Patent Application
20220178024
The present invention relates generally to a system and method for processing semiconductor substrates, and, in particular embodiments, to a system and method for processing a batch of semiconductor substrates in a furnace tube.
Semiconductor substrates such as semiconductor wafers can be processed individually in single wafer processing tools or can be processed many-at-a-time in batch wafer processing tools. Processes can include thin film depositions such as chemical vapor depositions (CVD), epitaxial growth of single crystal semiconductor layers, dielectric growth such as the oxidation of silicon to form silicon dioxide, and thermal anneals during the formation of buried diffusions and during hydrogen and forming gas sinters. Semiconductor furnace can be cold wall or hot wall furnaces. In cold wall furnaces, the temperature of the semiconductor substrates is different than the temperature of the inside wall of the furnace tube. In hot wall furnaces, the temperature of the semiconductor substrates is generally equal to the temperature of the inside wall of the furnace tube. Most single wafer furnaces are cold wall and most batch furnaces are hot wall.
In batch semiconductor wafer processing tools, multiple wafers are lined up in slots in a wafer boat and loaded into the furnace tube in a furnace cabinet. The furnace tube can be a horizontal furnace tube in a horizontal furnace cabinet or can be a vertical furnace tube in a vertical furnace cabinet. In horizontal furnace tubes, multiple wafers are lined up next to each other separated by gaps and are processed in a vertical orientation. Slight temperature variation from bottom to top across especially large diameter wafers in horizontal furnace tubes can result in slight across wafer non uniformity. In vertical furnace tubes, multiple wafers are stacked vertically one above the other separated by gaps and processed in a horizontal orientation.
In an embodiment, an apparatus comprises a metal furnace tube having an open first end and an opposite second end. The metal furnace tube comprises an inner chamber, a fluid inlet configured to intake a fluid into the inner chamber, and a fluid outlet configured to exhaust the fluid from the inner chamber, the inner chamber configured to support a plurality of substrates within the metal furnace tube. The apparatus comprises a first base plate or flange back plate coupling the fluid inlet to the inner chamber; a second base plate or flange back plate coupling the fluid outlet to the inner chamber; and a furnace comprising a heater configured to heat the metal furnace tube, the metal furnace tube being mounted within the furnace and the heater being disposed outside the metal furnace tube.
In an embodiment, a method comprises having a metal furnace tube, the metal furnace tube comprising an inner chamber to house a plurality of substrates, a fluid inlet configured to intake a fluid into the inner chamber, and a fluid outlet configured to exhaust the fluid from the inner chamber. The method includes having a tube flange at a first end of the metal furnace tube, mounting the metal furnace tube in a furnace configured to heat the metal furnace tube, having a base plate or a flange back plate in the furnace, and mating the tube flange with the base plate or the flange back plate.
In an embodiment, a method includes removing a glass or quartz furnace tube from a furnace from a tube mounting location of the furnace; mounting a metal furnace tube in the furnace at the tube mounting location, the metal furnace tube comprising an inner chamber to house a plurality of substrates, a fluid inlet configured to intake a fluid into the inner chamber, and a fluid outlet configured to exhaust the fluid from the inner chamber; and attaching a tube flange at a first end of the metal furnace tube to a base plate or to a flange back plate in the furnace.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Systems and methods are provided herein for the batch processing of semiconductor substrates in metal furnace tubes.
As will be evident from the detailed discussion of various embodiments below, metal furnace tubes offer a number of advantages over glass furnace tubes such as fused quartz and Pyrex. Metal furnace tube material is less expensive and metal furnace tubes are less expensive to fabricate. Metal furnace tubes are much less fragile. Metal furnace tubes can be fabricated with more complex shapes. Metal furnace tubes can be fabricated with flanges eliminating the more expensive clamping systems used to transition from glass furnace tubes to the metal fluid inlet manifold and to the metal fluid exhaust manifold. The inside surface of metal tubes can be easily roughened to increase surface area for improved adhesion of layers being deposited. This enables more layers to be deposited between periodic cleaning of the furnace tube, thereby reducing manufacturing cost. The coefficient of thermal expansion (CTE) between a metal furnace tube and the thin film being deposited is more closely matched than the CTE between a quartz or Pyrex furnace tube and the deposited thin film layers. With better matched CTE's, stress between the deposited thin film layers and the metal furnace tube is reduced, especially during the temperature changes when loading and unloading wafers. Reduced stress translates into reduced delamination and flaking of the deposited thin film. Reduced flaking translates into reduced particles, reduced defects, and higher yield. The improved CTE matching between the thin film being deposited and the metal furnace tube enables thicker layers of thin film to be deposited before the furnace tube is pulled to remove film buildup. For example, the CTE of aluminum oxide is better matched to an aluminum furnace tube than to a quartz tube. Likewise, the CTE of titanium nitride is better matched to a titanium furnace tube than to a quartz tube.
As discussed in various embodiments, metal furnace tubes can be fabricated to replace quartz tubes without changes to the furnace cabinet. The furnace system cost can be additionally reduced by welding tube flanges to the ends of the metal furnace tube and modifying the furnace cabinet to accept the metal furnace tubes with flanges.
The embodiment furnace systems significantly reduce cost of ownership (CoO) by reducing the initial cost of the furnace system, reducing tube breakage, reducing the cost of tube replacement, reducing maintenance costs, and extending the time between tube pulls and tube cleaning.
In the horizontal furnace 100 shown in
Furnace tubes 102 constructed of metal conduct heat better than quartz or Pyrex furnace tubes. This can increase the temperature of the clamping systems on the ends of the furnace tube 102. The temperature at the clamping systems can be reduced by providing an optional cooling section 136 between the flange clamp 114 and the inner chamber 126. Cooling fluid can be circulated through the cooling section 136.
The horizontal furnace 100 may be an annealing furnace in one or more embodiments. To process semiconductor substrates in this horizontal furnace 100, the backing plate 116 can be removed from the fluid inlet 104 end of the furnace tube 102 and a substrate boat containing multiple semiconductor substrates can be inserted into the inner chamber 126 where it can rest on the bottom inside wall of the furnace tube 102 during processing. The backing plate 116 is then reassembled to seal the fluid inlet 104 end before the furnace temperature is ramped to processing temperature and process fluids are introduced into the inner chamber 126 through the fluid inlet 104.
Manufacturing cost of a metal furnace tube 128 for the horizontal furnace 130 in
Metal furnace tubes 128 conduct heat better than quartz or Pyrex furnace tubes. This can increase the temperature of the clamping systems on the ends of the metal furnace tube 128. The temperature of the clamping systems can be reduced by providing an optional cooling section 136 between the metal tube flange 132 and the inner chamber 126. Cooling fluid can be circulated through the cooling section 136.
The vertical furnace 140 in
In the vertical furnace 140 shown in
Manufacturing cost of a vertical metal furnace tube 162 for the vertical furnace 160 in
In the vertical furnace 170 shown in
Manufacturing cost of a vertical metal furnace tube 192 for the vertical furnace 190 in
Processing costs can be significantly reduced when metal furnace tubes are used instead of quartz or Pyrex furnace tubes. In addition to eliminating tube breakage, and in addition to the reduced time for tubes to be exchanged during maintenance, the time between tube cleanings can be significantly extended. Differences in the coefficient of thermal expansion (CTE) of the thin film being deposited with the CTE of the furnace tube limits the number of depositions. Stress buildup due to CTE mismatch can cause delamination, which can cause particle contamination.
CTE's for various materials are given in Table 1. The CTE mismatch between deposited thin films (the film being coated on the semiconductor wafers) such as alumina and titanium nitride and a quartz tube is significantly larger than the mismatch created when the furnace tubes are made of aluminum, titanium, nickel, and stainless steel 310. The lower CTE mismatch enables more layers of thin films such as alumina or titanium nitride to be deposited before the onset of delamination. This improves furnace uptime by enabling more lots to be processed between tube cleanings. In an example arrangement, more than double the thickness of aluminum oxide can be deposited in an aluminum furnace tube with no delamination than can be deposited in a quartz furnace tube. This means that more than twice the number of semiconductor substrates can be processed before a furnace tube change and cleaning is required.
In one embodiment furnace system and method, aluminum oxide is deposited using a chemical vapor deposition (CVD) process in a furnace tube made of aluminum or an aluminum alloy.
In another embodiment furnace system and method, titanium nitride is deposited using CVD process in a furnace tube being made of titanium or a titanium alloy.
Unlike brittle quartz tubes, the inner surface of metal furnace tubes can be roughened by bead blasting to enhance adhesion of the thin film to the inner surface. Roughening the inner surface increases surface area. This improves adhesion between the deposited thin film and the furnace tube. Roughening the inner surface enables more layers of thin film to be deposited before the onset of delamination. Manufacturing cost is reduced because more lots can be processed before a tube change is required. With bead blasting the inside surface of metal furnace tubes can be roughened to a roughness Ra of greater than about 0.1.
The furnace heating coils no can emit mobile ions such as sodium, potassium, iron, and calcium. These ions can contaminate and degrade integrated circuits. In various embodiments, a barrier layer of thin film is deposited to coat the inside wall of the metal furnace tubes discussed in various embodiments and prevent these mobile ions from reaching the semiconductor substrates. Barrier materials can include silicon nitride, titanium nitride, tantalum nitride, and aluminum oxide.
Unlike, quartz tubes that are insulating, in various embodiments, metal furnace tubes can be configured to actively remove ion contamination. Mobile ions that are harmful to integrated circuits tend to be positively charged. To reduce positive ion contamination, the metal furnace tube can be electrically isolated from the furnace cabinet and can be biased to a fixed potential relative to the furnace cabinet. The fixed potential can attract ion contaminants to the inner walls of the metal furnace tube and away from the semiconductor substrates.
In various embodiments, furnaces described in various embodiment of
The cost savings when an embodiment metal furnace tube is used to replace a quartz tube in a high pressure, hot wall, batch furnace can be significant. High pressure processes can range from a few atmospheres to a dozen atmospheres or more. The final processing step in most semiconductor manufacturing flows is to anneal the substrates in hydrogen or forming gas (nitrogen plus hydrogen). This stabilizes the turn on voltage of transistors and narrows the turn on voltage distribution. To reduce processing time this anneal (often referred to as sintering) can be performed at elevated pressures. Since quartz cannot withstand large pressure differentials, the pressure of the ambient fluid surrounding the high pressure quartz furnace tube must be equal to the pressure of the process fluids inside the quartz furnace tube. This requires a special fluid pressure equalization system in the high pressure furnace. In high pressure quartz tube furnaces, the entire quartz furnace tube plus the tube support and the heating element are housed in a separate metal chamber capable of withstanding multiple atmospheres of pressure. An embodiment high pressure metal furnace tube can withstand the large pressure differentials required by high pressure processes.
Advantageously, in or more embodiments, the metal furnace tube has a thick metal wall that is able to withstand a pressure differential between the outside and the inside of the metal furnace tube of up to 20 atmospheres. Accordingly, in one embodiment, the plurality of substrates are loaded into an inner chamber of the metal furnace tube that is made of stainless steel, nickel, or a nickel alloy and an annealing process may be performed on the plurality of substrates while pressurizing the inner chamber of the metal furnace tube to a first pressure and the furnace outside of the metal furnace tube to a second pressure different from the first pressure, where a difference between the first pressure and the second pressure is in the range of 1 atm to about 10 atm. In another embodiment, the difference between the first pressure and the second pressure is in the range of 1 atm to about 20 atm. This eliminates the need for the separate metal high pressure chamber and also eliminates need for the special fluid pressure equalization system. Eliminating the separate high pressure chamber and fluid pressure equalization system with an embodiment high pressure, hot wall, metal furnace tube significantly reduces cost of the high pressure furnace.
As illustrated in the first method block moo, a metal furnace tube configured with an inner chamber is fabricated with the same dimensions as a quartz furnace tube.
As next illustrated in the second 1002 and third 1004 method blocks, a quartz furnace tube is removed from the furnace cabinet and the metal furnace tube is installed. In this arrangement, as described in
As next illustrated in the fourth method block 1006, a boat containing semiconductor substrates such as semiconductor wafers is loaded into the inner chamber of the metal furnace tube.
Referring to the fifth method block 1008, the furnace tube and the semiconductor substrates are heated to processing temperature.
As illustrated in the sixth method block 1010, the flow of the process fluids is initiated to process the semiconductor substrates until the endpoint is reached.
Referring to the seventh method block 1012, the flow of the process fluids is stopped and the temperature is ramped down to load/unload temperature.
Referring to the eighth method block 1014, the semiconductor substrates are unloaded from the metal furnace tube.
As illustrated in the first method block 1020, a metal furnace tube is fabricated and configured with an inner chamber and configured with a tube flange welded to the end of the metal furnace tube. The tube flange is configured to mate with a base plate or a flange back plate in the furnace cabinet as discussed in
As illustrated in the second method block 1022, a furnace cabinet is fabricated that is compatible with a metal furnace tube with a tube flange. The furnace cabinet is configured with a heating element that surrounds the inner chamber.
As illustrated in the third method block 1024, the metal furnace tube with tube flanges is installed into the furnace cabinet that is modified to be compatible with the metal furnace tube with tube flanges.
As illustrated in the fourth method block 1026, a boat containing semiconductor substrates such as semiconductor wafers is loaded into the inner chamber of the metal furnace tube.
As illustrated in the fifth method block 1028, the furnace tube and the semiconductor substrates are heated to processing temperature.
As illustrated in the sixth method block 1030, the flow of the process fluids is initiated to process the semiconductor substrates until the endpoint is reached.
As illustrated in the seventh method block 1032, the flow of the process fluids is stopped and the temperature is ramped down to load/unload temperature.
As illustrated in the eighth method block 1034, the semiconductor substrates are unloaded from the metal furnace tube.
Metal furnace tubes offer many advantages in terms of initial furnace system cost, furnace tube replacement cost, ease of handling, reduced maintenance cost, reduced breakage, and reduced manufacturing costs. Metal furnace tubes can be designed to replace existing quartz furnace tubes or can be designed with flanges to additionally reduce the initial cost of the furnace system and to reduce the cost of maintenance.
While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.
