WO2012163676A1

WO2012163676A1 - Method for placing a semiconductor wafer on a susceptor at a specified angular orientation

Info

Publication number: WO2012163676A1
Application number: PCT/EP2012/059092
Authority: WO
Inventors: Hannes Hecht; Alois Aigner
Original assignee: Siltronic Ag
Priority date: 2011-05-30
Filing date: 2012-05-16
Publication date: 2012-12-06
Also published as: DE102011076742B4; TW201248765A; DE102011076742A1

Abstract

The invention relates to a method for placing a semiconductor wafer on a susceptor at a specified angular orientation, comprising the following steps: a) removing the semiconductor wafer from a first station by means of a robot arm; b) determining the current angular orientation of the semiconductor wafer in that the location of a mark on the semiconductor wafer is detected by means of an optical sensor; c) determining the angular orientation at which the semiconductor wafer is to be placed on a susceptor that can rotate about the center axis thereof and is present in a process chamber; d) transferring the semiconductor wafer to the process chamber by means of the robot arm; e) rotating the susceptor about the center axis thereof into a position leading to the placement of the semiconductor wafer at the specified angular orientation subsequently in step f); and f) placing the semiconductor wafer on the susceptor.

Description

A method for depositing a semiconductor wafer on a susceptor with a predetermined angular orientation

The invention relates to a method for depositing a semiconductor wafer on a susceptor with a predetermined angular orientation.

During the vapor deposition of an epitaxial layer on the front side of a semiconductor wafer, the latter usually rests on a support called a susceptor.

It is necessary to produce the layer with a uniform layer thickness and to let the usable surface of the layer approach as close as possible to the edge of the semiconductor wafer. When trying to implement this requirement, you will be with the

Problem faced that depending on the

Crystal lattice orientation of monocrystalline

Semiconductor wafer at certain areas on the edge of the

Semiconductor disk an increased growth rate

occurs, resulting in a locally increased layer thickness in these

Areas leads. For example, in the case of silicon wafers of the crystal lattice orientation (100), locally increased layer thicknesses occur at angular positions of 0 °, 90 °, 180 ° and 270 ° in the edge region. This problem is described in US2009 / 0031954A1.

The above document proposes that the local

different growth rate in the edge area by constructive measures in the directly to the

Semiconductor disc adjacent area of the susceptor to compensate, so to improved

Layer thickness uniformity to arrive. According to

US2009 / 0031954A1 can determine the growth rate of

epitaxial layer in the edge region of the semiconductor wafer through the material on the surface of the susceptor in the region immediately adjacent to the semiconductor wafer to be influenced. Accordingly, for example, in positions where the growth rate is particularly high, materials are used for the surface of the susceptor which reduce the growth rate in the adjacent region of the semiconductor wafer. Also local

geometric adjustments of the susceptor (local elevations) to influence the local growth rate are proposed. In order to be able to develop their desired effect, however, these measures presuppose that the semiconductor wafer is in the correct position during the deposition of the epitaxial layer

Angular orientation on the appropriately equipped

Susceptor is located. US2009 / 0031954A1 does not indicate how this can be ensured.

US5102280 discloses a method and apparatus for transporting a semiconductor wafer to a processing station in a defined orientation. This is the

Semiconductor disk from a robotic arm first into a

inserted separate alignment station in which the orientation of the semiconductor wafer is determined. Is doing a

Determined misalignment, the semiconductor wafer is taken in a first case of the robot arm, placed in the correct orientation and back into the

Orientation station inserted. This procedure is repeated until the wafer in the desired

Orientation in the alignment station is located. Then, the semiconductor wafer is picked up again by the robot arm and on a predetermined path to a processing station

transported and inserted into this. In a second case, the information on the misorientation is used directly to correct the movement of the robot arm during transport of the semiconductor wafer to the processing station so that the semiconductor wafer in the correct position in the Processing station is inserted. In this case, the alignment in the alignment station is dispensed with. Correction of alignment takes place during transport to

Processing station.

In the first case, the method for the position correction takes comparatively much time, so off

For reasons of economy, the second case would be preferred. In the second case, however, the problem arises that the

The opening through which the robot arm inserts the semiconductor wafer into the processing station (eg into an epitaxy reactor) is not substantially wider than the diameter of the

Semiconductor wafer. The robot arm has several joints. Is the foremost joint so close to the gripper for the

Semiconductor wafer arranged that it when depositing the

Semiconductor wafer itself enters the processing station, the orientation of the semiconductor wafer can be corrected before depositing in a relatively large angular range. On the other hand, it is not desirable that moving parts, for example, reach the preheated to several hundred degrees Celsius process chamber of an epitaxial reactor because generated by the moving parts particles and in the

Process chamber can be registered.

On the other hand, if the foremost joint of the robot arm does not enter the process chamber of the epitaxy reactor, the angular range in which the alignment of the semiconductor wafer can be corrected is severely limited.

The invention was therefore based on the object to provide a way to correct the orientation of the semiconductor wafer when placed on the susceptor of a Epitaxiereaktors in a wide range of angles without

Moving parts of a robot arm in the process chamber and without delaying the transport of the semiconductor wafer to the process chamber too much. This should also be accomplished with the least possible expenditure on equipment. The object is achieved by a method for depositing a semiconductor wafer on a susceptor with a predetermined angular orientation, comprising the following steps:

a) removal of the semiconductor wafer by means of a robot arm from a first station,

b) Determination of the current angular orientation of the

Semiconductor wafer in that the position of a marking on the semiconductor wafer is detected by means of an optical sensor,

c) Definition with which angle orientation the

Semiconductor disk on a in a process chamber

located to store its central axis rotatably mounted susceptor,

d) transfer of the semiconductor wafer by means of the robot arm to the process chamber,

e) rotating the susceptor about its central axis to a position which subsequently leads in step f) for depositing the semiconductor wafer with the predetermined angular orientation and

f) depositing the semiconductor wafer on the susceptor. In the method according to the invention, in contrast to the prior art, not the semiconductor wafer is oriented, but the susceptor. The method according to the invention therefore does not require an additional module for aligning the semiconductor wafer

(Alignment station). Instead, the angle orientation of the semiconductor wafer is determined at an arbitrary point before depositing the semiconductor wafer on the susceptor in step f). From this information, a signal for the control of the susceptor rotation is then generated and the

Susceptor rotated so that the semiconductor wafer in step f) from the robotic arm in the desired or required Orientation can be placed on the properly aligned susceptor. Since the inventive method in addition to the already necessary components such as robot arm and

Process chamber with susceptor only requires a device for determining the angular orientation of the semiconductor wafer, the technical complexity for the implementation of the method is low.

In addition, no robotic arm capable of rotating the wafer at a large angle around its own is needed

To rotate center axis. The robotic arm must therefore be in the

Area that carries the semiconductor wafer and in the

Process chamber enters, have no moving parts. Therefore, the inventive method is also for the transfer of a semiconductor wafer in a several hundred degrees Celsius hot process chamber and thus for the loading of

Epitaxy reactors or reactors for others

High temperature processes suitable.

Brief description of the figure

1 shows by way of example a schematic diagram of a device with two process chambers according to the prior art, as they usually for epitaxial coating of

Semiconductor wafers is used.

List of reference numbers

1 cassette with semiconductor wafers

2 first transfer chamber

3 alignment station

4 lock chamber

5 second transfer chamber

6 process chamber First, a typical device according to the prior art will be described with reference to the schematic diagram shown in FIG

described, for example, for the epitaxial

Coating of semiconductor wafers is used. The

Device comprises one or more stations for receiving in each case a cassette 1 with semiconductor wafers. Shown are two cassettes 1. In a first transfer chamber 2 are one or more robots, not shown, which remove the semiconductor wafers individually from the cassettes 1 and in one of possibly several (shown two)

Transfer lock chambers 4 and place them there.

If it has to be ensured that the semiconductor wafers are placed in a defined orientation on the respective susceptor present in the process chambers 6, an additional alignment station 3 is necessary according to the prior art. In this case, the robot in the first transfer chamber 2 does not transfer the wafer directly from a cassette 1 to a lock chamber 4, but first from the cassette 1 to the alignment station 3, where the

Semiconductor wafer is brought into the required orientation. Subsequently, the semiconductor wafer is placed in the correct position in one of the lock chambers 4 by the robot located in the first transfer chamber 2. (The invention

Procedure does not need the alignment station 3.)

In the second transfer chamber 5 is another robot, the semiconductor wafer from one of

Lock chambers 4 extracts, they in one of possibly more (shown are again two) process chambers 6 transferred and stores them there on a rotatably mounted about its central axis susceptor. In the process chamber is then carried out, for example, an epitaxial coating at least one side of the

Semiconductor wafer. After treatment in the process chamber, the

Return transfer of the treated semiconductor wafer to one of the cassettes 1 in the reverse direction as just described.

In the following, the inventive method with

preferred embodiments described in detail:

The order of steps a) to f) does not necessarily have to correspond to the order mentioned above. Only steps a), d) and f) are necessarily in this order

perform.

In step a), a semiconductor wafer by means of a

Robotic arm taken from a first station. The first

Station may be, for example, a cassette 1 for receiving a plurality of semiconductor wafers or a lock chamber 4.

In step b) the current angular orientation of the

Semiconductor wafer determined. In this description, "angular orientation" is understood to mean a rotation angle around the central axis of the semiconductor wafer, which has an excellent direction

Semiconductor wafer (which in the case of a monocrystalline

Semiconductor disk is usually determined by the orientation of the crystal lattice and made visible by a marker) assumes a defined standard direction.

The angular orientation is determined by detecting the position of a mark on the semiconductor wafer by means of an optical sensor. The mark is usually a notch (English, "notch") or a flat place (English, "flat") on the circumference of an otherwise round semiconductor wafer. A laser mark on the surface of the semiconductor wafer can also serve as a mark for the crystal lattice orientation.

Regardless of the type of marking can be used as an optical sensor, a camera that a picture of the

Semiconductor wafer receives, the line of sight of the

Camera optics preferably perpendicular to the flat surface of the

Semiconductor disk is aligned. Preferably, a digital camera is used, since the image can be further processed electronically in this case without further intermediate steps. Preferably, the location of the mark is determined automatically by means of an image recognition program.

If the marking is a notch or a flattened spot on the otherwise circular circumference of the semiconductor wafer, can also be used to determine the angular orientation

Photoelectric sensor can be used. The light beam generated by a laser, for example, travels on a circular line directly within the circumference of the semiconductor wafer

along. Thus, the light beam constantly hits the

Surface of the semiconductor wafer, except in the area of the notch or flattened area. In this way, the location of the mark can be clearly determined. The relative movement between the light beam and the semiconductor wafer can be achieved by a rotation of the semiconductor wafer about its central axis

stationary light source or by a circular movement of the light source about the central axis of the stationary

Semiconductor wafer or be achieved by means of a movable optics.

The optical sensor for determining the angular orientation can be mounted at any point of the device, as long as it is ensured that the angular orientation before Step e) is determined. On the other hand, the

Angular orientation throughout the way from the determination of the angular orientation to the placement on the susceptor to be preserved or changed in a unique and well-known manner. The semiconductor wafer may therefore be rotated in the course of the subsequent transfer steps about its central axis, as long as this happens reproducibly without significant play and direction and amount of rotation are known exactly, so that a correlation between the determined in step b) angular orientation and the angular orientation when placing the Semiconductor disk on the susceptor in

Step f) can be produced.

Step b) may take place before step a) in the first station (eg lock chamber 4 or during step a) during the removal from the first station or during step d) during the transfer of the semiconductor wafer to the process chamber 6

(For example, within the transfer chamber 5) are performed. Step b) can either be done while the

Semiconductor wafer rests on a solid surface

(For example, in the first station) or while from one of the robot arms (for example, in one of the

Transfer chambers 2 or 4 or during the transfer into the process chamber 6) is held.

In a further step c) it is determined with which angle orientation the semiconductor wafer later on in step f) on the one located in the process chamber 6 to its

Center axis is rotatably mounted susceptor store. This desired angular orientation refers to a particular excellent direction of the susceptor, so it is an angular orientation relative to the susceptor.

This target orientation on the susceptor results

for example, from the fact that the susceptor certain Directional, to the crystal lattice orientation of

Semiconductor wafer adapted features for locally correcting the growth rate of the epitaxial layer, as described for example in US2009 / 0031954A1. In this case, the semiconductor wafer must be placed on the susceptor such that the orientation of its crystal lattice coincides with the location of the correction features on the susceptor such that the latter has its corrective effect on the local

Growth rate of the epitaxial layer can develop optimally.

Preferably, for each type of semiconductor wafer, the required angular orientation, resulting, for example, from the above considerations, is once defined and stored, for example, in a database. In order to determine the required angular orientation of the semiconductor wafer in relation to the susceptor in step c), the corresponding data are retrieved from the database. Step c) can occur at any point in the process

Step e), d. H. already before step a), simultaneously with one of the steps a), b) or d) or between two of said steps. In step d), the semiconductor wafer by means of a

Robot arm (attached, for example, in the transfer chamber 5) is transferred to a process chamber 6. It may be the same robot arm as in step a). However, different robot arms can be used. The transfer of the semiconductor wafer to the process chamber 6 preferably takes place on a predetermined path, ie the movement of the robot arm is predefined and is not adapted to the angular orientation of the semiconductor wafer determined in step b) in order to correct it. In step e) located in the process chamber 6

Susceptor according to the determined in step b)

Angle orientation of the semiconductor wafer and the determination made in step c), with which angle orientation the

Semiconductor wafer must be placed on the susceptor, rotated about its central axis to a position, which in step f) below for depositing the semiconductor wafer with the

required angle orientation leads. For the rotation of the susceptor preferably the same drive is used, the susceptor also during the subsequent process

(For example, the epitaxial coating) set in rotation. However, in order to turn the susceptor to the desired position, the current position of the susceptor must be known at all times. Corresponding drives are state of the art. These are usually stepper motors, which are also equipped with an angle encoder for the exact determination of the current rotation angle.

Step e) can take place as soon as the steps b) and c)

are performed, preferably while the semiconductor wafer is transferred to the process chamber 6 in step d).

In step f), the semiconductor wafer is deposited by the robot arm on the susceptor in the process chamber 6, wherein preferably no further position correction takes place.

The invention can be applied in the context of all methods in which it is important to place a semiconductor wafer in a predetermined angular orientation on a pad (susceptor). Of particular importance is this in the

Deposition of a gas phase epitaxial layer on a monocrystalline semiconductor wafer (for example, a silicon wafer) in an epitaxial reactor.

Claims

claims

A method of depositing a semiconductor wafer on a susceptor having a predetermined angular orientation, comprising the steps of:

b) Determination of the current angular orientation of the

c) Definition with which angle orientation the

Semiconductor disk on a in a process chamber

located to store its central axis rotatably mounted susceptor,

f) depositing the semiconductor wafer on the susceptor.

2. The method according to claim 1, wherein the first station is a cassette for receiving a plurality of semiconductor wafers or a lock chamber.

3. The method according to any one of claims 1 or 2, wherein the mark a notch or a flattened point on the circumference of a substantially round semiconductor wafer or a

Laser marking on the surface of the semiconductor wafer is.

4. The method according to any one of claims 1 to 3, wherein the optical sensor is a camera which forms an image of

Semiconductor wafer receives, and wherein the position of the marker is detected automatically by means of image recognition.

5. The method according to claim 3, wherein the optical sensor is a light barrier whose light beam relative to

Semiconductor wafer is moved on a circular line along the circumference of the semiconductor wafer, so that the light beam along the entire circumference except the notch or the

flattened spot hits the surface of the semiconductor wafer, so that the position of the notch or the flattened spot can be determined.

6. The method according to any one of claims 1 to 5, wherein the

Process chamber is used for depositing an epitaxial layer on the surface of the semiconductor wafer from the gas phase and wherein the susceptor one or more

Directional, to the crystal lattice orientation of

Semiconductor wafer adapted features for locally correcting the growth rate of the epitaxial layer.