JP2664288B2 - Measuring the temperature of multiple wafers stacked in a processing chamber using a pyrometer - Google Patents

Description

This application is a continuation-in-part of U.S. patent application Ser. No. 07 / 701,800, filed May 17, 1991, entitled "Wafer Processing Cluster Tool Batch Preheating and Degassing Method and Apparatus." .

FIELD OF THE INVENTION The present invention relates to measuring the temperature of a thin, flat article, such as a semiconductor wafer, and more particularly to the temperature of a plurality of such articles stacked in a processing chamber, for example, a rack in a processing chamber of a semiconductor wafer processing machine. Related to the measurement. More specifically, the present invention relates to a batch thermoforming process, e.g., a pyrometer thermometer useful during a semiconductor wafer processing machine, e.g., a batch thermoforming process performed in a batch preheating or degassing module of a semiconductor wafer processing cluster tool. Related to measurement technology.

BACKGROUND OF THE INVENTION Semiconductor wafers undergo various processing steps in the process of manufacturing semiconductor devices. These processing steps are usually performed in a sealed vacuum chamber of a wafer processing machine. Most of the processes performed on wafers require monitoring and controlling the temperature of the wafer during processing,
And some of these processes, such as degassing and annealing processes, include heat treatment of the wafer as their essential processing steps. In some of these processes, particularly in the essential heat treatment process, a plurality of wafers can be stacked on a rack in a processing chamber of a processing machine and processed simultaneously as one batch.

In various semiconductor wafer processing processes, various temperature sensing techniques are used to monitor the temperature of the wafer and often also control the wafer heating or cooling elements. For example, thermocouple devices are often used, especially when the wafer is being processed while being held in thermal contact with a temperature-controlled wafer support member. In such cases, the thermocouple is often kept in contact with the support member, and thus only measures indirectly the temperature of the wafer on the text member. In certain other situations, the thermocouple device is brought into direct contact with the wafer. Such positioning of the thermocouple is desirable, for example, if the radiant energy is used to heat the wafer, by exposing the sensor directly to heat from a wafer heating source or by direct contact with the wafer. Not cause wafer contamination.

Further, a technique has been proposed in which the temperature of a wafer is indirectly derived by measuring the thermal expansion of the wafer.
Such a technique has the disadvantage that such a measurement results in a reading proportional to the temperature difference. Thus, before the monitored temperature can be derived, the initial temperature of the wafer must be known, and the dimensions of the wafer must first be measured at the known initial temperature. Moreover, while such techniques are effective for reading the temperature of a single wafer, multiple wafers, especially closely spaced wafers, are processed and the temperature of the wafer batch is read. If so, it is difficult to apply these techniques.

In many wafer processing machines, pyrometers are used to measure the temperature of the wafer being processed in the machine. These pyrometers are objects to be heated,
For example, the irradiance of the wafer is measured. However,
This emissivity varies with the emissivity of the object. The emissivity of an object varies with temperature for some materials. The emissivity varies, inter alia, with the material from which the object is manufactured and the material of the coating applied to the object. In semiconductor wafer processing, there are many types of coatings found on wafers. These coatings vary depending on the process used for the wafer. Thus, accurate use of a pyrometer to measure the temperature of such coated wafers often requires initial measurements to determine the emissivity of the object.

As a result of the problems associated with pyrometers, several schemes have been devised for measuring wafer temperature in semiconductor wafer processing. These mechanisms measure the emissivity of the object or make some sort of modification to the output of the pyrometer. Often, the temperature measured by the pyrometer is the temperature of an object mounted in the processing chamber, for which the emissivity is known and known to be kept at the same temperature as the wafer being measured. Also, often a reference pyrometer sensor is used to generate the data that is then used to correct the temperature reading from the primary parameter sensor to determine the emissivity of the wafer being measured. Is made.

Measuring the temperature of the wafer from the backside of the wafer may reduce the effects of emissivity changes due to coatings on the frontside of the wafer, but the uniformity of the backside of the wafer is not precisely controlled One encounters the initial problem that it can vary from wafer to wafer.

Thus, the problem remains of accurately measuring the temperature of a semiconductor wafer or similar thin flat article during processing in a semiconductor wafer processing machine. In particular, when wafers are being thermally processed in batches and can be stacked and spaced closely together in the processing chamber, the temperature of the wafer must be measured without contacting the wafer.

SUMMARY OF THE INVENTION It is an object of the present invention to accurately measure the temperature of thin, flat articles, for example, semiconductor wafers, in a processing chamber of a processing apparatus in a non-contact state, and especially for stacking this stack during batch processing. It is to measure the temperature of such an article.

One specific object of the present invention is to accurately measure the temperature of a semiconductor wafer in a processing chamber of a semiconductor wafer processing apparatus,
It is another object of the present invention to provide a pyrometer temperature measurement technique for accurately measuring the temperature of a wafer regardless of the emissivity of the wafer or the coating of the wafer.

In accordance with the principles of the present invention, an article being processed in a processing chamber of a processing apparatus, in particular, viewing the article at an angle from a side of a stack of semiconductor wafers to a surface of the article. This provides a pyrometer for measuring the thermal radiation emitted from the stack. In this preferred embodiment of the present invention, one or more wafers located in the center of the stack are directed toward the backside of the wafers on which the pyrometers are stacked so that the wafer is observed by the directional pyrometer. Is tilted. The thermal energy accepted by the pyrometer is limited to the centrally located wafer due to the directional characteristics of the pyrometer having a limited field of view around the axis of the pyrometer, ie, the line-of-site.

In a preferred embodiment of the invention, the pyrometer is used for wafer processing, for example, in the case of a batch preheating degas module of a semiconductor wafer processing cluster tool in which a plurality of wafers are stacked for batch preprocessing. It is provided outside the processing chamber of the device. The pyrometer is directed at the side of the wafer stack, through a window in the wall of the processing chamber, along a direct straight path, or along a path guided by a mirror. Wafers are usually circular, and thus the circular edge of the wafer defines the surface of a cylinder that can be considered the boundary of a disk-like space between parallel wafers. Pyrometers typically respond to thermal energy at a wavelength in the infrared band, and the window is made of a material that transmits energy at this wavelength, for example, barium fluoride.

According to this preferred embodiment, the pyrometer is not radiated directly from the wafer or transmitted through the wafer, and the energy incident on the pyrometer is directed at the parallel spaced wafers of the batch. Tilted at a sufficient angle to a wafer of a given diameter and spacing to ensure that it is reflected multiple times, preferably at least 8 times, from the surface and along the space between the wafers . If one side of the wafer has a highly reflective coating, the number of reflections is preferably at least 14 and if both sides of the wafer have a reflective coating, the number of reflections is Is preferably at least 20 times.

In addition, the wafer observed by the pyrometer is
Preferably, the wafer is moved by at least one wafer from both ends of the stack and, in the case of highly transparent wafers, by several wafers from both ends of the stack, whereby an equal amount of Energy is transferred in both directions through the wafer adjacent to the space within the field of view of the pyrometer. If the wafer observed by the pyrometer is one or preferably more wafers moved from the wafer at the end of the stack, the energy transmitted through the wafer, if any,
It is approximately equal to the energy transmitted through the wafer from the opposite side and is nullified by that energy. The reason is that the transferred energy is generated from another wafer at the same temperature. As a result, the power received by the pyrometer is close to the power radiated from a black body at the same temperature as the wafer.

The pyrometer of the apparatus of the present invention is preferably configured to observe from the side of the stack and the back of the wafer, for example, from the bottom of the wafer facing upwards of the stack. Thus, the backside of one or more wafers and the space between the wafers is within the field of view of the pyrometer. The angle of the pyrometer relative to the plane of the wafer in the stack ensures that multiple reflected light from the parallel wafer surface meets the light reflected through the stack to the pyrometer at any angle within the pyrometer's field of view. Equal to or greater than the minimum angle required. This angle is a function of geometric parameters, including wafer diameter and spacing. The greater the diameter of the wafer and the closer the spacing between the wafers, the smaller this angle will be. This angle is such that the energy passes in a straight line from the processing chamber or the wall of the processing chamber opposite the wafer or passes with less reflection, eg, two or four reflections, before entering the pyrometer. It is important not to be as shallow as you can.

The maximum angle of the pyrometer direction towards the backside of the wafer must also not be too large, or may not be perfectly aligned within the stack and the shadows formed on one wafer by the edges of another wafer. The reflection from the edge of the wafer, which may not be possible, can disrupt the pyrometer reading. Ideally, the field of view of the pyrometer would be small so that the minimum proportion of the wafer edge falls within the field of view.

Accordingly, a plurality of semiconductor wafer processing cluster tools having a diameter of 150 mm or 200 mm or more and a thickness of 0.75 mm, for example, approximately 25 wafers are stacked and arranged at an interval of approximately 9 mm. In the degas chamber, the preferred angle of orientation of the pyrometer is about 40 ° for a pyrometer having a field of view of 7 ° or less.

In accordance with the present invention, a high temperature at a pyrometer angle directed at the boundary of the space between the three central wafers of a stack of five or more parallel wafers in a degassing chamber of a wafer processing apparatus. The energy accepted by the meter is almost 98% of the energy accepted from the blackbody
Was found to exceed.

For a bare silicon wafer, the emissivity of the wafer is about 0.4. In such wafers, if the net transmittance of these centrally located wafers is zero, the reflectivity is 60%, and the energy received is closer to the energy received from the blackbody. Become. The higher the reflectivity of the wafer or its coating, the greater the number of reflections required to obtain properties that are approximately the same as those of the black body. This can be achieved by steepening the angle of the pyrometer towards the stack.

The above and other objects and advantages of the present invention will become more readily apparent from the following detailed description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a partially cut-out part of a degassing module of a silicon wafer processing cluster tool apparatus according to an embodiment of the principle of the present invention. FIG. 2 is an embodiment of FIG. 2A is an enlarged schematic view of a portion surrounded by 2A-2A in FIG. 2, and FIG. 3 is a top view of a part of the schematic view in FIG. .

DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIG. 1, one embodiment of the present invention is a semiconductor wafer batch preheating module 10 of a semiconductor wafer processing cluster tool, for example, May 17, 1991, which was specifically incorporated herein by reference. Assignee entitled "Wafer Processing Cluster Tool Batch Preheating and Degassing Method and Apparatus," filed on Jan. 10, exemplifies a module disclosed in co-pending U.S. patent application Ser. Have been. The module 10 includes a sealed housing 11 surrounding a vacuum chamber 12 in which a wafer 14 is processed. In the illustrated embodiment of module 10, the process performed is to preheat wafer 14 for the purpose of removing absorbed gases and vapors before processing the wafer in other modules of the semiconductor wafer processing equipment or This is a process of adjusting in advance.

In the module 10, the wafer 14 is supported in a support member for supporting a large number of wafers, that is, a rack 16. Wafers 14 are vertically stacked on a rack 16. Wafer 14 is a typically circular thin plate or flat disk approximately 0.75 mm thick and 150 mm, 200 mm or more in diameter. Wafer
Each of the stacks 14 are arranged in a horizontal plane when stacked on a rack 16 and stacked 19 along a vertical axis 18.
Are spaced from and aligned with adjacent wafers.

The rack 16 is supported on a vertically movable and rotatable elevator 20 in the vacuum chamber 12. Rack 16 is 4
It has a plurality of wafer holders formed by a plurality of slots 22 of a vertical rod 24 made of quartz. Wafers 14 are individually loaded into rack 16 as elevator 20 is indexed vertically to sequentially align each of slots 22 with wafer loading port 26 of housing 12. The wafer loading port 26 is a vacuum chamber inside the housing 11.
A sealable connection is established between the vacuum chamber 12 and the vacuum chamber inside the wafer transfer module 28. Wafer transfer module 28
In the inside, the wafer is vented to module 10
It carries a robotic wafer handling mechanism (not shown) for transferring to and from the degassing chamber 12 and to and from other processing modules of the wafer processing apparatus. The vacuum in the vacuum chamber 12 is maintained by a conventional cryogenic vacuum pump 30 connected to the vacuum chamber 12 through the housing 11.

In a typical heat treatment process, for example, a batch preheating process performed by module 10, elevator
As the 20 is indexed beyond the wafer loading port 26, the wafers 14 are individually loaded into the slots, ie, holders 22, of the rack 16 through the open gate valve 26. Thereafter, the gate valve 27 is closed with the vacuum chamber 12 kept at the same pressure level as the pressure in the chamber of the wafer transfer module 28.

In the preheating or degassing process, the pressure in the vacuum chamber 12 is changed to a pressure different from the pressure in the wafer transfer module 28 by the operation of the pump assembly 30, or is maintained at the same pressure as the pressure in the module 28. Can be.
In this process, wafers 14 stacked on a rack 16 in a sealed vacuum chamber 12 are loaded into a housing 111
By heating a radiant heater 31 having a bulb 32 arranged in pairs outside the vacuum chamber 12 behind a quartz window 34 in the opposite wall, it is uniformly heated to a high temperature. This elevated temperature, i.e., the processing temperature, which can be, for example, 500 [deg.] C., is typically maintained for a predetermined processing time, e.g., 15 minutes, during which the processing temperature must be monitored and controlled Must.

According to a preferred embodiment of the present invention, the front of the housing 11 has an observation port located slightly above the lower part of the rack 16 when the elevator 20 is in the raised position, i.e., in the processing position. That is, a window 51 is provided. The viewing port 51 is tilted upward with an angle θ preferably equal to approximately 40 ° relative to the horizontal plane, as better exemplified by reference to FIG. 1 and to FIG. 2A. Is preferred. Observation port 51 is at its center line
FIG. 1 is oriented and oriented such that 52 is substantially oriented to the left of the stack 19.

The wafer 14 of the stack 19 has a generally circular shape with a boundary formed by circular edges 45. In the illustrated embodiment, each of the wafers 14 is arranged with the front side 46 facing upward and the back side 47 facing downward. Since the wafer is arranged this way, the edge 45
Is disposed on the surface of a virtual cylinder 48 having the axis 18 as a center line. Facing surfaces 46 of adjacent wafers 14 of stack 19
And 47 are parallel and form a space 49 between these planes. The space 49 may be considered to be surrounded by a circular boundary 50 arranged on the cylinder 48.

A pyrometer 53 is mounted on the window, i.e., outside the chamber adjacent to the viewing port 51, and is oriented along an axis 52 of the viewing port. The pyrometer 53 is physically straightened to accept energy from approximately three of the parallel spaces 49 between adjacent wafers in the centermost portion of the stack 19 from the sides of the stack 19. Or through the viewing port 51 with the aid of a mirror along the reflecting path. This is achieved by the fact that the field of view α of the pyrometer 53 of about 7 ° includes a disc of about 25 mm at about 200 mm from the stack.

The fact that the energy received by the pyrometer 53 is somewhat independent of the emissivity of the wafers in the stack can be better understood with reference to FIGS. 2 and 2A.

For illustrative purposes, the emissivity is equal to the absorption of the wafer 14, so the pyrometer 53 is rather a receiver,
Or it can be considered as a light source. Thus, pyrometers, ie, light emitted along the axis 52 from the light source 53, collide with a point on the backside surface of the central wafer of the stack. This light beam along axis 52 impinges on the first, preferably central, wafer backside 47 of wafer 14 at an angle θ of, for example, 40 °, and thereafter from the backside surface 47 of the wafer 14. Is reflected at a similar angle θ and collides with the front side surface 46 of the next adjacent one of the wafers 14 below the central wafer at a similar angle θ. If the emissivity or absorptance of the surface is, for example, 40%, the amount of incident energy reflected at the next wafer will be the first
It is believed to be about 60% of the energy incident on the wafer. Since the wafers 14 located within the field of view α are separated from the ends of the stack 19 by one or preferably several other similar wafers kept at the same temperature,
The energy transmitted in both directions via the wafer 14 located in the center of the stack 19 is approximately equal and therefore negligible.

The top surface of the wafer just below the center wafer, that is,
The light beam reflected at the same angle θ from the front side is further reflected, and if the emissivity of this surface is also 40%, the amount of reflected energy is the amount of energy incident on that surface.
60%, or 36% of the original total energy impacted along the axis 52 of the beam. Subsequent reflections continue to reduce the original energy reflected to 60% of the energy incident on each reflection point. Thus, the diameter of the wafer is about four times the spacing between the two wafers and the angle of incidence is initially
At 40 °, almost eight reflections occur. For the third to eighth reflections, the initial amount of energy reflected will be 22%, 13%, 7.8%, 4.7%, 2.8% and finally 1.7%. Therefore, the initial incident energy of 9
8.3% will be absorbed by the two wafers.
This 40% emissivity represents a bare silicon wafer.

Thus, when the stack of wafers is heated to a predetermined temperature, the energy radiated from the surface of the wafer is reflected from the surface of the adjacent wafer and, after several reflections, passes over the edge of the wafer However, some energy is released along the axis 52 of the pyrometer 53 and is read by the pyrometer 53. Such reflected energy would be 98.3% of the incident energy if the emissivity of the wafer in stack 19 is 1.0, ie, equal to the theoretical "blackbody" emissivity. If the emissivity of the material is 10%, as in the case of an aluminum coated wafer, the light incident on the pyrometer 53 will be a black body (for the eight reflections used in the above example). Would be more than 95% of the light emitted from In such an example, a wafer having an emissivity of 60% or more would emit more than 99% of the energy of the black body. Similarly, variations in the emissivity of the upper and lower surfaces at different locations on the surface of the wafer may be due to multiple reflections while the beam travels from one side of the wafer to the other before colliding with pyrometer 53. It will be insignificant. For a 150 mm wafer placed at 9 mm intervals, if θ = 40 °, more than 20 reflections will occur, so even highly reflective wafers may be pyrometers.
It will appear as a black body for 53.

For example, if the goal is to approximate a wafer that can provide high reflectivity by coaching to a black body,
The analysis is simple. If the back side of the wafer is bare and its front side is coated with a reflective metal, the reflectivity of the front side of the wafer will be approximately 90%. In such a case, the energy incident on the pyrometer is
To reach 98% would require nearly 14 reflections.
For a wafer coated on both sides with metal, nearly 20 reflections are required. In any case, 9mm
By setting the angle θ to 40 ° with respect to the 150 mm wafers arranged at the intervals, an acceptable number of reflections can be obtained. This angle is not just along the pyrometer's center line, i.e., the line of sight, but also at any angle in the field of view that can be defined as the angle α centered on the pyrometer's line of sight. Should be obtained for the shallowest angles. Thus, the minimum angle of the pyrometer's line of sight to the plane of the wafer can be predicted by:

θ = tan ⁻¹ (R · S / D) + α / 2 where R is equal to the number of reflections desired, S is equal to the spacing between wafers, and D is equal to the diameter of the wafer. More generally, dimension D is such that a pyrometer in any plane perpendicular to the wafer, including the path of energy incident on the pyrometer within the field of view of the pyrometer, as shown in FIG.
The smallest dimension that can be defined by the length parallel to the wafer in the portion that is in the space between the individual wafers.

From the above description, it will be apparent to one skilled in the art that various alternatives to the above described embodiments may be practiced without departing from the principles of the present invention.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-105223 (JP, A) JP-A-2-287228 (JP, A) JP-A-52-117682 (JP, A)

Claims (19)

(57) [Claims] 1. A method for measuring the temperature of a plurality (N) (N ≧ 4) of wafers each having a diameter D and a thickness T and bounded by edges. Are aligned with respect to one axis and are spaced apart from one another by a distance S, and are stacked and arranged in parallel planes perpendicular to the axis, the edge of the wafer being a cylindrical body centered on the axis. Disposed on a surface, the plane being located between adjacent planes having a boundary located on the surface of the cylinder (N-
1) A method in which a space is defined and the stack is housed in a sealed processing chamber surrounded by a chamber wall of a semiconductor wafer processing apparatus, the method comprising: providing a pyrometer outside the chamber. The pyrometer has a line of sight extending from the pyrometer and a view over an angle α centered on the line of sight, and the pyrometer impinges on the pyrometer at an angle within the field of view around the line of sight. In response to the radiant heat energy, the pyrometer is directed through the window in the wall of the chamber to the side of the stack and generally toward the axis so that the line of sight is at an angle θ to the plane. Wherein the pyrometer includes a first space and a (N-
1) oriented so that an angle α is set that excludes the boundaries of the space, tan ⁻¹ (R · S / D) θ <90 °, where R is at least equal to 5 and Generating signals representative of the temperature of the wafers in the stack in response to the energy incident on the applied pyrometer. 2. The method according to claim 1, wherein
Each of the wafers has a partially machined front side and an unprocessed back side, and the front side of the wafer is arranged so as to face a common axial direction, and the step of orienting the pyrometer further comprises a line of sight. Orienting the pyrometer at an angle θ with respect to the plane toward the backside of the wafer. 3. The method according to claim 2, wherein
The method wherein R is greater than or approximately equal to 14. 4. The method according to claim 3, wherein
N ≧ 7 and the field of view is at least the first space;
The second space, the (N-1) th space, and the (N-
2) A method of excluding space boundaries. 5. The method according to claim 1, wherein:
N ≧ 6 and the field of view is at least the first space;
The second space, the (N-1) th space, and the (N-
2) A method of excluding space boundaries. 6. The method according to claim 1, wherein:
A method wherein N ≧ 5 and the field of view includes a boundary of at least two spaces. 7. The method according to claim 1, wherein
The method further comprises controlling the temperature of the wafers in the stack in response to the generated signal. 8. A method for measuring a temperature of a plurality of wafers stacked in a parallel spaced relationship in a processing chamber of a wafer batch processing apparatus, wherein the plurality of wafers are opposed to both ends of a stacked body. The pair of terminal wafers and a plurality of central wafers disposed between the terminal wafers such that the field of view includes only the central wafer of the stack and the space between the wafers. Directing the directional pyrometer toward the side of the stack in a state limited to substantially all energy incident on the pyrometer from the stack is emitted from the wafer, transmitted through the wafer, and Substantially only the energy reflected from the wafer enough times so that the total energy accepted is close to the energy radiated from a black body of the same temperature Tilt the pyrometer to accept the energy from the stack at an acute angle to the wafer, and generate a signal representative of the temperature of the wafer in the stack in response to the energy incident on the pyrometer. A method comprising the steps of: 9. The method according to claim 8, wherein:
A method further comprising controlling the temperature of the stacked wafers in response to the generated signal. 10. An apparatus for simultaneously processing a plurality of thin planar articles each having a first side, a second side, and an edge, comprising: a processing chamber having a sealable wall; A rack enclosing the processing chamber and further having a plurality of devices mounted therein and spaced apart for simultaneously supporting a plurality of the at least four articles, the rack having the articles supported therein; Sometimes the first side of the article has a first end facing, and further has a pointing axis and accepts radiant heat energy, and at an angle within the limited field of view of the pyrometer pointing axis. A pyrometer including a device that generates an output signal in response to energy entering the receiving device, wherein the field of view includes only a first side of at least one of the articles and is closest to a first end. Part of the article and the first end A device for mounting a pyrometer such that a portion of one of the articles farthest from the eye does not enter the field of view, the at least one article being spaced a distance S from the article closest to the first side thereof; A space is formed between them, and the pyrometer follows a path in which all energy entering the receiving device within the field of view of its pointing axis forms an angle of at least θ with every first surface of the article in the field of view. A device directed to propagate from the stack, and wherein the angle θ for all such passages is given by: tan ^-1 (R.S / D) + α / 2θ <90 ° −α / 2 where R is at least equal to 5 and D is perpendicular to the article and in the space in the plane containing the passageway. The dimensions should be parallel. 11. The apparatus according to claim 10, wherein R ≧ 7. 12. The device according to claim 10, wherein R ≧ 12. 13. The apparatus according to claim 10, wherein R ≧ 20. 14. The apparatus of claim 10 wherein the rack includes a device on the rack for simultaneously supporting a plurality of spaced apart at least seven of the articles. 15. The apparatus according to claim 10, wherein the rack includes a device on the rack for simultaneously supporting a plurality of spaced apart at least approximately twenty-five such articles. 16. The apparatus according to claim 10, wherein θ is approximately equal to 40 °. 17. The apparatus according to claim 10, further comprising a window provided in a wall permeable to energy of wavelength λ, and wherein a pyrometer is provided on the window so that the field of view extends through the window. Equipment positioned outside. 18. The apparatus according to claim 10, wherein the rack simultaneously supports a plurality of spaced wafers having a diameter D equal to at least 150 mm at a spacing S equal to approximately 9 mm. Equipment including equipment. 19. The apparatus according to claim 10, further comprising a device for controlling the temperature of the stacked wafers in accordance with the generated signal.