Integrated circuit defect review and classification process

[0002] This application is a continuation of application Ser. No. 08/790,999, filed Jan. 30, 1997, now U.S. Pat. No. 6,072,574.

[0003] 1. Field of the Invention

[0004] The present invention relates in general to integrated circuit semiconductor device manufacturing. More specifically, the present invention relates to integrated circuit defect detection, classification, and review in the wafer stage of the integrated circuit semiconductor device manufacturing process.

[0005] 2. State of the Art

[0006] Integrated circuit semiconductor devices (IC's) are small electronic circuits formed on the surface of a wafer of semiconductor material, such as silicon, in a manufacturing process referred to as “fabrication”. Once fabricated while in wafer form, IC's are electronically probed to evaluate a variety of their electronic characteristics, subsequently cut from the wafer on which they were formed into discrete IC dice or “chips”, and then further tested and assembled for customer use through various well-known individual die IC testing and packaging techniques, including lead frame packaging, Chip-On-Board (COB) packaging, and flip-chip packaging.

[0007] Before being shipped to customers, packaged IC's are generally tested to ensure various functions thereof. Testing typically involves a variety of known test steps, such as pre-grade, burn-in, and final, which test IC's for defects and functionality and grade IC's for speed. As shown in FIG. 1, IC's that pass the described testing are generally shipped to customers, while IC's that fail the testing are typically rejected.

[0008] The testing standards for a particular IC product are sometimes relaxed as the product “matures” such that IC's previously rejected under strict testing standards may pass the relaxed testing standards. Consequently, reject bins containing previously rejected IC's are sometimes “culled” for IC's that are shippable under relaxed testing standards by testing the rejected IC's again using the relaxed testing standards. Unfortunately, while this “culling” process does retrieve shippable IC's from reject bins, it makes inefficient use of expensive and often limited testing resources by diverting those resources away from testing untested IC's in order to retest previously rejected IC's.

[0009] Similarly, as shown in FIG. 2, all the IC's from the wafers in a wafer lot typically undergo enhanced reliability testing that is more extensive and strict than normal testing when any of the wafers in the lot are deemed to be unreliable because of fabrication or other process errors. Since a wafer lot typically consists of fifty or more wafers, many of the IC's that undergo the enhanced reliability testing do not require it because they come from wafers that are not deemed unreliable. Performing enhanced reliability testing on IC's that do not need it is inefficient because such testing is typically more time-consuming and uses more resources than normal testing.

[0010] Likewise, as shown in FIG. 3, a new or special “recipe” for fabricating IC's on wafers is sometimes tested by fabricating some wafers from a wafer lot using the special recipe and other wafers from the wafer lot using a control recipe. IC's from the wafers then typically undergo separate assembly and test procedures so that the test results of IC's fabricated using the special recipe are not mixed with the test results of IC's fabricated using the control recipe, and vice versa. Test reports from the separate test procedures are then used to evaluate the special recipe and to determine whether the IC's are to be shipped to customers, reworked, repaired, retested, or rejected. Unfortunately, because the IC's undergo separate test and assembly procedures, undesirable variables, such as differences in assembly and test equipment, are introduced into the testing of the special recipe. It would be desirable, instead, to be able to assemble and test the IC's using the same assembly and test procedures, and to then sort the IC's and their test results into those IC's fabricated using the special recipe and those IC's fabricated using the control recipe.

[0011] As described above, IC's are typically tested for various characteristics before being shipped to customers. For example, as shown in FIG. 4, IC's may be graded in test for speed and placed in various bins according to their speed. If a customer subsequently requests a more stringent speed grade, IC's in one of the bins are re-tested and thereby sorted into IC's that meet the more stringent speed grade and those that do not. While this conventional process sorts the IC's into separate speed grades, it makes inefficient use of expensive and often limited testing resources by diverting those resources away from testing untested IC's in order to retest previously tested IC's.

[0012] As described in U.S. Pat. Nos. 5,301,143, 5,294,812, and 5,103,166, some methods have been devised to electronically identify individual IC's. Such methods take place “off” the manufacturing line, and involve the use of electrically retrievable ID codes, such as so-called “fuse-ID's”, programmed into individual IC's to identify the IC's. The programming of a fuse ID typically involves selectively blowing an arrangement of fuses and anti-fuses in an IC so that when the fuses or anti-fuses are accessed, they output a selected ID code. Unfortunately, none of these methods addresses the problem of identifying IC's on a manufacturing line which will probably fail during subsequent testing and processing to help minimize the use of processing resources and time.

[0013] As can be readily seen, since IC's which are ultimately sold to customers involve extensive testing and subsequent packaging of the IC device, it becomes important to identify potentially defective IC's as early as possible in the manufacturing process to help eliminate associated testing, processing, and packaging costs therewith. In particular, if defects in IC's can be identified early in the manufacturing process before any testing occurs while the IC's are still in wafer form, it is very beneficial in the manufacturing process. Particularly, if the defects in the IC's can be identified while the IC's are still in wafer form before any substantial testing has been done of the IC's on the wafer. It is also beneficial to identify and classify the defects of the IC's while in wafer form to determine if the wafer should proceed in the various processes of test, manufacture, and packaging with other wafers in the same manufacturing production lot when the inclusion of a wafer having IC's with numerous defects therein may cause the unnecessary testing of other IC's from other wafers in the manufacturing production lot.

[0014] The present invention relates to circuit defect detection, classification, and review in the wafer stage of the integrated circuit semiconductor device manufacturing process. The method of processing integrated circuit semiconductor dice on a wafer in a manufacturing process for dice comprises the steps of visually inspecting the dice on the wafer to determine defects thereon, summarizing the number, types, and ranges of sizes of the defects of the dice on the wafer, and determining if the wafer is acceptable to proceed in the manufacturing process.

[0015] FIG. 1 is a flow diagram illustrating a conventional procedure in an integrated circuit manufacturing process for culling shippable IC's from a reject bin;

[0016] FIG. 2 is a flow diagram illustrating a conventional procedure in an IC manufacturing process for directing IC's to enhanced reliability testing;

[0017] FIG. 3 is a flow diagram illustrating a conventional procedure in an IC manufacturing process for testing a new or special fabrication process recipe;

[0018] FIG. 4 is a flow diagram illustrating a conventional procedure in an IC manufacturing process for speed-sorting IC's;

[0019] FIGS. 5A and 5B are a flow diagram illustrating the process of the present invention in an IC manufacturing process;

[0020] FIG. 6 is a tubular summary of defect type, defect description, and total number of defects of preselected dice of a wafer according to the present invention; and

[0021] FIG. 7 is a graphical display of the dice of a wafer which has been inspected according to the present invention.

[0022] The present invention will be more fully understood when the drawings are taken in conjunction with the detailed description of the invention hereinafter.

[0023] Referring to drawing FIGS. 5A and 5B, the flow diagram 10 illustrating the process of the present invention in an integrated circuit semiconductor device manufacturing process is set forth.

[0024] Referring to the step set forth in box 12 of the present invention, the types of surface defects in individual IC's located on the wafer to be discovered from a visual inspection of individual dice on the wafer are determined. Typically, the surface defects are to be visually determined using any commercially available automated defect detector for such purpose well known in the industry. Typical types of surface defects to be determined from a visual inspection of the dice of the wafer may include particle contamination of the dice from processing, bond pad formation problems, incomplete formation (scumming) of the circuits of the dice, etc., the types of visual defects being representative of those observed in normal IC processing in the wafer stage.

[0025] Referring to the next step of the method of the present invention set forth in box 14 of the drawings, the size ranges of the surface defects from the inspection of the dice of the wafer to be visually inspected are determined. For instance, surface defects present on the dice of the wafer are selected to be determined in size ranges for tabulation purposes, such as surface defects in the ranges of 0.0-0.5 microns, 0.5-1.0 microns, 1.0-1.5 microns, 1.5-2.0 microns, 2.0-4.0 microns, greater than 4.0 microns, etc.

[0026] Referring to step 16 of the present invention, the location of the dice to be inspected for surface defects thereon is determined with respect to the dice located on the wafer. That is, the surface defects are to be determined based upon either a predetermined method of selection of specific dice located in specific areas of the wafer under inspection based upon previous experience of various equipment in the manufacturing process tending to cause certain types of surface defects in die or dice in certain areas of the wafers or a random selection method of selecting dice randomly located throughout the wafer based upon statistical sampling techniques which are well known in the industry.

[0027] At this juncture in the present invention, it is clear that prior to the visual inspection of the dice of the wafer, (1) the types of surface defects to be determined by the visual inspection, (2) the location of the dice of the wafer to be visually inspected for surface defects thereon, and (3) the various size ranges of the types of surface defects to be determined from the visual inspection have been preselected prior to the visual inspection process of the dice of the wafer. Furthermore, it is preferred that each of these criteria is based upon historical information concerning the process of manufacture of the integrated circuit semiconductor device and any relationship present between the preselected criteria and subsequent failures of dice from a wafer during further processing, testing, and packaging of the dice. Such relationships may be determined by well known statistical analytical methods and data collected therefore used in the manufacturing of IC's.

[0028] Continuing, at the next step of the present invention set forth as step 18 of drawing FIGS. 5A and 5B, the preselected locations of dice on the wafer are visually inspected using any well known, commercially available scanning electron microscope or suitable optical microscope with tabulations of the resulting types of defects, frequency of defects, and sizes of defects being made through suitable means, such as by using a digital computer for such purposes. Also, preferably, a photograph may be made of each predetermined surface defect located on the dice of the wafer for comparison purposes with other defects of the same type classification and a record made of each surface defect and the location of the die containing such a defect on the wafer.

[0029] As shown in step 20 of the present invention, the surface defects of the preselected dice are classified, such being determined by the individual conducting the visual inspection as to the type of defect, the relative defect size, and the range of defect size into which such surface defect is to be classified as identified by the individual from the visual inspection of predetermined dice of the wafer.

[0030] After the visual inspection of the dice of the wafer, referring to step 22 of the present invention, the results of the visual inspection process are summarized. Typically, the results of the visual inspection are summarized in a tabular format according to defect type, description of the defect type, total for each defect type, and size range for such surface defect, and are also summarized in a wafer map illustrating such information in a graphical display of the dice of the wafer and defects discovered during the visual inspection of the dice of the wafer. An example of the tabular display 100 of surface defect information is illustrated in drawing FIG. 6, while the graphical screen display 200 of the dice of the wafer having surface deflects thereon is illustrated in drawing FIG. 7. While generated by summarizing the surface defect data using a digital computer for such purposes, it is preferred that the screen display 200 from the computer be printed out with subsequent information added by an individual as illustrated by marks 202 thereon for a record of the visual inspection results of the dice of the wafer.

[0031] At this time, referring to step 24 of the present invention, a determination is made as to whether the wafer is to proceed for further processing, testing, singulation of the dice, and/or packaging of the dice. In the first instance, a determination is made based upon the number of visual surface defects, types of visual surface defects of the dice, size of visual surface defects of the dice, the location of the visual surface defects of the dice with respect to the wafer and other dice of the wafer, etc. Such a determination is based upon information of previous wafers having such visual surface defects of such determined size in such dice and the well known statistical analysis of such information from a reliability life history of such dice through well known statistical analysis techniques in the industry. Alternately, a determination may be made with respect to individual dice of the wafer as to subsequent processing by individually identifying each die through the use of electrically retrievable ID codes, such as so-called “fuse-ID's”, programmed into individual IC's to identify the IC's. The programming of a fuse ID typically involves selectively blowing an arrangement of fuses and anti-fuses in an IC so that when the fuses or anti-fuses are accessed, they output a selected ID code for each die unique to that die which may be readily determined during any subsequent processing through well known techniques hereinbefore set forth in the previously identified prior art patents which are incorporated herein by reference. In that manner, once the dice have been singulated from the wafer, the “fuse-ID” of each die may be determined and the desired subsequent processing, testing, and packaging be determined, if any, with respect to individual dice believed to have reliability or functionality defects from the identification of visual surface defects while the dice are in the wafer stage prior to any testing thereof based upon known historical statistical information from such dice.

[0032] From the foregoing it can be easily recognized that through the use of only the screen display 200 of the wafer and the tabular display 100 the individual reviewing the wafer has permanent record of the information relating to the population of the visual defects of the dice of the wafer, the size of the defects, the types of visual defects, and, if desired, a pictorial record of the defect illustrating the same and how such defect relates to defects classified the same on the tabular display 100 and wafer map 200. It should be clearly understood that the tabular summary 100 not only provides a summary of the defect types, general defect description, and number of defects, as set forth in table 102, but also provides a histogram of such defect information, as set forth in table 104, which sets forth the identification of the die on the wafer (for instance, ID 329), the class of the defect (for instance, CL 3), and such information summarized in a tabular format, in the size range of the defect (for instance 0.0-0.5 microns, 0.5-1 microns, 1-2 microns, 2-4 microns, etc.). In this manner, in a histogram format, such defect information is available and summarized for a wafer which has been inspected for defects. Also, the defect information contained within tables 102 and 104 has been inter-related or combined for wafer defect evaluation purposes. At such time, the further testing, processing, and packaging of the wafer and dice thereon may be determined either individually with respect to the wafer which has been inspected or collectively with respect to other wafers in the same production lot as the wafer which has been visually inspected. Alternately, the same may be determined regarding individual dice which have been discreetly identified through the use of a “fuse-ID” for further processing, testing, packaging and/or being discarded.

[0033] In this manner, prior to any subsequent testing, processing or packaging of any dice, a determination of the quality of the manufacture of the dice in the wafer may be made, thereby avoiding any unnecessary expense in manufacturing an IC from the wafer. This avoids unnecessary subsequent testing of dice as well as the packaging thereof which are known through statistical analysis to be likely defective. Also, the various processing apparatus and methods of process forming the dice on the wafer may be modified for other wafers in the manufacturing process to help eliminate defects thereon.

[0034] From the foregoing it can be seen to one of ordinary skill in the art that changes, additions, deletions, and modifications may be made to the present invention which are intended to fall within the scope of the claimed invention.