Programmable die identification circuits

Abstract: An identification section fabricated onto a semiconductor chip includes memory for use in preserving die-specific information that characterizes that particular semiconductor chip. The chip may also include programmable circuitry for use in programming the die-specific information into the memory.

Description: The present invention generally relates to systems for preserving information relating to semiconductor chips and, more particularly, systems for preserving information regarding the manufacturing history of semiconductor chips. Semiconductor chips, hereinafter referred to as die, are batch fabricated on wafers of semiconductor material generally five or six inches in diameter, each wafer containing a two-dimensional array of die. These wafers are processed in groups which are referred to as fabrication lots. The wafers in a given lot are numbered sequentially, and this wafer number, along with a unique fabrication lot number, are inscribed on the wafer in an area outside the array of die. Thus, during the initial fabrication process, each die may be uniquely identified by certain die-specific information such as its fabrication lot number, its wafer number, and its location within the array of die hereinafter referred to as its die position number. The unique identification of the die serves important functions in the analysis of regular production die (e.g., the analysis of die returned by customers) and of non-production or developmental die (e.g., die characterization, reliability testing). Engineers frequently need to characterize the die by analyzing the effect of a processing variable on the electrical properties of the die. To do this, the engineer will typically split a lot into groups of wafers during fabrication, each group to be processed with the particular processing variable set to a different value. After the die are processed and individually packaged, electrical parameters of each die are tested, and the test results are saved along with its wafer number and die position number. With this data an engineer is able to compare the performance of the groups of wafers with one another, and thus determine the effect of the processing variable on die performance. This information also enables an engineer to analyze the electrical performance of the die as a function of its position on the wafer during fabrication. The unique identification of a die serves a similar purpose in the reliability testing of the die. To test its reliability, the die may be subjected to conditions such as extreme temperatures or humidity for extended periods and then electrically tested. The unique identification of each die enables an engineer to analyze the test results and determine the reliability of the die as a function of processing parameters, and also as a function of its position on the wafer during fabrication. The fabrication lot number also serves an important function in the analysis of defective die returned by customers. The die from a particular lot may be sold to many different customers over a long period of time. When defective die from a particular fabrication lot are returned by a customer, an engineer will typically analyze the returned die to determine the cause of the malfunction. If the engineer knows which fabrication lot the die came from, he may be able to avoid repetitive analysis on future customer returns from that same lot. Currently, those skilled in the art view the retention of the unique identification of a die throughout the life of the die as a time-consuming, expensive, and error-prone process. In the course of normal production, the wafer number and die position number are lost after the wafer is sawed into individual die. A new assembly lot number is assigned to the lot and encoded onto each package into which the die was assembled. The fabrication lot number is retained only in the paper records for that assembly lot. Thus, an engineer faced with a die returned from a customer must search the assembly lot records for the fabrication lot number. These records are often misplaced or incomplete and are disposed of after a certain period of time. Without the information from these records, an engineer will not be able to determine which fabrication lot the die came from. In order to retain the unique identification of each die for purposes such as die characterization or reliability testing, the wafers are sent to a non-production assembly area with special instructions to preserve the identification of each die, typically by handwriting the information on each individual package into which the die are assembled. This process is not automated, and it is very likely that the die will be mixed up and identified incorrectly. Because there is no way to ensure that the die are identified correctly, confidence in the die characterization or reliability testing is diminished greatly. From PATENT ABSTRACTS OF JAPAN, vol.8, no.285. (E-287)(1722) 26 December 1984 & JP-A-59 150 464, it is known to provide an integrated circuit with a non-volatile memory for storing die-specific information. From the foregoing it can be seen that it would be quite desirable to ensure that the unique identification of each die is recorded correctly and retained throughout the life of the die. It may also be seen that it is a shortcoming and deficiency of the prior art that heretofore no system or method for accomplishing this has been developed. The invention overcomes the shortcomings and deficiencies of the prior art with the device set forth in the appended claims. It is disclosed a die characterized by die-specific information, where the die includes an integrated circuit and an identification section. The identification section includes a memory section for storing information and a means for programming the die-specific information into the memory section. In one aspect of the present invention, the memory section may comprise a non-volatile memory. Additionally, the non-volatile memory may be fuse-programmable. In certain embodiments, the programming is enabled by forcing the integrated circuit into a test mode. In addition, the means for programming may further include device pins which serve other functions when the integrated circuit is not in a test mode. The identification section of the die may further include means for reading the die-specific information from the storage means, where the reading means may be electrically connected to the storage means. In embodiments, the reading may be enabled by forcing the integrated circuit into a test mode. In addition, the means for reading may further include device pins which serve other functions when the integrated circuit is not in a test mode. In certain embodiments, the die-specific information may include the fabrication lot number, the wafer number, and the die position number associated with the particular die. We also provide a method of preserving die-specific information by providing the die with a means for storing information and then programming the manufacturing information into the storage means. In certain embodiments of the-method, the storage means may comprise a non-volatile memory which in some embodiments may be fuse-programmable. The manufacturing information may be programmed into the storage means by forcing the integrated circuit into a test mode. In addition, the die-specific information may be programmed via device pins which perform other functions when the integrated circuit is not in a test mode. In certain embodiments, the method for preserving die-specific information may further comprise the step of electronically reading the die-specific information from the means of storing information. Further, the die-specific information may be electronically read by forcing the integrated circuit into a test mode. Still further, the die-specific information may be read via device pins which may perform other functions when the integrated circuit is not in a test mode. In certain embodiments, the step of programming said die-specific information is accomplished during wafer sort testing, and may be performed by an automated test program. We also provide a method for conducting engineering analysis of an integrated circuit on a die characterized by die-specific information. This method includes the steps of storing the die-specific information on the die, reading the die-specific information from the die, tying the die-specific information to data relating to the integrated circuit, and sorting that data according to the die-specific information. Furthermore, we also provide a method of tracing manufacturing history of an integrated circuit on a die. This method includes the steps of fabricating a memory onto the die, storing information relating to the manufacturing history into the memory section, and retrieving that information from the memory section. Accordingly, we provide a storage means on a die that may be used to trace the manufacturing history of the die easily and with accuracy. We also provide a storage means on a die which affords an inexpensive and dependable means of identification. In the accompanying drawings, by way of example only: FIG. 1a is a top plan of a single wafer containing an array of die; FIG. 1b is an enlarged view of one of the die shown in FIG. 1a , this FIG. 1b showing that the die contains an identification portion according to the teachings of the present invention; FIG. 2 is a flowchart which illustrates the steps taken in a prior art method of handling die which method includes provisions for preserving die-specific information; FIG. 3 is a flowchart which illustrates the steps that may be taken in a die handling method that incorporates the teachings of the present invention; and FIG. 4 is a flowchart which illustrates a method of analyzing data relating to the electrical performance of a semiconductor device according to the present invention. Referring now to the drawings wherein depicted elements are not necessarily shown to scale, there is shown in FIG. 1a a single wafer generally designated by reference numeral 10 , having an array of die, this array is generally designated by reference numeral 12 . The array 12 is made up of a plurality of die 14 . As may be seen in FIG. 1b , each individual die 14 has an identification section 16 according to the teachings of the present invention as well as an integrated circuit 18 . The identification circuit 16 is designed to occupy an area on the die 14 small enough to allow for easy insertion into existing layouts but not so small as to push design rules to the point that overall device yield will be adversely affected. In the embodiment of the present invention shown in FIG. 1b , identification section 16 comprises three sections: a memory section 20 , programming circuitry 22 , and output circuitry 24 . The memory section 20 is used to store die-specific information which characterizes the die 14 . The memory section 20 may be, particularly in a preferred embodiment, of a non-volatile nature in order to preserve the die-specific information for the life of the die. In a preferred embodiment, the non-volatile memory section 20 may be fuse-programmable to allow retrieval of the die-specific information, even if the die 14 becomes non-functional, by visually decoding the fuses. The programming circuitry 22 is fabricated on the die 14 and is electrically connected by conventional means to the memory section 20 . In the embodiment shown in FIG. 1b , the programming circuitry 22 is also electrically connected to the die pads 23 which allow electrical connection to external electrical signals. The die pads 23 allow a user to instruct the programming circuitry 22 to program the die-specific information into the memory section 20 . The die pads 23 may serve other functions in the normal operation of the integrated circuit 18 , and may be converted for use in programming the memory section 20 by forcing the integrated circuit 18 into a test mode. Such dual operation of the die pads 23 can prove valuable to those skilled in the art because it may be employed to reduce device pin count in certain applications. The output circuitry 24 is fabricated on the die 14 and is electrically connected to the memory section 20 . The output circuitry 24 is also electrically connected to die pads 25 which allow external access via the output circuitry 24 to the information stored in the memory section 20 . The device pads 25 may serve other functions in the normal operation of the integrated circuit 18 , and may be converted for use in reading information out of the memory section 20 by forcing the integrated circuit 18 into a test mode. As with die pads 23 , the dual operation of the die pads 25 may prove valuable to those skilled in the art because it may be employed to reduce device pin count. Based upon the foregoing, those skilled in the art should now appreciate that, in essence, the present invention comprises a memory section on a die in which die-specific information may be stored. Associated with that memory section in embodiments of the present invention may be means for moving information into the memory and means for extracting that information. These latter two means may be the above mentioned programming circuitry 22 and output circuitry 24 . The importance of preserving die-specific information in an identification section 16 located on a die 14 can be seen by comparing the use of a prior art method of preserving the die-specific information, shown in FIG. 2 , with the use of the method taught by the present invention of preserving the die-specific information, shown in FIG. 3 . The flowchart in FIG. 2 shows steps typical of both the standard production and non-production flow of a die 14 . The die are batch-fabricated on a single wafer 10 , each wafer 10 having a two-dimensional array of die 12 (step 30) . As discussed previously in the background of the invention section, each die 14 may be uniquely identified by its fabrication lot number, its wafer number, and its die position number. Once fabrication is completed, each die 14 is electrically tested at the wafer sort step 32 while still in wafer format. After the wafer sort step 32 , the die 14 will enter either the standard production flow (designated by arrow 34 ) and ultimately be distributed to a customer, or a non-production flow (designated by arrow 36 ) usually for the purpose of engineering analysis. In the standard production flow 34 , the wafers 10 are sent to production assembly (step 38 ) where the wafers 10 are scribed and the die 14 separated from each other. At this point in a standard production process, the wafer number and die position number are irretrievably lost. The die 14 are assigned a unique assembly lot number and the fabrication lot number is preserved in manufacturing records for that assembly lot. The assembly lot number is encoded into a date code which is marked onto the package into which the die 14 was assembled. At the test step 40 following the production assembly step 38 , each packaged die 14 is electrically tested and units which pass the test are forwarded to a distributor (step 42 ) for shipment to a customer (step 44 ). If the customer determines that the packaged die is defective, it is customary for the customer to return the die to its manufacturer (shown as step 46 ) for failure analysis (shown as step 48 ). Failure analysis may often involve determining whether a die was misprocessed. In order to determine whether a die was misprocessed, those skilled in the art find it advantageous to know the fabrication lot from which the die 14 originated. The fabrication lot number can typically be found only in the manufacturing records for the assembly lot indicated on the device package. Because the packaged die may have remained at a distributor site for an extended period of time before shipment to the customer, by the time the die 14 is returned as defective, the manufacturing records are often lost or purged. Consequently, the manufacturer is unable to trace the die 14 back to a fabrication lot in order to determined whether the die 14 was misprocessed or not. In a non-production flow route 36 , the die 14 are typically used by engineers for engineering analysis such as device characterization or reliability testing. As discussed previously in the background of the invention section, this engineering analysis often involves splitting a fabrication lot into groups, each group being fabricated according to different settings of processing variables. In this context, the identification of each die 14 serves an essential function of correlating a particular die 14 to a particular setting of a processing variable. Referring back again to FIG. 2 and the non-production flow route 36 , after the wafer sort step 32 , the wafers 10 are sent to local assembly (step 50 ) where the workers are often instructed to preserve die-specific information such as the fabrication lot number, wafer number and die position number by handwriting the information on each package into which the die 14 is assembled. Those skilled in the art, (that is, the engineers that want to use the die for engineering analysis) view this step as expensive and exceedingly error-prone. Also, after the local assembly step 50 no means are available by which to verify the die-specific information marked on any particular package. When the packaged die are then returned to the engineers for testing (step 52 ), the die-specific information for each die is manually read off the package and recorded with the test results for that die. The test data is then sorted according to the fabrication lot number, wafer number or die position number to analyze lot to lot, wafer to wafer, or position to position variation in die electrical performance, respectively. This analysis takes place at step 54 shown in FIG. 2 . If the test results deviate from what was expected, those skilled in the art will typically suspect an error in die identification and will repeat the experiment with a new fabrication lot (step 56 ). The use of the identification section 16 according to the teachings of the present invention in a production and non-production flow of an integrated circuit is shown in the flowchart of FIG. 3 . Each die 14 is fabricated to include a programmable identification circuit (e.g. the circuit 16 as shown in FIG. 1b ). This fabrication step is shown as step 60 in FIG. 3. At the wafer sort step 62 , each die 14 on the wafer 10 may be electrically connected to an automated test machine which executes a series of routines testing the electrical properties of the die 14 . The test machine may also program the fabrication lot number, wafer number and die position number specific to a particular die into the identification section 16 of that die 14 . To do so, the test machine may force the die 14 into a test mode and apply electrical signals to the die pads 23 connected to the programming circuit 22 such that the information is stored in the memory section 20 . To eliminate the need for excess pads on the die 14 , existing pads that serve other functions during normal operation of the die may be converted for use in accessing the identification section 16 when the die is in a test mode. At any time following the programming of the die-specific information, this information can be retrieved from the die 14 either electronically, by forcing the die 14 into a test mode and reading the information stored in the identification section 16 , or by decapping the packaged die and visually examining the fuses in the identification section 16 . Other retrieval means may also be employed. In the standard production flow (designated by arrow 64 in FIG. 3 ), the die next enter the production assembly step 68 . Because the die-specific information is programmed into the identification section 16 of each die 14 , this information is not lost at the production assembly step 68 when the wafers 10 are scribed and the die 14 separated from each other. Following the production assembly step 68 , the packaged die are electronically tested (step 70 ) and the die which pass the test are advanced to the distribution step (shown as step 72 ) for eventual shipment to a customer (step 74 ). If the customer returns the packaged die to the manufacturer (step 76 ) for failure analysis (step 78 ), the manufacturer will be able to trace the die back to a fabrication lot by reading the die-specific information preserved in the identification section 16 of that die 14 , whether the die is functional or not. In a non-production flow (designated by arrow 66 in FIG. 3 ), the die 14 are sent to local assembly (step 80 ) following wafer sort test (step 62 ). Because the die-specific information is preserved in an identification section 16 on each die 14 , it is not necessary at this step 80 to manually track the die-specific information nor to handwrite the information on each package into which a die is assembled. At the following test step 82 , the die-specific information may be electronically read from the die 14 and this information is stored with the test data corresponding to that die (step 84 ). The data may then be analyzed to determine lot to lot, wafer to wafer, or position to position variations in electrical performance of the die. The use of the identification section 16 to preserve the die-specific information allows the engineer to be confident that the die are correctly identified. If the results are not as expected, the engineer may verify the die-specific information by electronically reading the information from the packated die (step 86 ). Thus, the use of a programmble identification circuit according to the teachings of the present invention may allow an engineer to at least eliminate the possibility of error at the local assembly step 80 in maintaining the correct die identification. Based on the foregoing, it should now be clear that the present invention provides an identification section on a die characterized by die-specific information that can be used to preserve the die-specific information. The identification section includes a memory section and in certain embodiments may include a means for putting information into the memory section and may also include a means for reading the information out of the memory section. The means for putting information into the memory section may be the programming circuitry 22 shown in FIG. 1b . The means for reading information out of the memory section may be the output circuitry 24 also shown in FIG. 1b . Referring now to FIG. 4 , it may be seen that the use of the identification section 16 for preserving die-specific information offers an advantageous method of analyzing data relating to the electrical performance of a die. During fabrication (shown as step 90 in FIG. 4 ), each die 14 is provided with a programmable identification section 16 . The die-specific information (which may include the fabrication lot number, wafer number, and die position number) is programmed into each die while still in wafer format at the wafer sort test step 92 . At the device test step 94 , an automated test machine performs a series of electrical tests on the device. The results of these tests are then stored in a file on disk, tape or other storage means (step 96 ). Also at the test step 94 , the automated tester may also force the die into a test mode and thereby access the die-specific information from the memory section 20 . This die-specific information is then stored on disk, tape, or other storage means and is tied to the test results for that particular die (step 96 ). By tying it is meant that any useful association is made with the data. At step 98 , both the stored test data and the stored die-specific data are read into a post-processor for data manipulation. The test data may be sorted according to fabrication lot number, wafer number, or die position number, or any combination thereof. The sorted test data may then be analyzed to detect lot to lot, wafer to wafer, or die position to die position variations in the electrical performance of the die. The foregoing description shows only certain particular embodiments of the present invention. For example, the die-specific information may also include other information such as but not limited to mask revisions, test program revisions, and results of certain tests. Accordingly, within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described hereinabove.

Claims: A die (14) comprising: a first integrated circuit portion (18); a second integrated circuit portion (16) adjacent the first portion, the second portion (16) comprising: a memory section (20) for storing die-specific information characterising the die; and a programming circuit (22); characterised in that the second integrated circuit portion (16) further comprises: at least one input die pad (23) connected to said programming circuit (22); the programming circuit (22) being connected to the memory section (20); the memory section (20) being connected to an output circuit (24); and the output circuit (24) being connected to at least one output die pad (25); wherein the input die pad(s) and the output die pad(s) are additionally connected to the first integrated circuit portion (18) and perform functions related to the operation of the first integrated circuit portion (18) and the said input die pads (23) and the said output die pads (25) are converted for use in programming and reading, respectively, the memory section (20) by operating the first integrated circuit portion (18) in a test mode. A die according to claim 1, wherein the memory section (20) comprises a plurality of non-volatile memory cells. A die according to claim 1, wherein the memory section (20) comprises a plurality of fusible links. A die according to claim 1, wherein the memory section (20) comprises a plurality of laser-blown fuses. A die according to any one of the preceding claims, wherein the die-specific information includes a fabrication lot number, the fabrication lot number identifying a fabrication lot from which the die originated. A die according to any one of the preceding claims, wherein the die-specific information includes a wafer number, the wafer number identifying a wafer from which the die originated. A die according to any one of the preceding claims, wherein the die-specific information includes die position information, the die position information relating to the position of the die on a wafer from which the die originated. A die according to any one of the preceding claims, wherein the die-specific information includes design rule information and/or process history information.

Inventors: JERNIGAN CLARK W, JERNIGAN, CLARK W., Jernigan, Clark W., c/o Advanced Micro Devices Inc
Applicants: ADVANCED MICRO DEVICES INC, ADVANCED MICRO DEVICES, INC.
Application year: 1993
Main classification: G06F11
IPC codes: H01L21, G06F11, H01L27, H01L23