 5 having a shower supply surface 51 disposed opposite to the substrata mount 4 Is attached to the vacu= chamber 1 through an Insulation bush 9 and Is connected to an RP electric power source 6. Further, a gas supply pipe 8 made of an insulating material in connected to the RP electrode 5 In order to mend a film-forming gas Into the back elde of the shower supply surface 51. In the drawingf reference numeral 7 designates a vacuum exhaust system for exhausting a gas contained in the vacuum chamber at a predetermined flow rate to keep the gas pressure of the vacuum chamber constant In a range of 0.5 to 10 torr In a state where a film-forming gas is continuously supplied Into a space between the shower supply surface 31 and the substrata 2 through the gas supply pipe 8.

At the time of torming a film on the substrata, the filmf orming gas Is sent into the RP electrode 5 after the substrata 2 is heated to a predetermined temperature by the cubstrate mount 4. TO form the film, the film-forming gas Is supplied 1 Into the space between the shower supply surface 51 and the substrata 2 through pores provided in the shower supply surf ace 51 of the RP electrode 5 and, at the same time, high frequency electric power is supplied from the RF electric power source 6 to the RP electrode 5.

The pores in the shower supply surface 51 of the RF electrodes 5 are formed as numerously as possible In a limited area. Zach.of the pores is disposed at the vortex position of a regular/ triangle as shown In rig. 1, so that the diameter of the po=o for supplying a predetermined amount of gas Into the discharge space (the space between the shower supply surface 51 and the substrata 2) can be reduced to easily satisfy the relation: d<OAD, dcO.75p. in the relation, ji represents the diameter of the pore, D represents the distance between the shower supply surface and the substrata, and p. represents the distance between the respective canters of adjacent pores.

The result of an experiment for examining the change of the discharge state in the space between the shower supply surface and the substrata according to the combination of the pore diameter d and the distance D between the shower supply surface and the substrate Is shown In Pig. 3. In the drawing, 0 represents that uniform glow discharge is formed, and X represents that a filament-shaped are is formed or in other word uniform glow discharge Is not formed. It In apparent from the result of the experiment that uniform glow discharge is f ormed when ji and D are in a right region with respect to z i the line d-0.4D, that In, uniform glow discharge Is formed when and D satisfy the relation d<0.4D.

The result of another experiment for examining the change of the discharge state according to the combination of the pore diameter d and the distance p. between the respective canters of adjacent pore is shown in Fig. 4. It is apparent from the result of the experiment that uniform glow discharge Is formed when A and..p are in a right region with respect to the line d-0.75p, that is, uniform glow discharge is formed when SL and p satisfy the relation d<0.75p.

rig. 5 shows the result of a further experiment for examining the change of density Dú of plasma produced between the shower supply surface and the substrata, according to the change of the distance D between the shower supply surface and the substrate, using gas pressure as a parameter, when the pore diameter i satisfies the aforementioned conditions d<OAD and d<0.75p. it In apparent from the result of the experiment that the plasma density in substantially proportional to the gas pressure when the distance D is constant and the plasma density is substantially inversely proportional to the distance D when the gas pressure in constant. Accordingly, when the distance D in reduced from the conventional range of 20 to 40 mm to a now range of not larger than 20 = and the gas pressure is increased under the condition that the poree are formed to obtain uniform glow discharge, plasma of remarkably high density compared with the conventional plasma can be produced and the distribution of active woods including neutral active code can be uniformized. By increasing the gas pressure to he maximum dischargeable value under.the Rr voltage supplied to the RP electrode, the plasma density reaches an allowable ultimate value so that the film forming rat Is increased to a limit.

Because, in the present Invention, the RP plasma WD apparatus is constructed as described above, the following effects can he obtained.

in the apparatus according to the present Invention, uniform and stable glow discharge In always generated between the two electrodes. Accordingly, by generating uniform and stable glow discharge under an increased pressure of film-forming gas and a reduced electrode distance under a given RP electric power souteei, high-density plasma or In other words high-density active seeds can be generated. Accordingly, the filmforming rate in the apparatus can be improved. Purther, all active moods can be distributed uniformly In the front surface of the substrate without forming the distribution of neutral active seed, because the electrode distance is sufficiently short. Accordingly, thin film uniform in both film thickness and film quality can be formed on a oubetrate oven though the substrata has a large area. Further, because a film can be formed stably in a short electrode distance, the reaction In a gas phase Is reduced. Accordingly, a secondary affect can be obtained in that socalled particle stain caused z t- i 1 i t by the phenomenon that particles produced by the reaction are deposited on the substrato surface can be suppressed.

As shown in Fig. 5, the plasma density In Inversely proportional to the electrode distance under a given RP electric power source if the gas pressure is constant. On the other hand, the plasma density Is substantially proportional to the gas pressure it th electrode distance In constant. Accordingly, by Increasing the gas pressure and reducing the electrode distance from the conventional range of 20 to 40 = to a minimum range of not larger than 20 m, for example, a range of 5 to 15 =p with paying attention to the pore diameter sufficient to keep predetermined accuracy, plasma remarkably high In density can be generated compared with the conventional plasma. Purther, active moods are distributed uniformlyr so that not only the film forming rate can be improved but both the film thickness and film quality can be uniformized.

When the pores are formed in the shower supply surface of the RP electrode at the vertex positions of a large nr of miniinum regular triangles formed by three groups of nuldistant. parallel lines, three lines# each separately contained In the groups, passing a common point and being shifted by 600 from ona, another, a maximum number of pores can be formed at the showr supply surface and the Can flow Is uniformized when the ininimum pore pitch in constant. Accordingly, the po=o diameter can be reduced to obtain a predetermined gas flow amount, to that the electrode distance sufficient to generate uniform glow 13 - i discharge can be reduced. consequently, uniform piazza donsity can be Increased more.

In the apparatus according to the present invention, an electrode system Is constructed so that uniform and stable glow discharge can be always generated. Therefore, according to a thin film forming method of forming a thin film on a substrate by using the above apparatus in which the electrode distance In kept at a small value and the pressure of film-forming gas Is set to a dischargeable pressure under an RP voltage supplied to the RP electrode, the plasma density In the plasma generation space (the space between the electrode&) can be increased. so that the film forming rate can be Increased. Furthermore, neutral active woods In high-denisity plasma generated an described above have no opportunity of forming their distribution because the electrode distance is sufficiently short. Accordingly, all active meads are distributed uniformlyi so that a thin film uniform In both film thickness and film quality can be formed on a substrata oven though the substrata has a large area.

1 J 1 1 i i i - 14 i

Claims

CLAIMS i. An RP plasma = apparatus comprising; vacuum chamber; substrate

mount having a built-in heater and having a flat upper curiae for mounting thercon a substrata on which a film is to be formed; and an RP electrode having a surface opposite to said substrata mounte said surface being formed as a shower supply surface having a large number of pores for supplying film-fo=ing gas as a shower Into a space between said shower supply surface and said substrata mount; wherein said pores are formed such that the diameter of each of said pores is act to be not larger than 0.4 times as large an the distance between said substrate mounted on said substrate mount and maid shower supply surface and to be not larger than 0.75 times as large as the distance between the respective canters of adjacent pores.
2. An RP plasma MD apparatus according to Claim 1, wherein the distance between said cubetrate and said shower supply surface of said RP electrode is set to be not larger than 20
3. An RP plasma CVD apparatus according to Claim 1, wherein said pores are formed at vortex positions of a large number of minimum regular triangles formed by three groups of equidistant parallel lineso three lines, each separately contained In said - is groups passing a common point and being shifted by 60 from one another.
4. A method of forming a thin film on a substrate by using the apparatus as defined in Claims 1, 2 or 3, wherein a pressure of film-forming gas is set to a dischargeable pressure under an RF voltage supplied to said RF electrode.
5. An apparatus as claimed in Claim 1, substantially as hereinbefore described with reference to the accompanying drawings.
6. A method as claimed in Claim 4, substantially as hereinbefore described with reference to the accompanying drawings.
7. A substrate having a thin film formed thereon by a method as claimed in Claim 4 or 6.

Published 199 1 ai The Patent Office. Concept House. Cardifr Road. Newport. Gwent NP9 1 RH. Further copies may be obtained frorn Sales Branch. Unit 6. Nine Mile Point. Cwmfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.

c i i 1 1 i I i