WO2007099490A1

WO2007099490A1 - Processing assembly and method for processing a batch of wafers

Info

Publication number: WO2007099490A1
Application number: PCT/IB2007/050607
Authority: WO
Inventors: Antonius M. C. P. L. Van De Kerkhof
Original assignee: Nxp B.V.
Priority date: 2006-02-28
Filing date: 2007-02-26
Publication date: 2007-09-07

Abstract

Processing assembly (1) comprising a processing device (Ia) having a processing chamber (2) in which a large number of wafers can be processed in a batch (B), the processing chamber (2) having a closable processing door (3) through which a boat for carrying a plurality of wafers can be placed in and removed from the processing chamber (2), the processing assembly (1) further being provided with a pump (4) being connectable in fluid connection with the processing chamber (2) for maintaining the pressure in the processing chamber (2) in a low pressure range when the door (3) is closed, wherein the processing assembly (1) is provided with a second pump (5) being connectable in fluid connection with the processing chamber (2) for lowering the pressure in the processing chamber (2) from atmospheric pressure to a value smaller than 1 mbar after the door (3) has been closed. Further a method is disclosed for processing a batch of wafers in such a processing assembly (1).

Description

Processing assembly and method for processing a batch of wafers

FIELD OF THE INVENTION

The invention relates to a processing assembly comprising a processing device having a processing chamber in which a large number of wafers can be processed in a batch, the processing chamber having a closable processing door through which a boat for carrying a plurality of wafers can be placed in and removed from the processing chamber, the processing assembly further being provided with a pump being connectable in fluid connection with the processing chamber for maintaining the pressure in the processing chamber in a low pressure range when the door is closed.

BACKGROUND OF THE INVENTION

It is known to use such processing assemblies for processing wafers, for instance for applying a layer with the aid of low pressure chemical vapor deposition (LPCVD). These known assemblies comprise a single pump. This pump, a process pump, has a dual function; on one hand it evacuates gas from the processing chamber and on the other hand it maintains the desired gas pressure during the processing of the wafers in the processing chamber. The process pump pumps with constant power, i.e. a constant velocity. A known problem of these assemblies is the occurrence of turbulence in the processing chamber while the gas is evacuated from said chamber. Due to said turbulence, small particles are released and are floating in the processing chamber with the risk of colliding with the wafers, thus contaminating and possibly damaging the wafers. This results in production losses and thus unnecessary costs and time.

To regulate the evacuation of the gas from the processing chamber and reduce the above-mentioned turbulence, a valve having orifices is provided that is used during the initial part of the evacuation process. In the pipe, which extends from the processing chamber to the process pump a closure valve is provided adjacent to the processing chamber. Parallel to the closure valve a bypass containing a valve having orifices is arranged. Usually, the amount of orifices is limited to three, each orifice having a different diameter. The use of more than three orifices would result in more time loss during the pumping process because of the additional changing between orifices. The initial part of the process comprises pumping through an orifice with a small diameter for removing the first amount of gas from the processing chamber. Later on in the evacuating process, said orifice is replaced by an orifice with a larger diameter to evacuate a large volume out of the processing chamber containing a little bit of gas. By using these orifices during the evacuating process, the pressure in the processing chamber reduces gradually, resulting in reduction of the turbulence in the processing chamber. When changing from one orifice to another, a pressure pulse occurs in the pipes. Said pressure pulse on its part causes turbulence as well and enables particles to release.

Furthermore, due to technical development in low pressure chemical vapor desposition processes, amongst which the ever decreasing scale of the semiconductor structures to be formed, the processes become more difficult because smaller floating particles result in damage or at least a smaller yield of the process. Release of these smaller particles is more difficult to prevent by the known processing assemblies having one pump.

A further disadvantage of the known processing assembly is the fact that the pipe connecting the processing chamber to the process pump has to be brought to atmospheric pressure each time the processing chamber has to be opened. This takes additional time between processing of different batches of wafers and is furthermore not advantageous for the life span of the processing assembly.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a processing assembly with a single processing chamber, wherein the pressure can be lowered and maintained at a low pressure range, wherein at the same time turbulence is minimized during pumping down to reduce the release of particles and particle collisions against wafers causing defects. To that end, a processing assembly according to the invention is characterized by the features of claim 1. The second pump can be designed for pumping relatively large amounts of gas, which is quite dense, in the sense that it has a pressure in the range between 1 mbar to 1 bar. The first pump can be designed to maintain a pressure in the range of 0.1 to 10 mbar. Each pump can be optimally designed for its own purpose. According to a further elaboration of the invention, the second pump has a controllable pumping velocity. This is very advantageous because the pumping velocity can be controlled in a way that the pressure reduction/time unit remains constant or follows a desired curve. No pressure pulses will occur and therefore turbulence in the processing chamber is minimized. This results in fewer particles released, which means less damage on the wafers. By using a second pump during the evacuation process, the pressure in the processing chamber is fluently decreased. Furthermore, by using a second pump, release of small particles can be minimized.

According to a further elaboration of the invention, the fluid connection is establishable by opening and closing a first valve provided between the first pump and the processing chamber and by opening and closing a second valve provided between the second pump and the processing chamber. The first and second valves enable the processing assembly to switch between the first and the second pump and vice versa. Preferably, only one pipe is connected to the processing chamber and extends to the pumps, both pumps using that same pipe for evacuating gas from the processing chamber. However, it is imaginable that more than one pipe is provided, for example that each pump is provided with a separate pipe connected to the processing chamber. The advantage of using a single pipe connected to the process chamber is that the switching between the second and the fist pump can be realized without pressure variations in the chamber. In further elaboration of the invention, a control is provided for controlling the first and second pumps and the first and second valves. With such a control opening of the second valve after the door of the processing chamber has been closed can be obtained. Furthermore, the second pump can be started to pump down the pressure in the processing chamber to a pressure of about 1 mbar. Then the second valve can be closed and the first valve can be opened so that the first pump can be started to evacuate the last amount of gas from the processing chamber and maintain the pressure in the chamber in a low pressure range. This low pressure range can be any range that is required for a certain wafer process, such as an LPCVD process. It is also possible that the control is connected to a computer system. According to a further elaboration of the invention, controlling the second pump comprises regulation of pumping velocity of said pump in relation to the pressure drop in the processing chamber. The pressure drop can, for instance, be measured with a gauge provided at the processing chamber. The pressure in the processing chamber is measured and a pressure signal is provided by the gauge and sent to the control. The control determines, by comparing the measured values with predetermined values, whether the pumping velocity of the second pump has to be adjusted. If the measured value differs from the predetermined value, the control adjusts the performance of the second pump by increasing or decreasing the pumping velocity. The control aims at maintaining a constant pressure reduction. If the pressure reaches a value smaller than 1 mbar, the control decides to switch pumps. The second valve is closed, the first valve is opened and the first pump further evacuates the processing chamber and maintains the pressure in the low pressure range.

According to another advantageous elaboration of the invention, the control is adapted to remain the gas flow in the processing chamber during lowering the pressure at a constant value. This results in a further minimization of occurrence of pressure pulses and therefore further prevention against particle bursts.

In such a design of the processing assembly, it is particularly favorable when the control for the second pump contains a pressure profile according to which profile the pressure in the processing chamber is decreaseable. Said pressure profile is a predetermined profile based on earlier pressure reduction behavior of the processing chamber. This profile can be saved in, for instance, a computer and optimized for each particular process. When a certain process is going to take place in the processing chamber, and a related pressure profile is available, the second pump can use the values from said profile to decrease the pressure in the processing chamber. This is very advantageous because the pressure can be decreased in a very rapid way. No time is used to change settings by measuring pressure and controlling the pumps and valves accordingly. An optimal evacuation cycle is provided and no valuable processing time is wasted.

The invention also relates to a method for processing a batch of wafers, the method comprising: - providing a processing assembly comprising a processing device having a processing chamber in which a large number of wafers can be processed in a batch, the processing chamber having a closable processing door through which a boat for carrying a plurality of wafers can be placed in and removed from the processing chamber, the processing assembly further being provided with a pump being connectable in fluid connection with the processing chamber for maintaining the pressure in the processing chamber in a low pressure range when the door is closed, wherein the processing assembly is provided with a second pump being connectable in fluid connection with the processing chamber for lowering the pressure in the processing chamber from atmospheric pressure to a value smaller than 10 mbar after the door has been closed; - providing a plurality of wafers to be treated; opening the door of the processing chamber; placing the plurality of wafers into the processing chamber; closing the door of the processing chamber; bringing the second pump into fluid connection with the processing chamber and lowering the pressure in the processing chamber to a value smaller than 10 mbar; bringing the first pump into fluid connection with the processing chamber and maintaining the pressure in the processing chamber in a low pressure range; - starting the process in the chamber.

According to a further elaboration of the invention, the method comprises injecting N₂ into a pipe between the second valve and the second pump for venting that pipe, after closing the second valve. Venting said pipe between the second valve and the second pump prevents the system against pressure impulses. By injecting N₂ into the pipe, the pressure is brought back to atmospheric pressure. When the processing chamber has been opened again, a new batch of wafers has been placed into the chamber and the door of the processing chamber has been closed, the second pump starts to perform a next pumping process. When the second valve is opened no impulses occur because the pressure in the pipe on both sides of the valve are equal, due to the venting. This elongates the life span of the pump. The venting process of said pipe is controlled by the control. A pipe pressure gauge measures the pressure in the pipe. According to that measured pressure, a control valve opens to inject N2 into the pipe. The control also determines the timing of the venting process between the opening and closing of the valve.

In further elaboration of the invention, the method comprises submitting a process gas in the processing chamber during maintaining the pressure in the low pressure range.

According to a further elaboration of the invention, the method comprises measuring an amount of particles in the processing chamber with a particle measurement device on a dummy wafer provided on the boat with wafers. It is very advantageous to detect defects on wafers in an early stage of the manufacturing process of said wafers. In the beginning of the process, the costs of a single wafer are relatively low. During the manufacturing process, the costs of a wafer increase enormously, which makes it worthwhile to detect defects at the moment that the costs of a wafer are relatively low.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be further elucidated by means of an exemplary embodiment with reference to the accompanying drawing in which:

Fig. 1 shows a schematic view of a processing assembly. DETAILED DESCRIPTION OF THE EMBODIMENT

A processing assembly 1 is shown in Fig. 1. This processing assembly comprises a processing device Ia having a processing chamber 2 in which a large number of wafers can be processed in a batch B. The processing chamber 2 has a closable processing door 3 through which a boat for carrying a plurality of wafers can be placed in and removed from the processing chamber 2. The processing assembly 1 is provided with a first pump 4 and a second pump 5. The first pump 4 is connectable in fluid connection with the processing chamber 2 for maintaining the pressure in the processing assembly 1 in a low pressure range when the door 3 is closed. The second pump 5 is connectable in fluid connection with the processing chamber 2 for lowering the pressure in the processing chamber 2 from atmospheric pressure to a value smaller than 10 mbar after the door 3 has been closed.

As can be seen in Fig. 1, the first pump 4 is situated distant below the processing chamber 2, for instance in a cellar C, approximately 10-15 meters below the level G of the processing chamber 2. The second pump 5 is situated directly below the processing chamber 2, for instance on a sub floor S, which can be arranged at about 60 cm below the level G of the processing chamber 2.

After a batch of wafers B has been brought into the processing chamber, the door 3 is closed. Before starting the processing of said wafers, for instance with the aid of a low pressure chemical vapor deposition (LPCVD) process, the pressure in the processing chamber 2 has to be decreased. First, the second pump 5 is brought into fluid connection with the processing chamber 2 by opening a second valve 7 that is provided in a pipe 11 between the processing chamber 2 and the second pump 5.

A control 8 is provided among other things for controlling the valve 7. A pressure gauge 9 provided at the processing chamber 2 measures the pressure in said processing chamber 2. The pressure gauge 9 sends a pressure signal to the control 8, which control 8 opens the second valve 7. The second pump 5 is started on a signal of control 8 and pumps with a constant pressure reduction or according to another prescribed pressure reduction profile. It is also possible that a fixed pump velocity profile is stored in the control. From this pump velocity profile is has been determined that it provides a desired pumping down process for the specific process chamber. To obtain this desired pressure reduction, the pressure gauge 9 keeps on measuring the pressure in the processing chamber 2 during the evacuation process and sending pressure signals to the control 8. At the initial part of the evacuation of the gas from the processing chamber 2, the pumping velocity is relatively slow since a volume unit comprises a lot of gas at that stage of the pumping process. The longer the pumping process is going on, the less gas per volume unit is available. Thus, to remove gas from the processing chamber 2 according to e.g. a constant pressure drop, the pumping velocity is to be increased during the evacuation process. Therefore, the pumping velocity of the second pump 5 is regulated by the control 8 in relation to the pressure drop in the processing chamber 2 measured by the pressure gauge 9. The second pump 7 can be a dry pump, with a capacity in the range of 10m³ - 50 m³ per hour.

The control 8 can also remain the gas flow in the processing chamber 2 during lowering the pressure at a constant value for further minimization of occurrence of turbulence. The gas flow Q is substantially equal to pressure times pumping velocity. Consequently, when the desired constant gas flow is known and the pressure is known, the pump velocity can be determined.

In another favorable embodiment the second pump 5 is provided with a pressure profile according to which profile the pressure in the processing chamber 2 is decreaseable. This profile can be saved on a computer and provided to the second pump 5 by the control 8, which is connected to said computer. This profile can be derived from a pumping down simulation of the processing chamber 2.

When the pressure in the processing chamber 2 reaches a value of about 1 mbar or less depending on the specifications of the assembly and the pumps, the control 8 closes the second valve 7 and opens the first valve 6 that is provided in a pipe 10 between the processing chamber 2 and the first pump 4. The first pump 4, a process pump, is brought into fluid connection with the processing chamber 2. The control 8 preferably has started the first pump 4, which pumps with a constant speed. The first pump 4 is a process pump with a capacity in the range of 500 m³ - 1500m³ per hour. The value of the pressure in the processing chamber 2 at which the first pump 4 takes over pumping from the second pump 5 preferably is a threshold value that is low enough to optimally avoid risk of turbulence in the process chamber 2.

For example:

When using a dry pump and a process pump with a peek pumping velocity of 292 1/s and assuming that the maximum gas flow in the processing chamber is 100 mbarl/s, the threshold value is about 0,34 mbar (¹⁰° ^mbarl/s/₂₉₂ i_/s). In this configuration switching to the first pump 4 when reaching a pressure in the processing chamber 2 of 0,34 mbar risk of floating particles is minimized. It should be clear that this is an example and that different processing assembly dimensions, different maximum gas flow and using different first and second pumps may result in different threshold values. The preferred threshold value, as it is defined above, will be mainly determined by the exact geometry of the processing chamber, the capacity of the first pump and the nature of the wafer process that is to be carried out. Preferably the threshold value is smaller than 10 mbar. For common LPCVD processes the threshold value is approximately lmbar. Other processes and process chambers require a threshold value of 0,lmbar.

The first pump 4 is arranged to maintain the pressure in the processing chamber in a low pressure range between 0,0133 mbar (0.01 Torr) - 13.3 mbar (10 Torr) during the processing of the wafers in the processing chamber 2. Depending on the threshold value and the process pressure that is required, the first pump 4 can also be used to evacuate the last amount of gas from the processing chamber 2. During the pumping process of the first pump 4 to maintain the pressure at a low value, a process gas can be submitted into the processing chamber. Furthermore, a dummy wafer can be provided on the boat with wafers, comprising a particle measurement device to measure the amount of particles floating in the processing chamber during evacuation of the gas. The amount of particles is related to the amount of defects of the wafers. Therefore, using a particle measurement device in an early stage of the manufacturing process enhances early detection of defects, resulting in cost savings.

After closing the second valve 7, the pipe 11 between the second valve 7 and the second pump 5 is vented. A control valve 13 is arranged at pipe 11 for injecting N₂ into said pipe according to the pressure measured by the pipe pressure gauge 12. Venting the pipe 11 is necessary to bring the pressure in said pipe back to atmospheric pressure to avoid pressure impulses when the second valve 7 is opened again after opening the door 3 of the processing chamber 2.

Although an illustrative embodiment of the present invention has been described in greater detail with reference to the accompanying drawing, it is to be understood that the invention is not limited to the embodiment. Various changes or modifications may be effected by one skilled in the art without departing from the scope or the spirit of the invention as defined in the claims.

For instance, modifications with respect to the configuration of the processing assembly, for instance using two pipes connected to the processing chamber, falls within the scope of the invention. Furthermore, the processing assembly can also be used for different kinds of processes, next to the mentioned LPCVD process.

Claims

CLAIMS:

1. Processing assembly comprising a processing device (Ia) having a processing chamber (2) in which a large number of wafers can be processed in a batch (B), the processing chamber (2) having a closable processing door (3) through which a boat for carrying a plurality of wafers can be placed in and removed from the processing chamber (2), the processing assembly (1) further being provided with a pump (4) being connectable in fluid connection with the processing chamber (2) for maintaining the pressure in the processing chamber (2) in a low pressure range when the door (3) is closed, wherein the processing assembly (1) is provided with a second pump (5) being connectable in fluid connection with the processing chamber (2) for lowering the pressure in the processing chamber (2) from atmospheric pressure to a value smaller than 10 mbar after the door (3) has been closed.

2. Processing assembly according to claim 1, wherein the second pump (5) has a controllable pumping velocity.

3. Processing assembly according to claim 1 or 2, wherein the fluid connection is establishable by opening and closing a first valve (6) provided between the first pump (4) and the processing chamber (2) and by opening and closing a second valve (7) provided between the second pump (5) and the processing chamber (2).

4. Processing assembly according to any one of claims 1-3, wherein a control (8) is provided for controlling the first (4) and second (5) pumps and the first (6) and second (7) valves.

5. Processing assembly according to at least claim 4, wherein controlling the second pump (5) comprises regulation of pumping velocity of said pump (5) in relation of the pressure drop in the processing chamber (2).

6. Processing assembly according to at least claim 4, wherein the control (8) is adapted to remain the gas flow in the processing chamber (2) during lowering the pressure at a constant value.

7. Processing assembly according to any of the preceding claims, wherein the control (8) of the second pump (5) is provided with a pressure profile according to which profile the pressure in the processing chamber (2) is decreaseable.

8. Processing assembly according to any of the preceding claims, wherein a control valve (13) is provided on a pipe (11) between the second valve (7) and the second pump (5), which control valve (13) is arranged for venting the pipe (11) by injecting N₂

9. Method for processing a batch (B) of wafers, the method comprising: providing a processing assembly (1) comprising a processing device (Ia) having a processing chamber (2) in which a large number of wafers can be processed in a batch (B), the processing chamber (2) having a closable processing door (3) through which a boat for carrying a plurality of wafers can be placed in and removed from the processing chamber (2), the processing assembly (1) further being provided with a pump (4) being connectable in fluid connection with the processing chamber (2) for maintaining the pressure in the processing chamber (2) in a low pressure range when the door (3) is closed, wherein the processing assembly (1) is provided with a second pump (5) being connectable in fluid connection with the processing chamber (2) for lowering the pressure in the processing chamber (2) from atmospheric pressure to a value smaller than 10 mbar after the door (3) has been closed; - providing a plurality of wafers to be treated; opening the door (3) of the processing chamber (2); placing the plurality of wafers into the processing chamber (2); closing the door (3) of the processing chamber (2); bringing the second pump (5) into fluid connection with the processing chamber (2) and lowering the pressure in the processing chamber (2) to a value smaller than 10 mbar; bringing the first pump (4) into fluid connection with the processing chamber (2) and maintaining the pressure in the processing chamber (2) in a low pressure range; starting the process in the chamber (2).

10. Method according to claim 9, wherein a control (8) provided in the processing assembly (1) is controlling the first (4) and second (5) pumps and the first (6) and second (7) valves.

11. Method according to claim 10, wherein controlling of the second pump (5) comprises regulating the pumping velocity of said pump (5) in relation to pressure drop in the processing chamber (2).

12. Method according to claim 10, wherein the control (8) remains the gas flow in the processing chamber (2) during lowering the pressure at a constant value.

13. Method according to any of claims 9-12, wherein the method comprises injecting N₂ into a pipe (11) between the second valve (7) and the second pump (5) for venting that pipe (11), after closing the second valve (7).

14. Method according to any of claims 9-13, wherein the method comprises submitting a process gas in the processing chamber (2) during maintaining the pressure.

15. Method according to any of claims 9-14, wherein the method comprises measuring an amount of particles in the processing chamber (2) with a particle measurement device on a dummy wafer provided on the boat of wafers.