DK173655B1 - Method of depositing layers on a substrate - Google Patents

Description

DK 173655 B1

The present invention relates to a method for depositing layers, e.g. by Plasma Enhanced Chemical Vapor Deposition (PECVD), on a substrate, the method comprising placing the substrate between an upper electrode and a lower electrode.

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State of the art

Using a parallel plate PECVD deposition chamber, much of the deposited material ends up on the chamber walls and the electrodes.

10 This causes a change in the system impedance and therefore slightly changes the properties of the deposited films. In many applications this is not a problem, but in waveguide production, where close control of the refractive index is important, this can lead to non-reproducible results.

15 It is therefore important to clean the chamber regularly. This can be done either by mechanical cleaning or chemical cleaning in situ. The chemical purification is a special plasma process used to etch the deposited layer.

An advantage of the chemical purification process is that it is performed without separating the system, thereby reducing the time the chamber is out of operation. However, in the process there is a problem with different etching rates on different surfaces. In particular, the etching rate on the live electrode is approximately one factor two greater than on the grounded electrode. Therefore, the live electrode is cleansed first.

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The aluminum walls of the chamber are exposed to the plasma when all the deposited glass has been removed. A continuation of the purification process thereafter will result in the formation of a polymer layer. Since the cleaning process does not stop until the grounded electrode is cleaned, a fairly thick polymer layer will be formed on the live conducting electrode.

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A polymer layer will also be formed immediately on the grounded electrode at the location of the wafer since no glass is deposited here. Therefore, after the purification process, the chamber is partially clean and partially covered with polymers. These polymers will affect the deposition process in a number of ways.

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First, after some time, the deposited glass tends to peel off the polymer layer, causing a particle contamination in the chamber. This will affect the film quality.

Secondly, the layer thickness of the polymers on the ground electrode is not necessarily the same from time to time. Consequently, the environment for the wafeme will not be the same between different deposits and cleaning periods. Use of different substrate sizes will also not be possible; eg. depositing a 5 "wafer after a 4" wafer will result in a different environment at the outer portion of the 5 "-15 wafer compared to the middle 4" wafer

Accordingly, two problems must be solved: 1) The chamber conditions must be reproducible and stable during a deposition cycle, and 2) the purification process must produce as few polymers as possible.

Finally, the cleaning process should be as short as possible to increase system operating time.

Prior art

British Patent Application GB 2312439 discloses a method for depositing layers by PECVD for the production of optical waveguides. It is stated that greater regeneration capability and control of / with the refractive index 3 DK 173655 B1 is obtained by placing the substrate on the live electrode, thereby maintaining a negative bias (bias) on the substrate during deposition. There is no mention of how to avoid unwanted formation of layers of deposited material on the electrodes, cleaning procedures, how to avoid formation of 5 polymers during the cleaning, or in general how to increase chamber operating time and stable chamber conditions.

DESCRIPTION OF THE INVENTION It is an object of the present invention to provide a process for improving the stability and reproducibility of the chamber conditions in a PECVD reactor for the production of silica-based planar waveguide components. It is a further object of the invention that the chemical plasma cleaning processes used to remove unwanted deposits of silica (SiO 2) 15 on the chamber walls produce as few polymers as possible. Finally, it is an object of the present invention for the purification process to be as short as possible thereby contributing to an increase in system operating time.

According to the invention, there is provided a method as defined in the preamble of claim 1. This method is characterized in that the substrate is placed on a support disposed on the lower electrode.

In this way, it is possible to reduce the out-of-operation time in Plasma Enhanced Chemical Vapor Deposition (PECVD) reactors when, e.g. used for the manufacture of silica-based, planar waveguide components. Using the method, the PECVD reactor remains in a uniform and road-controlled state for extended periods of time, resulting in greater capacity in the landfill processes used.

Suitable embodiments of the invention are outlined in claims 2-8.

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The invention will be described in the following by way of example with reference to the only figure which shows a principle construction of the inner parts of a horizontal plate with a parallel plate PECVD.

5 In the drawing, the inner parts of a horizontal PECVD chamber with parallel plate with lower and upper electrode are indicated 1 and 1 respectively. 2. As can be seen, a substrate 4 is placed on a support plate 3, such as a large molten quartz support 3. The diameter of the molten quartz support 3 should correspond to the diameter of the lower electrode 1 to keep it free of unwanted deposited material. Stop means 5 10 hold the substrate 4 in the indicated position on the support plate 3 during loading and unloading and during processing.

The effect of the molten quartz support 3 will now be explained: 15 By placing the wafer 4 on a support 3 of a material similar to the layer deposited in the PECVD chamber, the impedance of the system will be less affected by the deposited material. Deposition on different substrate size travels 4 can be done using either the same molten quartz support 3 or another carrier 3.

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The cleaning process is also performed with a molten quartz support 3. The cleaning process is then stopped as soon as the live electrode 2 has been cleaned. This avoids almost complete polymer formation.

The most significant advantage of the method is the increased operating time of the PECVD landfill system. Manufacturers of PECVD equipment recommend a plasma cleaning for every 5-6 pm deposited material. This would make waveguide making virtually impossible as the individual layers consist of 4 to 15 µm glass. Furthermore, the recommended cleaning time corresponds to the deposition time.

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Using the method of the invention, it is possible to deposit up to 200 µm of silica glass before plasma cleaning is necessary.

An additional benefit is improved reproducibility. The deposited material 5 behaves very similar to the molten quartz carrier 3, and therefore the plasma environment will not change upon deposition.

The polymer formation in the chamber is also dramatically reduced. This results in significantly better glass quality than with traditional methods.

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Many types of supports can be used, but it is usually preferred that both the dielectric properties and the heat properties of the support material correspond to the dielectric properties and heat properties of the material deposited in the PECVD chamber. Thus, if silica or surface-treated silica is deposited to produce planar waveguides, a molten quartz support is preferred.

(This means quartz, which melts over a short period of time, so that it is no longer crystalline - "fused silicia".)

Preferably, the carrier is provided with means for holding the wafer in place as the 20 wafer on the carrier is inserted or removed by the PECVD chamber and during processing. In one embodiment, the means for positioning the wafer consists of a recess in the carrier which fits the wafer. In another embodiment, stop means are provided on the carrier to hold the wafer in place.

Claims (8)

1. A method of depositing layers, e.g. by Plasma Enhanced Chemical Vapor Deposition (PECVD) on a substrate, the method comprising placing the substrate between an upper electrode and a lower electrode in a PECVD chamber, characterized in that the substrate is placed on a support disposed on the lower electrode . A method according to claim 1, characterized in that the carrier substantially covers the region of the lower electrode of the PECVD chamber. A method according to claims 1-2, characterized in that the dielectric properties of the carrier correspond substantially to the deposited layers. A method according to claims 1-3, characterized in that the thermal properties of the carrier correspond substantially to the deposited layers. A method according to claims 1-4, characterized in that the carrier has means for holding the substrate in place on the carrier. 20 A method according to claim 5, characterized in that the means for holding the substrate are constituted by stop means on the support. A method according to claim 5, characterized in that the means for holding the substrate are constituted by a depression in the carrier. A method according to claims 1-7, characterized in that the support is made of molten quartz. 30