JPS63224219A - Thin film deposition method - Google Patents

Abstract

PURPOSE:To make it possible to deposite the film having excellent uniformity on large type substrates in a mass productive manner by a method wherein, in the method in which raw gas is fed from the lower part and exhaust gas is discharged from the upper part, the substrates are arranged vertically erecting in parallel with the stream of gas. CONSTITUTION:Substrates 4 are fixed to a quartz jig 5, and the substrates 4 are constructed in such a manner that they are rotated together with the jig 5. Also, a heat-shielding plate 6 is provided under the substrates 4, the glass substrates are placed on the quartz holder 5 leaving the specified intervals, the entire holder is moved to a temperature-equalized region from under a vertical type furnace (room temperature region), and the air in the furnace is discharged by feeding N2 intermittently while the inside of the furnace is being formed into a depressed state. Then, inside the furnace is depressed, this state is maintained for the prescribed period (preheat), and monosilane (SiH4) gas of 20% of He base is allowed to flow. The pressure in the furnace is maintained constant by flowing the He between a reaction furnace and a pump, and also by controlling back pressure. As a result, a film of good quality having excellent uniformity can be deposited on a large type substrate in a mass productive manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film deposition method, and particularly to a reduced pressure deposition method suitable for depositing a thin film with good uniformity.

[Conventional technology]

Thin film transistors (TPTs) used in active matrix (AMX) type liquid crystal display elements and televisions (TVs)
) is positive? Amorphous 5i (a-8i) by CVD (PCVD) method or low pressure CVD (LPGVD)
With the increase in the area of 1 displays made using polycrystalline Si (Poly-3i) as a thin film material, it has become necessary to form these films with good uniformity on increasingly large substrates. became. Polycrystalline Si, which has higher carrier mobility than amorphous Si, can not only realize display elements and TVs with good responsiveness, but also reduce the cost of the entire display element by incorporating one peripheral circuit and integrating it with the display. Recently, it has been attracting particular attention because it is possible to measure the Therefore, LPG for forming a polycrystalline silicon film
The importance of VD equipment and its deposition methods is also increasing.

Technical magazine "Electronic Materials" 1 shows LPGVD equipment
There is an article titled ``Vertical LPGVD Device'' in the March 1986 issue.

[Problem that the invention seeks to solve]

Conventionally, two types of LPGVD furnaces have been used: vertical furnaces and horizontal furnaces. Figure 2 shows an outline of how the vertical furnace and substrates are arranged. This furnace has a raw material gas groove inlet 2 at the bottom of the reactor 1 and an exhaust gas outlet 3 at the top, and a plurality of substrates 4 are arranged horizontally on a jig 5 inside the furnace 1.

In a vertical furnace, it is easier to achieve temperature uniformity than in a horizontal furnace, and when taking out a sample after film deposition, less oxygen is involved in the air, which suppresses oxidation of the film surface and improves quality. It has the advantage that a membrane can be obtained. Regarding the film thickness distribution, by charging approximately 100 8-inch diameter circular substrates (for example, Si, "Eva"), values of ±7% for the substrate inward direction and approximately ±10% within the batch were obtained. .

tmax and tmLn indicate the maximum and minimum values of the film thickness.

However, with the increase in the size of the substrate 4, from the conventional circular 8 inch (approximately 200 am diameter) substrate to the square A4
The size (approximately 360 mm in the diagonal direction) corresponds to approximately doubling the size of the substrate. For this reason, non-uniformity in film thickness distribution has become a major problem. FIG. 5 shows the relationship between the substrate spacing and the film thickness distribution when a film is deposited on an A4 size substrate using the conventional method (FIG. 2). Increasing the distance between the substrates improves the film thickness distribution. However, if the interval is 1
Even if it is expanded to 50a, a distribution of ±10% cannot be obtained. Here, the film thickness distribution is improved by lowering the reactant gas pressure in the furnace, but even if the pressure is reduced to 0.3 Torr, a distribution of ±10% cannot be obtained. When the pressure is lower than 0.3 Torr, the deposition rate decreases and a long time deposition is required, resulting in poor quality.

Next, a conventional horizontal furnace will be described. Figure 3 shows an outline of the horizontal furnace. Components that are the same or equivalent to those in FIG. 2 are given the same symbols in FIG. 3.

This furnace was used as a mainstream technology when the substrate diameter was as small as 3 to 4 inches, and has the advantage of being easy to operate. However, when taking out a sample after film deposition, there is a problem in that oxygen in the air is drawn into the furnace and oxidizes the sample surface. Furthermore, as the size of the substrate increases, non-uniformity in film thickness within the substrate, particularly in the upper and lower positions, is a major problem.

As shown in Figure 4, a method has been proposed in which the substrates are arranged parallel to the gas flow in a horizontal furnace, but this method has not been successful in mass production for large substrates because of uneven film thickness in the upper and lower positions.

As described above, with the conventional method, it is difficult to mass-produce a film with good uniformity on an A4 size substrate.

An object of the present invention is to provide a method for mass-producing a high-quality film with good uniformity on a large substrate.

[Means for solving problems]

The present invention was achieved based on the results of visualizing and ampering the gas flow in a conventional vertical device. The present invention has been achieved by arranging large substrates in a conventional vertical furnace parallel to the gas flow, that is, in the vertical direction, and by reducing the spacing between the substrates.
It deposits a high-quality film with good uniformity on a large number of substrates under a certain reduced pressure.

[Effect]

Visualize the gas flow in a vertical furnace! As a result.

It has been found that the uniform film thickness distribution according to the present invention can be achieved for the following reasons. In the present invention, when the distance between the substrates is large, there is a complicated flow including a thin layer around the substrates. This thin flow violently supplies new raw material gas from the periphery of the furnace to the periphery of the substrate, increasing the deposition rate in this area. As the spacing between the substrates is made smaller, the above-mentioned ridges gradually disappear, and are hardly seen at a spacing of about 30 inches.

Accordingly, the gas flow flowing between the substrates becomes laminar, and this flow uniformly supplies the raw material gas onto the substrates to create a uniform film thickness distribution. Note that the conventional film deposition method (second
In Figure), the gas flow near the substrate is similar to gas diffusion when there is a concentration distribution.

Therefore, as the spacing between the substrates becomes smaller, the supply of gas to the center of the substrates becomes obstructed. Accordingly, the rate of decrease in the deposition rate at the central portion of the substrate is greater than that at the periphery of the substrate, and the uniformity of the film thickness distribution deteriorates.

FIG. 6 shows the relationship between the substrate spacing and the deposition rate when a thin film is deposited on an A4 size substrate using this method under a reduced pressure of Q, 6 Torr. As the substrate spacing decreases, the deposition rate decreases. However, what should be noted here is that there is a difference in how the deposition rate decreases between the center and the periphery of the substrate. That is, the decrease is small in the center and large in the periphery, and when the distance between the substrates is about 30 mm or less, the difference in deposition rate between the two becomes small. In other words, in the single-bokuto method, the uniformity of the film thickness distribution improves when the substrate spacing is reduced, which is the opposite trend compared to the conventional method. As in the present invention, being able to reduce the substrate spacing means increasing the number of batches.
This is also a big advantage.

FIG. 7 shows the relationship between substrate spacing and film thickness distribution in the present invention. When the pressure is 0.6 Torr, the distribution gets better as the substrate spacing becomes smaller, and at 30 m it is approximately ±7%.
can be achieved. Thereafter, even if the interval is made smaller, the film thickness distribution does not change much. When the pressure is reduced, the film thickness distribution generally improves, but the above-mentioned tendency with respect to the substrate spacing of about 30 ns++ remains unchanged.

〔Example〕

An embodiment of the present invention will be described below.

FIG. 1 schematically shows how large substrates are arranged vertically in a vertical furnace. Components that are the same or equivalent to those shown in FIG. 2 are given the same reference numerals. The substrate 4 is fixed to a quartz jig 5, and the substrate 4 is structured to rotate together with the jig 5. Further, a heat shielding plate 6 is placed below the substrate 4 (on the upstream side). Inner diameter 450mm, soaking length 500m
15 glass substrates of A4 size (thickness: 2 mm) were placed in a quartz holder 5 at intervals of 20 mm using a vertical furnace 1 of size 1.

The whole holder was removed from the bottom of the vertical furnace (room temperature area) at a temperature of 580 mm.
Move to soaking area 'C for 15 minutes. While reducing the pressure inside the furnace, N2 is intermittently supplied to exhaust the air inside the furnace. Next, reduce the pressure in the furnace and keep it for 15 minutes (
preheat). He-based 20% monosilane (SiH4) gas was applied at 1.5 rpm per minute while rotating the holder 6 times per minute.
0 Flow. By controlling the back pressure by flowing He between the reactor and the pump (turbo molecular pump), the pressure inside the reactor is maintained at 0.6 Torr. Deposit the film for 25 minutes. A polycrystalline silicon film of approximately 1500 in is obtained (deposition rate of approximately 60 in/+++ in). After stopping the supply of raw material gas, it is heated for 15 minutes (after heating).

Next, N2 is intermittently flowed into the furnace to completely exhaust the monosilane gas. Next, the gas exhaust is stopped and N2 is flowed into the furnace to bring it to atmospheric pressure over about 10 minutes.

The obtained film thickness distribution is ±6% both within the substrate and within the batch. Since the amount of oxygen involved in this device is small when the membrane is taken out, the membrane is not oxidized and the quality of the membrane is good.

〔Effect of the invention〕

According to the present invention, it is possible to mass-produce a high-quality film with good uniformity on a large substrate.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a vertical furnace used in an embodiment of the present invention;
Figures 2 to 4 are schematic diagrams of each reactor used in the conventional example, Figure 5 is a diagram showing the relationship between the film thickness distribution and the substrate spacing in the conventional example, and Figure 6 is the relationship between the substrate spacing and the substrate spacing in the present invention. A diagram showing the relationship between the deposition rate and FIG. 7 is a diagram showing the relationship between the substrate spacing and the film thickness distribution in the present invention. 1... Reactor, 2... Raw material gas inlet, 3... Exhaust gas outlet, 4... Substrate, 5... Jig (holder)
, 6... Heat-resistant board.
,),"H,H,);',1□,9"-・Agent Patent attorney Akio Takahashi も:;,-9-O3 Figure 4-B Right S figure ratio 60 Radical spacing, L( mm) Between boards 7M, L (mm)

Claims (1)

[Scope of Claims] 1. A thin film in which raw material gas is supplied from the bottom of the reactor, the pressure inside the reactor is reduced to perform a reaction, a thin film is deposited on a substrate placed in the reactor, and exhaust gas is discharged from above. A thin film deposition method characterized by arranging substrates vertically parallel to the gas flow. 2. In claim 1, the substrate spacing is set to 3.
The method for depositing a thin film as described above, characterized in that the thickness is 0 mm or less. 3. In claim 1, the pressure inside the furnace is set to 0.
The thin film deposition method described above, characterized in that the pressure is 6 Torr or less.