RU2849000C1 - Device for rapid thermal processing of semiconductor wafers - Google Patents

Abstract

FIELD: semiconductor devices.

SUBSTANCE: invention relates to semiconductor device manufacturing technology and, in particular, to well-controlled methods for heating semiconductor wafers. The device for rapid heat treatment of semiconductor wafers comprises a thin rectangular quartz reaction chamber with a first open end connected to a stainless steel flange with a flange loading window for loading wafers, a heater and a wafer holder. Additionally, the device includes two rods fixed to the loading window of the flange, to which the wafer holder is attached, a movable reaction chamber holder that can move from the heating zone to the cooling zone, a thermocouple for measuring temperature and controlling the annealing process, a gas inlet pipe, an electronic temperature controller and air cooling fans, with the second end of the reaction chamber having a gas outlet pipe.

EFFECT: simplification of the device design while maintaining the main capabilities related to increasing the maximum heating and cooling rates, increasing the heat treatment temperature of semiconductor wafers in a gas environment, and increasing the productivity of the installation by simplifying the annealing process.

5 cl, 1 dwg

Description

Rapid thermal processing is a popular optical heating method used for processing and as a general, well-controlled method for heating semiconductor wafers. Many semiconductor heating processes require heating the wafer to high temperatures to enable various chemical and physical reactions during device fabrication. During thermal processing, semiconductor wafers are typically heated to temperatures ranging from 200°C to 1000°C. High heating and cooling rates allow for a wide range of processing modes, particularly during the annealing of ohmic contacts.

Rapid heat treatment chambers, which heat wafers using light energy, typically operate in a nonequilibrium state. Specifically, the walls surrounding the wafer remain cold, which is why these chambers are commonly referred to as "cold-wall" systems. This nonequilibrium configuration refers to the fact that the filament temperature inside the radiation source is much higher than the wafer temperature. A key advantage of using rapid heat treatment systems is the ability to rapidly change the wafer temperature, enabling very short heating cycles.

One of the applications of this invention relates to the field of minimizing the contact resistance of deposited metallized contacts to semiconductor structures by means of their rapid thermal annealing and can find application both in semiconductor lasers and in any semiconductor devices where minimal contact resistance of deposited contacts is required: transistors, diodes, solar cells.

A device for rapid thermal processing of semiconductor wafers is known (US 5,710,407 A, IPC H01L21/68735, published 18.08.2000). The device is specifically designed for processing wafers during the production or processing of semiconductor or electrical solid-state devices or components. This invention generally relates to processing semiconductor wafers and, in particular, to a method and device for rapid thermal processing of several semiconductor wafers simultaneously and one large semiconductor wafer. A rapid thermal annealing reactor is characterized by a short process cycle time compared to the same process cycle time in a conventional reactor. Rapid heating of the wafer is one of the factors determining the shorter process cycle time characteristic of this reactor. A structure for processing semiconductors according to this invention comprises a reaction chamber with a rotating holder mounted inside the reaction chamber. The rotating holder has a first surface designed to accommodate one or more wafers, and a second surface. A radiant heat source is mounted outside the reaction chamber such that radiant heat from the heat source directly heats the wafer or wafers mounted on the rotating holder. The radiant heat source raises the temperature of the wafer or wafers to a substantially uniform processing temperature, i.e., to a temperature uniform enough to achieve acceptable processing results, in such a time that the semiconductor processing structure is characterized as a fast thermal process reactor. In another embodiment of the invention, the semiconductor processing structure also includes a heater mounted in the reaction chamber adjacent to the second surface of the rotating support. Preferably, the heater is a resistance heating element. In one embodiment of this invention, the rotating holder is made of quartz, and the first surface is sandblasted, while the second surface is flame polished. To supply process gases to the reactor according to the invention, either multiple gas jets mounted in the reaction chamber or a central gas supply head are used. The reaction chamber is bounded by a vessel with a water-cooled side wall, a water-cooled bottom wall, and a forced-air-cooled top wall. The forced-air-cooled top wall is a circular, domed quartz wall. The radiant energy source of this invention comprises multiple lamp assemblies, each lamp assembly containing at least one lamp. The lamps are quartz-halogen lamps with a tungsten filament.

A drawback of this invention is its excessive complexity due to the presence of a rotating wafer holder. Furthermore, in one embodiment, the semiconductor processing structure also includes a heater mounted in the reaction chamber near the second surface of the rotating support, resulting in excessive chamber volume. Furthermore, the reaction chamber includes water-cooled elements, which complicates its fabrication and reduces manufacturability.

A device is known that uses high-intensity continuous lamps to improve the heat treatment of semiconductor wafers (US 4680451 A, IPC F27D99/0006, published July 14, 1987). A first and second plurality of spaced and skewed lamps are used for radiation heating of a semiconductor wafer. The lamps in each plurality are grouped, starting with the innermost lamps and ending with the outermost lamps. Each group of lamps in one plurality of lamps is connected to a group of lamps in another plurality of lamps, as a result of which the connected groups of lamps are simultaneously and equally voltage-dependent. The lamp voltage is modulated according to a predetermined table for each wafer size and temperature cycle. Alternatively, temperature sensors can be used to provide feedback to a computer-controlled modulator. The lamps in different groups can be selected to have different power intensities in the steady-state mode for a given voltage, thereby establishing the desired temperature gradient.

The disadvantage of this device is the excessive complexity of the heating unit, expressed in the complex configuration of the lamps, which negatively affects the manufacturing technology and operational characteristics of the device.

A heat treatment device is known (TW 315493 B, IPC H01L21/324, published 18.11.2010), which is provided with a working chamber for heat treatment of a plate. The plate is loaded onto a loading chute inside the processing chamber. Working gas is supplied to the processing chamber. The main heating device for heating the plate is located in the lower part of the processing chamber through a window. The main heating device radiates heat rays onto the loading chute and is provided with: a plurality of heat sources for heating the plate; and a rotating carrier, on the surface of which heat sources are mounted. The heat treatment device is additionally provided with a compensating heating device for compensating for the unevenness of temperatures on the surface of the plate, arising due to heating of the plate by the main heating device. The heat source of the compensating heating device is mounted on the surface of the rotating carrier together with the heat sources of the main heating device, but has an output that can be controlled independently of the heat sources of the main heating device.

The disadvantage of this device is the excessive complexity of the heating unit, which negatively affects its performance characteristics.

Also known (US 6051512, IPC H01L21/67754 published 10.12.2011) is a reactor for thermal processing of semiconductor wafers in a gas environment or vacuum, comprising a vacuum chamber, the housing of which is made of quartz glass. The infrared radiation source is a set of halogen incandescent lamps placed on the upper and lower sides of the vacuum chamber housing outside it. A means for supporting the semiconductor wafer is located inside the housing. Due to the intense heating of the housing due to the arrangement of infrared radiation lamps on both sides of the vacuum chamber and the absence of a cooling system, the temperature and time of the thermal processing of semiconductor wafers are limited. In such chambers, at the maximum possible temperature of 1200°C, the process can be carried out for no more than 30 seconds, otherwise degradation of the vacuum chamber housing material occurs. In addition, the device does not have means for rapid cooling of the processed wafer, which reduces the productivity of the installation and limits the process modes for which rapid cooling is important.

A device and method for heat treating semiconductor wafers are known (US 5001327 A, IPC H01L21/67751, published March 19, 1991). Heaters located in a high-temperature furnace form at least one heating space therein. An insertion and extraction opening is located at the bottom of each heating space, allowing the wafers to pass through it. Each heating space is adapted to receive one or two wafers and ensure simultaneous and uniform heat treatment of the wafers.

The disadvantage of this device is the high inertia of the heating element, which negatively affects the speed of heating and cooling.

The known (SU 443234A1, IPC F26B 25/12 published 15.09.1974) utility model relates to the field of heat treatment of semiconductor materials intended for the manufacture of devices used in microelectronics. A device for heat treatment of semiconductor wafers, comprising a reflective screen with a water-cooling jacket, a source of infrared radiation and a gas supply system placed in a housing; the device is equipped with a transparent plate located above the reflective screen with through inclined holes made in it, serving for the passage of gas, and the source of infrared radiation is located between the reflective screen and the transparent plate.

This technical solution has several drawbacks. The presence of through holes in the transparent plate prevents the creation of a vacuum in the chamber and the thermal processing of semiconductor wafers under vacuum. Furthermore, the prototype device lacks means for rapid cooling of the processed wafer, reducing the system's throughput.

A device for rapid thermal processing is known (application US 5861609 A, IPC H05B3/0047, published 02.10.2015). The present invention relates to a device and method for rapid thermal processing of sensitive electronic materials. The present invention reduces thermal non-uniformity arising from the non-uniform structure of materials and optical absorption characteristics. Objects are placed in a chamber in which at least some parts of the walls are transparent and transmit radiation from powerful heating lamps. The transparent part of the walls is usually made of quartz, which transmits radiation with a wavelength of 3 to 4 microns. Typically, these lamps are tungsten-halogen lamps, but arc lamps or any other source of visible and/or near infrared radiation can be used. Radiation from the lamps is directed through the transparent sections of the walls onto the surface of the object being heated. Since objects absorb near-infrared or visible light transmitted through the transparent part of the walls, rapid heating technologies allow for rapid temperature and process gas changes for various processes and material processing conditions. A rapid heating device reduces the "heat budget" when processing various semiconductors.

The disadvantage of this device is the lack of additional technical solutions that ensure a high rate of temperature reduction.

A device for rapid thermal processing of semiconductor wafers (US 6051512 A, IPC H01L21/67754, published 13.03.2002) was selected as a prototype, containing a thin rectangular quartz reaction chamber with one end open (during operation of the wafer processing system, the reactor chamber is opened and closed using a pneumatic door), a heater, a wafer holder coupled with a first drive, a transfer chamber and a pumping module, while the vacuum complex also contains a cooling system located in the transfer chamber and is made in the form of a housing with a cavity coupled with a coolant source; at the stage of introducing semiconductor wafers into the chamber, the semiconductor wafers are introduced into the chamber by a linear movement of the robot manipulator.

The disadvantage of this invention is the presence of a loading chamber and a robotic manipulator, which increases the cost of the installation and makes it more difficult to operate.

The objective of the present invention is to simplify the design while maintaining the basic capabilities associated with increasing the maximum heating and cooling rate, increasing the temperature of thermal treatment of semiconductor wafers in a gas environment, and increasing the productivity of the installation by simplifying the annealing process.

The problem is solved by a device for rapid thermal processing of semiconductor wafers. It comprises a thin rectangular quartz reaction chamber with an open end mated with a stainless steel flange with a loading port for loading wafers, a heater, and a wafer holder. A novel feature of the device is the inclusion of two rods attached to the loading port, which support the wafer holder. A movable reaction chamber holder, which can be moved from the heating zone to the cooling zone, a thermocouple for measuring temperature and controlling the annealing process, a gas inlet, an electronic temperature controller, and air cooling fans. The other end of the reaction chamber has a gas outlet.

The plate holder can be made of graphite.

Along the perimeter of the plate holder there may be a limiting flange with a cross-section of 1×1 ^mm2 .

The heater can be designed as a bank of halogen lamps positioned at the top and bottom of the reaction chamber, offset from each other. The lower lamps are positioned between the upper ones to improve heating uniformity across the holder area.

The rods can be made of molybdenum.

The two rods introduced into the device and fixed to the loading window flange, on which the plate holder is attached, have a simple design and ensure quick loading and unloading of plates from the chamber.

A movable reaction chamber holder, which can move from the heating zone to the cooling zone, simplifies the design during its manufacture while maintaining the functional characteristics that ensure high cooling rates.

A thermocouple for measuring temperature and controlling the annealing process simplifies the design by eliminating complex processing elements, such as those required when using pyrometers, and also improves accuracy due to the fixed location.

The gas inlet pipe located in the loading window of the flange simplifies the design when solving the problem of providing an inert atmosphere, and also simplifies the design when solving the problem of increasing the cooling rate.

Electronic temperature controller provides control over temperature changes.

Air cooling fans provide high cooling rates, which is simpler and more technologically advanced than using water systems.

The halogen lamp heaters are positioned at the top and bottom of a thin quartz chamber, offset from each other, which simplifies the design while ensuring uniform temperature distribution and increased heating speed.

From above, the annealed plates are covered with a graphite plate of the same thickness as the thickness of the holder, which simplifies the design for equalizing the temperature field.

The essence of the invention is explained by a drawing showing a longitudinal section of the device.

The rapid thermal annealing device includes a reaction chamber 1, a loading flange window 2, a graphite holder 3, molybdenum rods 4 for fastening the graphite holder, a thermocouple 5, a block 6 of halogen incandescent lamps, polished reflectors 7 made of stainless steel, a movable holder 8 of the reaction chamber moving along guides 9, an electronic temperature controller 10, a block 11 of cooling fans, a gas inlet pipe 12 for introducing an inert gas into the reaction chamber, which is located in the loading flange window, a gas outlet pipe 13 for removing an inert gas from the reaction chamber, which is located on the side of the blind end of the reaction chamber, a stainless steel flange 14 for connecting the loading flange window and the reaction chamber.

The device works as follows.

The semiconductor wafers are loaded onto graphite holder 3 and covered with a graphite plate of identical size to the holder. The structure of graphite holder 3, secured to molybdenum rods 4, is then pushed into reaction chamber 1 and sealed by the loading window of flange 2. Reaction chamber 1, secured to movable holder 8, is pushed into the heating zone along guides 9, and the reactor is purged with nitrogen, supplied through gas inlet pipe 12 and removed from the reactor chamber through gas outlet pipe 13. Electronic temperature controller 10, using a signal from thermocouple 5, then controls the annealing process in accordance with the set program by supplying electrical power to halogen lamps. Upon completion of the annealing, block 6 of halogen incandescent lamps is switched off, and reaction chamber 1 is moved to the cooling zone, where it is cooled by fans 11.

Example

A device for rapid thermal processing of semiconductor wafers has been manufactured. The device includes a thin rectangular quartz reaction chamber with a first open end. The thin rectangular quartz reaction chamber transitions into a round one with an open end mated with a stainless steel flange. The flange is equipped with a flange loading window for sealing the reaction chamber and isolating it from the external atmosphere. A movable holder is attached to the flange, which can move the chamber from the heating zone to the cooling zone. Two molybdenum rods are attached to the flange loading window, on which a graphite wafer holder is fixed. A thermocouple for measuring the temperature and controlling the annealing process, as well as a gas supply pipe, are also brought out through it. The rods are made of molybdenum with a diameter of 4 mm. The wafer holder is made of graphite with an area of 80x80 ^{mm2 and} a thickness of 2 mm; along the perimeter of the holder there is a rim with a cross-section of 1x1 ^mm2 ; The samples are covered from above with a ² mm thick, 80 x 80 mm graphite plate to prevent reflection from the metallized surface of the samples and to achieve more uniform heating. The other end of the reaction chamber has a gas outlet. Cylindrical halogen lamps (5 at the top and 6 at the bottom, offset from the top) are located in the heating zone. Each lamp has a power of 500 W. The annealing process is controlled by an electronic temperature controller. After heating, the movable holder of the reaction chamber moves to the cooling zone, where four fans cool the reaction chamber.

The use of eleven high-power halogen lamps allows for an increase in the heating rate of the annealed wafers to 500°C/min and for annealing to temperatures up to 1000°C. The design of the graphite sample holder allows for the placement of several annealed wafers with a total area of up to 20 ^cm2 ; a rim along the perimeter of the holder prevents the samples from shifting and serves as a support for the upper cover of the graphite sample holder; the geometry of the placement of the heating halogen lamps, the design of the sample holder, and the design of the reaction chamber made of flat optical quartz allow for achieving a uniform heating of the samples over the holder area of 2-3°C. An electronic controller managing the annealing process maintains the set annealing temperature with an accuracy of 2-3°C. The design of the stainless steel flange and the loading window of the stainless steel flange with the sample holder fixed to it allows for loading and unloading of samples within a few minutes, which significantly reduces the time costs during operation of the facility. The ability to quickly move the reaction chamber from the heating zone to the cooling zone, and, if necessary, to use process gas cooled with liquid nitrogen, allows for an increase in the cooling rate to 200°C/min.

The simplicity of the design ensures technological feasibility, ease of manufacture, and ease of operation. Furthermore, the proposed design significantly reduces operating time by removing the reaction chamber from the heating zone and enables rapid thermal annealing and cooling technologies.

Claims (5)

1. A device for rapid thermal processing of semiconductor wafers, comprising a thin rectangular quartz reaction chamber with a first open window, a stainless steel flange, a loading window of the flange, a heater and a wafer holder, characterized in that two rods are introduced into it, secured to the loading window of the flange, on which the wafer holder is secured, a movable holder of the reaction chamber, which can move from the heating zone to the cooling zone, a thermocouple for measuring the temperature and controlling the annealing process, a branch pipe for inlet of gas, an electronic temperature controller and air cooling fans, wherein the second end of the reaction chamber has a branch pipe for outlet of gas. 2. The device according to paragraph 1, characterized in that the plate holder is made of graphite. 3. The device according to item 2, characterized in that along the perimeter of the plate holder there is a limiting flange with a cross-section of 1×1 ^mm2 . 4. The device according to paragraph 1, characterized in that the heater is made in the form of a block of halogen lamps located at the top and bottom of the reaction chamber with an offset relative to each other. 5. The device according to paragraph 1, characterized in that the rods are made of molybdenum.