JP3034263B2 - Thin film forming equipment - Google Patents

Description

Description: Object of the Invention (Industrial Application Field) The present invention relates to a thin film forming apparatus by a chemical vapor deposition method, and more particularly, to a method of manufacturing a semiconductor device by using a silicon oxide film doped with an impurity. The present invention relates to an apparatus for forming a thin film.

(Prior Art) In an integrated circuit, elements are being miniaturized in accordance with the proportional reduction rule, and densification is being further advanced. However, reducing the element size is approaching its limit, and it is difficult to manufacture an integrated circuit with higher density and higher performance simply by reducing the element size.

Therefore, at present, a device having a three-dimensional structure is formed by digging a groove on the surface of a semiconductor substrate or stacking a semiconductor film, an insulating film or a metal film. For example, as a method of increasing the capacitance of a capacitor which is a component of a MOS dynamic RAM (DRAM), a method of digging a groove in the surface of a silicon substrate and substantially increasing the capacitance of the capacitor without increasing the occupied area is known. Has been adopted. In the process of forming an element having such a three-dimensional structure, one of the important processes is a technique of introducing impurities into the surface of a three-dimensional silicon substrate. As a technology for introducing impurities into the surface of a three-dimensional silicon substrate, a silicon oxide film doped with impurities by low-pressure chemical vapor deposition (LPCVD), which has good coverage on steps, instead of the conventional ion implantation method Is formed on a three-dimensional silicon substrate surface, and the film is used as a diffusion source to diffuse impurities into the silicon substrate.

Further, in an integrated circuit, it is necessary to make the lower layer of the wiring as flat as possible in order to increase the reliability of the metal wiring in the upper layer and reduce the parasitic resistance and capacitance of the wiring to achieve higher speed and higher performance. As a planarization method, after forming transistors and wiring, an impurity-added silicon oxide film (hereinafter simply referred to as an impurity-doped silicon oxide film) is formed by atmospheric pressure chemical vapor deposition (APCVD), A method of fluidizing the membrane as a solid is generally used. However, as the size in the horizontal direction is reduced due to the miniaturization of the element, it becomes difficult to bury the impurity-doped silicon oxide film between transistors and wirings without any gaps. Therefore, LP that can uniformly form a film on the side wall of the step portion
A method of forming the impurity-doped silicon oxide film by a CVD method is considered as an effective means.

In the above-mentioned LPCVD method, tetraethoxysilane [chemical formula: Si (OC ₂ H ₅ ) ₄ , abbreviated as TEOS] and triethoxyarsine [chemical formula: As (OC ₂ H ₅ ) ₃ , abbreviated as TEOA] are used as source gases.
When a vaporized gas of an organic compound such as the above is used, it is possible to form an impurity-doped silicon oxide film having excellent step coverage.

As described above, in the process of manufacturing a semiconductor integrated circuit, a technique of forming an impurity-added silicon oxide film by an LPCVD method using a vaporized gas of an organic compound as a source gas has attracted attention. The conventional LPCVD apparatus used in this method has a structure in which all raw material gases are introduced from an inlet opening at one end of a reactor. However, the impurity concentration in the silicon oxide film formed on a large number of semiconductor substrates provided along the direction in which the source gas flows is higher in the semiconductor substrate located on the windward side of the source gas, and gradually decreases toward the leeward side of the source gas. As a result, it is impossible to add an impurity at an equal concentration to a silicon oxide film formed on a large number of semiconductor substrates.
This is because the temperature at which the reaction starts between the source gas of silicon oxide and the source gas of the added impurity is different, and the starting temperature of the source gas of silicon oxide is generally higher than that of the source gas of the added impurity. The reaction at the temperature normally used for film formation is caused by the reaction rate of the source gas for the silicon oxide film and the supply rate of the source gas of the impurity added. FIG. 6 (a) is a pyrolysis gas chromatography spectrum of TEOS which is a general source gas of silicon oxide, and FIG. 6 (b) is a TE gas which is a source gas of an impurity added.
It is a pyrolysis gas chromatography spectrum of OA. From this spectrum, TEOS, the source gas for silicon oxide,
In the case of (FIG. 6 (a)), it starts to decompose into diethyl ether at 550 ° C., and does not completely decompose even at 690 ° C. However, TEOA (FIG. 2 (b)) starts to decompose at a very low temperature of 250 ° C., and completely decomposes at 550 ° C. where the TEOS starts to decompose. Therefore, when an arsenic-added silicon oxide film is formed at a temperature of 700 ° C. using TEOA and TEOA, the reaction of TEOS is rate-determined by the surface reaction and TEOA, which is the arsenic-added source, is rate-controlled by supply. Arsenic cannot be added at the same concentration into the silicon oxide film formed thereon.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned conventional problems, and a silicon oxide film doped with an impurity of the same concentration on a large number of semiconductor substrates by one LPCVD method. An object of the present invention is to provide a thin film forming apparatus that can be formed.

[Means for Solving the Problems] The present invention relates to a thin film forming apparatus for forming a thin film comprising an impurity-doped semiconductor or an impurity-doped insulator on a substrate by a chemical vapor deposition method. A furnace which is housed in the reaction furnace, is rotated about a vertical axis in the reaction furnace, and has a large number of substrates loaded horizontally or almost horizontally; and a film of the reaction furnace. Means for heating a formation region; gas supply means for supplying a formation gas of a semiconductor or an insulator into the reaction furnace; and upper part from below so that an axis is located outside the boat in the reaction furnace. And a single gas introduction pipe for introducing an impurity doping gas of a semiconductor or an insulator into the reaction furnace, the gas introduction pipe having a plurality of openings provided in a vertical direction. And the gas introduction pipe A thin film forming apparatus, wherein the sum of the areas of the plurality of apertures is less than 2 times the cross-sectional area of the inside diameter.

The reason why the total area of the plurality of openings is limited to twice or less the cross-sectional area of the inner diameter of the gas introduction pipe is that when the cross-sectional area exceeds twice, the impurity-adding gas is uniformly distributed in the reaction furnace. This is because it is not possible to supply in a state of being dispersed in the water.

It is desirable that the inner diameter of the gas introduction pipe be in the range of 2 to 15 mm. The reason is that if the inner diameter is less than 2 mm, the raw material gas reacts in the introduction pipe, and the reaction product adheres to the low-temperature part and is easily clogged, while if the inner diameter exceeds 15 mm, the raw material gas becomes laminar in the introduction pipe. This is because there is a risk that gas may be retained.

(Operation) According to the present invention, a boat loaded with a large number of substrates (for example, semiconductor substrates) is loaded into a vertical reaction furnace by a transport means.
When an impurity-added thin film is formed on a large number of semiconductor substrates at a time by the LPCVD method, a gas that is likely to be supply-limited among the source gases is extended from one end of the reaction furnace to a film formation region where the semiconductor substrate is installed in the furnace. By dispersing and introducing the gas into the reaction furnace from the multiple openings through the gas introduction pipe, the gas can be transported to many semiconductor substrate surfaces in a state where the reaction of the gas is suppressed, and the surface reaction is controlled. can do. At this time, the gas that has flowed through the gas introduction pipe is allowed to pass through the plurality of openings by using a structure in which the sum of the areas of the plurality of openings is set to be equal to or less than twice the cross-sectional area of the pipe as the gas introduction pipe. It is possible to disperse and introduce the same amount in the reaction furnace. Further, by adopting a structure in which the boat on which the semiconductor substrate is loaded is rotated by the transfer means, the gas dispersed and introduced can be equally supplied to each part of the surface of the semiconductor substrate in a reaction-controlled state. This makes it possible to control the source gas on the surface of the semiconductor substrate in a reaction-controlled state, and to form a thin film in which impurities are uniformly added to a large number of semiconductor substrates loaded on the boat.

In particular, using an organic compound containing silicon as a constituent element and an organic compound containing an added impurity element as a constituent element, an impurity-doped silicon oxide film is loaded on a boat using a gas obtained by evaporating and vaporizing these raw materials. When formed by a single LPCVD method on a large number of semiconductor substrates, only the vaporization gas of an organic compound containing, as a constituent element, an additive impurity element having a low reaction initiation temperature, which is likely to be supply-limited, among the raw material gases, By dispersing and introducing into the reaction furnace from a plurality of openings through a gas introduction pipe extending from one end of the reaction furnace to the film forming region where the substrate sample in the furnace is installed, and rotating the boat, the impurity element added is removed. Enables the transport of organic compound gas containing gas to various parts of the surface of a large number of semiconductor substrates while suppressing the progress of its own reaction. It can be. As a result, it becomes possible for both the source gas of the organic compound containing silicon and the organic gas containing the additional impurity element to be in a state where the surface reaction is controlled, and the same concentration on a large number of semiconductor substrates and the entire surface of the substrate surface. It is possible to form a silicon oxide film to which impurities are added at a uniform concentration.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic sectional view showing an LPCVD apparatus according to one embodiment of the present invention. Reference numeral 1 in the figure denotes a reaction furnace made of quartz installed on the flange 2. A zone heater 3 of a resistance heating type is disposed on the outer periphery of the reaction furnace. In the vicinity of the center of the flange 2, a hole 4 through which a boat described later is put in and out is formed. On the flange 2 in the reaction furnace 1, a quartz tube 5 having a diameter larger than that of the hole 4 is provided in an airtight manner via an O-ring (not shown). An exhaust port 6 is opened in the flange 2 located between the reaction furnace 1 and the quartz tube 5, and a vacuum pump 7 for reducing the pressure inside the reaction furnace 1 is provided in the exhaust port 6. Are linked.

Reference numeral 8 in the figure denotes a door that can move up and down. On this door 8, a quartz boat 10 loaded with a large number of semiconductor wafers 9 is mounted.
Is mounted, and by moving the door 8 upward, the quartz boat 10 is connected to the hole 4 of the flange 2.
And charged into the high temperature region of the reactor 1 through
The door 8 is attached to the bottom of the flange 2 via an O-ring (not shown) so that the reactor 1 is vacuum-sealed. The boat 10 can be rotated about the moving direction of the door 8 as an axis.

Also, 11 and 12 in the figure are thermostats,
Cylinders 13 and 12 filled with an organic compound containing silicon as a component (eg, TEOS) and a cylinder 14 filled with an organic compound containing an additional impurity element as a component (eg, TEOA) are stored in the respective cylinders. 13,
14 is maintained at, for example, 80 ° C. One end of a first supply pipe 15 is connected to the cylinder 13, and the other end of the supply pipe 15 extends to the inner surface of the hole 4 across the flange 2. A precision flow control device (mass flow controller) 16 is interposed in the first supply pipe 15. One end of a second supply pipe 17 is connected to the cylinder 14, and the supply pipe
The other end of 17 is connected to the lower end of a gas introduction pipe 18 extending vertically in the quartz tube 5 across the flange 2. A mass flow controller is provided in the second supply pipe 17.
19 are interposed.

As shown in FIG. 2, the gas introduction pipe 18 has a plurality of circular openings 20 formed vertically. The cross-sectional area of the gas introduction pipe 18 is, for example, 32.2 mm ² (6.4 mm in diameter),
The diameter of the opening 20 is 1.5 mm, the number of which is 18 and the total area is 31.8 m
It has become m ^2. In other words, the total area of the opening 20 (31.8m
m ²⁾ is set to be more than twice the cross-sectional area of the gas inlet tube 18 (32.2mm ^2). The distance between the openings 20 is 70 mm
It has become. The function of the opening 20 does not vary greatly depending on its shape, and may be elliptical or polygonal in addition to circular. In the drawing, reference numeral 21 denotes a purge passage penetrating the flange 2 and having one end extending into the hole 4, and an inert gas introduction pipe for the purpose of opening to the atmosphere, dilution, and the like.

Next, formation of an arsenic-added silicon oxide film by the above-described LPCVD apparatus will be described.

First, a quartz boat 10 on which a large number of semiconductor wafers 9 are loaded is mounted on a door 8, and the door 8 is moved upward to fit the quartz boat 10 into the hole 4 of the flange 2. Into the high temperature area of the reactor 1 and the reactor 8 is vacuum-sealed by attaching the door 8 to the bottom of the flange 2 via an O-ring (not shown). Subsequently, after operating the vacuum pump 7 to evacuate the gas in the reaction furnace 1, the inside of the reaction furnace 1 is heated by the zone heater 3 of the resistance heating system, and the boat 10 is set at 3 rpm. While rotating under the conditions,
The gas vaporized from TEOS in the cylinder 13 is mass-flow-controlled.
The flow rate is adjusted by a ra 16 and supplied into the reactor 1 through the first supply pipe 15, and an inert gas is supplied into the reactor 1 through an inert gas introduction pipe 21. At the same time, cylinder 14 TEOA
The vaporized gas is flow-adjusted by the mass flow controller 19 and supplied to the gas introduction pipe 18 through the second supply pipe 17 and supplied into the reaction furnace 1 through the plurality of openings 20 of the introduction pipe 18. An arsenic-added silicon oxide film is formed on a large number of semiconductor wafers 9 loaded on a quartz boat 10 in the reactor 1. In this film forming step, the vaporized gases of TEOS and TEOA are introduced into the reactor 1 heated to 700 ° C. by the zone heater 3 at a flow rate of 50 sccm and 51 sccm, respectively, and the semiconductor wafer 9 is formed under a pressure of 1 torr. An arsenic-added silicon oxide film is formed thereon.

According to the LPCVD apparatus of such an embodiment, since TEOS has a high reaction initiation temperature and is close to the film formation temperature, the surface reaction is rate-determined from upwind to downwind of the gas. TEOA has the above-mentioned opening
20 is supplied into the reactor 1 from a plurality of openings 20 of a specific gas introduction pipe 18 having a total area of not more than twice the cross-sectional area,
Since most of the semiconductor wafers 9 loaded on the quartz boat 10 are supplied almost unreacted to near the surface thereof, the surface reaction is rate-determined over the entire film formation region despite the low reaction start temperature. As a result, an arsenic-doped silicon oxide film having the same film thickness and the same impurity concentration as the large number of semiconductor wafers 9 installed over the entire film formation region is formed.

FIG. 3 shows the use of an LPCVD apparatus of the present embodiment and a conventional LPCVD apparatus in which no gas introduction pipe is arranged in a reaction furnace.
FIG. 4 is a characteristic diagram showing the arsenic concentration in an arsenic-added silicon oxide film formed on each semiconductor wafer, arranged at m pitches. The horizontal axis in FIG. 3 shows the position of another semiconductor wafer with respect to the semiconductor wafer at the lower end of the quartz boat, and the vertical axis shows the arsenic concentration.

As is clear from FIG. 3, in the case of the conventional LPCVD apparatus, 7.5 × 10 ²⁰ atoms / cm ³ to 5.
In contrast to the case where the concentration greatly changes to 0 × 10 ²⁰ atoms / cm ³ , in the case of the LPCVD apparatus of the present embodiment, 6.3 × 10 ²⁰ at
It can be seen that the concentration change is suppressed between oms / cm ³ and 5.7 × 10 ²⁰ atoms / cm ³ .

FIG. 4 shows arsenic addition formed on a semiconductor wafer in a boat installed in a film formation region when the area of a plurality of openings formed in a gas introduction pipe provided in a reaction furnace is changed. 5 shows the arsenic concentration in the silicon oxide film. The cross-sectional area of the gas inlet pipe 18 is 32.2 mm ² (6.4 mm in diameter) and the opening 20
Are 18 and the distance between the openings 20 is 70 mm.

As is clear from FIG. 4, when the total area of the openings 20 is twice or less the cross-sectional area of the gas introduction pipe 18, the uniformity of the arsenic concentration is improved.

In the above-described embodiment, one type of the source gas of the additional impurity is used, but two or more types of the source gas of the additional impurity may be used. For example, boron and phosphorus-doped silicon oxide film (BP
In the case of using two kinds of additive impurity source gases such as SG film), as shown in FIGS. 5 (a) and 5 (b), a boron source triethyl borate [chemical formula: B (OC ₂ H ₅ )] _3. Abbreviation T
EB], and triethyl phosphate [chemical formula: PO (OC ₂ H ₅ ) ₃ , abbreviated as TEP] as a raw material of phosphorus, for example, each of 8
Gas cylinders 24 and 25 stored in constant temperature baths 22 and 23 maintained at 0 ° C. are filled, and gas vaporized in the cylinders 24 and 25 is supplied to mass flows interposed in supply pipes 26 and 27. Control
A predetermined amount is introduced into the reactor 1 through the tubes 28 and 29. At this time, as shown in FIG.
27, TEB and TEP are mixed and introduced into the reaction furnace 1 through the plurality of openings 20 of the gas introduction pipe 18 as shown in FIG. 5 (b). The gas may be introduced into the reactor 1 through a plurality of openings 20, 20 'of the introduction tubes 18, 18' connected to the supply tubes 26, 27, respectively.

Note that the present invention is not limited to the above-described embodiment, and may be configured as follows.

The present invention is not limited to the reduced pressure vapor phase growth apparatus, but can be similarly applied to other vapor phase growth apparatuses, for example, a normal pressure vapor phase growth apparatus.

The present invention is not limited to the vertical type vapor phase growth apparatus, and can be similarly applied to a so-called horizontal type vapor phase growth apparatus in which a reaction furnace is provided horizontally.

Raw materials other than the impurity-adding gas may be introduced not only from below the reaction furnace as in the embodiment but also from above or from the side.

[Effects of the Invention] As described above in detail, according to the present invention, when forming a thin film in which an impurity element is added to a large number of semiconductor substrates by a single LPVCVD method, the total area of the openings is cut off by the source gas of the additional impurity. By dispersing and introducing the impurities from the plurality of openings through a specific gas introduction pipe set to be equal to or less than twice the area, impurities can be uniformly distributed over the entire surface of the semiconductor substrate, and can be uniformly distributed over many semiconductor substrates. It is possible to provide a thin film forming apparatus that can be added.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an LPCVD apparatus showing one embodiment of the present invention, FIG. 2 is an enlarged front view of a gas introduction pipe of FIG. 1, and FIG. 3 is an LPCVD apparatus of this embodiment and a conventional LPCVD apparatus. FIG. 4 is a characteristic diagram showing a change in arsenic concentration in an arsenic-doped silicon oxide film formed by using a wafer apparatus, and FIG. 4 is formed by using an LPCVD apparatus in which an area of an opening provided in a gas introduction pipe is changed. FIG. 5 (a) and FIG. 5 (b) are each a schematic sectional view of an LPCVD apparatus showing another embodiment of the present invention, and FIG. 6 is a characteristic diagram showing a change in arsenic concentration in an arsenic-doped silicon oxide film depending on a wafer position. FIG. 2 is a spectrum diagram of TEOS and TEOA by hot gas chromatography. 1 ... reactor, 2 ... flange, 3 ... zone heater,
5 ... Quartz tube, 7 ... Vacuum pump, 8 ... Door, 9 ... Semiconductor wafer, 10 ... Boat, 11, 12, 22, 23 ... Constant temperature bath, 13, 14, 24, 25 ... ... cylinder, 16, 19, 28, 28 ... mass flow controller, 18, 18 '... gas introduction pipe, 20,
20 '... Opening.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-239537 (JP, A) JP-A-63-7373 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 16/00-16/56 H01L 21/205 H01L 21/22 H01L 21/31

Claims (2)

(57) [Claims] 1. A thin film forming apparatus for forming a thin film made of an impurity-doped semiconductor or an impurity-doped insulator on a substrate by a chemical vapor deposition method, comprising: a vertical reaction furnace; A boat which is rotated about a vertical axis in the reactor and has a large number of substrates loaded horizontally or almost horizontally, means for heating a film formation region of the reactor, Gas supply means for supplying a forming gas of a semiconductor or an insulator, wherein the shaft extends upward from below so as to be positioned outside the boat in the reaction furnace, and extends vertically. A single gas introduction pipe for introducing into the reaction furnace a gas for adding impurities of a semiconductor or an insulator provided with a plurality of openings, and wherein the gas introduction pipe has the plurality of openings. Is the sum of the area of A thin film forming apparatus characterized in that the cross-sectional area is not more than twice as large. 2. The method according to claim 1, further comprising: evacuation means for reducing the pressure in the reaction furnace, wherein a thin film made of an impurity-doped semiconductor or an impurity-doped insulator is formed on the substrate by low-pressure chemical vapor deposition. The thin film forming apparatus according to claim 1.